Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => 3D Design & Printing => Topic started by: IKB on December 11, 2015, 12:31:43 AM

Title: Water Jet Drives & 3D Printing
Post by: IKB on December 11, 2015, 12:31:43 AM
 A few months ago now, I decided it was about time to have a proper crack at a project I have always wanted to do, that of a fully functioning RC Alvis Stalwart, a quick rummage unearthed my old plans for this project from many, many moons ago and a google search for additional reference very quickly unearthed Bob Hinton's article in the July 2011 edition of Model Boats.
One quick online order later furnished me with the article in question, which was a fascinating read as well as a treasure trove of information, as Bob clearly lays out in his article, the trials and tribulations of squeezing a lot of mechanics into a very small space.

Using his article as a guide for parts, as it seemed silly to reinvent the wheel when he had already solved many of the problems and got them to work reliably, I started to search the internet for the component parts. Most of the drive train is based on Tamiya Dual Hunter kits, which are no longer made, but they shared a lot of individual parts with other kits that you can still get hold of, so after a bit of searching, I had all of the land drive components that I required, the water drive parts were another story.

The Alvis Stalwart propels itself along the water using a twin set of Dowty water jet units, in the model version, these were substituted for Graupner Jet Drive unit 2340, unfortunately Graupner have decided to discontinue manufacture of, along with the rest of the range.
Now, there are a couple of places you can get jet drive units from, but they are either too small or way to big, which left me with a bit of a problem, however, one of my regular eBay trawling sessions yielded results, a pair of as new, in the box 2340 units, one swift purchase later had them sitting on my work bench. With eager anticipation I waited for the units to arrive, only to find to my horror, that the impeller housing mating flange on each unit had been badly hack sawed off, rendering the units unusable, fortunately for me, the seller was very good about the whole affair and refunded my money upon return of the items.
This got me thinking, I had a pair of jet drive units, before I sent them back, could I replicate them?
One option would be to mold and cast them in a resin such as fast cast, but this is not always a reliable method for reproducing dimensionally accurate components, another option would be to turn to technology and 3D print new versions.
So this is exactly what I decided to do, before posting the units back, I drew them up in SolidWorks, the 3D CAD package we use at work, then sent the files to be printed at www.shapeways.com (http://www.shapeways.com/)

 
A couple of weeks later, my very own jet drive was delivered, (Photo: 3D Printed Jet Drive Parts) I had already designed and machined a basic test bed hull at work during my breaks, (Photo: 3D Printed Jet Drive Prototype) which was quickly assembled and given the all important bath tub shakedown. Below is a link to the video of the first test, apologies for the shaky video.

 
https://youtu.be/CfaUvGJ08gY (https://youtu.be/CfaUvGJ08gY)

 
This test was performed using a 555 motor I had spare in the workshop, a 25Amp Mtroniks ESC and run at 14.4v off two NiMh stick packs.
The results looked promising, especially as I was not using the standard impeller design, but a revised four bladed version I had drawn.
For some time I have been toying with the notion of buying a 3D printer, I have had parts 3D printed in the past at work for projects and always been disappointed by the cost and  time it took to receive the end result.
Like most people, I do not have a lot of space at home to devote solely to my hobbies, my workshop is a standard 6x8' shed in the garden, but this is more than compensated for by having access to a milling machine, lathe, CNC router and laser cutter at work.
However, as awesome as all the kit at work is, it is not readily available to tinker with at home, but a 3D printer I could make room for, so after several weeks of reading up about different types, models, materials and processes, I decided to take the plunge and buy one for myself. As luck would have it, I came across the model I wanted for sale on eBay, the seller was upgrading to a larger machine and was selling at a very reasonable price. (Photo: Lulzbot Mini)
Being able to have an idea, draw, print and test it all in the same day is amazing, it allowed me to explore the difference in performance between a 2, 3 & 4 blade impeller design easily.
(Photo: 3D Printed Jet Drive Parts [Orange impellers by me, white parts by ShapeWays])
This did lead to a small problem, when I took the prototype to the club lake for open water trials, the performance was some what under whelming, I later realised, that I had the four blade impeller fitted, which was more than likely causing so much drag, the motor was just not powerful enough to turn it at the desired speed. Looking further into the problem, the original Graupner units, which have a two bladed impeller, have an operational speed of 18-20K RPM, where as the motor I had to hand maxed out at around 14.5K RPM, hey ho, you live and learn, but that is what I like about prototype work, you are always discovering something new.
One avenue I have been meaning to explore is brushless motors, which are perfect for this application, so after a bit of reading and asking around at the club, I bought  a basic HobbyKing 80A ESC and a cheap ZTW Black Mantis B3660 Kv1900 inrunner brushless motor from eBay.
With a swap back to the twin blade impeller, just to start with, I am hoping to get back down the lake this weekend for more trials.

 
Title: Re: Water Jet Drives & 3D Printing
Post by: Umi_Ryuzuki on December 11, 2015, 05:13:23 AM
That's a gorgeous print out. :-)) :-)) :-))


I can not see inside your tail cone, but don't forget, there should be some

stators, or vanes behind the impeller to "straighten" the flow of water.
Otherwise the water will swirl inside the pipe, and disrupt the flow.
I made a pretty good blender my first attempt at a jet pump.
I also tried a four blade impeller vs a two blade impeller, and burned up the motor and ESC.
I also modeled my setups after the Graupner drives.


Title: Re: Water Jet Drives & 3D Printing
Post by: TomHugill on December 11, 2015, 07:19:15 AM

That you for taking the time to post this, I love all things jet drive and this really interests me. Out of interest what was the price from shapeways to print this? I've looked into getting parts made but they were always hideously expensive
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 11, 2015, 12:42:58 PM
 :-))nice post Alex, keep up the good work :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: essex2visuvesi on December 11, 2015, 12:51:56 PM
How do you find the eSun Filament?
Mine seemed to be quite hit and miss as to the quality (the diameter of the filament seemed quite variable)
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 11, 2015, 03:12:50 PM
Hi Guys,

Thanks for all the positive comments on my latest project:

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: TomHugill on December 11, 2015, 03:26:42 PM
Are they 28mm units?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 11, 2015, 06:46:59 PM
Hi TomHugill,

No, like the original Graupner ones, these are 40mm  :-))

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Umi_Ryuzuki on December 11, 2015, 07:44:59 PM
I was building them up and then casting them out of polyurethane.
Your impeller designs are interesting, with the curved leading edge.
I seem to recall that most jet ski and other impellers are more squared off.
Take a look at how the rc jet sprint boat guys have built up their pumps.
I look forward to seeing more of your results.
 8)
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 13, 2015, 11:23:52 PM
Hi Everyone,

First a quick reply, Umi_Ryuzuki: My impeller design very closely follows the original Graupner one, as blade design is something I know very little about, the one I copied had a curved leading edge, just like you see in the photo.

Today's results:

So, "what now?" I hear you ask, well, as much fun as this has been, as I originally stated at the beginning, this has been a tangent of my actual project, namely, an RC Alvis Stalwart. I will carry on working on the design of the drive unit, with a view to printing my own, from scratch, in ABS.
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 13, 2015, 11:35:15 PM
Glad you've finally had a successful test!
It must have been pretty nippy lakeside today I'm guessing it must have been one of the diehard scale chaps that came to your rescue!  :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: TomHugill on December 14, 2015, 08:03:34 AM
Very impressive stuff, I would love to see a video at some point. Out of interest are the 3d printed parts available to buy on shapeways?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 14, 2015, 01:05:43 PM
Hi TomHugill,

Sorry, the parts are not available to buy on Shapeways, I have done this all very much for my own amusement and although different to the original Graupner units, they are still a complete rip off, so not sure where I would stand legally if anything did come back at me.

I tried to take a video using a GoPro attached to the top of one of my other boats, unfortunately, the POV is to low to get any good footage, next time I down the lake, I will try and get some better video and post in this thread.

Regards,

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 14, 2015, 09:06:13 PM
Great pic Alex, although for a moment there I thought your Go-pro was on fire! %%
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 19, 2015, 05:03:03 PM
Hi Guys,

Next stage is under way as I type, I have split the jet housing into two halves, as it won't fit in the printer as one piece... well, it will, but not in a nice way. So with this I plan to print and build a complete jet unit from scratch, without any bought in printed parts, more updates to follow soon.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 19, 2015, 05:37:51 PM
Very professional job Alex :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 20, 2015, 10:41:08 PM
Hi Guys,

Finished the first stage of my home print jet drive, need to include some tabs / lugs to help locate the two halves, but apart from that, I am really happy with it.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 21, 2015, 07:55:04 AM
Funky colour Alex! BTW have you done any paint tests on that material yet? (I'm presuming you don't want an orange Stoley!) :}
Title: Re: Water Jet Drives & 3D Printing
Post by: essex2visuvesi on December 21, 2015, 08:48:39 AM
IS that ABS or PLA?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 21, 2015, 01:04:02 PM
Hi Guys,

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 21, 2015, 01:09:43 PM
Hi Guys,
  • PeachyPM - All the final prints will be in ABS


 :-)) Good, ABS will take paint well as long as its primed properly.  :-))

Title: Re: Water Jet Drives & 3D Printing
Post by: essex2visuvesi on December 21, 2015, 05:41:43 PM
PLA will take paint as. Long as you use a plastic primer, for example tamiyas surface primer
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on December 21, 2015, 05:56:09 PM
PLA will take paint as. Long as you use a plastic primer, for example tamiyas surface primer


True, and would be perfectly acceptable for a display model or gentle use, but I know IKB and I've seen how he handles his boats!  {-) only joking Alex. if you've got the option of ABS I'd personally go with it, the cellulose primer you have at work will bond nicely with it.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 22, 2015, 12:43:40 AM
I intend to use ABS so that I can chemically weld it to other ABS printed / CNC parts with Acetone
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 07, 2016, 11:58:54 PM
Hi Guys,

Another new year, finally got back into all things boating for the first time this year and I have to be honest, it has not been the greatest start to the year.
Down at the lake today, the conditions were good, bit cold and windy, but the sun was out, so decided to take the prototype for a spin and capture some clearer video. First run was good but ended abruptly when part of the intake grill broke free and was ingested by the jet drive unit... not a pleasant sound  {:-{ But on closer inspection, no damage had been done, so on to the second run of the day, which... well, I'll let you all see for yourselves, thanks to my good friend, "PeachyPM" for waving the camera and enthusiastic commentary.

https://youtu.be/j-XUCE27GO0

So, with waders donned, the boat was saved and it is currently drying out on the radiator, if I'm lucky, some of the electronics might survive!  :embarrassed:

But it was not all bad, the first sail of my second hand Yorkshireman tug went much better than expected.
Title: Re: Water Jet Drives & 3D Printing
Post by: Umi_Ryuzuki on February 08, 2016, 04:46:06 AM
So much for the no wake zone,...  {-)
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on February 08, 2016, 07:20:23 AM
 :-)) what a glorious way to go! In the name of EWTP! (Engineering Workshop Theory & Practise) may I suggest some sort of cunning lid/deck on the next test vessel? %%
Oh! & well done on not throwing every laughing club mate (inc me & Jimmy) into the water. That shows a marked development in general  Bon Hom!   :}
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 08, 2016, 01:00:32 PM
Hi Guys,

Yeah, I learnt the hard way that jet boats off throttle don't steer and due to the hull design, with no rudder or other low hanging machinery like a prop, there is very little drag to slow you down either!

The water cooling jacket that I ordered for this boat seems a little bit OTT after this weekends exploits  {-)
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 10, 2016, 11:39:33 PM
Hi Guys,

Some great news this evening, after sitting on the radiator since the weekend, I put the prototype back on the bench and everything works, outstanding!

Video here: https://youtu.be/8IPqc-KSh54

Although, where the brass rod went through the impeller, it has left some pretty ugly gouges, but that is one of the great things about owning a 3D printer! :-))

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on February 11, 2016, 02:36:56 PM
If at first you sink...dry,dry & dry again {:-{
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 11, 2016, 03:00:53 PM
Groan... yes mate, very good  O0
Title: Re: Water Jet Drives & 3D Printing
Post by: essex2visuvesi on February 11, 2016, 05:07:51 PM
If at first you sink...dry,dry & dry again {:-{


(http://i1209.photobucket.com/albums/cc395/scout03060/smileys/4827fdff_tumbleweed.gif)
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on February 11, 2016, 08:54:06 PM
Tough crowd! :embarrassed:
Title: Re: Water Jet Drives & 3D Printing
Post by: essex2visuvesi on February 11, 2016, 09:43:31 PM
Tough crowd! :embarrassed:


Actually I thought it was rather good
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 21, 2016, 09:07:59 PM
Hi Guys,

Quick update on the jet drive, I am currently working on a reversing mechanism... can't imagine why  :embarrassed: The design i progressing nicely, unfortunately, multiple printing failures this weekend have scuppered a prototype being completed, so here are a couple of screen grabs of the CAD and a short animation of the motion.

Animated motion: https://youtu.be/Q-vVDgnZxAQ

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: hopeitfloats on February 22, 2016, 07:47:41 AM
going to take a good servo to work it with the link to the bucket being so close to the pivot point. possible it may lose water out the side rather than redirecting it back. not that it wont work but it might be a bit slow reversing.  sorry if it sounds so negative because the unit is a nice build. just a couple of potential problems you could have.  nice simple way to do it though
Title: Re: Water Jet Drives & 3D Printing
Post by: tigertiger on February 22, 2016, 09:32:32 AM
As an aside, I saw a news report from an Indian tech/entrepreneur show. A guy there has developed a portable 3D printer. Once the big companies follow, that will see more 3D printing generally. This will drive down prices, increase use, and see development of both machines and software applications.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 26, 2016, 10:44:02 AM
Hi Guys,

Quick update on the new reversing mechanism, managed to get out to the shed last night and test assemble the new design, one small issue is the reversing lever needs to be taller to allow clearance for the steering linkage on the bucket and there are a couple of minor tolerance tweeks to be made here and there, but overall I am very pleased with it so far.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Charlie on February 26, 2016, 04:20:56 PM
Hi Alex,
That is an impressive piece of work, well done! Would i be right in thinking that you have now gone beyond creating a Jet Unit specifically for the Stolly, and that you are now intending to create one suitable for a boat? Reason i ask, is that i was intrigued by how the Stolly Jets worked, and came upon this illustration, when i was Googling. It appears to have a reversing Mechanism, but no Steering, so presumably they steered 'Tank Style'.
Charlie
Title: Re: Water Jet Drives & 3D Printing
Post by: Danny on February 26, 2016, 04:48:01 PM
The Stolly had two levers in the cab for left and right bucket (tank steering). This was aided by turning the wheels (front four steer) which gave a sort of multiple rudder assistance.
Cheers
Danny
 
Title: Re: Water Jet Drives & 3D Printing
Post by: hopeitfloats on March 01, 2016, 06:36:13 AM
certainly looks good alex. very professional
 :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 01, 2016, 03:12:05 PM
Thanks for the positive comments guys, always appreciated, few quick replies:

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 04, 2016, 11:12:11 PM
Hi Guys,

Been working hard to rebuild the jet boat prototype this week, last night I finished the CAD for the improved MK2 model with reverse and the printer churned out all the parts in just under 13 hours  :o
Plan on doing the assembly tomorrow, so hopefully more photos and maybe some bath trial videos in the next couple of days.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Captain fizz on March 05, 2016, 09:10:10 AM
I continue to be amazed by the capability of 3D printing! Well done Alex, superb work!


Simon
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 06, 2016, 12:07:56 AM
Hi Guys,

Made good progress on the jet boat prototype today, couple of minor tweeks to be made and a couple of small changes to be printed in the morning, but apart from that all is going well.

With the new and improved MK2 version, I am replacing everything that is outside the hull with new components, which means removing and replacing the stator nozzle, but this means I can replace the damaged impeller that ingested a brass rod, which ironically, was meant to keep foreign objects out!  %%
I knew from the noise it made on the lake that the damage was bad, but it still performed well after removal of the brass rod, on closer inspection, it is pretty messed up

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Captain fizz on March 06, 2016, 08:01:39 AM
Yes, it hasn't done that a lot of good!
As you say, a certain irony that it was caused by part of the intake strainer. It just reinforces the fact that there is a huge volume of work involved in developing this sort of project.
Keep smiling Alex!


Simon
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 06, 2016, 06:53:40 PM
Hi Guys,

Well, lots of progress made today, unfortunately no test video of the boat as there was a yacht regatta on the club lake today, so first trials will have to wait until next Saturday.

She is complete though and ready to go with many new features installed:

Video from the workbench showing servo test:
https://youtu.be/5Aai8rE8klk
Alex


Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 13, 2016, 06:26:26 PM
Hi Guys,

Made it down to the lake today and conditions were favorable, next to no wind and very calm waters, had a couple of runs with the boat and drew the following conclusions:

Overall I am very pleased with today's performance and after a redesign of the reverse mechanism, I will be moving swiftly on with the Stolly version.
Youtube videos of today's exploits:Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Captain fizz on March 13, 2016, 06:39:34 PM
I would say that that was a very successful test run Alex. :-))


Simon
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on March 14, 2016, 02:33:37 PM
It looks like the reversing flap isn't sealing against the main body, giving you a nice fan effect of water spraying past the reversing flap...  seal that, and your reverse will improve.
Title: Re: Water Jet Drives & 3D Printing
Post by: hopeitfloats on March 17, 2016, 08:41:36 AM
reversing bucket is the answer Alex. :-)) or if you can put sides on your flap would help. I don't think water fanning out the top is causing your problem. more like its running out the sides
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 19, 2016, 11:03:53 PM
Hi Guys,

Managed to get another testing session down on the lake today with the following results:

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on March 20, 2016, 03:10:11 AM
IKB,

the tamiya connectors are incapable of handling more than 10 amps max load.  replace them with connectors that can handle 30 to 60 amps, either Deans or PowerPole or EC3 or larger.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 20, 2016, 02:04:22 PM
Hi tsenecal,

Thanks for your reply, I had not realised that Tamiya connectors had such a low rating, I use XT60 connectors on everything else, which according to some quick googling, can take 60 amps, so will swap to them.

I am also going to look at a different motor spec, which will hopefully give me more torque but fewer amps, as I suspect the one I have is cavitating quite badly

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 21, 2016, 01:32:10 AM
Hi Guys,

Finished the design for my new jet drive, will be printing the parts out tomorrow, more to come in the next few days

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 23, 2016, 10:55:10 PM
Hi Guys,

Jetdrive MK3 done and ready for testing.

On order is a Tornado Thumper V3 4260/06 500KV outrunner, at the moment I am running a ZTW Black Mantis B3660 Kv1900 inrunner on 14.4v which gives 27,360 Rpm, a tad excessive for the upper rev range of 20K for this type of jetdrive.
The other issue that I seem to be having, is that the current motor is struggling under full load, so I am replacing with the Tornado Thumper, which is slower revving, but has more torque, I can compensate for the lack of RPM with three blades on the impeller.
Well that is the theory, we shall see when I do the lake testing, but this is the fun of it.  {-)

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 04, 2016, 12:06:41 AM
Hi Guys,

Well, success is how you determine it I suppose, on the one hand I learnt a lot and have several ideas about how to progress forward, on the other hand, not a great deal worked.  {:-{
I have also made a couple of small additional changes since my last post, as well as installing the new motor, I have also added a proper nitrile shaft seal to hopefully stop the suspected water increase into the hull through the prop shaft, along with a new new steering nozzle, which has a 3 degree down angle, which should help the boat up on the plane, as most real jet drives do.
A new less restrictive intake grill, with integral scoop has also been fitted to replace the hacked about old one, I have also decided to conduct all of my future tests using 3S Lipos, as these will more than likely be the power source for my Stolly, so everything need to be compatible with that.
On the plus side I have learnt much today and there were some small successes, I have a better understanding of brushless motors and the 3D printed fan attachment I made for the new outrunner seems to be working really well, with the motor staying nice and cool throughout testing.
But what of the new reversing bucket I hear you all cry? Well, yeah, that too is on the re-deign list, it is great at throwing water directly downwards, but there is not enough reach on the bucket to throw the water under the boat. But whilst chatting to a friend at the lakeside, we came up with a simple redesign which should do the trick, so watch this space.


Alex

Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 08, 2016, 12:49:46 PM
Hi Guys,

MK4 Reversing bucket is designed and will be lake testing on Sunday, high hopes for this design, but I have been wrong before!

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 08, 2016, 01:40:13 PM
Very tidy Alex  :-)) , but wouldn't a closer fit when closed (where the inside surface at the top of the bucket meets the out-pipe/jet) be more efficient? or is this a test to see if the bucket shape works first?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 08, 2016, 03:11:59 PM
Hi Chris,

Yes, this is very much still in development, the cross section view shows the reversing bucket almost in the fully down position, it is very much at a, "get it to work" stage in the development before moving on to a more polished final product.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 10, 2016, 07:47:23 PM
Hi Guys,

So, mixed results again at the lake today, good news is, the reversing bucket design works like a dream and I am so happy with it, I don't think I am going to change anything, bad news is I somehow managed to launch the boat out of the lake and break the motor coupling the process. Going back over the on board GoPro footage, everything is going well, crossing the lake at full power, boat is sitting nicely and the tweaked jet nozzle is producing a good pattern, then the motor suddenly stops for a few seconds; the boat is now traveling without control of direction and covering quite a bit of ground, this is really bad, as we all remember from the sinking in the harbor, no power, equals no steering, finally the motor kicks back in, but I am too close to the bank and launch off one of the tires onto the dirt.
Thinking about this, I am really unclear as to what actually happened and probably never will know, I think the coupling exploded as the boat left the lake, excessive torque not being the culprit, but excessive RPM as the motor at full throttle went from full load to no load in a split second, causing the plastic arms to splay out due to centrifugal force, allowing the spider to escape.

On the plus side, the boat performed very well with the 1900Kv motor on a 3S Lipo, this has lowered the RPMs and as the video shows, produces a jet stream with less cavitation bubbles in it, which is backed up by the video audio as well.

Overall I am pleased with today's results and will return to the lake next weekend with a new coupling to do more thorough testing of the new setup.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Stavros on April 10, 2016, 09:57:12 PM
Hi Alex been there had the tee shirt with those couplings sorry to say this but get rid....contact Steve Tranter of Model boat bits and get a PROPER coupling....I will gte you it was already damaged before you launched it out of the lake.....those coupling if truth be know are not designed for RPM over 5k....if you really want to persist with that type of coupling then simply wrap some insultaing tape around it or even use some electrical shrink wrap over it BUT your alignment must be 100% if you use such tricks

Dave
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 10, 2016, 10:33:19 PM
Dave is quite right Alex, bin the plastic couplings, they're ok on a tug, but that's about it, I've even had one go on a Club500, it robbed young Jim of his first victory! Also I might be wrong but it looks from the photos that your motor is mounted squarely to the bulkhead? Does the prop shaft then dip down slightly? If it's even a degree out with a fast reving brushless that coupling was gonna go sooner rather than latter and a straight replacement will do like wise I'm afraid!
BTW great job on your first race day and well done for keeping your cool when you got black flagged!  :-)) >>:-(
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 11, 2016, 07:43:23 AM
Hi Guys,

Thanks for the comments, GoPro video from the test sail:

https://youtu.be/iEJILl3cvS8

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 11, 2016, 09:08:06 AM
Dude! Awesome footage, really showed the reversing very well. Great POV manouvering in our harbour, & what can I say about the ski jump? Superb! %% {-) :embarrassed: <:( :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: Captain fizz on April 11, 2016, 12:46:50 PM
Not withstanding the motor glitch, that unit is now looking seriously good :-))
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 11, 2016, 12:50:55 PM
Cheers Captain Fizz,

I am very happy with the unit now, I am going to machine a solid coupling this week and get back on the lake this weekend for some better runs, hopefully get some lakeside video footage as well

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on April 11, 2016, 02:29:39 PM
the bigger question is why did the motor cut out?  i see that you have water cooling to the motor, do you have water cooling on the speed control as well?  if not, perhaps the speed control cut out after overheating....  i know that you didn't have it running for long, and you have run it on higher voltage, but until that gets sorted out, i fear you might need to reinforce the bow with something like an aluminum sheet :)
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 11, 2016, 03:27:43 PM
Hi Tsenecal,

The motor cutting out is a bit of a mystery, the motor is indeed water cooled but the ESC has no inbuilt water cooling and it is one of the heat shrunk in line jobs that don't really lend themselves to cooling on a plate.
At the moment, I think it was interference, or it could be a dodgy motor connector, I changed the bullet connectors on the motor to match what the other motor is using, so that I could swap quickly between motors if needs be, but I got to the lake and found I had one mismatched bullet connector size, so smashed them together with some pliers and then reinforced it with tape. It is more than feasible that this lakeside bodge came back to bite me.  :embarrassed:

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: martno1fan on April 13, 2016, 07:05:28 AM
Nice work but surely you would be better off using a flex shaft to stub shaft arrangement rather than using a universal joint or at least do away with the uni joint and use a rubber type coupling that can handle the high rpm,if you really want to stick with a uni joint then id go with a stainless one from pmb. Also be a good idea to use a boat esc with water cooling,boats with high rpm need that or things overheat very quickly.
Mart
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 17, 2016, 12:18:38 AM
Hi Guys,

Down the lake this evening and another mixed bag of results, although, I did manage one very positive full power run, which proved once and for all that the nozzle design is sorted, planing flat at high speed across the lake, there are however, some other issues to contend with.
The first problem I had, was the new pumped cooling system, which once primed, worked very well, but getting it to prim was another story, I ended up injecting water into the system with the boat in the lake; a fundamental rethink is required here.
Second issue I am having is a very nasty vibration in the impeller shaft at certain RPM ranges, the noise is so severe that at first I thought the impeller was rubbing on the inside of the housing, but after everything had been checked, it is clear that there is something very wrong when the motor is revved, so much so, that at times, the vibrations disrupt the water flow through the drive causing a momentary loss of pump prime, leading to another rescue by a fellow club member, a full strip down will reveal what is wrong.
Third issue, water ingress, it's getting in some where, I just don't know where.

So now that I am happy with the power run achieved today, I am going to rip out the jet drive and install a new home print version, main tunnel and all that will hopefully fix all of the above problems.

Video of the best run from today: https://youtu.be/iNsUIvYS7KM

Alex
 
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on April 17, 2016, 01:33:27 AM
Alex....we can clearly hear the vibration pulses....17+ seconds, 37+ seconds & 55+ seconds

It does not appear to be water or wave related
For these momentary pulses [less than ~~ 0.2 of a second] we cannot perceive a motor speed increase

In mechanics, many rotating element groups have 'critical speeds' where transient mechanical resonance amplifies itself

Essentially in this high speed scenario, the rigidity of an element in the drive becomes unstable

Just a matter of understanding which element it is & then how to harness the instability without drawing power

On the 11th, you mentioned a new machined motor to shaft coupling........if your brushless motor has sealed ball bearing/s on the output shaft........& you have a solid coupling with no resilient element....the next point of contact is the diametrical clearance between the prop shaft tube & the shaft

You could try using a stroboscope to visually see what is moving when the critical speed/s are reached...using a strobe here is like watching a spoked train when suddenly visually appearing to run in reverse

The questions in the image below may assist  %)

Derek 
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 20, 2016, 03:11:59 PM
Hi Derek,

To answer your questions:

The next incarnation of this unit will have a redesigned main body, which will incorporate an integral motor mount, which will shorten the impeller shaft greatly, I will also be swapping to a solid coupling for extra rigidity.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 22, 2016, 11:31:27 PM
Hi Guys,

Finished the design for the new jet drive impeller housing tonight, going to print the parts off tomorrow and hopefully be on the lake Sunday

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on April 23, 2016, 02:37:35 AM
IKB,


don't know if it has been asked or not, but i am curious which 3d cad software you are using to design this? your illustrations of the different mods look very nice, and i was wondering if they are just edited screen shots, or are you exporting "scenes"?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 23, 2016, 08:08:40 AM
Hi tsenecal,

At work we use Solidworks 2016, I can transfer my licence to my home machine to work in the evenings, so I design everything in that. The pictures I post of the cad models are screen grabs from the program, no Photoshop here.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 24, 2016, 10:37:15 PM
Hi Guys,

So, many hours in the shedshop last night and this morning later, I completely stripped out the old jet drive unit, which was painful to say the least, at the same time I also investigated the source of the vibrations in the old unit, which is when I found the old impeller had slipped forward on the shaft causing the leading edge of the blades to grind against the inside of the tunnel.
The impellers were originally designed to be grub screwed onto the shaft, but that was quickly discarded as they are such a tight press fit onto the shaft and they have never given any bother, I suspect what has happened, is the impeller has been subjected to speeds and loads it can't withstand during testing and as load increases, the impeller expands to the point where it can walk up the shaft, the stuttering on the last run is the impeller hitting the tunnel, stopping, the shaft then rotates separately to the impeller, the friction this causes heats up the PLA and when PLA gets warm it becomes really sticky, at this point the impeller grips the shaft and drive is restored.
Examining the original tunnel body, which is now the oldest part of the entire build, the walls are relatively thin, or more precisely, the same thickness as a Graupner unit, this allows the rather long impeller shaft to flex in the shaft tube, the new unit addresses this and many other issues.

When I set out to redesign the tunnel housing, I had several points in mind:

With these points in mind I had to alter quite a few key aspects about the original design, the biggest of which was that it was just to big to fit into the build envelope of my Lulzbot Mini, which has a build volume of 150 x 152 x 158mm, the original Graupner unit is a relatively long and tall unit, so I lowered everything, included a base plate to tie everything together and knocked around 40mm off the overall length.
Some limitations are placed upon me when designing things to be 3D printed, namely, that they are 3D printed and certain shapes are very problematic to print, this is what lead to the motor mount being a bolt on item, but it turned out not to be a problem, as the entire structure is remarkably rigid. During a break at work I machined up a solid shaft coupling from some scrap Brass stock, this sits nicely between the motor and impeller shaft, which is effectively half the length of the old one at 120mm, the dual bearings in the motor support the drive end nicely, with the other end of the impeller shaft being supported by a Bronzelite top hat bush in the stator housing.

Cooling has always been somewhat of an issue on this project, the passive cooling system worked well, by just didn't provide the throughput necessary to keep the motor cool, my active pumped system was a bit of a flop altogether and best forgotten about, but I am very pleased with the latest system, tapping into the positive pressure inside the stator housing, the harder the jet drive works, the higher the pressure and the more cooling is provided, which is evident in the video as cooling water expelled increases proportionately with speed.
Testing on the lake today:In conclusion:Video from today: https://youtu.be/1fIXD4WxVa0
Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Captain fizz on April 25, 2016, 08:18:43 AM
That is looking really good.
it sounds much happier too. Real progress. :-))


Simon.
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 25, 2016, 01:40:14 PM
 :} SPRINGER TIME! :}

Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on April 25, 2016, 03:08:41 PM
Alex......the design layout certainly appears far more rigid, and from the run sounds, is just that :-))......in the final design, would a metal impellor be a practical option?........... Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 25, 2016, 03:16:22 PM
Hi Derek,

Yes, I have been thinking about this for the final V-hull version, I am going to look into the cost of getting a metal one from shapeways, but for the moment, I have just ordered a larger water cooled ESC, so hopefully, I will be able to get some lakeside footage next weekend.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 22, 2016, 12:49:17 AM
Hi Guys,

Now that the craziness of the last couple of weeks is over, I managed to find some time to repair the jet boat and get back down the lake today for another round of tests, changes this time around are as follows:

Out on the lake today conditions were not bad, just a bit damp, I was conducting tests in the 2 minute intervals between bouts of some of the heaviest rain I have seen for a while... but the water was really calm and no one else was stupid enough to be at the lake, so I had the place to myself.
Results from today were very mixed:I am going to go back and look at motor selections again, I like an inrunner design with a water jacket, as jet drives place a lot of strain on a motor and I don't think fan cooled outrunners will be up to the task. Impeller slip has again blighted another day of testing, I am pinning my next impeller to the shaft and hopefully I can then really test the limits of the 3D printed design, this only leaves the last limiting factor and that is the hull design, there is no way around it, if I want to continue development of this drive, I am going to need a proper hull, I have something in mind, so watch this space.
One good thing that came out of today, was I managed to get some lakeside footage of the boat running, it is not the best, as I was trying to sail and film at the same time, but it shows the most successful run of the day, which was between half and three quarter throttle: https://youtu.be/smtkWQN6FW0
On board GoPro footage of same run: https://youtu.be/yl1Pu__KHQQ
Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on May 22, 2016, 05:45:43 AM
two choices on hobbyking:

http://www.hobbyking.com/hobbyking/store/__38657__Turnigy_AquaStar_3660_2050KV_Water_Cooled_Brushless_Motor.html (http://www.hobbyking.com/hobbyking/store/__38657__Turnigy_AquaStar_3660_2050KV_Water_Cooled_Brushless_Motor.html)

or

http://www.hobbyking.com/hobbyking/store/__38658__Turnigy_AquaStar_3660_1700KV_Water_Cooled_Brushless_Motor.html (http://www.hobbyking.com/hobbyking/store/__38658__Turnigy_AquaStar_3660_1700KV_Water_Cooled_Brushless_Motor.html)

same basic size, inrunners with water cooling jackets.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 22, 2016, 10:14:40 AM
Hi tsenecal,

Thanks for the info, I was looking at the second choice you list last night and will probably use one in the next version, as it is a very resonable price for a motor that includes a long water jacket.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 24, 2016, 01:00:19 PM
Hi Guys,

Planning the next stage of this project, I am going to address one of the main limitations of the design, that being the lack of a decent hull, I am looking around for a deep vee style into which I plan to drop a twin jet system; so far I have found this on eBay, any other suggestions are gratefully received:

http://www.ebay.co.uk/itm/111999310282?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 06, 2016, 01:04:18 AM
Hi Guys,

Glorious day down at the lake today, near mill pond conditions out on the water and new improvements to try out, changes this time around:

So it was clearly evident from the debacle of a test session last time that the impeller keeps shaft walking and this really needs addressing, so I went back to my initial impeller designs, which incorporated a metal coupling onto the 3D printed impeller hub to help with torque transmission between the shaft and impeller body.

Originally I was going to use an Oldham coupling hub, but these are very expensive for what they are and I had a spare UJ Brass insert in the parts bin, so I used that instead; the impeller body was lengthened to incorporate the new coupling, which meant I could also increase the blade length, this gives a slightly shallower angle, but both blades now cover 180 degrees.
Results from the lake:Every run I do is recorded by the onboard GoPro camera, this has proved invaluable in diagnosing some of the problems, for instance, towards the end of run three, from the lake side, what appeared to be a drop in performance turned out to be motor surging. Reading into this phenomenon online, this is caused by the ESC making continuous high demands on the batteries, as the voltage drops, the ESC battery protection kicks in and decreases demand, the battery voltage recovers and the ESC makes higher demands once again and so the cycle continues... in short, more LiPos needed.

A very successful day of testing with run three being the longest continuous run to date, going forward from this, I am going to tweek the impeller design slightly, it could do with a bit more clearance in the impeller tunnel, which should cut out the extraneous vibrations that are left; I am also going to explore the feasibility of completely 3D printing a  deep Vee hull.

GoPro footage of test run three, I have shortened it some what, as after the end of this segment, it is really uneventful: https://youtu.be/4TNh3FjTems

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 13, 2016, 12:47:55 PM
Hi Guys,

With good results from the last round of testing behind me, I have finally found a hull that I like and have placed an order, so as soon as it arrives I will start work on a twin jet power boat  :}

Link to the eBay listing for anyone interested: http://www.ebay.co.uk/itm/Fast-Electric-Model-Boat-hull-Zoom-I-fibreglass-moulding-/142008150793?_trksid=p2141725.m3641.l6368

In the mean time, I am going to address the slight rubbing issue of the impeller and try some different motors out to find an optimal setup

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 20, 2016, 10:58:35 PM
Hi Guys,

Exciting news, new hull arrived in the post today, it is very nice, but I fear a twin drive system may be a tad overkill for such a small hull, I honestly thought it was going to be bigger, oh well, a single drive will be pokey enough.  :}

I tried to do a write up of Saturday's testing last night, but as I hit the post button, I was asked to log back in and lost an hour and a halfs work  >>:-( so here is a shortened version.

Modifications this time around are as follows:

As you all know, I keep coming up against the problems caused by the rudimentary design of the prototype hull, namely any rough water lifts the bow and the drive gulps air causing a loss of pump prime, to combat this I have printed and installed  some fixed angle trim tabs to keep the bow planted; what a difference, even at low speed, the boat sits properly in the water and handles quite rough conditions without any hesitation.
In order to gain a better understanding of brushless motors under load, I installed a Turnigy Watt meter on the deck lid inline with the GoPro, with the intention of being able to read off current draw figures for know throttle settings, this was fine in theory, but glare from the waterproof casing obscured most of the results, however, a lot of useful data was collected.
New impeller, as the old one was quite clearly rubbing on the inside of the impeller tunnel, so a slightly smaller version solved all the problems and several people remarked how quite the boat was on the lake.
Results from the lake:After rescuing the boat and upon finding the motor unable to do anything but vibrate feebly, I swapped in my original 1900Kv inrunner, this performed well, but it is not as efficient as the outrunner at low speeds, the top end current draw was the same, but I suspect that is more to do with limitations imposed by the batteries and ESC, which are both not specced for the kind of numbers I am getting.

Going forward from this, after doing some further reading into brushless motors and brushing up on some of the basics of Ohm's law, I am going to try another motor, but this time on a higher voltage, this will give me the extra watts that the drive needs. Following 6705russell's recent post of a new build Graupner Atlantic Challenger, (http://www.modelboatmayhem.co.uk/forum/index.php/topic,55129.0.html) which uses the same jet units that I have based my design on, I asked him what he was planning to run motor wise and he suggested the following: http://www.overlander.co.uk/motors/brushless-motors/tornado-thumper-v2-4240-10-890kv-brushless-outrunner-rc-motor-latest-model.html (http://www.overlander.co.uk/motors/brushless-motors/tornado-thumper-v2-4240-10-890kv-brushless-outrunner-rc-motor-latest-model.html)
I really like Overlander motors, I am using two in my Model Slipways 1/16th Trent at the moment, so the plan is to run one of these on 6s giving a top end 19758 RPM & 540 Watts.
Video from the lake tests:

First Run - https://youtu.be/gt3CHycXozo (http://www.overlander.co.uk/motors/brushless-motors/tornado-thumper-v2-4240-10-890kv-brushless-outrunner-rc-motor-latest-model.html)
Second Run - https://youtu.be/6tJLQaqKI0I (http://www.overlander.co.uk/motors/brushless-motors/tornado-thumper-v2-4240-10-890kv-brushless-outrunner-rc-motor-latest-model.html)
Lakeside (Half Throttle Cruise) - https://youtu.be/jAkk3XtKe2E (http://www.overlander.co.uk/motors/brushless-motors/tornado-thumper-v2-4240-10-890kv-brushless-outrunner-rc-motor-latest-model.html)

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on June 20, 2016, 11:58:09 PM
Alex.....it's the same old frustrating story  >>:-(..& probably due to the Internet Server....so.......

When you have a post that occupies more than 1/2 a dozen lines.......create it in Word ...or the like....save/edit...come back after dinner...copy & paste it into the MBM page  O0

People do like reading long & detailed postings on subject matter that appeals......one of the great things when members post detail .....and if we are not sure of the specification we can search on it without closing the page

Keep up the good work :-)) .... Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on June 21, 2016, 07:05:20 AM
Alex - your links reposted - I was getting the overlander link rather than a youtube one

Video from the lake tests:

First Run - https://youtu.be/gt3CHycXozo (https://youtu.be/gt3CHycXozo)
Second Run - https://youtu.be/6tJLQaqKI0I (https://youtu.be/6tJLQaqKI0I)
Lakeside (Half Throttle Cruise) - https://youtu.be/jAkk3XtKe2E (https://youtu.be/jAkk3XtKe2E)

Also consider an alternative (cheap) wattmeter. I use a http://www.4-max.co.uk/wattmeter-budget.htm (http://www.4-max.co.uk/wattmeter-budget.htm) (recommended by Inertia too1)
I have mine mounted in a semi-waterproof box - the advantage if this one is that the display is 7 segment LED rather LCD
so should give better visibilty on your vids.

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 21, 2016, 10:43:58 AM
Hi Richard,

Thanks for that, I normally cut and paste web page links into the body of the text, but for some reason last night, everything after the Overlander link became part of the same link, I thought I had separated the text from the link, but it was obviously just the formatting I had corrected

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on June 21, 2016, 11:10:23 AM
Been there, Done That !

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 26, 2016, 07:29:07 PM
Hi Guys,


Ok, let's just say things could of gone better today, several new parts bought and fitted and I went to the lake with high hopes of finally cracking the battery / ESC / Motor combo issue, that is stopping me from progressing this build much further.


Modifications this time around are as follows:


The new Watt meter has an 7 segment LED, 4 digit display, which is nice and bright, I designed and printed a new housing for it and dutifully installed it onto the boat lid, what I failed to realise is that, LED displays are not constantly on, they are just displaying information very quickly and the persistence of vision phenomenon, which makes all motion pictures possible, makes the rapidly changing display as constantly on, without flickering. For a sequence of images to appear fluid in motion, anything above 25fps will fool the eye, however, a digital camera records the outside world at a given rate, one frame at a time, if it is not in sync with the LED display, then it will capture the numbers being displayed at any point during the, "Off, turn on to display for a set period, turn off for next refresh loop" cycle, which makes the film of the display dim, jumpy and very hard to make out, not helped by my recording at 25fps, where a higher frame rate would elevate some of the issue.
One thing this Watt meter does is display peak figures from the run and as suspected, it peaked out at 99.9A, in other words, I need to put the Turnigy meter back on as this one is not rated for the job it turns out.


Results from the lake:


Upon repeated viewing of the onboard GoPro footage, you are just able to make out what the Watt meter reading is and my theory as to what happened is this:


The ESC is not a problem, to be fair, I am surprised it has kept going as long as it did, I have a new 120A water cooled ESC on the shelf and ready to go, I will definitely be programming it with the softest acceleration rate I can. The biggest issue I have at the moment is the boat itself, having a small fire in a confined, sealed space means that everything is covered in an acrid smelling coating of burnt electronics, I just cannot put into words ho much this stinks, I am very tempted to throw the boat away and start again, but we shall see.


Videos from lake testing:


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 29, 2016, 12:51:44 PM
Hi Guys,

Looking into the ESC fiasco, I have discovered that I may have been a bit of a clot, after discovering what I thought was a 90A ESC, is actually an 80A and looking at the specs on HobbyKing's website, the burst current is only 100A with a continuous rating of 80A, no wonder it went south  {:-{
But not to worry, I have a HK 120A water cooled ESC on the shelf and that has a burst rating of 150A, Turnigy also do a 120A ESC with a burst rating of 750A!!  %%

So the plan is to gut the current hull, give it a really good wash, as it is stinking out the shedshop currently, then rip out the current jet unit and replace with a revised version:

To help with all of these mods, I am currently constructing an enclosure for my 3D printer to make it quiet enough to print overnight, which will speed up things enormously, separate post on this shortly.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 05, 2016, 10:44:04 PM
Hi Guys,


Progress on the rebuild today, I have stripped out the charred remains of the old ESC and took the hull into work to introduce the hull to the table saw. No, don't worry, I'm not binning the prototype just yet, as it is on it's second drive unit tunnel already, the bottom of the hull has been chopped and repaired quite extensively already and the easiest way to fit a new tunnel in is to chop out the back half of the hull and graft a new one back in.


I am planning to get back on the lake with the new version this weekend, so watch this space for more updates to come, I am also making good progress on the 3D printer enclosure, separate post to follow soon.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 11, 2016, 12:06:08 AM
Hi Guys,


Well I may of not quite made it to the lake this weekend, but I have rebuilt the jet boat prototype and even staying in the shedshop, things have been eventful.


Changes made during rebuild:


The new impeller tunnel is slightly redesigned, this time I have incorporated captive nuts in the base which allow the entire motor mount to be removed with the motor attached, allowing another to be swapped in quickly and easily, this will greatly aid the motor comparison work that I am wanting to complete, it was possible to do a motor change lakeside, but it was a long and fiddly process with little to no access to the bolts, each test motor also has a shiny new redesigned mounting bracket, so it is almost plug and play.
Another problem I am also trying to address is my long running battle with water ingress into the hull, I think this is down to the old design, where the tunnel just clamped to the transom, the tunnel was bonded to the inner transom surface, but any cracks would lead to pressurised jet water escaping into the hull. This time however, the inlet grate is a bonded integral piece and the outlet is stepped to allow the body of the impeller tunnel to carry through the transom, so any leakage will occur outside the hull, in theory.
The old seemingly indestructible 1900Kv inrunner I have been using is great, but I would like to test a motor on 3s which doesn't over speed the jet drive, which means a step down from 1900-1700Kv in the form of Turnigy's Aquastar 1700Kv...


Pah! "Aquastar" my a**! How can a motor that blows smoke on the work bench be an Aquastar?  >>:-(  I tell you, I got it all setup in the freshly rebuilt hull and was doing a systems test after programming the new ESC and poof, just after touching 100% throttle, smoke out the back of the motor.
It doesn't help that the HobbyKing instructions for setting up their ESC are all in badly translated Chinese and even after reading them several times, the grammar is so bad, some details are unclear to say the least.


So next weekend I will be back down the lake for more tests, this time I will take the Overlander outrunner and the old standby 1900Kv inrunner, I may also upgrade to a Turnigy 120A ESC, as I have used their ESCs with no trouble in the past and I am not convinced the HK one is doing what it should do.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 18, 2016, 12:13:36 AM
Hi Guys,


Well, made it down the lake today and conditions were a bit choppy for testing, but I threw it in anyway and watching the GoPro footage back, the boat took a real hammering traversing the lake, so much so, that on the second run I nearly shook the reversing bucket off.


Mixed bag of results from the runs today:


The first run was quite encouraging, except for the rough conditions, which meant full power runs were all but impossible, the sun was so bright today I couldn't read anything from the watt meter at all, this has to be the most disappointing part of the testing today.
But i is not all bad news, the new ESC survived and although quite warm to the touch, it was by no means worryingly hot, what was worrying however, was the amount of water ingress into the hull again, I am going to have to get to the bottom of this once and for all, which will probably mean testing in the bath to see where the water is coming in.


The second run started well and below three quarter throttle, the outrunner performs really well, until full throttle, when there was an almighty scream from the motor and a loss of drive, but as quickly as it stopped, upon re-application of throttle it was off again like nothing had happened... until it did it again and then nothing, had to be rescued.
Watching the GoPro footage back, after the first loss of drive, white smoke can be seen inside the hull and then the second time much more smoke, it is clear that something has gone horribly wrong and by the smell of the motor and the yellow / orange discolouration of the motor mounting, I would surmise that I've managed to pull too many amps through another motor, the smell being from the winding insulation which has simply melted away.


So more work to do, I will post GoPro footage tomorrow.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 20, 2016, 07:54:05 PM
Hi Guys,


Apologies for the delay, had some trouble encoding the video for YouTube:


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 21, 2016, 11:12:09 PM
Hi Guys,


News from the Shedshop, have been playing around with how to get a legible recording from the watt meter and the Turnigy one is proving to be a royal pain in the ass, which go me thinking about the LED one I have, what if I increased the frame rate of the recording? Would this resolve the flickering issue I am having?


My GoPro Hero 2 will record @ 720 60fps and as you can see from the screen grab, the readout is perfectly readable, so will swap back to this one for the time being.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: grasshopper on July 21, 2016, 11:40:41 PM
Really impressed with this thread and been following with interest. I have a couple of NIB graupner water jets for a future project when I retire......
When you're going at high speed and the scream comes, could it be the duct goes suddenly dry causing the impeller/motor  to become unloaded and spin at higher revs, slowing down allows it to refill and then drive correctly again?

If the hull you're experimenting with is flat bottomed, could this be the problem? Even a shallow ve hull would put the intake below the water level and lessen the chance of the duct running dry.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 22, 2016, 12:09:59 AM
Hi Grasshopper,


Thanks for the positive comments, depending upon which video you are watching, inrunner or outrunner, the reasons for the screaming are different:


As for the hull, you are absolutely correct, the air boat type hull, although very quick and easy to bang together, is completely rubbish at keeping the jet unit in the water, I am hoping to take delivery of a new hull tomorrow, 39" long by 11" beam, once I have nailed the water ingress problem once and for all, (I am planning on some bath testing for this) I plan to do a final stage prototype with twin drives, this will allow me to further develop different designs of the reversing buckets I have plans for.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 23, 2016, 11:20:15 PM
Hi Guys,


So got the prototype back together and did an autopsy on the outrunner, at first I thought it was water ingress shorting out the motor, but on closer inspection of the windings it looks much more likely that the insulation on the wire simply melted to an excessive heat build up.
The problem with a lot of motors is that they are designed for the aircraft crowd, which means there is a pretty stiff breeze for cooling purposes, but inside a boat hull no such luck, to try and combat this I have installed the 3D printed fan from a previous outrunner I tried, onto a replacement identical Overlander outrunner, so tomorrows lake trials will be interesting and hopefully I will also get some useful info from the watt meter this time.


Along with a replacement motor, the final prototype hull arrived and this time it is a much better size.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: TheLongBuild on July 24, 2016, 12:44:09 AM
I tried to do a write up of Saturday's testing last night, but as I hit the post button, I was asked to log back in and lost an hour and a halfs work  >>:-( so here is a shortened version.
Alex

If a long post I always draft it first in outlook and then copy and paste..
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 25, 2016, 12:44:50 AM
Hi Guys,


Great day down at the lake today, conditions were excellent, with the lake surface flat like glass, definitely getting some power runs in today!  :-))

The first run went very well, before the run I sealed the joint between impeller tunnel and transom which reduced water ingress significantly and after several successful full power runs around the lake, I brought it back in to asses component health. The ESC was warm, but not worryingly so, the motor on the other hand was a different matter, even with water cooling it was finger scorching to the touch.


Second run I took the watt meter out of the equation, as it had come back reading 99.9A as a peak value, out on the lake I thought the top end was a bit slugish, so took the watt meter out to test if it was becoming a strangle point and I was right, much livelier.


Third run is the same setup as above, but this on was recorded from the lakeside and it ended very abruptly, part way through a turn with the motor making a very low rumbling noise and then cutting out, with boat completely unresponsive for about 30 seconds. I don't really understand what went wrong here, it may of been an inbuilt ESC safeguard that I tripped, I just don't know, it all appears to be working fine now.


Fourth run saw a change of kit over to a shiny new replacement outrunner and 6s pack, as I knew from previous outings that this motor would stay within the 100A threshold of the watt meter, it was duly reconnected. Just to play it safe I only ran this test upto 3/4 throttle and upon examination of the GoPro footage later, it was clear to see that the Outrunner is much more efficient, returning half throttle cruising figures of 25A compared to the inrunner's 40A. All went well and it was a very successful run, the motor did get worryingly hot, even with the new fan, which now needs to be made in a more robust material, as the PLA got so hot it turned rubbery and stretched under the centrifugal force of the motor.


Videos from today:


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 30, 2016, 01:15:32 AM
Hi Guys,


Some upgrades to the prototype today in preparation for testing on Sunday, in order to try and address the inrunner cooling issue, I have bought and added water cooled Aluminium motor mount blocks as part of the cooling system.
I have also decided to ditch the Outrunner and bought a different inrunner to try, this time an Overlander BM600 3650/09 1500KV:


http://www.overlander.co.uk/motors/brushless-motors/inrunner-motors/bm600-3650-09-1500kv-brushless-inrunner-rc-motor-latest-model.html


It will be interesting to see how the lower KV motor performs and how much juice it draws whilst doing it.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 04, 2016, 10:36:28 AM
Hi Guys,

Was on the lake last Sunday testing the jet boat, unfortunately work has gotten on top of me this week and I haven't had time to do a proper write up yet, but I have got the videos up:

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 15, 2016, 12:36:02 AM
Hi Guys,
 
Finally got around to sitting down and writing up some results, second to last test session was on 31/07/16, conditions were very rough and the prototype took a real pounding, but lots of useful data was collected over four runs:
So in summary, despite the rough conditions, I did mange to get quite a bit of testing done and the 1500KV motor was showing promise, admittedly it was a bit slower, but across  the board it was a good 10A less power hungry than the 1900KV, or at least it was until the windings melted, destroying the motor.
Thoroughly fed up about melting yet another motor, I decided to go back to the drawing board, the original Graupner jet drive was supposed to be paired with a Speed 700BB Turbo, so I scratched my head for a while and tried to come up with similar solutions.
The biggest problem I have at the moment is that when brushless motors are pushed, they don't slow down, they just keep pulling more and more amps until the windings melt... ask me how I know this.
So the long and short of it is, I need more power, or to put it another way, I need a higher wattage motor, to this affect I have decided to explore several different avenues:
Now, some of the parts for this are on order and as I type this, I am already changing things around in my head, as ideally I would like a solution that works off 12v / 3S as well as the surprising out come of yesterday's trials.
So although power train two will be done in some form, I will most likely get a ZTW Black Mantis B3640 3400KV inrunner running on 3S, (11.1) which will give me 37740 RPM, then stick a 2:1 gearbox on it to give 18870 RPM.
But what is the point of all of this gearbox faff?” I hear you cry, well, the big ongoing issue at the moment, besides the hull design, is amp draw, I am over stressing the motors with direct drive, so the easiest way to combat this using the same motor, or there abouts is with a reduction gearbox, which will allow a faster motor to produce more torque, by giving it greater mechanical advantage.
Most of this drivetrain work is now redundant after yesterdays results, but at the same time I want to increase my understanding of how brushless motors perform given different scenarios, so it is more of a technical exercise for my own satisfaction.
 
Results from 13/08/16 were, very uncharacteristically, a huge success:
So this all came about because I wanted to do some testing and didn't have any of the new parts yet, the 775 is coming from China, at some point, the new inrunner did arrive, but turned out the eBay seller had sent a 1900KV model instead of the 2300KV one I wanted and the 2:1 reduction gearbox I haven't designed yet, but I have done the research and found something to base it on.
Then rummaging in the Shedshop I came across the 500KV outrunner I had bought right back in the very early prototype stages, when I was still running Nimh packs and experimenting with a three bladed impeller, the results from back then were lack luster to say the least, but now with a better understanding of brushless motors I knew that I could connect my 6S (22.2v) battery to it and it should perform half way decently, giving a top end of 11100 RPM.
Installing the motor was easy enough and it fitted within the motor mounting system I have designed, I used one of the water cooled motor mounts and refitted the 3D printed cooling fan I designed originally for this motor, what I did notice though, is that the motor mounts are warping due to the excessive temperatures the inrunners are exposing them to and both will need replacing at some point.
 
Out on the lake I wasn't expecting anything that impressive from the 11100 RPM top end, how wrong could I be? Very, very wrong, whilst it may not have the all out blistering performance of the 1900KV, the 500KV is a torque monster and it span the jet drive like it wasn't even there:
 
The short shake down run went well, with one minor glitch, the motor mount being slightly compromised has introduced a low end vibration that is quiet bad at times, but once you throttle past around 15% it goes away, so I wasn't too concerned on this outing.
Apart from the overall performance in the choppy conditions, I was slightly disbelieving when the watt meter came back after the initial run with a peak reading of 31.8A, yes you read that correctly and yes the decimal point is in the correct position.
Back out onto the lake for more testing and the motor just kept going and going, only failing on a few occasions when the prototype actually caught air in the rough conditions, which caused a loss of pump prime.
Pushing hard I stayed vigilant and routinely brought the prototype in to test the motor temperature and for water ingress into the hull and on all occasions the motor was only warm to the touch with next to no water ingress present.
Progressing on from this very successful day of testing, I am very tempted to try another one of Overlander's big Outrunners, they have another sightly faster model, the 5045/10 720KV, which on 6S would give a top end of 15984 RPM compared to the current motor giving 11100 RPM, also worthy of note, the current 500KV motor has a listed idle current of 4.3A with a rating of 900W compared to the 720KV motor, which has a listed idle current of just 1.7A and a rating of 860W; the bigger can size would also mean it has more torque than it's smaller sibling.
With a current draw of just under 32A we can calculate that the current motor was producing somewhere between 720-800W, this fluctuates as the battery voltage drops off, but is well within the maximum 900W rating, this was all carried out with my Turnigy 6S 5000mah Lipo pack, which when reconnected to the charger that evening, was still reading a 25% charge after an accumulated 20 mins of run time on the lake with the majority of that being at three quarter to full throttle.
 
 
Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 21, 2016, 09:49:50 PM
Hi Guys,


Managed to get things bolted together and down the lake for some late night testing yesterday, hence some of the footage being a bit on the dark side.


Surprisingly there are no reduction gearboxes available off the shelf for a custom jet drive project like this, shocking I know, so I had to design and build my own to suit, which in the end was not such a big ordeal, I had seen some other reduction systems for planes and just decided to modify the basic principle. With a couple of Brass 0.8 MOD gears from www.MotionCo.co.uk (http://www.MotionCo.co.uk)  and some flanged bearings to suit the shaft size I am using, I fashioned a gearbox using some laser cut Acrylic and standoffs to keep the separation correct.
With the 3400KV inrunner fitted and running on 3S, I was getting an input of 37740 RPM and an output speed of 18870 to the jet drive... in theory, unfortunately because of the motor's short can length, none of the water cooling jackets I have fitted it, so testing would have to be brief and uncooled.
Down at the lake I held the prototype steady in the water on the slipway and did some static power tests so that I could make sure the gearbox would hold together under load and also to see the readings of the watt meter before setting off for the other side of the lake.
The first run went well and despite and initial reading of 80A at full throttle, the drive seemed to settle down at around about the 65A mark for full throttle cruising, it is by no means the quickest run I have done, the performance seemed a bit sluggish to be honest, but the gearbox held together very well, despite taking a pounding from the rough water and with no ingress into the hull, I set out for the second run.
Second run lasted about the same length of time as the first, although it didn't end nearly as well, for starters I forgot to press record on the GoPro and I also forgot that there was no water cooling on the motor, so when the boat started getting slower and slower, I thought it was the battery dying, alas it turned out to be the motor had completely melted internally, I mean totally, there is no rescuing this one, even the anodising on the outside is a different colour now.  <:(


Third run saw the new Overlander 5045/10 720KV Outrunner take a turn, running on 6S I should be making 15984 RPM, as before I did static tests at the lakeside which showed a higher amperage draw over the 500KV motor of roughly two fold. With light rapidly fading by this point and the wind making conditions very rough, I sent the prototype out to try and put down some power runs, full throttle was not achieved for any great length of time due to the rough water throwing the prototype around and every time I got up to full power the motor would make a high pitched squeal, loose all power and then stop, I have had this happen before with another outrunner, reduce throttle and feeding the power back in gets you under way, but it doesn't resolve the problem, after some googling about this it turns out that it may be an issue with the timing setting of the ESC.
If I can get this sorted and find some calm water, then I would really like to open the prototype up properly as even in the swell it was flying along, one problem though is that the motor was quiet warm by the end of the run, compared to the 500KV which was only warm to the touch, it didn't help though that the cooling fan had come loose due to the rough conditions.

Videos from testing:

Onwards from this I will be working on the timing issue of the 720KV, replacing the burnt out 3400KV with a 2300KV for testing on 3S & 4S and at some point the 775 should turn up from China as well, Overlander have another motor that I would like to try, a 5055/06 580KV Outrunner which is rated at 1280W, I am also going to print some new impellers and see how the design impacts upon the performance / amperage balance.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 21, 2016, 09:54:17 PM
Hi Guys,


Thought I would post some other stuff in the interim between testing, following are some photos showing just how much stuff I have gotten though already on this project, no wonder my wallet is felling a little light these days!  {:-{


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 21, 2016, 10:07:45 PM
Hi Guys,


Digging through some old photos I came across a real trip down memory lane, back in 2002 I designed and built my first jet boat using Graupner mini jet units, powered by twin Speed 500 Race motors on a 7.2V stick pack from a radio controlled car I had.
The hull is made out of lite ply and styrene sheet to my own design, I didn't know much about boats back then and it was what I thought would work.


Video of the first test on my Uncle's lake in Wales - https://youtu.be/us6i85Hkxd0


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on August 24, 2016, 04:37:42 PM
Great stuff Alex, you couldnt dream of the 3d printing stuff you are doing back then could you?
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on August 24, 2016, 04:38:19 PM
And look at all that hair!!!!!!! :}
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 27, 2016, 07:58:33 PM
Hi Guys,


We had a night sail last night so took the prototype down for some impromptu testing whilst we were waiting for it to get dark, this time around I wanted to test out different timing settings in the  to see if I could find one that would suit the 5045/10 720KV Outrunner and stop all the nasty squealing at high RPM.
After much testing on every setting, none of the timing settings in the HobbyKing ESC solved the problem, after more reading about this issue in other forums it looks like it may be a simple case of the ESC is not 100% compatible with the motor, so I am going to buy either a Turnigy marine ESC or get an Overlander branded ESC to see if that solves the problem.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: tsenecal on August 27, 2016, 10:32:32 PM
most of your outrunner motors ( 99% ) work best with zero timing.  a lot of the cheap car ESCs designed for inrunners will not give you zero timing... even the basic hobbyking branded 30/50/90/120 amp boat ESCs ship with 15 degrees of timing as default and need to be reprogrammed before they will work right with an outrunner.  ask me how i know this :)
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 27, 2016, 10:37:12 PM
Hi tsenecal,

I am running a HobbyKing marine 120A ESC, it does 0, 5, 10, 15, 20, 25, 30 and auto as degrees of timing, all options were tried, none seemed to work, although one did seem to hit a sweet spot with the motor, the top end still squealed.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 29, 2016, 11:15:47 PM
Hi Guys,


Did some testing down at the lake today, I was planning to test the 1900KV 3660 inrunner with the 2:1 reduction boz on 6S to see what the current draw would be like, but unfortunately my plans were thwarted by my own incompetence by forgetting to install the shaft coupling!  :embarrassed:
I did however do another test with the 5045 720KV Outrunner on 6S, with 25 degrees of timing, a new cooling fan, (which still fell off) as well as a modification to the watt meter housing to incorporate a mini servo, which shows me how much throttle input is being applied at any given time.


Video from testing: https://youtu.be/vfNzwhzS_Qg


It was interesting to note that, although appearing quite calm from the lake side, the prototype was thrown about quite a bit on the more exposed sections of the lake, it is also very apparent that the timing is off as current draw against RPM becomes very disproportionate above three quarter throttle.


Alex   
Title: Re: Water Jet Drives & 3D Printing
Post by: dirkske on September 08, 2016, 07:00:03 AM
To save you from burning more windings; maybe get one of the below. When used properly, will save you money on the long run.  Assuming you have one of the more common brands of telemetry capable transmitters:

https://www.sm-modellbau.de/UniSens-E (https://www.sm-modellbau.de/UniSens-E)

At very least you can program a warning in your transmitter when nearing max motor amps
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on September 08, 2016, 11:04:04 AM
Hi dirkske,

That is a very interesting looking module, unfortunately I am using an F14 Navy which I have retro-fitted with a corona 2.4ghz module, giving me dual 2.4 and 27mhz for my sub.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on September 27, 2016, 02:48:27 PM
Hi Guys,


Finally getting around to catching up on my write ups now that I am on holiday, my last testing session down at the lake was on 17/09/16 and it was very successful, armed with a new Turnigy marine 120A ESC, it has cured all of the running issues that I was experiencing, it was however not without its problems in the beginning.
I bought the ESC, like most of my RC stuff, from HobbyKing, I already have two of these lower rated ESCs in my brushless Trent so already had a programming card for it, I didn't come across any programming issues for the Trent as I only wanted to change the ESCs to forward and reverse operation, which is the first option on the menu.
The real confusion arose when I wanted to start changing the timing settings, which as the picture shows, is item 09 in the menu system, but the LED readout on the card only went as high as 04 items!?!?
In the end after a lot of searching around the internet on various forums, it became clear that this programming card is shipped with various sets of software and stick on menu plates, which do not always match, fortunately, the programming card was displaying the correct number of menu items, with the correct number of options per menu item as according to the manual, so using that as a guide I programmed the ESC and all appeared to be fine.


So with new ESC installed and operational I went down to the lake armed with a couple of large Overlander outrunners and my 6S 5000mAh Lipo pack, testing consisted of installing each motor in turn, programming in a timing option, then recording a static thrust test on the slipway using the POV GoPro, at the end of each run I recorded the results down in my notebook and this is what I found.


Outrunner 5045/10 720KV on 6S (16128 RPM)
Outrunner 5055/06 580KV on 6S (12992 RPM)
Now it must be stressed that these figures are not going to be super accurate, the watt meter didn't want to settle quite a lot of the time, so most of the figures are averaged to try and give some kind of meaningful comparison.
Comparing my result to other tests done online, I am not very surprised with the outcome, I started testing at one end of the timing range, the motor will run, but will more than likely be running very warm with a high current draw, you then cross a threshold and the timing starts to match the motor configuration much better, which is indicated by a sudden drop in overall current draw, this can be seen in the 720KV results when I drop below 22.5º of timing, half throttle is reduced by 5A and full throttle draw is reduced by 11A!
As far as I understand, this proves that 18.75º with the 720KV motor is the best compromise for a balance of max power and efficiency, whilst keeping within the motor's maximum operating rating of 80A, which means there will be no overheating issues, so no melted windings!  :-)) 

Looking further into the results it is important to note that static lakeside testing will give different results to running up and down the lake under normal operating conditions, this can be seen from the, "on lake" figures in the chart, the reason behind this is that the loadings within the drive are different whilst running static as apposed to free running on the lake, the brunt of the force being transferred from the impeller comes back up the impeller shaft and into the coupling and on a couple of occasions I had the coupling slip and the impeller start the catch the inside of the impeller tunnel, when I do my next redesign I will be looking into different couplings methods and may introduce a force plate to isolate the motor and coupling from longitudinal loading.
After static testing was completed for each motor, I chose what I thought was the best timing setting and sent the prototype out for a couple of power laps around the lake for comparison. The 720KV motor was sent out with a timing setting of 15.00º, which gave an overall lower full throttle reading than the static testing, but I think this is more down to the motor not spooling fully before the ESC stepped in to protect the battery from over discharging. The opposite was found for the 580KV on 15.00º of timing, with a full throttle power run returning a higher figure than the static tests, but looking at the figures, it would appear that this motor would respond better to a lower timing input and at a later date I will go back and retest the 580KV on the 3.75º and 0º settings.
As with any development process, a fair amount of trial and error is required and this project is by no means any different, every time I take another step forward in overall output I run into one or more problems to be solved. I am fairly confident that I have got a handle on the motor / battery / ESC combination issue, which means that I can put the power into the drive, I am facing new challenges at the upper power levels due to the fairly in-compressible nature of water, effectively, to make better use of the power I am putting in, I need to change the design of the jet unit to allow for a more efficient through put at high speed, allowing for easier ingestion and expulsion of water.
By smoothing out the flow through the unit this should stop the impeller trying to pass more water through the stator housing than it is capable of flowing, because if you exceed the available flow rate out of the unit, all you will end up doing is causing the internal pressure of the unit to rise, which can be very crudely measured by the flow of water coming out of the cooling water port, which is tapped off the side of the stator housing, so the higher the stator housing pressure, the more cooling water output there will be.
Cooling water doesn't flow below 15% throttle and upto to around 70% it is quite proportional to throttle input, above and beyond 70% the output increases significantly, suggesting that pressure is increasing disproportionately to throttle response, some ideas to combat this that I am going to explore are:

On this outing I very briefly tried putting a ramp behind the inlet on the bottom of the hull, the idea was to slow the flow of water passing the inlet and force it up into the jet inlet, this kind of worked up to a point, but at higher speeds the water pressure in front of the ramp built up until the back of the hull would jump to equalise the pressure, the cycle would then repeat which lead to the back of the prototype jumping up and down at high speed, so the ramp was removed and the whole exercise chalked up to experience.

Moving forwards I am starting the design and build of the MK2 prototype, which will consist of twin jet units in the large white and orange fibreglass hull I bought a while back, this means larger jet units will be required and to this end I have just bought a larger 3D printer, which will allow me to make tunnel housings upto 250mm in length if I want to.
But the MK1 prototype is not finished with just yet, I intend to go back to the lake and re-test the 809KV outrunner I have, as well as the seemingly indestructible 1900KV inrunner, I also have a 775 brushed motor that I might test as well just for kicks.
One last improvement that I have on the cards is a redesign of the reversing scoop mechanism, it takes a real beating hammering across the lake and the bolts that hold it together keep falling out and although it does make the prototype move backwards, there is no real control, so I will try and address these issues as well.

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on September 27, 2016, 07:10:47 PM
Hi Guys,


Uploaded the video of the 580KV first run to show the skipping affect of the inlet ramp, enjoy!


https://youtu.be/vhwHL1u55WI


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on November 15, 2016, 03:16:15 PM
Hi Guys,

Quick update as I have been really busy of late, been down the lake a couple of times testing the jet drive prototype, both time with the 500KV Outrunner on 6S, but testing different impeller designs:

I might do some more testing with this hull, but I am more inclined to either move on or refit it with the next evolution of drive, either way, lots more jet drive fun to come!  :-))
Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: g6swj on November 15, 2016, 04:13:53 PM
Alex,

Reading your 3D forum postings is like when you are a kid and got the latest release of your favourite comic - can't wait to see what you have got upto and what results and learning you have got from your latest experiments.

Your posts are very inspiring and what you have achieved is remarkable.

What is the spec of the latest printer you are using (version etc) and is it standard or have you upgraded/changed any of the components?

I am writing my list to Santa shortly and a 3D printer ( maybe second hand) will be a possible "wish list" item

Do keep up the posts and pics - absolutely fascinating!!  - Love IT.......

Regards
Jonathan
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on November 15, 2016, 10:22:56 PM
Hi Jonathan,


I have two printers currently, one Lulzbot Mini & one Lulzbot TAZ 4, which was upgraded by the previous owner to TAZ 5 specification, since then I have upgraded the extruder unit to the latest 2.1 model, apart from that I have not modified the printers, I do run each off their own dedicated Raspberry Pi, both running OctoPrint server, which allows me to control them both from anywhere I can connect to the internet, very useful for stopping a print that h gone wrong whilst I am at work. http://octoprint.org/
I bought both of my printers secondhand off eBay, searching every day until the right deal came along, which meant I got both for a little under half or their respective retail values.


Many thanks for the kind comments, it is always a pleasure to hear from people who are enjoying what I do, if you have not already read some of my other posts, you may enjoy these:
[/size]


Alex

Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on November 24, 2016, 11:48:37 PM
Hi Guys,


Quick update as things happen, doing some preparation work for my next trip to the lake this weekend, namely printing a new motor mount for the brushed 775 I bought a while back, really curious to see how it performs, I will also be testing the old steadfast 1900Kv on 6S with the 2:1 reduction gearbox I built, but this time around I'll remember the motor coupling.
I would really like to brake out the larger MK2 hull, but getting that ready is not going to happen this side of Christmas realistically, so I have decided to bodge the prototype hull again, but this time in an effort to make it more boat like by 3D printing a 300mm long extension for the bow, how successful this will be is anybodies guess, but rest assured I will report back either way.


Alex 
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on November 24, 2016, 11:55:47 PM
Alex,

The bow add-on looks interesting - should perhaps fix the porpoising I think you
have mentioned in previous posts

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on November 29, 2016, 12:06:12 AM
Hi Guys,


Quick update from the weekend, I didn't achieve as much as I was hoping to, this is mainly due to a couple of 3D print failures, which meant that the new bow I had planned had a massive chunk missing from the middle, so I am waiting for more filament to arrive and then have another go at printing the largest part for the third time!  >>:-(


I did however have a successful run of the brushed 775 on 3S, it performed well, not getting noticeably hot and cruised at full power pulling around 60A, I would like to do a test in the future  on either 5 or 6S to see what the power consumption is like.
I had also taken the 1900KV inrunner setup with the 2:1 ratio gearbox and was all ready to run on 6S, when I discovered that, despite bringing a motor coupling this time, it was the incorrect one and meant for a different motor, oh well, next time maybe.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 07, 2016, 12:18:52 AM
Hi Guys,


Quick update on how the 3D printed bow extension is going, finally managed to successfully print the centre sections and found some time to assemble everything in the shedshop tonight, hopefully testing down the lake this weekend.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on December 18, 2016, 11:41:11 PM
Hi Guys,

So got the jet boat on the lake today, testing with the new bow extension and running the old 1900KV inrunner on 6S through a 2:1 reduction gearbox giving 21280 RPM.

On the plus side, the boat didn't sink, catch fire or blow anything up... however, although the new bow extension works really well at cutting through surface swell, it throws up one hell of a bow wave and by the end of the run there was over an inch of water inside the hull due to the huge amounts of water flowing over the not so water tight lid, it is a really good thing that the Turnigy ESC I am using is 100% waterproof!
Nevermind, that motor, along with the rest of the boat has been to the bottom of the lake before and survived, so I am sure that after a few days drying out on the radiator, all will be well again, wish I could say the same for the gearbox, where there was  minor failing of the grubscrews which held the spur gear onto the output shaft, this lead to the drive shaft walking forward, the shaft coupling mining it's way through the 3d printed motor mount and the impeller to mince itself on the inside of the tunnel, again.
Unfortunately the brass gears are also a little worse for wear, but this has more to do with the approximate 2240W they had to endure, rather than some dodgy grub screws giving way, this all means the inside of the hull now sparkles with the remnants of the gears and I will be rebuilding the gearbox with something stronger, maybe helical this time.
But it is easy to fixate on the negative where as today was an overall success with the prototype tearing across the club lake, it is a real shame that I killed the watt meter on the last outing, but a new year will soon be upon us and I feel the need to break out the proper hulls.

GoPro POV of part of today's run: https://youtu.be/QJnZFSgUa2U

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Yogibear on January 30, 2017, 12:28:19 AM
I drew this up a few years ago


https://grabcad.com/library/water-jet--1


Got some time in my hands recently so I've been printing out versions.


Some of it prints fine, other bits are a pain trying to account for shrinkage
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on January 30, 2017, 10:41:58 AM
Hi Yogibear,

That's a very nice looking model, designing one of these Kamewa style reversing buckets is something that is on the list to do, please post some photos of how you are getting on

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 18, 2017, 06:33:48 PM
Hi Guys,


Not been getting much done of lat due to pressures at work, (stupid reality getting in the way of my fun!  >>:-( ) but I have found some time this weekend to sit down and get some work done on the jet boat design, this time building on the success of the 6S 1900Kv inrunner 2:1 gearbox, I am making the following mods:


Good reasons for these changes, new motor, bigger, better and who doesn't like more power?!?!  :-))  On a more serious note, jetdrive's are phenomenally power hungry devices, the 1900Kv works well, but even with water cooling, it is still very hot at the end of each run, so the thinking is this, bigger motor equals more torque due to increased mechanical advantage, this means more power and more power, leading to a less stressed motor, which means cooler running... well that's the theory.
With the new GOOLRC motor having a rating of 2000Kv, I decided to change the gear ratio, as I was changing the gears anyway, dropping the overall RPM will drop the current draw, which means cooler running and longer run times, I have also noticed from the GoPro POV footage that the jet unit sounds very laboured above 85% throttle, I believe this is due to a lack of flow through the unit, due to restrictions in the design, water in / out is not equal to demand, the new design of drive should address these issues.
At the moment, with the  1900Kv 6S setup we are getting a drive input speed of: 1900 x 22.4 = 42560 x 0.5 = 21280RPM, now this appears to be a tad fast, as I have found that this unit prefers speeds in the 18 - 19K RPM range, anything more than that suffers badly from the rules of diminishing returns, the new setup will give: 2000 x 22.4 = 44800 x 0.43 = 19264RPM, the parts for the new gearbox are printing as I type, so hopefully I can bolt it together tonight and get down the lake for testing tomorrow.


I also have news of the twin jet unit and some early work in progress screen grabs to share with you guys, as over the festive period I managed to start designing the new and improved unit, bigger, better and more free flowing than the old one, this will be a true 40mm unit, with the impeller OD being 40mm and the tunnel being 42mm ID, I have also redesigned the stator housing, opening it up to drastically improve through flow, the trade off is a slight decrease in flow velocity, but the increase in flow volume should compensate for this.
After a thorough inspection of the large fibreglass hull I bought, I have decided it will be less work in the ShedShop to 3D print an entire hull, instead of trying to make the new hull work with what I have, this works for me as I have very little time to physically get out to the ShedShop and do stuff, but my 3D printers can get a huge amount done when I am at work.
The new jet design will also come with a range of new and improved reversing nozzles, I have taken the excellent work that Yogibar has done and reworked his drawing to make it work with the larger unit I am designing.


With any luck more updates tomorrow after a morning of tearing it up at the lake!  :}


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Yogibear on February 18, 2017, 09:16:44 PM
Hi Alex


Good progress, I'm collecting a second machine next week with dual extrudes and a
3D scanner.


I was browsing the MHZ website and they do some bigger jet drives which I think
Are designed for small petrol engines but are worth a look.


When I printed out the main body I was thinking there must be a good reason the the geometry changing at the impeller. I think it's to induce an increase of pressure difference at the inlet by increasing the area which would usually slow the flow but the impeller than accelerates the water. Something I'll have to have a look into a bit more closely.


Niall


Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on February 19, 2017, 07:06:14 PM
Hi Guys,


A successful afternoon down at the lake, the gearbox survived, the new motor runs smoothly, as well as coolly and I appear to have fixed the water ingress issue with some prop shaft grease on the shaft seal, result. The only minor flaw was a recurring electrical issue which is proving a pain to track down and annoyingly intermittent, however, I got some power runs on film, the best footage can be seen here:


https://youtu.be/lkX9wtkYwy0


I am extremely happy with how the new gearbox / motor combo performed today, the new gears absorbed all of the abuse I threw at them and the prototype now sounds like it is powered by a jet engine, at no point after a run did the motor ever feel hot or even warm to the touch, meaning that it is operating well within it's comfort zone, as well as returning very promising figures from the Watt meter, which I may be able to improve with a bit of tuning on the timing of the ESC, half throttle is around 27 - 30A and flat out is around 93A, a big improvement over the 110A full throttle figure for the 1900Kv motor.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on February 23, 2017, 06:50:45 PM
You have got some serious thrust there Alex. Excellent design work and glad the improvements have been a success.
Will keep tabs on this thread, may pick up some clever ideas for my thruster.


Regards


Stewart
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on March 05, 2017, 04:49:13 PM
Hi Guys,


Been super busy recently with work and family celebrations, hence the lack of updates on anything, but I have acquired a new toy recently, not really intentionally, but whilst visiting my parents the other weekend, it came up on eBay, I managed to negotiate a good price and most importantly, it was only a few miles off my route home to collect it, so no worries with couriers damaging the package in transit.
So I am now the proud owner of a secondhand Formlabs 1+ SLA printer, sure it doesn't come with some of the fancier features of the Form 2, but it is still a very capable printer, the quality of which is in a different league to what a well setup FDM printer can produce.
To put this into perspective, the best I can reliably get out of my Lulzbot mini is a 0.14mm layer height using a 0.5mm diameter nozzle, this naturally places limitations on the resolution you can print at, where as the Formlabs 1+ can print down to a layer height of 0.025mm, combine that with a laser tracing out the parts, (I don't know the spot size of the laser) this produces parts which are seamless in comparison.
The photo of an impeller is printed at a layer height of 0.05mm and took around 2.5 hours, it is not very clear in the photos, but you can see layer lines, but they are very minimal and overall the part looks more like it was injection molded than printed, compare this to the FDM prints, which have much more pronounced layer lines, then the comparison in quality is like night and day.
I didn't actually buy this printer to produce jet drive impellers, although they are unarguably better quality in every respect and should perform much better than their FDM counterparts, as the surface is so smooth when compared to FDM, this should all but eliminate the effects of rough surface induced cavitation, I actually bought it to produce parts that the FDM machines are not suitable for, small detail parts for example, the Formlabs machine can produce small, intricate parts that, with very little work, are ready to be painted and stuck onto the model, it also opens up a range of alternative materials that were not previously available to me before, custom flexible rubber Stolly tires anyone? Clear resin is also very useful.


More as things progress,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 15, 2017, 11:13:09 PM
Hi Guys,


So progress has been a little slow of late on the Jet Drive, partly due to the start of a new Club 500 season, my Trent refurb, but mostly due to me gacking a bolt on the jet unit trying to take it apart, non-stainless bolt in a non-stainless nut with no anti-seize, the two were fused together pretty well, in an attempt to remove the bolt I tried drilling it out, but all this did was overheat the 3D printed stator housing and the bolt melted straight through it.  :embarrassed:
Oh well, I had intended to make some improvements to the unit anyway, plus it gave me an excuse to reprint the stator housing with the cooling water outlet not in line with one of the fixing bolts, yeeah, not was of my more genius moments that, improvements made this time around are:


More updates as they happen


Alex



Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on April 15, 2017, 11:42:50 PM
Alex.....are there any issues with the mechanical stability of these plastics?....[in metals we consider creep resistance in turbine blades rotating a high RPM and heat].......so is diametrical growth an issue with the rotor of the jet drives?

Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 16, 2017, 12:00:59 AM
Hi Derek,


I have had the PLA impeller up to 22K Rpm with no real issues, on the earlier version it did expand slightly allowing it to spin on the shaft, as it was only a press fit, but since the inclusion of a Brass uj insert to lock the impeller onto the shaft, I have had no such issues.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 16, 2017, 05:14:49 PM
Great work Alex, you printing anything for your Springer on that magic box?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 16, 2017, 05:22:07 PM
Hi Chris,

No plans as yet, but it is still early days yet!  {-)

Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Charlie on April 16, 2017, 06:48:00 PM

Hi Alex,
In an earlier post you mentioned the merits of an SLA printer as compared to an FDM printer. Can you briefly explain what the difference is, and what the abbreviations stand for?
TIA,
Charlie
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 17, 2017, 12:42:25 AM
Hi Charlie,


FDM stands for, "Fused Deposition Modeling" this is where the printer heats up a plastic filament from a spool and lays it onto the print bed in a very precise manner one layer at a time to build up the model, it is essentially a computer controlled glue gun, just a lot more precise.
SLA stands for, "Stereolithography" this one is a bit more special, but basically what happens is, photosensitive liquid resin is place in a special tank with a clear bottom, through the bottom of the tank a UV laser traces out each layer, the build plate then separates from the bottom of the tank taking the first layer with it in a, "peal" process, the build plate then resets slightly higher to allow the next layer of the model to be formed by the laser, this building process allows the model to form out of the resin vat.


This video shows the process nicely: https://youtu.be/b-sIcYo8isI


Hope this helps,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 17, 2017, 12:52:03 AM
Hi Guys,


Finished prepping the jet boat for the lake tomorrow ready to test all of the upgrades I listed in a previous post, below is a link to a quick bench test video of my reworked SLA printed version of Yogibear's design: https://youtu.be/iOFpeOZ-X-8


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 17, 2017, 11:46:57 PM
Hi Guys,


Much success down at the lake today testing out the new reversing mechanism, it works like a dream, a couple of minor tweaks to be made for the twin jet drive versions, but apart from that I am extremely happy  with the results, short video showing maneuvers on the lake: https://youtu.be/Usji9Mtm32E


The rest of the upgrades to the jet drive unit kind of worked, the single shaft design makes the unit really smooth, the SLA impeller withstood the pounding brilliantly, unfortunately, something has gone wrong in the unit which has  introduced insane amounts of end float into the equation, I am attempting to do a diagnostic  on the unit at the moment, but can't remove the main drive shaft, as soon as I make some progress I will post my findings.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 19, 2017, 09:18:00 PM
Very tidy reversing, you should try her on the scale steering course! %%
Title: Re: Water Jet Drives & 3D Printing
Post by: Charlie on April 19, 2017, 09:54:02 PM

Thanks for the reply Alex, very helpful.


Hi Charlie,

FDM stands for, "Fused Deposition Modeling" this is where the printer heats up a plastic filament from a spool and lays it onto the print bed in a very precise manner one layer at a time to build up the model, it is essentially a computer controlled glue gun, just a lot more precise.
SLA stands for, "Stereolithography" this one is a bit more special, but basically what happens is, photosensitive liquid resin is place in a special tank with a clear bottom, through the bottom of the tank a UV laser traces out each layer, the build plate then separates from the bottom of the tank taking the first layer with it in a, "peal" process, the build plate then resets slightly higher to allow the next layer of the model to be formed by the laser, this building process allows the model to form out of the resin vat.


This video shows the process nicely: https://youtu.be/b-sIcYo8isI (https://youtu.be/b-sIcYo8isI)


Hope this helps,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 20, 2017, 09:52:02 PM
Hi Guys,


So finally got the gearbox apart to assess the root cause of the failure and it looks to me that this is down to my own stupidity, where I should of bought Stainless Steel rod for the impeller shaft, I accidentally bought Silver Steel bar instead, this means that it rusts really badly, not only this, but I should of realised that pushing a thrust bearing against a 3D printed part would inevitably end badly, the rotating bearing heated up due to it's small size, this melted the PLA just enough to cause it to stick to the bearing race and then that ripped out the centre of  the housing, causing it to fuse to the impeller shaft, no wonder I was seeing higher amp draws on this run!  %%


But rest assured I am already on with yet another modification to have the boat up and running this weekend.


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on April 20, 2017, 10:04:01 PM
What does the T shirt say? "Don't worry, I'm an engineer " %% {-) :embarrassed:
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 20, 2017, 10:36:40 PM
It says, "Trust me, I'm an engineer" actually, "mate"  <*<
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on April 21, 2017, 12:16:57 AM
I could say you've been shafted but I thought better of it ! %%
( >>:-( ducks down in the trench with the tin hat on!)

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on April 21, 2017, 04:50:35 AM
Alex.....you have an interesting issue to resolve ie., “how to eliminate unwanted heat created by the thrust of the impeller being reverse transmitted to the drive shaft thrust bearing and the subsequent heat build up that occurs between the interface of the housing and the thrust bearing”

1. to what temperature does the plastic filament material remain mechanically stable?
2. will the material accept a brass bush being inserted into the housing, during or post manufacture?
3. the brass bush could be spider legged to the thrust bearing to allow air flow between the thrust washer and the bush
4. could sufficient air flow be achieved even with a small finned centrifugal fan mounted to the shaft?
5. could water cooling of the brass bush be an option?....[similar to the water cooling of motor jackets?]

Your CooLRC 4074 motors is listed as a draw of 2800W……..[it also has an option of a water coiling coil]

6. after efficiencies & losses, some of this energy is consumed in providing the rotation power to the rotor
7. some of the energy is the transmitted opposite reaction being the inboard thrust of the rotor shaft and the heat transfer you are experiencing

All of the hypothetical calculations to where this energy dissipates will only confuse you

Manufacture/Print another housing to the latest [as failed] design & install the current rotor & thrust bearing……with a $20.00 digital pyrometer determine, confirm and document  the running temperatures of the thrust bearing, the housing interface and all associated motor/gearbox attachments under full water load conditions ……maintain the full load testing until all temperatures peak and then maintain/stabilise

From there you can progress your thoughts in what and how you will remove this heat from  the housing

Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on April 21, 2017, 11:36:21 PM
Alex....just a few points to consider :o

1. manufacture the motor mounting plate from aluminium
2. mount the thrust bearing the aluminium mounting plate [as you had shown a week or so ago]
3. install a needle roller bearing in the housing plate [just next to the point of failure which will accommodate the longitudinal thrust movement]

Lubrication of the free floating needle roller bearing may need further consideration, however the aluminium mounting plate should adsorb the heat gradient created from the rotational thrust [bearing] without any issue

Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 22, 2017, 01:29:40 PM
Hi Derek,


A well considered and thought out response as always, I did look at needle roller bearings but unfortunately they are of no use as at the required size they top out at 5K RPM, which is a bit low compared to the 19.5K RPM operational speed of the jet drive, on closer inspection of the thrust bearing, it looks like the problem had arisen from one half of the race, which is pushing against the 3D printed gearbox is a sliding fit on the shaft, where as the other half rotates freely, this was a complete over sight on my part and is explained in the attached image.
The bearing is designed to be installed with one half of the race supporting the rotational side, in my case, this would be the clamp collar on the shaft, the bearing race rotates with the clamp collar relative to the second half of the race which is stationary in relation to the impeller shaft, this half of the race therefore has a larger clearance to allow free rotation of the shaft within, in short I installed the bearing in backwards, the race locked onto the shaft and friction welded itself to the gearbox  :embarrassed:

So a much quicker fix than I thought, I can print a replacement gearbox part, (got to love 3D printing) ready for more testing down the lake tomorrow! 


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on April 22, 2017, 03:25:56 PM
Nice to see you have found the problem Alex, bearings this small are notoriously difficult at best of times but when you are supposed to fit one way, you need to be on your toes to ensure correct orientation.
Look forward to your next run.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on April 23, 2017, 11:23:47 PM
Hi Guys,


Well, got the prototype rebuilt and on the lake today, on the plus side, the thrust bearing appears to be working, on the other hand, this was one of the shortest runs ever at just under 40 seconds when the impeller exploded!  >>:-(
No idea what caused this, sailing along at half throttle and halfway through the acceleration to full throttle the impeller explodes, now there are a couple of possibilities as to why this might happen:


Whatever the reason may be, it is clear I need another impeller, it may be that the SLA resin I am using is just too brittle to withstand the forces a jet drive imparts, so I will more than likely go back to the PLA impeller which has withstood all kinds of abuse and lived to be abused another day, video from today:


https://youtu.be/-Qb9pNazcqE


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 01, 2017, 05:12:08 PM
Hi Guys,


No testing this weekend as I have taken some time out to redesign the jet unit from scratch, now on the surface it may not look a whole lot different to the old version, but it is all new and there are many small, but important differences, I have started printing the new parts already and hope to be on the lake next weekend.
The majority of the design modifications are centred around getting better flow through the unit, as at full throttle there is a noticeable change in motor note, which I believe is due to the unit attempting to flow a greater volume than the unit is able to support, this just leads to back pressure building up and consuming much more power for little extra forward drive, to help improve flow and hopefully remedy this situation, I have increased the internal bore of the unit to 42mm, this allows room for a 30 x 40mm impeller, the tunnel housing is also 42mm all the way from intake to stator housing, which has a much larger cross sectional area for better flow.
The larger unit also necessitates that the reversing mechanism is also bigger to fit over the larger stator housing, so the entire design has had a size increase of 6mm in all directions, on this prototype version I also printing a section of transom so that I can graft this unit into the existing hull without hacking it up too much.


More as it happens,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on May 02, 2017, 12:48:23 AM
Can I make a suggestion Alex, the cross sectional area through the pump shoul  be the same volume, looking at your very impressive design it looks as though when the flow gets to the impeller it is getting crompressed and at high revs this will throttle the flow down and increase power consumption with no gain in performance. Take the cross sectional area of the impeller hub and blades and add this to the intake diameter, this will then become the new diameter for your impeller, theoretically this should give full flow at all speeds. Hope this makes sense Alex.
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on May 02, 2017, 02:05:20 AM
Morning stew ....I too have been following %) these impressive designs & redesigns & builds by Alex

I understand and agree that the compression of the volume of water via the rotor will draw additional [motor current], however if this [additional] force is available, the net result is accelerated fluid or the velocity of the discharge water is increased

The secondary side of this difference in diameters or 'flooded suction' is tending to minimise pump cavitation

This cavitation issue is mentioned by Alex in an earlier video...........

Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on May 02, 2017, 08:11:28 AM
Certainly agree with your points Derek.
Cavitation could be reduced by increasing the intake diameter making the whole intake tapered, increasing pressure into the impeller, taper the impeller (jet turbine style) to increase output thrust even more, the down side is increase in component stress levels? Just a thought?
Title: Re: Water Jet Drives & 3D Printing
Post by: C-3PO on May 02, 2017, 12:38:21 PM
I follow this thread and find it fascinating.

Alex could you help with an answer to my question regarding Jet Drives.

I believe the drives need to be "primed" otherwise they are sucking air.

But my main question relates to the vertical positioning of the water jet output - what's best/acceptable to get the maximum thrust from the water expelled from the drive - the drive exhaust submerged under water / above water or something else?

Thanks in advance

C-3PO
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 02, 2017, 03:19:20 PM
Hi Guys,


Answers to questions below:


Derek - I don't know how you produce your screen grabs and correct me if I am wrong here, but you may find it easier to use windows snipping tool, as it looks like you are taking a photograph of the monitor? https://support.microsoft.com/en-gb/help/13776/windows-use-snipping-tool-to-capture-screenshots


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 02, 2017, 10:23:18 PM
Hi Guys,


Progress being made with all of the new components printed for the tear down of the prototype hull, 19.5 hours worth of printing to get to this stage alone, just imagine what an entire boat is going to be like!  %%
I have also printed a new larger reversing mechanism which is curing over the next day or so


More as it happens,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: hopeitfloats on May 03, 2017, 10:45:57 AM
I think you will find the jet nozzle angle is more to do with trimming  than to produce more thrust althought I guess if the boat is trimmed properly it will perform better anyway. jet racing boats actually have hydraulically operated trim nozzles.  commercial models generally have either a set angle or manually adjusted. better thrust is produced with the nozzle above the water line. the original jet unit was basically a centrifugal pump stood on its end with the outlet under water. when bill Hamilton of Hamilton jets changed it to above water discharge there was a pretty significant increase in thrust.
Title: Re: Water Jet Drives & 3D Printing
Post by: hopeitfloats on May 03, 2017, 11:34:14 AM
and the last improvement I have heard of was 3 bladed impellors. apparently increases thrust and lowers cavitation. haven't looked into it any further than reading about it. don't have a lot to do with water jets now.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 04, 2017, 11:13:35 PM
Hi Guys,


Quick update, got some time in the ShedShop tonight and started tearing into the prototype, which gave me an opportunity for a side by side comparison between the old style unit and the new one, as you can see from the photos, I have lengthened the trim tabs slightly, they also have a ten degree down angle instead of five degrees, to try and keep the bow planted in rough water, the stator housing outlet cross sectional area is much larger as is the tunnel inlet, whereas the impeller diameter is only marginally larger in comparison


More as it happens,


Alex




Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 05, 2017, 10:27:10 PM
Hi Guys,


More progress tonight, ripped out the old drive unit and made good the hull for installation of the new one, this is the major draw back to jet drives, they are pretty integral once installed, so swapping one is not a five minute job


Alex

Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on May 17, 2017, 03:13:22 PM
Hi Guys,


Quick update, not a huge amount to share at the moment, I have decided to do a practice run on the prototype, filling, sanding & painting, to give me some idea of the standard of finish I can achieve with the 3D printed hull sections and how much effort it is going to take to do an entire 3D printed boat, so far it is looking good, I put a second coat of plastic filler primer on it lastnight and I am very pleased with progress so far.


More as it happens,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on June 27, 2017, 11:29:21 PM
Hi Guys,


Slow but steady progress at the moment, the painting is coming along nicely with the top coat applied now, I am going to cut back the paint on the hull and then polish it to get it as smooth as possible, the finish doesn't stand up to close scrutiny, but I more than happy for this test phase having sprayed it with a rattle can during my breaks at work.
I am also working on a new drive setup, reusing existing parts, I want to see if the large 500Kv Outrunner will spin the jet unit when driving through a step up gearbox, if it works the way I think it will, then this should be a much less power hungry system when compared to the current unit.


More as it happens,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 10, 2017, 10:51:20 PM
Hi Guys,


So finally got the 2nd GEN drive installed fully into the prototype in time to take it to Kirklees open day and had a fantastic time, weather was great, gentle breeze to keep us all cool and then I tried to actually sail the jet boat, at first everything seemed to be going well, new trim tabs are doing a great job and it is much more stable whilst cornering, just gently cruising around, testing the steering and listening for any untoward noises, but there were none, so decided to open it up and then it happened, some idiot had forgotten to tighten the grub screw that holds the impeller to the shaft, the impeller walked forwards and chewed up the leading edge of the blades on the inside of the tunnel.
One rescue later I had the unit stripped down and back together in relatively short order, so back onto the lake we went, got up to about 2/3rds throttle, all was well and then a dead stop, this time the unit had ingested something, bird feathers I think, with that cleared out, back out again only to have the same thing happen again, at which point I decided to put it away for the day and sail my puffer.
This is the only real problem with the Kirklees lake, it looks quite clear, but there is lots of stuff floating about and a jet drive is essentially a very powerful hoover, I even had issues with my puffer getting stuff wrapped around the propeller, even the Kirklees rescue dingy's electric outboard suffered the same fate.


It is very easy to focus on the negative, on the flip side of all of this, we had a cracking day, lots of good sailing, made some new friends and when the jet boat was working, the new unit appeared to be performing very well indeed, it does however desperately need some spray rails fitting, as at speed it just vanished in a haze of spray.


Video of the first run: https://youtu.be/_B2X4-uHDKw


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: derekwarner_decoy on July 11, 2017, 02:33:00 AM
 :-)..... "this time the unit had ingested something, bird feathers I think" ...

1. Is this what happened at 1:16 minutes Alex?
2. It also appears to be a very wet at most speeds....
3. Will the orange polymer accept a paint color change?

Derek
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on July 11, 2017, 10:43:08 AM
Hi Derek,


Answers to your questions:


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 06, 2017, 10:48:57 PM
Hi Guys,


So finally getting around to posting an update of a test I did on 23/07/17 at the club lake, same basic setup that I was running at Kirklees, but with the addition of spray rails and a second stern mounted camera observing just what the jet nozzle is doing / reacting, the additional weight of the second camera was making the prototype list to port, so additional ballast was added internally on the starboard side, I got the hull to sit level in the water, but the water line was much higher than I would've ideally liked, but with so much power on tap, this is not really an issue.   :-))


The first run went well, priming is not an issue with the raised water line, the new spray rails did a really good job, with hardly any water on the deck, as opposed to last time, where it was awash pretty much constantly, the new trim tab angle is also working well and in conjunction with the spray rails, the boat sits very flat in the water; the only issues I had were the steering servo mount got ripped off the bulkhead it was attached to, (which is why I end up on the lakeside at the end of the video) due to the larger nozzle requiring more effort to turn it and the unit shifting a greater volume of water, I was also having an issue with the prototype rolling to starboard at full throttle, now this could be down to unbalanced loads, or the spray rails not being exactly the same, (they were just glued on at the side of the lake, five minutes before the test run) whatever it is, I need to have a closer look at the setup, I am also going to remove the second camera, which will give me a better understanding of how the new unit behaves compared to the last one.


I still intend to try my old 500Kv Outrunner with a step up gearbox, I am also going to see if I can improve upon the actuation of the reversing mechanism, as well as redesigning the steering linkage to be a two bar setup.


Lastly, I have been trying for a while now to produce a video which shows both camera views at the same time, after much struggling I gave up on using the free software that I had and after playing with a trial version of, Movavi Video Editor, took the plunge and bought a copy for £35, which is much more economical than paying £20 odd a month for Adobe's cloud system!  :o


Video of the first run: https://youtu.be/AkTWQfZgA4g


Thanks to fellow BMBS member richald for the photos from the day


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: PeachyPM on August 08, 2017, 01:04:46 PM
He he, i do like the end of your videos chum!  :embarrassed:
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 08, 2017, 09:02:38 PM
Hi Chris,


I may of crashed into the lakeside, but do you notice how my boat still works and is not in two pieces like some I could mention?  {-)


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 25, 2017, 12:06:09 AM
Hi Guys,


Quick progress update, I am back in CAD, this time working on improving the steering and reversing mechanisms, as the MK2 unit exerts too much pressure on the steering linkages, not to mention if you try to engage reverse with the unt running, the force of the water passing over the reversing flap holds it in the down position, this leads to the first problem, the reversing mechanism in real life would be operated by a hydraulic ram mounted on top of the steering nozzle, so why not do miniature hydraulics I thought? You see RC trucks & diggers using mini rams, how hard can it be?
Well, it's not very hard, but it is stupidly expensive and the rams don't come in the sizes I require, so after much pondering and looking around the internet, I came across a couple of YouTube videos of people using liquid in Lego Technic Pneumatic cylinders to create a hydraulic system, why not? I thought, if I take two cylinders, link them both together and actuate one with a servo, the other, should in theory copy the motion of the first, this is the idea, I have parts coming in the post and I am modifying the 3D printed files to accommodate the new system


More as it happens,


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: Martin (Admin) on August 26, 2017, 02:09:26 PM
 
Could you set up the Tx or ESC to give, say, a one second pause between forward and reverse to allow the bucket to move?
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 26, 2017, 03:07:21 PM
Hi Martin,


I'm sure it is possible with a modern computerised TX, but not with my old school F14, plus, who wouldn't want working hydraulics on their boat?  O0


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on August 26, 2017, 04:12:46 PM
Oil try it if it works . . . :P

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 26, 2017, 04:58:14 PM
Groan, yes Richard, very drole  :((
Planning to have new sysetm installed and tedt next club sunday, how's the race prep of your 500 going?


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: richald on August 26, 2017, 05:18:03 PM
It was either that or Oil get me coat!

Don't want to divert/hijack your thread so will PM you

Richard
Title: Re: Water Jet Drives & 3D Printing
Post by: Martin (Admin) on August 26, 2017, 06:55:18 PM
 
I had a Lego technic set with hydraulics, there weren't very efficient.... what about cycle hydraulic brakes .... or are they way too expensive?

.... medical syringes?!
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on August 26, 2017, 07:06:32 PM
Wheelspin models have a set of shocks (spring and oil filled), think about £15 a pair. Got to be better than Lego methinks?


Stewart
Title: Re: Water Jet Drives & 3D Printing
Post by: bfgstew on August 26, 2017, 07:24:13 PM
Something like these?


https://wheelspinmodels.co.uk/i/116185/
Title: Re: Water Jet Drives & 3D Printing
Post by: grendel on August 26, 2017, 08:12:05 PM
what about pneumatic rams - http://www.ebay.co.uk/itm/16-x-15mm-Dual-Acting-Mini-Pneumatic-Air-Cylinder-M5x0-8-CDJ2B16-15/272562592731?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3De607dae779bd4aa98b80fea096e47a4b%26pid%3D100338%26rk%3D1%26rkt%3D30%26sd%3D252504317997&_trksid=p2141725.c100338.m3726
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 26, 2017, 08:37:32 PM
Hi Guys,


Answers below:


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: grendel on August 26, 2017, 10:20:23 PM
http://www.nzmeccano.com/image-116933
how about the meccano hydraulics on their new John deer excavator, these have water as an operating medium.
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on August 26, 2017, 10:25:19 PM
Hi Grendel,


That is essentially the idea I am going for, except a servo will be doing the job of actuating the cylinders


Alex
Title: Re: Water Jet Drives & 3D Printing
Post by: IKB on October 20, 2017, 06:41:10 PM
Hi Guys,


Quick update to explain my recent absence, well work basically, well that and with BMBS having built a storming rock crawling track recently, I have kind of got caught up in all the excitement of new things to do, plus as I type I am on site in Riyadh for 3 weeks for work, but fear not, the jet boat will return, I am currently trying to iron out the kinks from the latest reversing mechanism and then there will be updates.


Alex