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Author Topic: Water Jet Drives & 3D Printing  (Read 44750 times)

IKB

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Re: Water Jet Drives & 3D Printing
« Reply #100 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:


  • Inrunner - Flat bottomed hull boat with a lot of chop, even with the trim tabs, prime was lost because air got under the boat and up into the tunnel, causing a sudden increase in RPM
  • Outrunner - Either too many amps or water shorting out the motor,either way it is electrical and after each scream you can see white smoke appear through the clear deck of the boat
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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #101 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
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TheLongBuild

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Re: Water Jet Drives & 3D Printing
« Reply #102 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..

IKB

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Re: Water Jet Drives & 3D Printing
« Reply #103 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!  :-))

  • First Run - Running old 1900KV Inrunner on 3S, with 4Max 100A Watt meter, good run, started out slowly and built up to full power runs across the lake
  • Second Run -  Same setup, no watt meter, took the meter out as it was recording peak currents of 99.9A and I know this setup can demand north of 110A, so removed it from circuit to see if it would improve the top end speed.
  • Thris Run - Same as above but record this one from lake side as well, ended suddenly with a loss of power and the boat going unresponsive for about 30 seconds before limping back to shore.
  • Fourth Run - Running Outrunner on 6s with watt meter re-installed, Only ran up to 3/4 throttle as a precaution and I was right to do so, with peak amp readings of 52A, I am exceeding the rating of this motor at full throttle, but it is much more efficient than the inrunner.
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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #104 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #105 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #106 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:
  • First Run - Overlander brushless inrunner BM600 3650/09 1500KV running on 3S (11.1v) with 4Max watt meter (Forgot to put meter into amps only mode)
  • Second Run - Same as above but remembered to put meter in correct mode
  • Third Run - Same as above except some idiot let the smoke out of the motor!
  • Fourth Run - ZTW Black Mantis 3660/10 1900KV running on 3S (11.1v) with 4Max watt meter
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:
  • Power Train One One eBay sourced: MABUCHI RS-775WC DC6V-20V 19500RPM High Speed Power DC Motor For Electric Drill, which is a 5 pole 700 size motor, which running on 4S should be interesting.
  • Power Train Two ZTW Black Mantis inrunner B3660 2300KV, running on 4S (14.8v) will give 34040 RPM, which is a little quick, so I am going to build a 2:1 ration gearbox to go with it, which will give 17020 RPM.
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:
  • First Run Overlander Outrunner 4260/06 500KV running on 6S (22.2v) with a 4Max 100A watt meter
  • Second Run Same as above
  • Third Run - Same as above (Longest run ever by jet drive)
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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #107 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.


  • First Run - 3640 3400KV Inrunner running on 3S, driving through a custom 2:1 reduction gearbox and a 4Max watt meter
  • Second Run - Same as above
  • Third Run - Overlander 5045/10 720KV Outrunner on 6S with a custom 3D printed cooling fan and 4Max watt meter
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  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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #108 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #109 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
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PeachyPM

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Re: Water Jet Drives & 3D Printing
« Reply #110 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?
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Re: Water Jet Drives & 3D Printing
« Reply #111 on: August 24, 2016, 04:38:19 PM »

And look at all that hair!!!!!!! :}
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #112 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
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tsenecal

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Re: Water Jet Drives & 3D Printing
« Reply #113 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 :)
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #114 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #115 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   
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dirkske

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Re: Water Jet Drives & 3D Printing
« Reply #116 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

At very least you can program a warning in your transmitter when nearing max motor amps
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #117 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #118 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)
  • 26.25 Half Throttle 17A Full Throttle 84A
  • 22.5   Half Throttle 20A Full Throttle 85A
  • 18.75 Half Throttle 15A Full Throttle 76A
  • 15.00 Half Throttle 14A Full Throttle 76A (73.7A on lake)
  • 11.25 Half Throttle 15A Full Throttle 75A
  • 7.5     Half Throttle 15A Full Throttle 74A
  • 3.75   Half Throttle 16A Full Throttle 73A
Outrunner 5055/06 580KV on 6S (12992 RPM)
  • 26.25 Half Throttle 16A Full Throttle 67A
  • 22.5   Half Throttle 15A Full Throttle 66A
  • 18.75 Half Throttle 15A Full Throttle 66A
  • 15.00 Half Throttle 15A Full Throttle 78A (on lake)
  • 11.25 Half Throttle 14A Full Throttle 65A
  • 7.5     Half Throttle 15A Full Throttle 58A
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 22.5 of timing, half throttle is reduced by 5A and full throttle draw is reduced by 11A!
As far as I understand, this proves that 18.75 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 15.00, 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 15.00 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 3.75 and 0 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:

  • Increased overall length of the tunnel section - This will allow for a longer, larger inlet which can be shaped to allow water to flow upwards more naturally instead of relying on the the drive sucking water out of the lake
  • Increased stator housing diameter - At the the moment the stator housing is smaller than the impeller tunnel, a bigger housing allows for a greater volume to flow
  • Impeller design - Searching on the internet there is quite a wide variety of impeller designs, I intend to try different configurations to see what affect there is on performance and current draw
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
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Re: Water Jet Drives & 3D Printing
« Reply #119 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
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Re: Water Jet Drives & 3D Printing
« Reply #120 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:

  • Three Blade - Made it a fraction oversized and it rubbed horribly on the housing, but I did manage to get some sailing time with it and it performed ok with no real increase in current draw
  • Four Blade - Got the sizing right this time, the lake was dead calm and all ran smoothly, good performance overall and again very little additional current draw, we are still under the 32A mark
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
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Re: Water Jet Drives & 3D Printing
« Reply #121 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
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Re: Water Jet Drives & 3D Printing
« Reply #122 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:
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Alex

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Re: Water Jet Drives & 3D Printing
« Reply #123 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 
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Re: Water Jet Drives & 3D Printing
« Reply #124 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
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