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Author Topic: Water Jet Drives & 3D Printing  (Read 15168 times)

IKB

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Re: Water Jet Drives & 3D Printing
« Reply #125 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #126 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #127 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
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Yogibear

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Re: Water Jet Drives & 3D Printing
« Reply #128 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #129 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #130 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:


  • New gears, this time hardened steel, MOD 1, 13T & 30T
  • New gear ratio of 1:2.3
  • New larger motor, GOOLRC 4074 2000Kv
  • New 3D printed motor mount, gearbox plates (due to change in gear PCD & motor mounting holes)
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
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Yogibear

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Re: Water Jet Drives & 3D Printing
« Reply #131 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


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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #132 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
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bfgstew

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Re: Water Jet Drives & 3D Printing
« Reply #133 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
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IKB

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Re: Water Jet Drives & 3D Printing
« Reply #134 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
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