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Jan 05, 2020, 09:12 PM
Registered User
Oh sorry kayaker, yes it was either low voltage cutoff or heat cutoff, when the esc blew the caps we were approximately 50% throttle doing static in water testing trying to work out what was going on as I first thought it must of been the battery as it performed flawlessly the day prior except for the receiver range being garbage

Short video a friend took, cant really see to much, it goes quite well so I think with some changes it should be great!

3d printed jet boat testing (1 min 19 sec)
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Jan 05, 2020, 10:21 PM
Registered User
Also noticed that it sprays a fair bit out of the sides of the steering nozzle, should that be tweaked aswell to tighten the gaps up?

Are you guys able to point me too some info relating to stators or explain the concept to me for the best shape to use?

Jan 06, 2020, 12:52 AM
Jetdrives R Us
sundogz's Avatar
Thread OP
40mm pump driven with a 4200kv motor on 2S with a 120A esc is out of the ballpark in as many ways. You've already learned better reading these pages. That stator reminds me of the way the new imported drives are designed - to look legitimate without paying attention to details. Maybe Grael will help you out, he has been into designing stators lately.

Edit: Your boat runs surprisingly well, all things considered!
Last edited by sundogz; Jan 06, 2020 at 01:06 AM.
Jan 06, 2020, 03:32 AM
Registered User
Hi rav3n87,
sundogz sounds right about a 4200kv motor being too high an RPM for the impellor, especially with the high pitch and bad release of the trailing edge. At a rough guess, looking at that impellor, considering the pitch difference, the 2S and the slightly increased diameter from my 35mm stator, I'd be looking at the longest and fattest 1350kv motor you can fit, running at around 110 amps on your 2S. And I'd then be wanting a battery that could deliver around 200 amps, so if you had 50C batteries then that's minimum 4amp hours. Were your batteries hot after the ESC failed? The leads? It's possible that the combination only lasted because of internal resistances of the various devices heating up, and even if the motor and ESC are running cold, that's likely effective water cooling, you might be loosing a massive amount of battery power simply to heating up the coolant water.
Also, the capacitors on your ESC are shuffling around voltage at high frequencies during high motor load and I think some of this flow (a very small amount) goes back into the battery. If you have a low C rating battery then it takes a long time for these little peaks to get back into the battery so the flow and voltage to the ESC capacitors will increase. I'm kind of guessing/theorising here, but if I'm right, the worst thing for your ESC caps is to have a low C rated battery.
As far as stator design goes, I've only been doing 35mm sized ones compatible with the FJD intake and impellors so far. You could look at my 4BDN stators thread and download the V3 Stators and nozzles, I just wrote about some testing I did on a Dr. Mad Thrust Series Motor B3682 - 1700kv For 90mm EDF / 6S motor, running it on 3S. I'm not pushing the bleeding edge as much as some on here with ultimate power, it's a good combo though with some wicked thrust. The stators I've designed are matched to spherical steering nozzles and you won't see any frontwash. I'd recommend the 4BDN 7 vane V3 stator with the 1.5mm extended 2n'd generation nozzle which shapeways can print for you if you need. The 7 stator vanes and the nozzle restriction will give you good compression and should result in a higher top speed.
If you are jetting in a lot of gravel bottom streams then I'd use the first release 7 vane stator instead which has thicker profile at the vane entry.

I haven't tried it yet but the "Multi Jet Fusion PA12" shapeways product looks like a good bet for stator, steering nozzle and impellors or if you want to go a more pricey but quality route, then their experimental stainless steel for the impellor and aluminium for the stator. You MUST use a flexible plastic for the nozzles as they are press fit and can be levered off to swap out the exit hole sizes to change the amount of speed up to the exit water. This lets you fiddle with the motor load (and power output) a bit.
Jan 06, 2020, 03:53 AM
Registered User
Adding to my theory about low C rating batteries and ESC caps:
Note that extending the battery to ESC wire length raises the battery circuit resistance which is the same thing as using low C rating batteries.
At half throttle, when your failure occurred, the ESC is half on, half off, you are sending massive but short pulses to the motor windings and then turning the MOSFETs off, the motor coils collapse their surplus energy into the ESC capacitors and the battery/s.
So the capacitors are running at maximum current, highest stress.
The manufacturers should ideally use low ESR(electrostatic resistance) capacitors, like we should use high C rating batteries.(Low internal resistance batteries) And short leads!
So clean your battery connectors, seal up your batteries right after leaving them somewhere quite hot for a half hour or so and don't extend the leads!
Jan 06, 2020, 05:50 AM
Registered User
Hi Grael,

Thanks for the reply mate, I'm just about to sit down and see what i can combine in cad to make things operate a little more smoothly lol, thanks everyone for your suggestions!

My electronics atm are a
fvt 200a esc (i have another one to use)
sss motor 3674 2600kv
Running on 3s @ 5000mah 50c-100c b

hopefully i can get the amp draw below 200a using the fdj impeller and i might try and remove the stator center from the stl on thingiverse and add the fdj one into it and see what happens from there, id really like to get this one running well, Then maybe i will try a hull and fdj drive or just experiment in general a bit more with other options
Last edited by rav3n87; Jan 06, 2020 at 06:04 AM.
Jan 06, 2020, 06:12 AM
Registered User
Hey sdg,

I tried pulling the impeller for the 35mm v2 fdj drive into cura to scale it up to 40mm so i could dump it into cad and reduce the shaft size too 4mm and add the drive dog location, but it doesnt import "centered" as such, not sure if that makes sense That has a pitch that would be far more suitable to the motor im using yeah?

Jan 06, 2020, 07:41 AM
Registered User
sorry for the double thread on this one guys, please reply over at,

Thanks for your help
Jan 06, 2020, 11:43 AM
Jetdrives R Us
sundogz's Avatar
Thread OP
removed and re-posted here
Last edited by sundogz; Jan 06, 2020 at 11:48 AM.
Jan 08, 2020, 02:47 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Originally Posted by grael
Adding to my theory about low C rating batteries and ESC caps:
Note that extending the battery to ESC wire length raises the battery circuit resistance which is the same thing as using low C rating batteries. ...
Wire inductance increases as well, causing voltage spikes higher than battery voltage, hammering away at the semi-conductors. And capacitors will get hotter.

More info in
Too long wires batteryside will kill ESC over time: precautions, solutions & workarounds - RCG
  • Two problems
    ◦ Voltage spikes higher than battery voltage: transistor/FET/chip breakdown.
    ◦ Current through input capacitors too high: overheating/popping/exploding.
  • Example four costly controllers consecutively cremated
  • Solution I: simply lengthen the motor wires instead
  • Solution II: add extra capacitors, rules of thumb
    Calculation spreadsheet
  • Capacitor type and polarity/orientation!
  • How & where (not) to add extra capacitors
    As close to or on controller.
  • DIY capacitor pack pictures
  • Capacitor & pack suppliers
  • Expert/manufacturer opinions & their rules of thumb
    They all say the same ... noise_reduction_101, switching_power_supply_design_101.
  • Cause, explanation, water hammer/knock analogy&video, theory
  • Measurements & scope traces

Gelukkig Nieuw Jaar Ron
Without a watt-meter you are in the dark ... until something starts to glow
e-flight calculators watt-meters diy motor tips&tricks Cumulus MFC

Last edited by Ron van Sommeren; Jan 09, 2020 at 08:59 AM.
Jan 08, 2020, 11:36 PM
Registered User
Thanks Ron,
thanks for the confirmation and hopefully our notes here will save some $ in fried ESCs down the line!
Jan 09, 2020, 08:20 AM
Registered User
Ahh yes another thing I have been looking into, I think I will also need to add a few more to my system too make it safe
Jan 13, 2020, 10:17 AM
Jetdrives R Us
sundogz's Avatar
Thread OP

Ebay find - Fiberglass PBR Hull, cabin and foredeck

From time to time I find what I think is a bargain in possible jetboat hulls on Ebay. Today I spotted this 32" PBR hull and it seems to be well made. Would make for a nice project to fit a couple of 25-35mm? jet pumps such as the FJD.
Last edited by sundogz; Jan 13, 2020 at 10:29 AM. Reason: added pics
Jan 18, 2020, 11:57 AM
Jetdrives R Us
sundogz's Avatar
Thread OP

And another...

And I spotted this on Ebay this morning. It's a big one at 45 inches long! Too bad they don't have any superstructure to go with it. But that's not a problem - especially at this price.
Feb 13, 2020, 09:39 AM
Jetdrives R Us
sundogz's Avatar
Thread OP

ABC Jet Ski

Another Ebay find - an ABC Kawasaki Jet Ski. These have a 25mm jet drive and are easy to convert to brushless. I had three of these at one time and we 'raced' them. Fun boats. Sale probably won't last long at that price.

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