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Jan 04, 2020, 07:05 AM
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help with 40mm jet drive, 3d printed boat


Hi everyone,

I'm Dave from western Australia,.

I've recently finished printing a 23" jet drive boat, the impeller is 40mm

I've just picked up a 200a esc and 2600kv sss motor 4074 to run it, took it for some testing yesterday and it performed well but had issues with the receiver range haha almost had to go swimming,

Fixed the receiver issue today and took it out for more testing and fried the esc within 5 minutes

went into protection mode very quickly which it didn't do last night at all and we were on our second battery when I lost it

Was running it on a 3s 5000mah battery

The link to the boat I printed is
https://www.thingiverse.com/thing:3852220

Are any of you much more experienced people able to look at the design and possibly provide some feedback?

I think from reading on here I should have chosen a motor with a lower kv rating, but I did notice on the throttle range that it was at its fastest at full throttle

I'm a bit lost this is my first jet boat lol I'm blaming my mate that bought a proboat river jet for this one hahaha I decided to have a crack at making one instead lol

Thanks everyone
(I'll try Chuck the video on my YouTube so you lot can have a look)
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Jan 05, 2020, 04:27 PM
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Here are some things to try: The impeller was made using a right hand Ďthreadí and should be a left hand thread, see photos. If the stator blade curve matches, this may not matter. I didn't check your stator. Look at the photo of the three KMB impellers. The impeller on top of the stator is a right hand thread but the stator is made for left hand thread impellers.

The impeller pitch looks like a lot so will pull a lot of amps. It should be around 40mm for a 40mm impeller.

The photo of my 35mm impeller has a pitch of 39mm and is a left hand thread. My impeller has 1.6mm thick blades and a radius of 4mm at the hub so the Shapeways Versatile Plastic in my print doesn't bend much. Bending blades give more pitch and higher amp draws.

My overlapping blades in the photo need a bigger motor, Iím currently using a 40x83mm TP because the 40x74mm motor I was using is small for my hungry jet drive. Iím spinning my 35mm jet at 30k RPM and this seems to be itís limit (2100kv on 4s). This jet drive needs 2160 watts to spin this high. Your motor is spinning at 28k. A 40mm jet drive like yours may max out at 15-20k. Try 2s batteries but this may overheat connectors from lower voltage.

The hub on your axial impeller shouldnít be tapered unless the blades are progressive pitched or it will try to compress water, taking the amps way up.

I think making the above changes to the impeller will fix most of your problems.
Last edited by Kayaker; Jan 05, 2020 at 04:32 PM.
Jan 05, 2020, 08:47 PM
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Hey mate thanks for the reply, I'm currently using the 4 blade prop on the design as the designer hadn't done a 3 blade, but made one for me yesterday to try it out, dropping from the 4 blade to the 3 will that help at all?

I've grabbed the fdj jet drive 45mm impeller and scaled that to 40mm will that work? The stator isnt curved at all so im not sure if that would also cause issues
Jan 05, 2020, 10:14 PM
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Forgot too add that i see what you mean about the taper on the impeller, i never even gave that a thought! thanks for pointing it out mate
Jan 05, 2020, 10:23 PM
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It’s hard for me to see the impeller with out holding it in my hands. It could be progressive pitch so should work.

If the impeller’s hub more or less matches the stator’s hub you can scale impellers. You may need to add a new shaft hole.

A stick went throw my KMB jet drive and took out three of the stator blades. I replaced them with flat aluminum and it ran that way a long time. It lost prime a little more. KMB’s already have this problem.

I have a feeling we haven’t found the cause of the problem.
Jan 05, 2020, 10:34 PM
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i don't think its progressive pitch at all, awesome ill have a play and adjust the shaft hole and dog to suit my shaft and see how it all looks, shouldn't take too long when i get home from work, worst case with the stator i'll sit down and figure out how to improve it myself and print a new one to test, already have a few ideas for the output nozzle and steering nozzle aswell

Thanks Mate
Jan 05, 2020, 10:59 PM
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Here’s a good discussion of stators and nozzles: https://www.rcgroups.com/forums/show...or-alternative
Jan 06, 2020, 12:15 AM
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Awesome thanks for that, didn't realise just how much simple things can load up the entire system, should be interesting to see the results, I may try and modify the fdj stator and nozzle and swap that over too see how it behaves

Thanks for the help, wish I knew about these forums before I started building, but love a challenge though so will see this one through and it will help the other people that decide to make the same one aswell
Jan 06, 2020, 04:19 AM
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Ouch... just looked at that stator on thingiverse and it's letting the rest of the design down big time. That stator would work equally disappointingly with either direction of impellor spin.
The basic principle of axial jet pump stator blade design is to catch spinning water from the impellor and curve it straight. That stator's blades are just wrong.
Well done that you got the boat going though If you look at my two replies here: https://www.rcgroups.com/forums/show...-Boats/page161 , you'll see I'm worried about your battery C rating and a few other things. Sounds like you've got a 3D printer so I'd have a try printing some of sundogz stuff and some of mine. I like his and unusualrc's intake and impellors on the FJD thread but I've done my own stator and steering nozzle variants on my 4BDN thread.
Graham
Jan 06, 2020, 05:53 AM
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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, 07:39 AM
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well im printing the 35mm short prop from the v2 kit, managed to modify the hole size and add the dog drive slot and of course re scale it to 40mm, i also chopped the stator/nozzle up a fair bit and added my bearing size socket to it as well and added the transom mount that suits my boat, if i use the nozzle i think ill have to majorly rework my steering setup or modify the nozzle to suit we shall see, Thanks for the inspiration guys!
Jan 06, 2020, 11:47 AM
Jetdrives R Us
sundogz's Avatar
Quote:
Originally Posted by rav3n87
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?

Thanks
Here's another. Don't pay attention to any off-center circle around the drive dog (I threw a core on it to use Boolean removal/subtraction for the drive dog core), it should be centered.
Jan 06, 2020, 06:31 PM
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Legend thanks Mate! Will throw it on when I get home, stator/nozzle and steering nozzle are done, should be able to get a coat of resin on the impellers tonight and assemble it tomorrow hopefully
Jan 07, 2020, 12:33 AM
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Hi rav3n87,
Here's some of the vane shapes I made with openscad and one of my modified cylinder generator programs:
Jan 07, 2020, 03:22 AM
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Wow thats awesome thanks grael, is that what you use to make the stators?


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