3D Printable Jet Drive project - RC Groups
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Feb 02, 2017, 01:05 PM
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sundogz's Avatar
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3D Printable Jet Drive project


Recent participation in the Home built jet drive boat 3D printed thread got me thinking how interesting it would be to design a jet drive that people could download the plans for to use for printing their own pump. And while I have plenty of ideas, I really lack the skills necessary to properly put it to .sdl for a printer, and since Justin won't have the time, I've enlisted professional SolidWorks user and engineer Unusual_RC to do that. So in thinking of what I would look for in a 'perfect' jet drive I came up with a wish list. We'll call them 'features':

1. Easy installation.
2. Scale-able, can be scaled for different sizes/applications
*Can not be scale-able due to off the shelf bearing sizes and differing impellers See post 72
3. Easy printing - no need for supports or special treatment
4. Off the shelf parts (bearings, shaft, etc)
5. Custom designed impeller
6. Strong design - not likely to be able to break anything
7. High efficiency - power to thrust ratio. To be determined by field testing
8. Integrated motor mount
9. Adaptable for means to reverse (reverse bucket, etc)
10. Option to use a thrust bearing (may be needed in the larger scales 40mm+)
11. Means for greasing the shaft without having to remove it from the drive.
12. Integrated steering servo mount (bolt-on)
13. Adaptability for use with gas engines ( just use 2 couplers and short piece of flex shaft)

Edit 7/28/17: Not bad. Those items in blue were incorporated into the design, while the one in red was not. Due to off the shelf bearing sizes, we will be scaling each drive and customizing bearing pocket sizes & motor mount screw spacing for each. No problem.

Here is an index to important pages if you don't want to read the whole thread:


Page__ Post ______________ Subject
6--------- 83 -----------------Suggested bearing, shaft, motor sizes, scale multiplier, etc.
11--------154----------------45mm 3D Jet Drive .stl files
11--------164 ---------------Build: trimming the freshly printed model
12--------169----------------Build - cont. Part 2
17--------253----------------Assembling the steering nozzle/stator housing
18--------261----------------19mm (NQD) version 3D .stl files
20--------292----------------27mm (KMB) version 3D .stl files
23--------335----------------35mm 3D Jet Drive .stl files
24--------357----------------75mm 3D Jet Drive .stl files.
Last edited by sundogz; Oct 14, 2017 at 11:39 AM. Reason: Update 10/14/17 Added 75mm Jet Drive .stl files
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Feb 02, 2017, 07:11 PM
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Agree with everything but #5.

Boat props are designed for a completely different purpose/running condition so they will not be efficient when used in a jet drive. Using a boat prop would also require the user to cut/grind/machine it to size and shape, which not everyone will be able to do. Careful design and quality 3D printing allows the production of purpose-built impellers specific to the drive, which will be more efficient, and have the bonus of being very cheap and easy to replace if something sneaks past the grate and chews up the impeller.

I'm completely staying out of the overall design of this drive because I'm curious to see what you guys come up with, but I will chime in if I feel there's anything helpful I can add outside of the design geometry. If my input isn't welcome, that's fine too.
Feb 02, 2017, 07:43 PM
Just Plane Nutts
AirDOGGe's Avatar
I'm sure everyone's input is welcome. Just nobody get upset if a suggestion is not accepted or applied. There are more ways than one to cook a hot dog...

Dammit. I just made myself hungry.....Be back later...................................
Feb 02, 2017, 07:55 PM
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Quote:
Originally Posted by AirDOGGe
Just nobody get upset if a suggestion is not accepted or applied.
Agreed.
Feb 02, 2017, 07:58 PM
Just Plane Nutts
AirDOGGe's Avatar
Ummm...Gonna share that popcorn?.......
Feb 02, 2017, 08:19 PM
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helir22's Avatar
Sounds like a good plan... I like the idea of some sorta thrust washer between the brass tubing(if that is part of the design) and impeller like the kmb, or even better an actual thrust bearing somewhere in the jet body. Not just an extra radial bearing acting as a thrust bearing, that is either ignorant or dishonest and I am not reffering to any previous 3d printed design....
Feb 02, 2017, 09:12 PM
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sundogz's Avatar
Quote:
Originally Posted by Firehawk989
Agree with everything but #5.

Boat props are designed for a completely different purpose/running condition so they will not be efficient when used in a jet drive. Using a boat prop would also require the user to cut/grind/machine it to size and shape, which not everyone will be able to do. Careful design and quality 3D printing allows the production of purpose-built impellers specific to the drive, which will be more efficient, and have the bonus of being very cheap and easy to replace if something sneaks past the grate and chews up the impeller.

I'm completely staying out of the overall design of this drive because I'm curious to see what you guys come up with, but I will chime in if I feel there's anything helpful I can add outside of the design geometry. If my input isn't welcome, that's fine too.
I agree a prop won't be as efficient, my thinking was that props were readily available, easy to adapt (turn it down with a stone and drill), and easy to fasten to the shaft with a drive dog. The printed impellers I've seen so far didn't give me a warm and fuzzy feeling as far as durability and fastening methods. We should try both, for sure.

Quote:
Originally Posted by helir22
Sounds like a good plan... I like the idea of some sorta thrust washer between the brass tubing(if that is part of the design) and impeller like the kmb, or even better an actual thrust bearing somewhere in the jet body. Not just an extra radial bearing acting as a thrust bearing, that is either ignorant or dishonest and I am not reffering to any previous 3d printed design....
Good idea. Since we're making this scalable, anything 40mm and larger will surely benefit from a thrust bearing absorbing the thrust instead of having the motor bearings take the brunt of the abuse. I'll add it to the 'wish list'.

All good stuff. Keep it coming.
Feb 02, 2017, 09:20 PM
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helir22's Avatar
Also saves the coupler from an unwanted load.
Feb 02, 2017, 09:48 PM
Registered User
The first impeller I got from Steve was printed; it looked as though it would break if you so much as looked at it funny. It did eventually break, but I think from some stringy algae getting sucked into the drive rather than just use. The ones Justin has sent me so far appear to be a lot more durable and should last longer. Significantly better print quality too.

Boat props also make toxic dust when you grind them as they are usually a copper/beryllium alloy which is bad for you if inhaled. Not so much of a problem if you are just balancing and sharpening by hand, but reshaping I would think about wearing a mask.
Feb 02, 2017, 09:49 PM
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sundogz's Avatar
Quote:
Originally Posted by helir22
Also saves the coupler from an unwanted load.
Where is that dad-gummed 'thumbs up' imogee when you need it?!
Last edited by sundogz; Feb 02, 2017 at 10:57 PM.
Feb 02, 2017, 09:52 PM
Registered User
Quote:
Originally Posted by AirDOGGe
Ummm...Gonna share that popcorn?.......
Not sure if it would go well with your hot dogs, but only one way to find out I guess!
Feb 02, 2017, 09:56 PM
Fast electric boats maybe
Jeffro Bodine's Avatar
Keep it coming reading every thread
Feb 02, 2017, 10:17 PM
Just Plane Nutts
AirDOGGe's Avatar
Quote:
Originally Posted by Firehawk989
Boat props also make toxic dust when you grind them as they are usually a copper/beryllium alloy which is bad for you if inhaled.

Also brass, bronze, aluminum and stainless steel. One might also consider a PLASTIC prop, which would be far easier to mod for testing purposes before going to a metal one.

So true the toxicity of CuBe props. When I drilled out my Octura props to 4mm, I use a thick cutting oil like 30w motor oil to lube the drill. The bonus is the elimination of any chance of dust production.

My choice would be a CNC'd aluminum prop first. Durable enough, easier to mod than stainless or CuBe , and the light weight means less vibration and bearing wear at the very high rpms that impellers run at.
Last edited by AirDOGGe; Feb 02, 2017 at 11:41 PM.
Feb 02, 2017, 10:30 PM
Registered User
Shapeways will "print" things in a few different metals too. I've thought about trying this when the designs are finalized.

The CNC machined delrin impeller I got from Steve via Joe appears to be nearly indestructible.
Feb 02, 2017, 10:40 PM
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helir22's Avatar
Also, I am not sure of the material they use but, the Thrasher and the Jettec use a water lubricated stator bushing with a hole at the end of the stator cone to facilitate flow. It's a nice low maintenance design.