Crank temp?

Ted Hamilton

Ted Hamilton

Helmet Painter / Racer
Anyone know what kinda' temps a PTO crank end sees? I'd like to try 3D printing a belt driver for my UAS ride for a PRD Fireball... Hegar doesn't make a core for them, nor does anyone else -- they were too "rare" to justify it. But a 3D printed part would be cheap and easy to try. As long as the crank temp stays below 200° I think I'll be fine on tensile strength of material. With no clutch to build heat, I'm thinking that it's do-able? What are your thoughts.... 20mm crank stub with a rotax taper...
 
phantomkartracer said:
Are you thinking of printing the whole driver or just a hub to be able to put a sleeve on it?

Brian #89
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Whole driver -- I feel like having less shear interfaces would be better. I plan to do it 100% fill a very small bit undersize, and will use the key on crank also.
 
I think the problem you will have is keeping the hub attached to the crank when you step on the throttle and the clutch locks up and not being able to have the hub secured to the crank strong enough. If you have a crank half to send me I made a hub a long time ago for the dyno, not sure which one it is but if I hade a crank to compare pay shipping I'll send
 
flattop1 said:
I would think the belt too driver interface would be a problem .
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What makes you think this? It will match the 8mm pitch profile, and the material is pretty hard, so I don't see wear being a big issue. In my favor, the whole part will cost maybe $2 in materials...if it wears, print another.
 
michael collins said:
I think the problem you will have is keeping the hub attached to the crank when you step on the throttle and the clutch locks up and not being able to have the hub secured to the crank strong enough. If you have a crank half to send me I made a hub a long time ago for the dyno, not sure which one it is but if I hade a crank to compare pay shipping I'll send
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Mike -- it's a 20mm crank stub with a rotax taper. I can make a print and send it to you.
If I was going to machine it, I'd get a Hegar KT-100 core and machine it out to match desired profile.
But I'm a machinist without machines at the moment...
I'll let you know what the results of my experiment are. I plan to engage the clutch at a low (non-peak-torque) RPM, so that will help.

I also have contemplated using this engine for my ultralight trike and wing, so in that case I think that with it direct-driving the prop hub there won't be the same slip issue...
 
In my opinion not even fancy non printable engineered plastic will have the shear strength to handle the forces at the interface. Save yourself a bunch of time and get something different (better) than a PRD that exactly what you want is available. If you have a SLS machine or anything that does metal available that is a different story. If the design is machinable there are a couple places like https://www.protofab.us/ that are spendy but good.
 
Ted Hamilton said:
Unsure...PLA has a high melt point, but I feel like polypropylene or PETG. Suggestions?
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If your printer has the temperature capability, I'd go at a minimum to ASA or ABS. Better yet, some carbon-filled nylon or PC. Ultimately though, I suspect plastic-to-crank interface will "creep" over time and become loose.

A solution would be making an aluminum hub for the interface to the crank which has a more "robust" interface from that hub to your belt driver. That would open up the possibility of quickly making/printing different tooth-count drivers, and they would all fit onto the aluminum hub.

PM
 
I’m sure you’ve seen what a belt can do to a steel cog. I wouldn’t expect a printed cog core to hold up. You’d be further ahead to just use the printed part for mock up and use the file to have a machinist program and make the part out of proper stock.
 
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