recumpence said:
I will be using a oneway bearing pressed into my outdrive sprocket for freewheeling. I am not sure how much torque it will take, though.
I cant wait to see some photos of this box complete!
I thought i might be able to share some experience on this question.
I started designing from scratch, a cam-clutch based freewheeling crank setup to replace the ratchet-pawl style used in the Cyclone freewheel cranks -Known for their fast bearing failure rate. I wanted to improve the durability/lifespan of the system without the noise of a ratchet-pawl one-way which would be constantly ticking away unless the rider was pedal assisting the motor. This was to be an improvement on the durable White-Industries ENO 22t freewheel that ES members often build onto their freewheel cranks to replace the Cyclone supplied unit.
My research indicated 3 options for different style one-way freewheels. Sprag clutches, cam-clutches, and needle-spring style freewheels.
Unfortunately none can compete with the small size/torque ratio of standard ratchet-pawl style used in bicycles.
You can rule out sprag's immediately because of their large size required for high torque, and the fact that they are designed for high speed overrunning based on the cetrifugal force used to disengage.
Needle-spring style often have no inner ring and so are designed to be built onto the shaft. The shaft then has to be hardened steel, any wear that occurs requires the shaft to be replaced. Not ideal for easy repair/replacement.
Cam-clutches looked the best choice. To keep the bearing rings narrow, I found you have to select quite large ID/OD versions to get close to the torque rating of a standard BMX/singlespeed freewheel (>200Nm?). (35mm ID/72mm OD/22mm WIDTH gives 173Nm).
BTW i was looking only at versions with built in dust seals and ball bearing support so parallel support bearings would not be needed.
Selecting some with wider rings can bring down the ID and OD significantly, but is difficult to build these into the narrow wall of a gear casing or sprocket without protruding past the outer ring support surface.
Anyway i ended up giving up trying to find one small enough that had the torque capability. I ended up just building a WI ENO style freewheel crank.
I hope your case dimensions don't limit you the same as me because the silence and increased efficiency offered by cam clutches would be a valuable addition to the gearunit.
Tsubaki make the most competitively priced cam clutches i could find. Japanese made. Keep in mind they are still VERY expensive compared with regular bearings and mass produced bicycle freewheels.
The BB series is what you'd probably want. They come in both keyed and press fit in the sizes i think you' d be looking at. you'll notice the size/torque ratio is much poorer than you might imagine.
http://tsubakimoto.com/tem/pdf/CAM_CLUTCH.pdf
Also another link to a company that make cam clutches integrated with chain sprockets.
http://www.daytonsuperiorproducts.com/pdfs/OneWaySprockClutch.pdf