[marshall]

Originally Posted by GeeTwo

OK, a CIM has a stall torque of 343.4 in-oz. Using two and a 70:1 reduction means that you anticipate a stall torque around 48,100 in-oz, or 250+ ft-lb. On the AndyMark PG gearbox pages, they note that 39 ft-lb will shear a (round keyed) 10mm steel shaft. A bit of hind-brain physics tells me that the shear torque of a shaft is proportional to the cube of its diameter (someone please correct me if this is wrong! -- verified by equation 2b of engineering toolbox website). Assuming the same shaft material, the diameter would have to be about 18.6 mm, or essentially 3/4" diameter. I've never heard of anything with a 3/4" hex shaft. I'm not aware of anything that's "FIRST standard" with a 3/4" shaft, keyed or hex. If you need this sort of torque and power from an electric drive, my best guess for sourcing affordable motors and gears would be from the golf cart industry.

I haven't hit the search yet but does anyone know of any teams that have used golf cart gearbox parts in the past? I'm genuinely curious about what else is out there. The fact is that 900 does derpy stuff from time to time and I think the AndyMark folks might appreciate it if we quit ruining their pretty gearboxes.

EDIT: Anyone looked at RC Cart gearboxes? Any of those worthwhile?