High Torque Gearboxes

[GeeTwo]

Originally Posted by Ginger Power

Is anybody aware of a gearbox with a ratio on the order of 70:1 that is compatible with 2 cim motors and has a hex output shaft? I can't seem to find something that fits all three characteristics anywhere.

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.