[Psychotechnoid]

After doing some calculations for my team's manipulator, I realized that a particular shaft needs to be able to take about 190 ft-lbs. of torque. While we have a motor and sprocket ratios that can handle it, we can't quite figure out how to set up the shaft itself and the hubs attached to it. We intend to use the Taigene van door motor mounted to a 22-tooth IFI sprocket linked to a 48-tooth IFI sprocket on the same shaft as a 9-tooth McMaster sprocket going to a 60-tooth IFI sprocket on a third shaft attached to a lever mechanism.

As stated, the shaft attached to the 60-tooth sprocket needs to be capable of exerting a maximum of about 190 ft-lbs. of torque. My problem is that I have absolutely no idea how to calculate the thickness of the shaft required, what material it should be comprised of, or how to couple the 60-tooth sprocket to it if the shaft must be thicker than .5 inches (since IFI sprockets have a 1.875" bolt circle, AndyMark hubs with a 1.875" bolt circle only go up to .5" bore, and I can't find any other hubs for this sort of application on the internet). Further, the only 9-tooth ANSI #35 roller chain sprockets that I can find with keyed bores use a 3/8" bore (McMaster 2500T11). Maybe this middle shaft really can be just a steel 3/8" diameter one like McMaster 1497K952 (since 190*9/60 is only 28.5 ft-lbs.), but I must admit that I really have no idea.

Perhaps this wouldn't be such a big deal if my school had a machine shop (to simply make really big hubs and widen the bore on the 9-tooth sprocket) or engineering classes (so that we could do these calculations) or my team had any mechanical engineers as mentors (so that they could tell us how to do these things), but as the situation is right now, we're pretty much stuck.

Can someone tell me how big the shafts to take 190 ft-lbs. should be and what material? Does anyone know whether a 3/8" keyed steel shaft would be sufficient for 28.5 ft-lbs. of torque? Is it possible to get something other than an AndyMark hub to translate these forces to the axles? Or would it be better to do a dead-axle design and put bearings in the sprockets instead (somehow linking the tiny 9-tooth one to the huge 48-tooth one)? Can regular ball bearings like the KoP ones even take these sort of loads? My team and I are almost completely out of options, and I hope that this design doesn't turn out to be impossible, too (we first tried a scissor lift... that will never happen again).