[Psychotechnoid]

Yes, I have definitely decided not to use the shaft for torque transmission to the arm (the 190 ft-lb. joint) - it would have to be really thick and thus heavy and hard to work with. If we put bolts through the arm and the sprocket, then the torque will be transferred at a greater distance, and hence with a smaller force, leaving the shaft to deal with just the downward forces - a much more practical solution.

The AndyMark hub is intended for the middle shaft, where a 9-tooth sprocket has to be coupled to a 48-tooth sprocket, so a large bolt several inches from the axle isn't much of an option there (since the 9-tooth sprocket is so small), so the torque will be at least partly transmitted through the shaft (we do intend to put bolts through the sprockets, but they likely will not be able to be far enough out to take all of the torque safely). That axle only has to take ~30 ft-lbs., though, and based on the calculations that squirrel so generously demonstrated, the shaft and the key should both be alright. Now it's just a matter of determining whether the 3/8" AndyMark hub can take it, and if not, then the bolts through the sprockets should be able to take some of the load off.