Manipulator Torque (A Bit Scary for Us)

[Psychotechnoid]

So I need to find a shaft made of a material with a shear strength of at least (a safe margin from) 33,000 psi? Based on what I've seen so far, that should be doable.

I'm not entirely sure how to handle the key. 30 ft-lbs. = 1920 lbs. at .1875", which would have to be resisted by a 3/32" x 3/32" key about 1.5" long in total (to go under the two 3/4" wide 9-tooth sprockets), and I'm not sure what to do from there to determine if it can handle it or not. I think that it would go something like: (3/32)^2 = ~0.008789 in.^2, and 1920 lbs. / 0.008789 in. = ~218,453.3 psi. I'm not sure whether I did that correctly or that that is a reasonable number, though....