[ZZII 527]

Maybe a small bit of good news. We've been using the 42mm 256:1 w/ FP setup for our arm. After the output shaft, there is an aditional 72:10 chain reduction to the arm itself. The arm is just a light 1x1 Al box extrusion, no more than 2 lbs and 4 feet long. It hasn't been put through anything rigorous or a ton of cycles yet, but we have used it to right the whole robot a few times. We tore it down today to check out the internals and the carrier looks pretty good to me (picture attached). There is slight deformation at the corners, but it's only at the surface (maybe 10% of the total depth).

Obviously more demanding and cyclic loads need to be tested before this proves anything, but maybe with TLC the 42mm can be used effectively for light arms.

I tried a possible quick fix: pinning the shaft to the carrier, but after a couple broken bits, I can confirm that the shaft is, to use technical terms, really, really hard. The carrier hardness falls somewhere between a filing drawer hanger and a screwdriver. Note to self: leave the real engineering to Dr. Joe. But 119 ksi is pretty hard, am I right? Can we do a lot better with a different steel? Heat treatment?

What about shims to take out the small bit of play between the shaft and the carrier? This might help since the corners won't dig in so much. It would approach Dr. Joe's linearly-distributed loading condition more. I'm thinking of what happens when you use a metric hex wrench in an English hole. It might work, but will be a bit too small and as a result will strip the hole more easily.