[apples000]

Okay, I have a few more questions.
I think we're going to be using some gearbox with a single chain reduction.
We are going to drive the arm pivot because we want the arm to be able to rotate 180 degrees.

This transmission can backdrive, so I'm looking for ways to prevent it.

I have three ideas:

Worm gearbox (worm reduction + chain):
I need a single start worm. The goal is (at stall) 180 ft-lbs at the joint, or 43 ft-lbs at the drive sprocket. In in-lbs, that's 518 in-lbs on the worm gear.

At half speed, I have 7.2 rpm at the arm, 30 rpm at the worm gear, and 900 rpm at the worm.

Both of these meet operating specs for 12 pitch ground/hardened worms running with 30 tooth bronze worm gears.

The disadvantage is that it is expensive, and large shock loads could damage it.

Locking gearbox:
I'd use a dog clutch somewhere. My concern is backlash if it's early in the reduction, and force to engage/disengage it if it's near the end.

Also, I could go with something like the robonaut's claw locking thing where they have preset positions it locks in. I'm not sure if I like limiting myself to only a handful of presets though.

Any ideas/suggestions?