Disclaimer: I haven’t read through this whole thread yet.
In 2018 we put a pneumaticly actuated bike brake on the elevator which worked well, but was hard to package due to its size and the awkward mounting of the caliper. In 2019 we stole an idea from 971’s 2018 robot, and put a hex hub on a relatively fast moving axle, that we could then use a pneumatic pancake piston to drive a stationary plate into. Hard to describe nicely and hard to see in the CAD, but it looks like this:
It packaged well into the robot and has worked flawlessly all year. See 971’s CAD for the “gold standard” implimentation.