Hi @drj I've reclosed your question, marking it as a duplicate of robotics.stackexchange.com/questions/1270/…

Essentially you just need to detect stalls, and there are lots of ways to do that.

For your application, I would recommend using a compliant coupler between your motors and your pots: encrypted-tbn0.gstatic.com/…

In combination with hard rotary end stops on the motor shaft, you can ensure that the motor never applies its full force to the pot.

Oh, and images like this are fine to add to your question. The more specific you are, the less likely a question will be closed as Too Broad or Primarily Opinion based.

Best of luck with your project, it looks fascinating.