I tried my hand at using a beefier stepper, one that draws 2A. Using a driver rated for 1.2A to drive this motor was a bad idea.

At first I thought that the driver was not working correctly. However, upon adding a makeshift heatsink, the stepper made one complete revolution... and then the driver resumed shutting off after that. I guess that's progress?

I have ordered a different stepper that has less torque and that draws less current. Hopefully the torque is sufficient to move the commutator. That is an empirical question. If not, I might have to get a beefier driver.

Central optic fiber movement detection: 

I will be using a pair of hall sensors to detect the movement of a magnet attached to the mobile component of the central optic commutator. The last time I tried this, the readings contained a lot of noise, but large changes in magnetic field were detected reliably. I'm either going to have to get a more precise/sensitive hall sensor or I'm going to have to smooth the data coming into the arduino with some code.

To be continued.