Ah, the servomotors whose parts you’re denied. “It needs a feedback sensor. Tells it where it is. I can’t make Hall sensors or photodetectors so I need to make these dumb inter-meshing electrical contacts, embedded in two glass plates that rub against each other. The miniaturization spell we’ve been testing will work well for that, but they wear down in time, and making them smaller makes them thinner, so they’ll wear out faster.”