Thinking about what to use to drive the Nipkow disk from the cassette motor - my original televisor used a rubber band, of all things. This is about the worst possible way to do it, because the rubber band dampens any effect the motor might have in accurately controlling disk speed. At work I have some surplus O-rings used for sealing a robotic submarine hull. Anyway, although rather "long" (i.e., large diameter loop), they seem about right in terms of fitting in the pulley mechanisms I have on my motor/disk.
In particular, the diameter of the ring profile is 2.6 mm and the diameter of the ring itself about 130 mm.
I was also thinking of a toothed belt drive as a possibility. This would require some toothed wheels on both the disk and motor shaft - will look into that possibility as it seems to provide the most direct coupling without any stretching involved. If I'm going to put toothed belt wheels on, then I need to be looking at shaft diameters and avaialble tooth wheel sizes. Actually, these are candidates for 3D printing, although the wear could be a bit much. If I go with a large wheel on the disk, then the motor's going to have to spin much faster. Large on the motor, small on the disk, and the motor doesn't have to spin fast at all.
So there's probably an optimal speed to spin the motor, and I could/should choose a toothed wheel ratio (if I go that way) so that at 750 rpm (12.5 frames/second) the motor is happy. The length of the toothed band won't matter so much - it's
a) can I get toothed wheels for the shaft sizes I have
b) can I get (roughly) appropriately sized wheels to optimise motor speed