[roland35]

A very cool style gear is a harmonic drive. It has a somewhat flexible inner gear driven by a cam which engages it to the outer gear. It allows for extreme gear ratios with high torque in very small packages (think helicopter pitch control).

https://en.wikipedia.org/wiki/Harmonic_drive

[beachy]

Very cool! It looks like the output shaft has quite a bit of lateral movement, perhaps something like a Schmidt coupling (https://www.thingiverse.com/thing:233667) could be used to remove that movement and allow a fixed output shaft.

I last saw one of these inside an IBM 3890 check reader machine.