144:1 Differential Cyclodial

This is a differential cyclodial gearbox which achieves a large ratio by a similar mechanism to the "split planetary" gearbox, but with far fewer and much less delicate parts.

With this large a gear reduction ratio, small & light "tin can" or "pancake" stepper motors, usually considered useless, may be useful for things like extruders. This one is designed to fit a PF-35T-48L4 motor I got from salvage. (Very similar one on sparkfun https://www.sparkfun.com/products/10551 )

Sources availa