That assembly is explained and posted in Thingiverse:
https://www.thingiverse.com/thing:23030

One of our makerspace members built this with about a ten inch span. The ratio was astonishing. He had been spinning it with a hand crank for about a month and got one tooth progress on the final stage. Anytime someone new came into picture, he would be enlisted to crank for as long as tolerable.