I designed this back in 2013. It is incomplete, but its a good start. There is currently no way to constrain the planet gears in the carrier planets axially. And although we could constrain the ring gears together by forced fit pins, its not ideal and might be pretty difficult to do. The gear teeth on the planet gears and the ring gears are actual involute curves modeled with splines. So if printed with good settings, they should roll fairly well. Each stage is a 4:1 ratio, and I designed them to be stackable - like there is a 16:1 ratio shown in the picture. I haven't actually tried printing it because the design isn't complete but I thought I'd post it so you guys can try. Or if you want to scavenge it for gears. Thanks!
