caution: The code needs to be updated to use the new library: http://www.thingiverse.com/thing:777936 A bit about some hidden logic in planetary gears: Not every combination of tooth numbers allows to distribute the planets equally around the circumference. If the combination allows equal (equiangular) distribution it can be that the planets are a multiple of the minimal mounting distance away from one another (they are not maximally closely packed) making the assembly weaker than it could be. To allow more tooth number combinations and have the planets as closely/tightly packed as possible the planets can be organised in groups (which is done here). For this the greatest common divisor of the gear teeth numbers defines the number of planet groups (starting points for filling). The number of sun and planet teeth is then defined by multiplicators to that common divisor. The cycloidical shape of the teeth allows (and requires for small prints) toothnumbers smaller than in involute gears. The compatible tooth number combinations thus become more sparse. Groupling planets by the gcd value and distributing then in patches around the circumference allows more options. Cycloidical profile pros and cons: If you print splitted parts you need their mirrored versions too. The grooves on the outside of the ring are for blocking rotation with pieces of filament. The cylinder where the bearing goes in needs to have matching grooves. Use jitter if your slicer offers this option. Printing parts seperately for post assembly makes stringing impossible and may allow for tighter tolerances. But keep the minimum time per layer high enough for the small planets to not deform. Use nylon if you have such filament at hand. The 45° bevel cutoffs help preventing fusion of planets with sun and ring when the part is printed assambled and the first layer is squished. The bevel cutoffs also can aid assembly when the part is printed in seperate pieces. They look nice too but also weaken the bearings strenght a bit and make it harder to judge the choosen clearance by eye.