Update: Added 1mm extra Z thickness to the edges of the ring gear. This is to reduce friction when the screws are fully tightened on the mounting bracket. A simple, compact planetary gearbox. Only requires 4x 30mm M3 screws (assuming your mounting bracket is 4-5mm thick) and some 4.5mm steel balls to fill the bearing. (You can also now use 25mm screws, as long as you use the 25mm version of the base.) Has a hex-shaped shaft and comes in two sizes. You will have to customize your designs to fit it. I had designed one before prior to this, but it had too much friction to be of any use for high speed applications. This one should fare much better. All gears should be printed with a -0.1 horizontal expansion and with a 0.4mm nozzle on most printers. Some filing on the d-cut may be necessary to get the sun gear to fit the shaft. Demo: https://youtu.be/rY7NDBnz7Cw https://www.youtube.com/watch?v=yUTXTRjAOak