Nema 17 -12:1 Compound Gearbox

thingiverse

Yet again another take on the compound epicyclic planetary gearbox. With split sun gears (one idler), un-synchronized rings and meshed planet gears, the goal is to achieve a reduction/torque increase sufficient to drive a 130mm (2.2") R/C wheel from a NEMA 17 stepper up-to about 60 rpm. Many thanks to [Troy](https://www.thingiverse.com/tmackay/about) for his Potentiometer Planetary Reduction Drive Knob and the OpenSCAD file. This design is essentially the same as before with split rings and 5 planets, featuring: - Sun and Idler have 10 teeth each - Fixed and Output rings have 20 teeth each - Lower Planets 4 teeth - Upper Planets 5 teeth The reduction ratio is calculated to be **-9.6 to 1**, but I made an error in my math; the actual ratio is probably -12 to 1. I attached the updated SCAD file, which has minor changes: - gear_h2 = 10 - drive_t2 = 10 - ring_t2 = 20 - outer_d = 36.4 - planets = 5 - pot_shaft = 5.20 - pot_knob = 5.00 - ChamferBottom = 0 - Removed lines 147-161 (remove cap) - Uncommented line 226 (for split rings) I exported the STL to sketchup to finish the design. I should really update the SCAD file to include lock pins and an output cover/bearing holder for testing other gear setups directly. I am also considering adding a selection of which sun will drive to position the stepper shaft and a larger space for the idler. Given that my wheel is rather heavy, I chose 6802 2RS (15*24*50) bearings from [Amazon](https://www.amazon.com/dp/B07R4WZV9R) to support the output shaft.