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 objective 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](https://www.thingiverse.com/thing:3562490) and the OpenSCAD file. This is essentially the same design with split rings and 5 planets with the following characteristics: - Sun and Idler have 10 teeth each - Fixed and Output rings have 20 teeth each - Lower Planets 4 teeth - Upper Planets 5 teeth If I got the math right, the reduction ration is **-9.6 to 1** (update: I got that one wrong, in fact the ratio is probably -12 to 1...) I attached the updated SCAD file which is mostly same as Troy's with 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) - **uncomment** 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 the output 'cover i.e bearing holder and 12mm hex) so I can test other gear setups directly. I am also thinking about adding selection of which sun will drive to position the stepper shaft* on it and a larger space for the idler. Given in my case the wheel is rather heavy, To support the output shaft I went with 6802 2RS (15*24*50) bearings which I got from [Amazon](https://www.amazon.fr/gp/product/B07R4WZV9R/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1).