This is a planetary Drive, based on Nema 17 Stepper. Which could be use as a standard Engine for Robotic Arms. As the Planetary gear, I used the 50:1 compound Planetary gear form "Gear Down for What" (https://www.youtube.com/watch?v=PishH0qRVZA). You could find the detail description and the assembly Documentation on my Website here: https://www.trust-point.com/page/blog-2/