AstroTrackerHD Prototype 4 in testing, with pics. (HD = harmonic drive, which is a high-precision, high-torque, zero backlash gear set. See: https://youtu.be/3mWemlMEzFk). I did some code cleanup and refactoring for version 4.0.7, and added the ability to adjust the speed in small increments and save the speed values to eeprom. I have a couple posts on this earlier in the year, but if you haven't seen them: AstroTrackerHD is my project to build a very accurate star tracker using a NEMA 17 stepper, 139:1 ratio planetary gear feeding a 100:1 ratio harmonic drive. I'm running updated software in this one, and I'm in the process of 3D printing some brackets for the stepper.