Thank you to IZ5RZR for writing in and sharing his two SatNOGS rotator builds with us. SatNOGS is an open source project that aims to make it easy for volunteers to build and run RTL-SDR or other SDR based RF ground stations that automatically monitor satellites, and upload that data to the internet for public access.
IZ5RZR writes that he's now made two rotators and one was modified to use a 5:18 stepper motor (which is upgradable to 50:1) to give more torque so that heavier antennas can be turned smoothly. His rotators are powered by a 12V battery charged by solar, and they can be controlled over WiFi with a PC/tablet/phone. He's also tested the rotators with a 24 dB parabolic grid antenna and found that the rotator could handle it even without a counterweight. He also notes that together with IK5XWA they've fixed a "Meridian Flip" bug in the firmware.
The video below shows the two rotators in action.