OnStep is a computerized goto system, usually for stepper motor equipped mounts though any step/dir interface motor driver (including servo) should work. It was designed, from the beginning, as a more or less general purpose system and provisions were made in the firmware to allow for use on a variety of mounts including Equatorial and Alt/Az (GEM, Fork, Dobsonian, etc.) It uses an LX200 like computer command set with a few extensions to suit hand controller-less operation. (Quoted from the original site.)
https://onstep.groups.io/g/main/wiki
How to make it!
https://mr-deep-addicted.com/?p=1873
*Written in Japanese but you can change language setting.
I uploaded also Finder Arimizo Attachment Thin Type for Keen-One EQ.
https://www.printables.com/model/273812-keen-one-harmonic-drive-eq-mount
The author hasn't provided the model origin yet.