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HarmonicDrive Mount
admin / 28.04.2023

Harmonic Drive Equatorial Mount

Item Type

Alan Zhao, a PhD student with the Perceptual Science Group at MIT CSAIL, created this Harmonic Drive equatorial mount. He graciously shared his design under GNU GENERAL PUBLIC LICENSE.

This is a rather complex project that requires access to a metal shop and some knowledge of electronics. However, we are posting this project with the hope that it will inspire some to build mounts like this.

If you can manufacture mounts like this and need help to comercialize them at a reasonable price, feel free to reach out to us using our contact form.


Video log Crafted By JZ documenting the build


The Parts You'll Need

BOM - Hardware

Harmonic Drive CSF-17-100-2UH-LW2DrawingsDatasheet
Nema 17 with 27:1 Planetary Gearbox2DrawingsDatasheet
1/8" Aluminum plate12"x12" minimum--
1/4" Aluminum plate---
M4x8many :)--
M3x8not that many :]--
M5x8a few :{--

BOM - Electronics

Teensy 4.01--
ESP-32 (for wifi control)1--

For parts on the PCB, see PCB/parts.txt.

Manufacturing Guide

Most parts were made with 2D water-jetting, with not too much post-processing (tab removal, tapping if needed). 

Some parts have holes on the side, so some milling was involved.

More documentation is available on the GitHub repository of this project.

CAD Model ofHarmonic Drive mount

CAD Model

The CAD model is publicaly available at

Accesss to Onshape Standard is available free for non-commercial projects where all user data is stored in a public work space.


OnStep Telescope Controller

OnStep is a computerized telescope goto controller, based on Teensy or Arduino control of stepper motors.

It supports Equatorial Mounts (GEM, Fork, etc.) as well as Alt-Az mounts (including Dobsonians, and the like.)

OnStep 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.

Website of the author od OnStep: