Project Description
In December of 2022, I came across a video on YouTube in which Alan Zhao, a student at MIT, created his own DIY equatorial mount for astrophotography using a gearing mechanism called a Harmonic Drive. Since I have always been interested in outer space and astronomy, I found the idea of astrophotography quite fascinating.
By January, I had learned much more about the field and decided to build my own telescope mount. Using CAD and PCB design skills that I had acquired from my first two semesters on the Harvard Satellite Team, I began designing my own adaptation of Alan Zhao's equatorial mount. I decided to call it the H.E.I.S.T. Mount, which stands for Harvard-Engineered Imaging System and Telescope Mount.
The H.E.I.S.T. Mount is designed to be portable, powerful, and precise. Through its use of Harmonic Drives, a.k.a. strain-wave gearing, the mount is able to drive a heavy payload with minimal backlash and without the need for counterweights. Furthermore, the mount's internal electronics were designed to be compatible with OnStep, an open-source telescope control system.
After all of the components were designed, it was time to begin the process of ordering components and manufacturing the mount. Note that this project was financially supported by the NECTAR Funding program of Harvard SEAS.
Build Process
To simplify the manufacturing process, most of the metal parts were designed to be cut from 6061 aluminum on a waterjet machine. The remaining two components (the dovetail clamp and a knob to lock the altitude adjustment) were manually machined on a milling machine and a lathe.
This was my first time using the waterjet machine, so it was a very exciting experience with the help of the incredible machine shop staff! The OMAX software to control the machine was fairly intuitive, and the machine itself functioned incredibly smoothly. Here are what the waterjetted components looked like after being cut:
After the aluminum parts were cut with the waterjet, all of the side holes required manual drilling and tapping using a milling machine. This was a time-consuming process, but it was a great opportunity for me to improve my machining skills. Here are some pictures of the completed aluminum parts after being cut, deburred, and sanded:
The next step was to 3D print the remaining enclosures using a Prusa i3 MK3 printer. This process was fairly straightforward.
Next, I began to assemble the electronics. The PCB was powered with a 24V power supply, and the internal software was run on a Teensy 4.0 microcontroller. The stepper motors were driven by two TMC2130 stepper drivers, and the PCB contained a USB-B port for connecting to a PC and an ST-4 port for autoguiding functionality. Here is what the PCB looked like after being soldered and mounted in the 3D-printed enclosure:
Before assembling the mount, I decided to test the electronics to make sure that everything was working properly. Nothing caught on fire or exploded, so I considered the test to be a success!
Finally, it was time to assemble the mount and test it out!
Final Result
Here are some photos of the completed mount assembly:
Here is a video of the mount in action:
Here is the first image that I captured with the H.E.I.S.T. Mount, my Askar V telescope, and a ZWO ASI533MC-Pro camera. It is a stacked image of the Omega Nebula (Messier 17).
You can check out some of my other astrophotography images in the gallery!