qizaizi/alkaidmount

HarmonicDrive equatorial mount

Alkaid Mount - DIY Equatorial Mount with HarmonicDrive

Built by JZ.

For my build log, checkout this page on my website.

The following YouTube video documents all the processes with no explaination:

The same video can also be found on bilibili.

Introduction

AlkaidMount is a DIY aluminum HarmonicDrive German style equatorial mount with a ~25lbs unbalanced or >70lbs balanced load capacity, with a self weight of only ~16lbs. Each axis consists of a 100:1 HarmonicDrive gearbox, followed by a 27:1 planetary gearbox, driven by a Nema17 stepper motor.

Weight capacity is calculated with gearbox load limits as well as rigid body simulation. Note that I have not yet done any torture tests, so those numbers are all theoratical. I've only tested it on the two scopes I own - an unbalanced Williams Optics GT71 setup (~15lbs) and balanced a Meade LX200 8" SCT setup (~25lbs not including the counterweights). Both setups worked beautifully.

This repo contains ALL the design files (CAD, manufacture drawings, PCB files, software) to make the AlkaidMount. I made this repo public to inspire other ideas. Due to the difficulty in sourcing the exact same model of the two HarmonicDrive's (unless you buy new:), replicating the exact same mount would be hard. However modifying this design to suite other HD models shouldn't be too hard.

BOM - Hardware

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Name	Quantity	Drawings	Datasheet
Harmonic Drive CSF-17-100-2UH-LW	2	Drawings	Datasheet
Nema 17 with 27:1 Planetary Gearbox	2	Drawings	Datasheet
1/8" Aluminum plate	12"x12" minimum	-	-
1/4" Aluminum plate	-	-	-
M4x8	many :)	-	-
M3x8	not that many :]	-	-
M5x8	a few :{	-	-

BOM - Electronics

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Name	Quantity	Drawings	Datasheet
Teensy 4.0	1	-	-
ESP-32 (for wifi control)	1	-	-

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

Manufacturing guide

Most parts were made with 2D waterjetting, with not too much post-processing (tab removal, tapping if needed). Some parts have holes on the side, so some milling was involved.