3D Printable Harmonic Drive Equatorial Telescope Mount

Introduction

Hello! I'm Zach, and over the last few months I've been working on designing and building a 3d-printable harmonic drive equatorial mount that can accurately track the sky for astrophotography. I've gone through a few iterations of this design, and I've had several successful nights under the stars with it. This guide should help you build your own mount that provides tracking performance similar to commercial options costing 3x as much. For reference, I have experienced guiding performance in the .6" RMS range with a 7kg payload.

EDIT 04/21/2026: Last night, I tested the mount with a 26.5lb/12kg payload (Edge HD 8" along with guide scope, camera, filter wheel, and other accessories) with a 5kg counterweight. I was guiding between .4" RMS and .6" RMS through the whole night. It was an extremely still night, but the mount can handle at least 12kg in ideal conditions.

The mount itself cost me around $300 in materials, but cost will vary based on what hardware you have laying around. If you had to buy everything including the hardware from nothing, you'll likely be looking at closer to $400. This price does NOT include a tripod, an equatorial wedge, or computer control like a miniPC or ASIAIR, which are all substantial additional costs.

Here's a picture from the first light on this mount! 4 Hours on the Heart and Soul Nebulae, with a Rokinon 135mm with ASI294mm Pro. Needs a reprocess at some point, but the stars are nice, round, and sharp.

While researching telescope mounts, I came across Astrophilos' CNC design and loved the concept. But CNC machining isn't accessible to most hobbyists without outsourcing manufacturing (which I prefer to avoid), so I set out to create a fully 3D-printable implementation with my own take on the mechanics. If you want to see his original project that inspired me, take a look here:

Astrophilos' original CNC design: https://tinyurl.com/33nwdryu

Fair warning, this is NOT a weekend project. It will require a decent bit of troubleshooting, but if I can build it, I'm confident that you can, too! Let's get building.

P.S. These designs are free, and anybody is welcome to make them! However, the design process took many hours and I spent a fair bit on materials, so if you love the design and want to throw a few dollars my way, I would love your support!
https://buymeacoffee.com/zachsnow

P.P.S. If you are confused about how pieces come together, please take a look at this Onshape project, which you can view or copy to see everything. Onshape accounts are free, and you can also use this to modify hole layouts if you need to use different harmonic drives.
https://cad.onshape.com/documents/2de2fb051a714e058f64595f/w/df6a35b163715e407189e8d9/e/983432291db10df55c6b0fc7?renderMode=0&uiState=699f682de8d31e0cf29f9484

3D Printable Harmonic Drive Assembly Guide

Required Parts

Motion Components

- 2x ZXS17 Harmonic Drives (60 arc sec, 100:1 ratio for NEMA17 stepper) - AliExpress Link: https://www.aliexpress.us/item/3256806003797473.html

Note - You can purchase the ZXS14 drive from the same page, but you will need different bearings with an 8mm inner diameter. Standard skate bearings are this size. This may require slightly modifying the bearing mount brackets, and you'll need different 60 tooth pulleys. This should be a simple change to make. This will also require purchasing 2x M8x60mm for the chassis instead of M5x60mm

- 2x NEMA17 Stepper Motors - Amazon Link: https://www.amazon.com/dp/B0B8HB5N4S

- 2x M5x60mm Locating Pins (4 if making the dual Vixen/Losmandy Saddle or Vixen Saddle as well) - Amazon Link: https://www.amazon.com/dp/B0F5HCG3TH

Belt Drive System

- 2x 2GT 16T Pulleys (5mm bore) - AliExpress Link: https://www.aliexpress.com/item/3256808690745852.html

- 2x 2GT 60T Pulleys (5mm bore, or 8mm bore if using a harmonic drive with an 8mm bore, like the ZXS14) - Amazon Link: https://www.amazon.com/dp/B0BLV7ZHWJ

- 2x 2GT 158mm × 6mm Timing Belts - AliExpress Link: https://www.aliexpress.us/item/3256806230785397.html

- 2x 5x11x4 Bearings - AliExpress Link: https://www.aliexpress.com/item/3256805799872664.html

Electronics

- 1x FYSETC E4 Control Board - AliExpress Link: https://www.aliexpress.com/item/3256805350436493.html

- 1x DC Power Jack - Amazon Link: https://www.amazon.com/dp/B0CR8TH2X2

- 1x Jumper Cable (you literally only need one female-female wire) - Amazon Link: https://www.amazon.com/dp/B01EV70C78

Fasteners and Hardware

- Assorted M3, M4, and M5 Screws and Washers - Amazon Link: https://www.amazon.com/dp/B0CBMMPPKF

- M3 Heat Set Inserts - Amazon Link: https://www.amazon.com/dp/B0D5V3TZLB

- Long M3 Bolts (for stepper mounting) - Amazon Link: https://www.amazon.com/dp/B0CHMHYCFV

- Threaded Insert (for counterweight bar. I only used one of the largest one. You may be able to find a smaller quantity, but make sure the inner and outer threads are the same as the M12 one in this pack. Optional if not using a counterweight) - Amazon Link: https://www.amazon.com/dp/B0CHM6B1J7?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1

- Note: the threads listed above will work with counterweight bars with M12 male threads, such as the ZWO counterweight bars.

- M5 x 35mm Bolts (for dual vixen/losmandy saddle) - Hard to source, but you only need 2. I found mine at a local fastener shop

- Compression Springs (for dual vixen/losmandy saddle) - Optional, but will make the saddle spring out automatically - Amazon Link: https://www.amazon.com/dp/B0BVTDP29W?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

Printing Materials

- 2kg PET-CF Filament (If you're patient, this often goes on sale for around $33/kg) You may want an extra kilogram if your printer fails often - Amazon Link: https://www.amazon.com/dp/B0F1CYXVSN

Printed Parts Required

All parts should be printed with 100% infill using properly dried filament

Main Chassis Components

- 2x NEMA17 Stepper Brackets

- 2x Pulley Support Brackets

- 1x Full Chassis (Either ZXS17 or ZXS14 size, and either 5mm bore or 8mm bore, depending on your drives.)

- 1x Chassis Cover (Either ZXS17 or ZXS14 size, depending on your chassis. The solid chassis cover will work as-is, and the frame will require you to cut plastic panels to fit in the holes. This will allow you to see inside your mount. The panels are a pain to cut and glue, but it was worth it for me) I don't have a picture of the new version of the frame chassis cover, but below you can find a picture of what it looked like with the panels installed for a previous version of the mount. Not the nicest picture, but it's the only one I have!

- 1x Electronics Port Cover (customize to match your FYSETC E4 board ports)

Mounting Accessories

- 1x Vixen Bar

- 2x M5 Thumb Screw

For dual Vixen/Losmandy Saddle:

- 1x Vixen Losmandy Clamp Part 1 (Either normal, or without springs)

- 1x Vixen Losmandy Clamp Part 2

For Vixen-only Saddle:

- 1x Vixen Clamp Part 1 (Either normal, or without springs)

- 1x Vixen Clamp Part 2

Print Instructions

- It matters! Following these guidelines will ensure your parts are strong in all the right directions.

- All parts printed at 100% infill. Yes, this will use a lot of plastic. If you print everything, including the dovetail and bracket, you're looking at just shy of 2kg of filament.

- Pulley brackets and NEMA brackets should be printed 'upside down.' You should not need any support.

- Chassis covers should be printed 'upright,' with the thin 'skis' at the bottom. I printed with a 5mm brim, and automatic tree supports.

- The chassis should be printed on its 'side.' You'll have only one large overhang that needs supports, which is the overhang of the opposing diagonal support. You can put support blockers everywhere else, or simply let supports generate automatically and pry support material out of all the little nooks and crannies. Automatically generated tree support worked best for me here.

- The vixen bar should be printed on the large, flat side. No support needed.

- The vixen or vixen/losmandy bracket part 1 should be printed 'upright.' You'll need supports for the primary cantilever, but nowhere else. You should be able to see the layer lines in the picture below to see which direction I printed this part.

- The vixen or vixen/losmandy bracket part 2 should be printed on the side where the thumb screws will thread in. This is on the large, flat side. No support needed.

Assembly Instructions

Preparation

1. Before beginning assembly, verify all parts are present and inspect 3D printed components for any defects.

2. Install heat set inserts:

- M3 inserts into all chassis cover mounting holes on the outside of the chassis

- M3 inserts into the non-through holes on each axis face (for pulley support brackets)

3. Install threaded insert for your counterweight bar

- You can thread this in using the counterweight bar itself. It should fit snugly, but I also added a drop of superglue to ensure the insert doesn't come loose. Try not to glue the counterweight bar into the insert!

Harmonic Drive Installation

1. Attach the M5×60mm locating pins to each harmonic drive's wave generator:

- Ensure the protruding end of the wave generator faces into the grease

- The M5 locating pin should extend in the opposite direction (towards where the chassis will be)

2. Mount the ZXS17 (or ZXS14) harmonic drives to the chassis:

- Place the large O-ring in the matching slot of the drive (prevents grease leakage)

- Secure each drive using 6× M4 washers and 6× M4×20 bolts. You'll need to install the 2GT 60T pulleys to the protruding M5x60mm locating pins as you do this, as you won't have clearance to attach them after the drives are secured. You can leave the pulleys loose for now (worm gear not tightened)

- You will not need to use the included mounting flange for the harmonic drive.

Pulley System Assembly

1. Tighten the 2GT 60T pulleys to the locating pins using the worm gears:

- Leave approximately 0.5mm clearance between the pulley and chassis to avoid friction

2. Install the bearings into the pulley support brackets. The fit is intentionally snug. If these brackets snap, try widening the hole by a couple tenths of a mm

3. Put the 158mm belts on the 2GT 60T pulleys, and secure the pulley support brackets to the chassis with M3 screws into the heat set inserts

Stepper Motor Installation

1. Attach the NEMA17 support brackets to the stepper motors:

- Orient both steppers so cables face the INTO the chassis (towards the chassis' corner)

- First secure the brackets to the motors using one short m3 screw on the arched side

2. Belt installation and tensioning:

- Place the timing belt around the stepper pulley. It may be a bit finicky getting this into place

- While mounting the stepper/bracket assembly to the chassis, tension the belt

- Secure the assembly with 3 long M3 screws, using washers to protect the chassis

- Ensure proper belt tension during final tightening. You can do this by pulling the stepper motor and mount away from the 60T pulley. After guesstimating proper tension and tightening the bolts, I like to poke the belt with an allen key. It should give a little bit, but there should be no slack. It should be taut.

Electronics Installation

1. Mount the FYSETC E4 board to the chassis cover:

- Use M3 bolts and nuts

2. Connect all wiring according to the FYSETC E4 pinout diagram. You may need to swap the inner 2 wires in the cord connecting the steppers to the board. Look into repinning a stepper for more info!

3. Secure the chassis cover using M3 bolts. You're likely to do some troubleshooting. If you only install the back two screws (closest to the counterweight hole), you can hinge the top on and off to make it easier to troubleshoot things.

Vixen Losmandy Bracket Assembly (Same instructions with the vixen-only bracket)

1. Prepare the thumb screws:

- Pre-thread the M5×35mm bolts into the thumb screws (fit is intentionally tight)

- Apply superglue to secure the bolts in the thumb screws

- This part is designed so that it can still be tightened with a hex key if desired.

2. Prepare Vixen Losmandy Clamp Part 1:

- Insert M5×12 heat set inserts into the INNER two holes (work slowly to prevent surface bulging. You can also clamp a metal bar or straightedge to the surface of this part to prevent bulging)

3. Prepare Vixen Losmandy Clamp Part 2

- Insert M5×60mm locating pins into the OUTER two holes with a small amount of superglue

- Gently tap pins into place with a mallet if needed

4. Test fit Part 2 with Part 1 and verify proper alignment, then screw together, with the springs slotting around the dowel pins in the outer two holes of Part 1.

Final Mounting

- Both the Vixen Losmandy Bracket and Vixen Bar can be attached directly to the ZXS17 Harmonic Drives using 6× M5×16 bolts and 6× M5 washers each

Configuring the Electronics

Congrats! Now you have an expensive block of plastic and metal. To get that expensive block of plastic and metal to actually do anything for you, you'll need to get Onstep configured on your Fysetc E4 board. If you're anything like me, this will be the hardest (and most frustrating) part of the process. However, the Onstep team has done a fantastic job putting together instructions to get this board working. Check it out here, and don't forget to place a jumper wire at the position shown below.

https://onstep.groups.io/g/main/wiki/32747

One of the most common issues I've seen with getting the electronics working is the stepper motors making noise but not actually spinning. If you encounter this, try swapping only the middle two wires of the stepper motor wire. Here's a video on how to do that!

https://tinyurl.com/5b7v5mrx

You'll also need to calculate the exact values for steps per degree, decide which current values you want, etc. If you purchased the exact same parts as me, you can use these values! Otherwise, you'll need to determine them yourself based on your reduction. The 'steps per degree' is the value you'll need to change with different harmonic drives. To figure that number out, do the following:

(Total Gear Reduction) x (Steps per degree of your stepper motor) x (Microsteps of your stepper)

For mine, this was:

(100:1 for the harmonic drive, 3.75:1 for the pulleys for total of 375) x (1 / .9) x (32) = 13333.333

Troubleshooting

If you encounter any issues during assembly or have questions about specific steps, please reach out to me for clarification at [email protected]!

Note: Parts were sourced from both Amazon and AliExpress based on price and delivery considerations. If you can find alternative parts for cheaper, great!