DIY Harmonic German Equatorial Mount (GEM)

A compact DIY harmonic German equatorial mount designed for lightweight astrophotography setups.

The mount is based on the Fysetc E4 v1.0 controller board running OnStepX firmware.

Designed for payloads up to approximately 3 kg. If you plan to use heavier equipment, do so at your own risk. The author assumes no responsibility for damage or failures caused by overloading.

An archive with a modified version of OnStepX firmware is also attached. It includes several bug fixes and improvements and can be flashed directly to the controller and used as-is.

Included Parts

• Core
• Case A
• Case B
• 2 × NEMA motor mounts

Main Components

• 1 × FYSETC E4 v1.0 controller board https://www.aliexpress.com/item/1005001704413148.html
• 2 × NEMA 17 Stepper Motor stepper motors https://www.aliexpress.com/item/1005004586903773.html
• 2 × 1:100 harmonic drives for NEMA 17 https://www.aliexpress.com/item/1005008658589981.html
• 2 × GT2 60T pulleys, 6 mm belt width, 5 mm bore https://www.aliexpress.com/item/1005008672459615.html
• 2 × GT2 20T pulleys, 6 mm belt width, 5 mm bore https://www.aliexpress.com/item/1005008672459615.html
• 2 × GT2 belts, 158 mm, 6 mm width
• 2 × D-type shafts, 35 mm length, 5 mm diameter https://www.aliexpress.com/item/1005008459963157.html

Hardware Required

• 8 × M4x5x6 heat-set inserts
• 8 × M4x6 mm screws
• 8 × M3x6x5 heat-set inserts
• 4 × M3x10 mm screws
• 8 × M3x6 mm screws
• 4 × M3x12 mm screws
• 12 × M4x25 mm screws
• 12 × M5x20 mm screws
• 1 × DC power jack 5.5×2.1 mm (8 mm mounting diameter)
• 1 × 40×40×10 mm cooling fan
• 1 × 16 mm latching push button (power switch)

Print Settings

Recommended print orientation and support placement are shown in the provided images.

Core

• 8 walls
• 8 top/bottom layers
• 70% infill

NEMA Mounts

• 3 walls
• 3 top/bottom layers
• 30% infill

Case A / Case B

• 3 walls
• 3 top/bottom layers
• 15% infill

Material

Printed in PETG (333 Print) at 245°C.