compare with a few others
Motors:
Drive – Harmonic drive + Synchronous belt (Reduction ratio: 300:1)
Reducer specification (RA) – NEMA 17 (Reduction ratio: 100:1)
ZWO-17-100-C1-TTT
Reducer specification (DEC) – NEMA14 (Reduction ratio: 100:1)
Periodic error – ＜±20”
PE duration – 432s
Drive (RA) – Harmonic NEMA17 stepper motor + Brake
17D4401-19BK Bipolar
Drive (DEC) – Harmonic NEMA14 stepper motor
14M3404 Bipolar
They mentioned that 900mm focal length is probably the maximum practical for this mount
Btw, The Alt Az base and adjustment knobs has so much resemblance to Rainbow 's RST135
faq ,
on periodic error and others
Rainbow comments on periodic error, even incorporation of an encoder, will not remove those irregular periodic error from strain wave spline gear
Great technical breakdown of the ZWO AM5 harmonic drive mount. I really appreciate how you included the motor specifications, reduction ratios, and periodic error details — information that many reviews usually skip. Harmonic drive mounts are becoming very popular because they offer compact design and minimal backlash compared to traditional worm gear mounts, making them ideal for portable astrophotography setups. Your comparison and notes about focal length limits and drive mechanics are very insightful for astrophotographers considering this type of mount. Thanks for sharing such detailed research!
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