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Harmonic Drive mounts such as the RST-135e - question on total payloads for AP


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Hi all,

A quick question re: harmonic drive mounts such as the Rainbow RST-135e, 300 etc.... do the typical payload rules apply to these as they do for traditional worm drive mounts for astrophotogrpahy?

E.g. there is a general rule for the latter to take the manufacturers total payload for AP and then take 60-75 (ish) % of that figure to get the true viable magic number. Is this also true for harmonic drive mounts? Taking the 13.5kg payload (without counterweights) for the RST-135e for example, does this infact mean it can realistically support just 8.5kg (ish) for AP use (without counterweights)?

I am curious is all :)




Edited by Jonny_H
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  • Jonny_H changed the title to Harmonic Drive mounts such as the RST-135e - question on total payloads for AP
  • 2 weeks later...

The answer seems to be yes. I had about 6-7kg of an imaging train on it (with a fairly long scope, mind you) and it did not have any issues. I was getting about 0.7" RMS guided on my RST-135.

Most people with a 7kg-class imaging scope (FSQ-106 for example) seems to use a counterweight though, not because the mount can't handle it but because they worry the tripod might fall over. So with a 8.5kg payload you might want to have the counterweight.

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  • 8 months later...

Hi Jon,

I have been testing my new RST-135E with various scopes that I have. In summary: with a fully loaded Takahashi FSQ-85EDP, at 11kG total weight, I use the mount without counterweight ad the mount operates flawlessly with a total guiding error in the range 0.2" to 0.4". With a heavier fully loaded Takahashi FSQ-106EDX4 scope, at 16kg, I use the small RST counterweight and I get similarly small guiding errors. Under windy conditions, the guiding errors change little going up to 0.3"-0.4" only, as the mount motors have a very large torque and handle the lod firmly.

This is a fabulous mount.

Best regards,


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