Harmonic Mounts and Belt Replacement (Ioptron HAE29C)

andrea tasselli · Sep 15, 2025, 11:22 AM

Apparently there is a lot more torque there than those belts can take (another good reason to avoid them). As for replacing the belts themselves, just keep the RA tight but not too tight, let's say a couple of millimeters either way and you are good. Backlash is a non-issue for the RA axis.

Avoid the mount or the belts the company provides?

andrea tasselli · Sep 15, 2025, 11:22 AM

Apparently there is a lot more torque there than those belts can take (another good reason to avoid them). As for replacing the belts themselves, just keep the RA tight but not too tight, let's say a couple of millimeters either way and you are good. Backlash is a non-issue for the RA axis.

First time hearing of this issue on belt driven SWG mounts. Assuming the mounts are loaded below maximum capacity and no catastrophic collisions occurred, this is not something these mounts are “known for”, certainly not a “reason to avoid them”. I have two HAE69s that have been operating remotely with more than a 1000 hours of integration on both of them for a year now.

Not saying what happened to the OP is not possible with normal use, but certainly any piece of equipment can break down.

Ashraf AbuSara · Sep 15, 2025, 12:17 PM

andrea tasselli · Sep 15, 2025, 11:22 AM

Apparently there is a lot more torque there than those belts can take (another good reason to avoid them). As for replacing the belts themselves, just keep the RA tight but not too tight, let's say a couple of millimeters either way and you are good. Backlash is a non-issue for the RA axis.

First time hearing of this issue on belt driven SWG mounts. Assuming the mounts are loaded below maximum capacity and no catastrophic collisions occurred, this is not something these mounts are “known for”, certainly not a “reason to avoid them”. I have two HAE69s that have been operating remotely with more than a 1000 hours of integration on both of them for a year now.

Not saying what happened to the OP is not possible with normal use, but certainly any piece of equipment can break down.

Yes, I agree.. I have been using it normally. For the last 11 months or so I have been using it with 70mm refractor+OSC set up and it worked fine. Recently, I changed my scope to GSO RC6 Carbon Fibre with OSC Camera. The gear slippage issue happened when I was trying to collimate my scope, and I did not even have any guiding equipment on the scope. Even Ioptron support said that they don’t know what could be the reason for the belt. I would have sent it to the US for repair but it is expensive, and more importantly, a time-consuming process. As of now, the company is trying to help as much as possible. They will provide some technical help.. lets see how that goes.

Thank you, Tony! As of now, that is the plan. To systematically dismantle the scope and fix the issue. The jitters come from the fact that there is no precedent for this on the internet. :D

That’s a good idea. I will try to document the process in some manner and share it here.

SkyHoinar · Sep 15, 2025, 05:49 PM

I didn't know harmonic drive mounts have belts. It is good to know!
I have a HEM27 with harmonic only on the RA. I opted for it because it is very convenient for air travel as it doesn't need conterweights. I really like it and it works fine and I hope it will be OK still for some time, but I have to admit that now I am starting to have some worries.
Thank you for sharing your experience! I hope you will solve your problem as soon as possible! Good luck!

Hey, I can’t say that “all” harmonic mounts have belt, but at least AM5/3 - the most popular option - has belts on both axes. The difference between HEM27 and HAE29 is that the latter has SWG on both axes. I don’t think there is anything to be worried about. Mechanical errors can appear anytime in any machine.