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Harmonic Mounts and Belt Replacement (Ioptron HAE29C)

iOptron HAE29 Harmonic Mount DIY How-to
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Rajat Kumar avatar
Rajat Kumar avatar

To cut a long story short:

Recently, the RA Axis of my Ioptron HAE29C (both axis Harmonic gears) mount stopped responding. After some email exchanges with Ioptron, I decided to open the front panel of the mount. The belt on the RA Axis was broken. Now I have two options: one is to send the mount to Ioptron in the US for repair - expensive, issues of customs,

The second option is to fix it myself. Ioptron has sent me a manual to adjust the backlash of the belt, but there are no specific instructions regarding changing the RA belt. I wanted to ask if someone has undertaken this sort of endeavour on their respective harmonic mounts? The process seems to be to take out both RA and DEC motors and reach the innermost layer of the mount to install the belt, put back the motor + reattach the sockets to the PC board and tighten the belts

The mount otherwise is under warranty, and Ioptron has agreed to send me the belts to perform the replacement. I am speaking to them, but I wanted to know if there is anyone who has undergone a similar issue, not just with the Ioptron mount but in general with the harmonic gear mount.

Video showing broken belt - RA Axis broken belt.mp4

andrea tasselli avatar
andrea tasselli avatar
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.
Rajat Kumar avatar
Rajat Kumar avatar

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 avatar
andrea tasselli avatar
Avoid the mount but since you already have one check what belts you've got and how they compare to the best in class.
Ashraf AbuSara avatar
Ashraf AbuSara avatar

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.

Rajat Kumar avatar
Rajat Kumar avatar

Ah, surely! The belts are being shipped today by Ioptron, but I will check the model and see if I can get better ones. Thanks for underlining that.

Rajat Kumar avatar
Rajat Kumar avatar

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.

Tony Gondola avatar
Tony Gondola avatar

I just want to give some encouragement here. Take the mount apart step by step and take pictures as you go. Put all the screws in a tray or cups and label to keep track. I think you’ll find it easier than you expect.

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Rajat Kumar avatar
Rajat Kumar avatar

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

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Tony Gondola avatar
Tony Gondola avatar

Isn’t it great to be a pioneer? 🙄

Since you’ll be taking pictures all the way you could always post that somewhere as a guide to anyone else who might have a similar issue.

Rajat Kumar avatar
Rajat Kumar avatar

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

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SkyHoinar avatar
SkyHoinar avatar
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!
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Rajat Kumar avatar
Rajat Kumar avatar

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.

SkyHoinar avatar
SkyHoinar avatar
How is the HAE29 in terms of tracking/guiding and also polar alignment (does it still have the iPolar)?
I was considering buying a second mount and I was thinking to this one because of its SWG on both axes, but I am not sure if that makes any difference (compared to the HEM27). Some feedback from owners would be welcome.
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Rajat Kumar avatar
Rajat Kumar avatar

SkyHoinar · Sep 15, 2025, 07:51 PM

How is the HAE29 in terms of tracking/guiding and also polar alignment (does it still have the iPolar)?
I was considering buying a second mount and I was thinking to this one because of its SWG on both axes, but I am not sure if that makes any difference (compared to the HEM27). Some feedback from owners would be welcome.

I have been quite happy with it so far. Have no complaints except the polar alignment mechanism (this is my second Ioptron mount and it's the same story). The knobs which are there for RA axis adjustment are small. Apart from that there is no complaint as such. Having said that I have always managed to get PA below 1” without much issue. I can't say if it makes any difference in guiding but one doesn't need to balance the DEC axis in HAE. That's a plus for me - allows for quick set up. But that's just a minor issue, if your guiding on hem has been fine.