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HEQ5 Pro - Quick question on backlash sources (and binding)

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#1 davidarseneau

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Posted 25 January 2022 - 02:23 AM

I have just received my new Sky-Watcher HEQ5 Pro mount, and having read up on the mount before hand I went in with eyes wide open on backlash issues. I've already ordered the Rowan belt mod, so in all likelihood this won't be a question much longer, but anyways:

 

Is there any way to adjust the relative positions of the motor gears to mesh better? Upon inspection, and not tested in the field yet, there is the potential for backlash that originates from improper spacing between the three gears...the small motor gear meshes reasonably well with the central gear, but there is delay in both Dec and RA axes between the central gear and larger gear that drives the worm. Will 100% be solved by the belt mod, but thought I would ask anyways.

 

Also...what do binding gears sound like? I suspect my RA is a bit too tight, but honestly have no idea what I'm listening for.

 

Cheers and thanks!



#2 steveward53

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Posted 25 January 2022 - 03:31 AM

I have always viewed belt mods , regreasing , backlash fettling and suchlike tinkering to be the pastimes of the unlucky ones who have predominantly grey skies and have nothing else to do with their mounts ... lol.gif

 

My second-hand HEQ5-Pro has never been touched 'inappropriately' but can still deliver 15 minutes "unguided" subs with a careful drift align ... wink.gif

 

My advice would be to stick a telescope on top of it , point it skywards at night and start enjoying it before you ruin it with unskilled DIY.


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#3 maxsid

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Posted 25 January 2022 - 04:53 AM

I also have an HEQ5 which is maybe fourth-hand. It looks pretty old. No modifications.

Works well. Guides below 1" RMS total on a good crisp night. Bortle 8/9.

Never tried longer than 10 min for a single exposure though. Worked fine at 432mm.



#4 IonClad

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Posted 25 January 2022 - 07:07 AM

There are several guides out there that show how to better engage the worm and worm and motor gears and reduce backlash. The gear engagement can be adjusted by loosening the 3 (of 6) screws that hold the motor in place. Here is some starting material:

https://www.astro-ba...n-sirius-mount/

https://www.youtube....h?v=lwZnLkzNQlw

 

Note that there are also two points on the side under rubber stops where the worm gear side-side tightness can be adjusted. This helped with mine, but I'd suggest starting with the worm gear engagement push-pull screws and repositioning the motor slightly first. As for binding, you will definitely know when it occurs smile.gif. Be sure to test a full revolution around the axis after each adjustment, as binding may only occur on part of it.

 

My HEQ5-Pro showed the typical 13.6 second oscillation in RA due to gear contact points, large enough that guiding was necessary and 0.5s guiding exposures worked best. This is too short a cycle to be affected by Periodic Error Correction. After doing the belt mod, which was relatively simple, that 13.6s oscillation essentially disappeared and I get even better guiding and the option of using longer guiding exposures.

 

All told I started out-of-the-box with about 1.5-2'' RMS errors with guiding, and now consistently get < 0.8'' RMS all the time and < 0.6'' RMS on nights with good seeing. That's with about 15lb of equipment on top using both counter-weights and is sufficient for 540mm. I have not done a full tear-down to try and improve it further.

 

Cable management is also an important aspect, and I found that routing them around the main rotation shaft (with sufficient slack) helped a lot with sporadic pointing jumps.


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#5 davidarseneau

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Posted 26 January 2022 - 01:09 AM

Thank you IonClad, that is very useful/helpful feedback!

 

Appreciate the opinions on just strapping on the telescope and going at it, fully intend to, but there are documented, observable, measurable quality variances in these mounts that can be addressed in through careful "unskilled DIY", and I think anyone who spends this amount of money on a hobby would like to try to get the best results they can. Happy that your mount is working well for you! smile.gif




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