NexStar SE8 excessive backlash due to drive axis shifting. How to fix

[Artik]

The video below explains it the best.

The axis that suppose to move the alt grear is shifting and creates huge backlash...

Have anybody an idea how to fix it?

 

 

[Artik]

Just to want to summarize the issue and solution (in case somebody finds it).

The problem is load bearing that failed. It is apparently a very common issue.

• One solution is to get a new motor (and I assume there is a good reason why it is listed as one of common spare parts by Celestron) I've seen them online for around $150 before taxes/shipment
• Another is to replace bearings. Here is a good description of how to do it and were to order a new bearing: https://www.nexstarsite.com/download/ReplacementNexStarIAltitudeBearingsV2.pdf 
• However, when I originally got the NexStar SE8 I wanted a manual mount in first place. So I went 3rd way and disassembled both motors, board and the cover with batteries tray and converted the mount to manual! 

I strapped a phone with AstroHopper for finding objects as I wanted from the beginning, removing the board and batteries tray allowed me to reach zenith with 2" diagonal and 2" visual back without problems (on NexStar SE it limited to around 65-70 degrees due to diagonal size), and make it all much more convenient

The only issue I find that there is no clutch on Alt Axis, so when I remove/add heavy diagonal CG changes and I need to be careful so the scope does not move forward/backward on its own. I think I'll add a small lock to prevent movement for assembling/disassembling the mount.

Now I'm much happier because I didn't liked/wanted the robot in first place. Yesterday I observed many open clusters M35, 36, 37, 38, M41, M48, M47, M50 and of course Moon and M42 Orion - it was much better! 

[Knighty2112]

Out of curiosity did you own the 8SE mount from new, and how long had you had it before the bearing failed? 
 

Sorry, that was for Artik.

Edited February 21 by Knighty2112

[Artik]

I got it used from B&H Photo so I have no idea when it failed.

It was actually under 3 month warranty. The problem was from the start, but I didn't diagnose it properly and I thought it was just a basic backlash. Only after 4-5 month of use I tried to configure backlash compensation I realized that even value 100 is not enough I understood something wrong and found some other video with the same issue so I got a hint.

I disassembled the cover and found what happens. Unfortunately the warranty was not valid any more.

[michael8554]

You'll have to take the motor/worm assembly off the mount and investigate.

Mchael

[Artik]

6 minutes ago, michael8554 said:

You'll have to take the motor/worm assembly off the mount and investigate.

 

I did and actually there is a good manual on how to fix it: https://www.nexstarsite.com/download/ReplacementNexStarIAltitudeBearingsV2.pdf

I probably will do it. But actually I prefer manual mount and I wanted manual mount from the beginning. Tracking isn't important for me.

[Artik]

I took it yesterday to some 1/2 dark location (Bortle 5) I was there before with the 1/2 working mount.

Such a huge difference: 

• No need to realign if somebody bumps into my tripod (several times)
• No need to worry about batteries
• It reaches zenith and no need to worry about bumping into mount.
• I can easily browse the sky from cluster to cluster manually
• I observed a flying plane from a distance
• It is so much faster/easier to find targets with astrohopper than with device and see what is around
• observed some nebulae, galaxies etc.

I wanted a manual mount and it is an excellent one!

Edited March 12 by Artik

[tico]

Hello,
How much weight can the Nexstar SE8 mount hold?

Edited March 13 by Cornelius Varley
formatting corrected

[Artik]

On 12/03/2024 at 17:02, tico said:

How much weight can the Nexstar SE8 mount hold?

It holds C8 - so it is around 5kg... without motors probably more.