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Exos 2 GOTO slew issues?

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#1 cgreendyk104

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Posted 25 November 2021 - 06:42 AM

Hi everyone,

 

This is my first post on Cloudy Nights. I am reaching out in hope that somebody may have an idea of what is causing the issue which I am experiencing with my GOTO mount.

Equipment:

  • Bresser Exos 2 Mount
  • Bresser GOTO Upgrade Kit
  • Meade 6" Newtonian

Issue:
After a successful 3-star alignment, the slewing is inaccurate on most targets. For example, after a succesful 3-star alignment, when I slew to m27, it is dead center in my frame of view. However, when I slew to m31, it is quite off ( I can't say how much but it takes quite a bit of movement to get m31 in the frame of view). When I slew back to m27, it is dead on target again. This problem persists as well for all targets outside of NGC2024, M27 and M45. Here are the steps I have take several nights in a row and then experienced this issue.

Step 1) Balanced everything
Step 2) Polar aligned (stays on point for hours)

Step 3) Handset, double check data inputs (location, time, daylight savings)
Step 4) 3-Star Alignment

 

3-star alignment information:
(Vega, Deneb, Altair). First star, off target and then centered, second star somewhat off target and then centered. Third star, dead center.

Looking forward to any feedback at all! Thanks in advance,
Chris



#2 Grounddweller

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Posted 25 November 2021 - 07:42 AM

How level is the ground you are setting the tripod on? If you have a bubble level on the tripod check it, maybe you will have to adjust the legs somewhat. 



#3 michael8554

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Posted 25 November 2021 - 10:38 AM

Vega, Deneb, and Altair are all within a RA range of about 2 hours, whereas M31 is about 6 hours away.

 

To get a good Star Alignment over a wide area of sky you need Alignment stars that are further apart.

 

Or Star Align on stars nearer your target.



#4 Dwight J

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Posted 25 November 2021 - 12:01 PM

Are M27 and M31 are on opposite sides of the meridian when you are slewing to them?  If so, your optical tube is not orthogonal to your mount’s polar axis.  Try a two star alignment instead.  When slewing to the other side of the meridian slew to a bright star, center and sync on it and gotos should be ok on that side.  Alternatively, shim your OTA so the optical and mechanical axes are orthogonal. 



#5 cgreendyk104

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Posted 25 November 2021 - 01:13 PM

How level is the ground you are setting the tripod on? If you have a bubble level on the tripod check it, maybe you will have to adjust the legs somewhat. 

I will double check this saturday afternoon, but last time I checked it seemed to be level! Thanks though, will give feedback!



#6 cgreendyk104

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Posted 25 November 2021 - 01:19 PM

Are M27 and M31 are on opposite sides of the meridian when you are slewing to them?  If so, your optical tube is not orthogonal to your mount’s polar axis.  Try a two star alignment instead.  When slewing to the other side of the meridian slew to a bright star, center and sync on it and gotos should be ok on that side.  Alternatively, shim your OTA so the optical and mechanical axes are orthogonal. 

M27 and M31 are on opposite sides of the meridian in my case. So I just watched a YouTube video on this after reading this reply. I think this may be the problem! So this is what I found:

On my vixen dovetail bar, there is a screw which goes into the tube ring on each side, however each side also have two smaller screw slots which don't actually screw into the tube ring (I guess these are for fixing cone errors?). Anyways, I realized that on both sides of the dovetail bar, both left sides are lifted due to me screwing them in to deep. I have attached an image. Maybe this is what was creating the OTA not to be orthognal to the mount's polar axis. 

I have attached an image, does this look like this could be the root to my issue? Also thanks for the reply, I am quite new to all of this.
Webp.net-compress-image.jpg?alt=media&to
 



#7 Dwight J

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Posted 25 November 2021 - 01:54 PM

It certainly looks like it.  A fairly easy fix compared to shims.  



#8 rmollise

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Posted 25 November 2021 - 03:30 PM

I will double check this saturday afternoon, but last time I checked it seemed to be level! Thanks though, will give feedback!

You can level until you are blue in the face and that won't help with this problem. As others have observed, the problem is the alignment stars you are using...




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