Trying to interpret guide log results from my EQ8-R

[Jeff Nibler]

I had a guiding issue I wasn't able to solve with this mount last year and I put it to the side as a result. I need to get it working now so am picking back up from where I left off. 

https://openphdguiding.org/logs/dl/PHD2_logs_2cFQ.zip

The main issue is Dec axis behavior. I'm aware that the worm gears are not spring-loaded on these mounts which causes a lot of issues for people but I'm not sure if what I'm seeing in the guide logs is pointing to too much Dec backlash or Dec axis binding. 

From the guiding assistant runs I performed, it does seem that there is ~3,800ms of Dec backlash which is a lot. I am happy to adjust that manually on the mount if I need to but I want to be sure that's the problem first. 

Note that in the attached log, between midnight and around 1am or 1:30am I was remotely adjusting settings so if you see changes around that time, that is why. One of the last things I did was configure Dither to RA-only around that time. That helped mask the issue but I still see things in guiding that don't make sense. 

Given that guiding assistant showed a lot of Dec backlash, what is confusing me is that later in the night after my adjustments (one of the main adjustments I did was to switch dither to RA-only but I also played around with setting Dec Guide Mode to North or South, but ultimately left it on Auto), I see instances where the guide pulses could not correct sudden and substantial Dec drift. I understand that is exactly what backlash looks like but in the log at the time, the dec pulses were always in the same direction, and the same-direction pulses looked like they were working fine to correct Dec drift until they suddenly were not and no amount of pulses in the same direction seemed to correct it for six whole minutes (example 2:48am). When I installed the mount last night, I set the PA so it had 1-2 minutes of PA error so a bit of Dec drift would help with backlash. 

Thanks in advance for any help interpreting these. 

Jeff

[steve]

Hi
If it is backlash, you should easily be able to detect 3 seconds worth mechanically by rocking DEC clockwise and anticlockwise whilst the clutch is engaged. Stiction and tight mesh manifests itself more by overshooting at the end of a guide pulse sequence. I don't see much overshoot on your runs. 
The adjustment is quite straightforward, but note that most guides forget to tell you that the easy way to loosen the dec block is by loosening the motor to gain access to the remaining -difficult access-  bolt.
HTH

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[Jeff Nibler]

Thanks for the reply Steve. I did do that mechanical test and there is backlash on the Dec axis for sure. I've read up on how to adjust the Dec worm mesh and feel comfortable doing it but looking at the guide logs, note 2:48am - you see how it corrects dec in the same direction continuously as it should since Dec is constantly, slowly drifting in one direction due to the small PA alignment error I set, guide pulses are all in the same direction, yet Dec just starts drifting out. Looking at all those dec pulses in the guide log, I would expect to see exactly this for high backlash but only in a situation where the worm gear was unloaded and it changed directions. I don't think it changed directions in this case. Am I interpreting what I'm seeing in the guide log incorrectly? I'm definitely not an expert in interpreting these. 

Thanks again,

Jeff

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[steve]

Hi Jeff. 

We just go by the old adage: the mount has to be better than perfect for the software to be effective. If you can feel backlash, fix that first. You'll then be in a much better position to assess the guide log. Many eq8rs are unusable out of the box, usually due to the Dec worm adjustment. Ours were no exception. We speak from bitter experience!

Sorry can't interpret your issue at 2:48 but to my untrained eyes it looks like it could be runout on the crown and you've hit a low zone. I'm sure the software gurus will have a more specific advice. 

Good luck and get those hex wrenches clean and ready.

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