Guiding change after replacing RA motor assembly

[sai...@suddenlink.net]

Please compare the two session logs from 7-9 and 8-4 uploaded here: https://openphdguiding.org/logs/dl/PHD2_logs_4vDY.zip

The guiding on 7-9 was good but after replacing the RA motor assembly on my CGEM DX mount, I can't seem to get it as good anymore.  During trouble shooting the RA motor issue, I accidentally used the wrong ST4 extension cable for my StarSense hand control and it quit working.  I replaced that hand control and the extension cable and all worked well again.  I am getting good Polar Alignments with Polemaster and sky mapping with StarSense.  But my PHD2 guiding is not what it was before.   I have uninstalled and reinstalled software and drivers until I've lost track of what all I've done.  I am hopeful that the logs will reveal what I've done wrong or failed to do.

Equipment: 

CGEM DX mount (hypertuned)

Orion 60mm guidescope with Starshoot camera

StarSense Autoalign camera and hand control

Celestron 8" scope with Nikon DSLR

Windows 10 Professional

Thanks in advance.  

John

[wave...@talktalk.net]

Hello John, I'm unfamiliar with CGEM mounts, but I guess hypertuning involves refining the RA drive system, primarily to minimise periodic errors. Was this procedure applied before or after you replaced the RA motor assembly? If before, then your findings now most likely relate to that. The two traces do show significant differences in their PE frequency analysis.

Here's the earlier one from 2021_08_03:

- and from 2021_07_09:

The marked frequency at 484 seconds is, I assume, the worm primary and has a peak to peak range of 19arcsec. The earlier trace is way lower. So, whether that's the crux of the guiding RMS difference or it's something else, I'm not expert enough to tell.

Cheers,

- Jack

[sai...@suddenlink.net]

Thanks, Jack.   Hypertuning involves replacing the sticky grease in the bearing surfaces and polishing the load bearing surfaces to make the mount operation far smoother than factory.  The factory configuration makes both axis "sticky" and hard to move or balance.   After tuning, the mount moves freely and is incredible easy to balance.   The mount has performed extremely well following hypertune until the encoder on the RA mount started to fail.   All my problems have been post troubleshooting that issue and repairing it with a new motor assembly.   The imaging session on 7/9/2021 was a very good one.   The attempts and the sessions between then and the 8/3/2021 sessions were nowhere near as good as far as guiding.  I was having cable and software issues (self inflicted, I'm sure) and I've never been able to get back to the same guiding as I had follwing the advent of the multi-star guiding.  I'm not a technician so I'm not really understanding what you are showing me with the two graphs.   My apologies for that.

[wave...@talktalk.net]

Hello John,

I think I've interpretted the dates of your Guidelogs. Being from the UK, I took the log dated 2021_07_09 to be the later one (i.e. 7th September 2021) .So, my suggestion of a greater Periodic Error in the replacement drive isn't the answer to your question. However, it is interesting that the hypertuned drive trace (2021_07_09) shows a larger periodic error at 484 seconds ( which I assume is the worm's cycle period) than the replacement.

The two graphs are analytical tools available within the Guidelog Viewer software, which you can download from the PHD2 website. This allows you to 'replay' your guiding sessions and examine various aspects of drive performance, including its periodic errors. Having read a bit more, it seems Hypertuning also includes reduction of periodic error, probably by a combination of the mechanical refinements you described and through periodic error correction using specialised software like PEMpro.

Hopefully, someone with a deeper insight will offer help.

Cheers,

- Jack

[sai...@suddenlink.net]

Many thanks, Jack.   That helps me a bit.  I, too, am hopeful I can find a solution to this.  PHD2 was amazing when it added multi-stars.   My graphs and numbers looked great.   I've done something to mess that up and I have exhausted my knowledge and experience (a bit over 2 years now).   Cheers.

John