Help needed with my new Pegasus Astro NYX-88 mount

[Ventura Valderrábano Ornedo]

Hello everyone.

I need help understanding what's happening with my new NYX-88 mount.

Link to PHD2 files

Last night I performed polar alignment with Polemaster (screenshot attached). Following the instructions in the document "How to create a baseline for guiding results using PHD2," I created a new profile for the following guiding equipment (QHY5III200M + Player One OAG Max + TS Optics CF90 APO 90/540). It was in focus.

Since it's a new mount, I pointed it towards the confluence of the meridian and 60° (Alnitak was the chosen star). The Calibration Assistant showed that the ratios on the RA and DEC axes differed from what was expected. I performed the polar alignment again. 

After performing a new "Calibration Assistant" with the same result, I ran the "Guiding Assistant" for 15 minutes, selecting "Measure Declination Backlash". After accepting the Guiding Assistant's recommendations, I let the system guiding for 38 minutes of  madness.

I've been using PHD2 for many years with various mounts without major issues, but with this new mount, I'm completely lost.

[pollya...@gmail.com]

Hello  ventura.a...
I'm pretty sure the experts will require your guide and debug logs to give you the best advice. Images don't provide enough info. So, on the PHD2 interface, go to the Help tab > Upload Log Files and select the relevant session date. The logs will upload automatically with your request.
More info here:  https://openphdguiding.org/getting-help/
Cheers,
- Jack T

[Ventura Valderrábano Ornedo]

Thank you Jack.

I've already included the link to the PHD2 files (https://openphdguiding.org/logs/dl/PHD2_logs_ewFy.zip)

Cheers,

Ventura

Ventura Valderrábano Ornedo 
ventura.a...@gmail.com 

+34 607142000

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[Bruce Waddington]

Hi Ventura, thanks for doing a thorough job of collecting useful data.  The biggest problem you have at the moment is a huge periodic error in the RA drive:

This shows a periodic error of about 40 arc-sec peak-peak which is pretty bad.  Periodic error is typically a problem with these strain-wave mounts but I would say this is unusually large.  This is coming from a mechanical tracking error that occurs at a period of about 440  seconds:

This problem is why you generally can't get the RA guiding RMS below 1 arc-sec and it's also why you're having so many problems with the calibrations.  I think you should take this up with the manufacturer and see if you can get it repaired.  In any case, you probably won't be able to use guide camera exposures greater than 1 second because the mount requires essentially constant corrections.  If you are going to be stuck with this for some period of time, you could try guiding in RA using the PPEC algorithm, giving it a period length of 440 seconds and disabling the 'auto-adjust' checkbox.  If you can get suitable guide stars using 0.5 sec exposures, you can also do that. All of this will help PHD2 to mitigate the mechanical problem.

On a different point, it looks like you have a pretty sizable polar alignment error, reflected on both sides of the pier.  Here's the Guiding Assistant view of that (Dec is in green):

This is about an 8-10 arc-min alignment error, which is not a big deal but you could probably improve on it without much effort.  It will also mean you will have fewer Dec guide corrections that need to be made which will help maintain a rapid guiding cadence.

Hope you can get some assistance on the RA drive problem.

Bruce

[Ventura Valderrábano Ornedo]

Thank you very much, Bruce.

The mount was purchased last January, so I will contact the distributor about it.

Regards and thanks.

Ventura Valderrábano Ornedo 
ventura.a...@gmail.com 

+34 607142000

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/895b1525-193f-49d2-9d60-8a3109f9977an%40googlegroups.com.