PHD2 guiding issues in RA

[Graham Smith]

Hi

I'm seeing occasional large spikes in RA during guiding, peaking > 40", while DEC looks okay. I'd love to get some guidance on likely issues, thanks in advance.

The mount is an EQ6-R and I'm running PHD2 2.6.13Dev7. The OTA is a ED127 (~ 18lbs) and polar alignment was double checked and within 50" (according to NINA TPA), very little wind.

Attaching a zip of the log file. The longer sessions all show the spikes, but also periods were the guiding seems to be okay. 

 

[Michael Waring]

The experts will require the GuideLog and the DebugLog.

See the instructions at the top of the home page "How to ask for help with PHD2"

See https://openphdguiding.org/getting-help/

[Bruce Waddington]

Yes, you haven't really followed the instructions to get us everything we need.  Judging from the limited information we do have, you shouldn't be binning the camera, that's creating a very coarse guider image scale.  I can see the large, abrupt excursions in RA however.  I think the most likely source of the problem is with the finder-scope style guiding assembly you have.  If it's one of the popular, low-cost stalk-mounted devices, it's probably able to move around on its own.  Also, it's equally likely that your cable routing arrangement isn't sufficient. A less likely source of the RA excursions could be grit or dried grease in the RA drive system but I wouldn't start the investigation there.  You should also start using the Calibration Assistant and follow its instructions - the calibration you're trying to use had poor quality.  It's likely that you can get better results if you increase the mount guide speed up to 0.9x sidereal instead of the 0.5x sidereal rate you're using now.

Regards,

Bruce

[Graham Smith]

Great suggestions, thanks.

I never thought to check the guide scope and there was a little play. I tightened that up and also tried to reduce backlash in RA & DEC, then checked for binding.

I will calibrate and test again tonight (clouds permitting).

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[Bruce Waddington]

Backlash in RA is irrelevant to guiding because the motor direction is never reversed.  RA backlash only affects slewing accuracy so there is little upside to tinkering with it and a significant risk of creating binding for the low-power, low-speed activity of pulse-guiding.  I forgot to mention you should stop binning the guide camera, it's creating a guider image scale that is too coarse which also exacerbates the effects of unwanted mechanical movement.  I think you should slow down and start by creating a new PHD2 profile using the new-profile-wizard.  Increase the mount guide speed, un-bin the camera, then run the Calibration and Guiding Assistants.

Good luck,

Bruce

[Graham Smith]

I tried to remove backlash, tightened up the guide scope and re-calibrated last night. PHD2 was not happy with the calibration and I may still have some backlash in DEC? I then imaged for a couple of hours to test the guiding and it looks a lot better, although I'd love to get average RMS below 1. Last night there was almost a full moon, so very bright skies and I see PHD2 has lots of dropped stars, would that effect calibration at all?

I uploaded the logs to https://openphdguiding.org/logs/dl/PHD2_logs_fcFu.zip

Thanks again for the help.

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[Brian Valente]

Hi Graham

Do you have a few pics from different angles of your guiding setup? 

You started the night with a good calibration, and then a later re-calibration was pretty bad and done far from 0 Dec, so everything after that was compromised. 

You are getting a lot of lost star events during calibration, can you increase your exposure time at least during calibration and make sure to use the calibration assistant. i'd go with 2.5-3 seconds for now. Your camera gain is set to 1 so another possibility is also increasing that gain a bit to help here. You can switch by to 1 second exposures during guiding if needed. 

Looking at the rest of the guidelog, there are too many lost star events to really tell much more. It's possible your guidescope may be rotating or moving in the connection. 

I suggest you update your exposure settings, use the calibration assistant to calibrate at the ideal point in the sky, and then run the guiding assistant for about 15 minutes so we can see what's going on with your mount. 

The short GA run you did (althoug full of lost star events) reported dec backlash was over 2 seconds, so that is still quite large and will be difficult to automatically guide. you may have to guide in one direction. The one spot where dec guiding confirmed significant backlash

On RA, I suggest you go back to the default hysteresis and stick with that for now. Your PPEC settings are not tuned for your mount and are fairly low aggression, so RA is not as responsive as it could be (1. below). You can switch back to PPEC once we get a clearer picture of your GA results. Also there are some big jumps in RA (2. below) that likely indicate mechanical issues. It could be the worm has lateral movement, some debris in the gear that's causing this, etc. but again, hard to pinpoint without seeing a clean GA run

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Brian 

Brian Valente

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[Graham Smith]

Thanks Brian

I recalibrated when DEC started going crazy. I see now that was when it was on the East side of the pier and I'd forgotten to set Reverse DEC after the meridian for my EQ6-R when I remade the profile. I will change the setting as you suggest above and try again tonight. 

BTW. I did not set the gain when I created the new profile and if I change it and then hit reset it goes to '1'. However when I hover over the input the tooltip says the default is 95. Should I start at 95 and lower if I get a lot of noise? The camera is a SV305 Pro (IMX 662).

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[Brian Valente]

>>> I see now that was when it was on the East side of the pier and I'd forgotten to set Reverse DEC after the meridian for my EQ6-R when I remade the profile. I will change the setting as you suggest above and try again tonight. 

yep, that was it

  >>>Should I start at 95 and lower if I get a lot of noise? The camera is a SV305 Pro (IMX 662).

Your issue is you have a lot of lost stars. I think it's because your guidestar signal is too low, so increase your exposure time and/or increase your camera gain

Another thing you can do is increase your min SNR for autofind to around 20 for higher minimum guide star selection

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[Graham Smith]

I changed the settings as advised above and re-calibrated. The calibration looked good to PHD2 (and to me). I then tried guiding, but every 1-2 minutes RA was way off again, (DEC is better and now < 0.50).

I tried and narrow down the issue I turn off PHD2 and started capturing images in NINA every 5 secs. At the start they looked great and I could not see star movement between images (moved mouse icon over star to check). Several images in a row looked good and no movement so PA seems okay, but then massive star trailing in one image and then back to good images. This seems to match what PHD2 was reacting to. I turned off tracking and the star trail angle matched the previous bad image. Looks like I have an RA issue in my EQ6R.

[Brian Valente]

Graham I agree there is something amiss with your RA. You should be able to share your unguided data with the mount manufacturer and see what advice they offer you. I hope it is an adjustment but may require factory servicing

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[Graham Smith]

I found I could tighten the weight bar collar on my EQ6-R quite a bit and still have enough movement to balance the scope. After this I readjusted the RA backlash.

The results are better but not perfect. I still get large RA spikes (up to 42"), but far less of them and the guiding between spikes looks decent. The average RMS over ~ 2hrs is now 2.27 RA and 0.61 DEC, Previously average RA RMS was 8.29. I'd estimate I'm now losing ~15% of my subs to star streaks, which is far better than before.  

Thanks for the help, I now have a usable mount again, but I will plan to clean and lubricate plus replace the worm roller bearings in the near future.

[Brian Valente]

Graham

That's good to hear you are making progress

>>>The results are better but not perfect. I still get large RA spikes (up to 42"),

42" spikes is still quite far from what I would expect from your mount model. Did you try contacting the manufacturer with your data and see what recommendations they had?

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