Guiding is very sporadic

[Tom Horner]

I made a lot of setting changes and I have tried to eliminate as much of the backlash as I can but it's still really terrible. I haven't been able to determine why the model of the mount is not recognized. Guiding is good and also very sporadic. Not sure what else to do. I welcome any recommendations. Attached are the logs from last night.

Thanks in advance!

Tom

[Bruce Waddington]

We can do a better job of this if you would post both your guide and debug log files.  To do that, follow the instructions for Getting Help and use the built-in Upload Logs facility in PHD2:

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

Regards,

Bruce

[Tom Horner]

I tried to post the debug log file but the system gave me an error that the file was too large and try again. Suggestions?

[Brian Valente]

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

follow the instructions listed here, which describe using the built-in logzipper and posting a *link* to the resulting zipped files

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Brian Valente

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[Tom Horner]

https://openphdguiding.org/logs/dl/PHD2_logs_ajts.zip

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i5wkyrNY4gqn0Okq76kQc-Lu9hM8iTnGUv0miuLa2dZjA%40mail.gmail.com.

[Bruce Waddington]

You've clearly got some mechanical problems interfering with your mount's performance.  To start, look at how the mount responded during the GA backlash measurement - a direct measure of how long it takes to effectively reverse direction in declination:

The red data points show the mount responding to a stream of large guide pulses to the north - each move is intended to last 1.25 seconds.  Where the arrow is pointing, the direction of guide pulses was reversed - from north to south.  You can see that basically nothing happened for 4 guide pulses, then movement slowly began for the next 4 guide pulses.  Only after that did the axis begin moving at the expected rate.  This could be pure backlash but I suspect it's possibly exacerbated by binding in the gear system, often because of too-tight mesh.  You may be able to mitigate this to some extent by increasing the mount guide speed up close to 1x sidereal - this has to be done using the mount firmware and/or driver, not PHD2.  If you do make the change, you must recalibrate using the Calibration Assistant and follow all its suggestions.

Next, we can see there is some kind of instability in the Dec axis during normal guiding.  It has nothing to do with guiding because the very large excursions are happening spontaneously even when the Dec drive system isn't running at all:

The red arrows point to the beginning of an episode and we know the Dec motor was idle at these points.  These things are caused by external factors such as cable snags or drags or instability in the mounting of the guiding assembly.  The oscillating behavior goes back to the previous discussion of the backlash test and the likelihood that the drive system is over-meshed and is creating stiction.  Since you were pointing at Dec = 68 degrees during these periods, you may also need to look into whether there was a serious imbalance of the OTA in declination. 

Net result, I think you will need to track down and eliminate these mechanical issues to make progress.  Fiddling around with PHD2 parameters is at best a waste of time and is more likely to just make things worse.

Good luck,

Bruce

[Tom Horner]

"Since you were pointing at Dec = 68 degrees during these periods, you may also need to look into whether there was a serious imbalance of the OTA in declination." With respect to balance, I pay particular attention to the balance on both axes. After a near perfect balance (LOL) on the Dec, I typically have it slightly heavy on the East side. I'v looked at my ASCOM setup and can't determine why the Mount model is Not Recognized. - Suggestions on where to look.

I'm going to look at the possibility of loosening the mesh tightness. Thanks, I'll get back to you with any results - hopefully soon.

Thanks again

Tom

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[Bruce Waddington]

The mount model warning is being returned by the ASCOM mount driver, nothing to do with PHD2.  You would have to ask the supplier of the driver why this message is being generated.

Bruce

[Tom Horner]

Continued -  Guiding is very sporadic

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/4ab77143-e41d-4e27-b31a-9f810f60e953n%40googlegroups.com.

[Tom Horner]

https://openphdguiding.org/logs/dl/PHD2_logs_ZdXu.zip

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/4ab77143-e41d-4e27-b31a-9f810f60e953n%40googlegroups.com.

[Bruce Waddington]

Before we spend more time analyzing the logs, can you tell us what you've done since the last round of advice.  For example, the original analysis pointed to a significant number of large, spontaneous Dec excursions - have you tracked down the source of those?  What exact mount are you using and what is the total weight of the payload - that is, all the gear that's riding on the mount.  Have you re-adjusted the mesh on the Dec drive system to eliminate any binding? 

Regards,

Bruce

[Tom Horner]

Bruce,

Before the last guiding attempt, I made a small Dec drive mesh adjustment. The mount I use is a Skywatcher EQ6R-Pro. I have several different payload configurations. The previous guide logs were with a payload of 32.6 lbs. (which doesn't include the cables). These last guide logs were with a payload of 24.6 lbs. These were weighed on a digital scale with a tolerance of +/- 0.1lb.

Tom

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[Bruce Waddington]

The log shows mostly short guiding sequences, generally too short for us to see much.  The last one ran for just over 2 hours, which is fine, but you were pointing clear down in the weeds where the Earth's atmosphere is 2x the density of the zenith value.  That session shows nearly equal guiding stats for both RA and Dec, suggesting that both were mostly limited by seeing effects.  One of the short guiding sessions indicates you still have problems with something moving around in the guiding assembly, same as before - these are always in declination:

Again, these are caused by something moving around, not because of guiding.  These are tiny amounts of movement, under 10 microns - a human hair is about 50 microns thick. But because of your relative coarse image scale, a shift of 10 microns translates to a guiding error of over 5 arc-sec.  Also, if your mount driver supports it, you should increase the mount guide speed to something like 0.9x sidereal vs. the default speed of 0.5x sidereal you're using now.  If you make that change, you will have to re-run the Calibration Assistant so it can adjust the calibration-step-size parameter.

Good luck,

Bruce

[Tom Horner]

Thanks for the time to evaluate and comment. Greatly appreciated.

Tom