Guiding stopped working for no apparent reason

[Eric Giraud]

Hello,

I am experiencing loss of guiding for no apparent reason.

I am running my sessions via NINA and I have realized that sometimes the guiding stops operating. The sky conditions are good, the stars are clear as seen from the guide camera though. I tried to start the guiding from PHD2 but nothing happens, the stars are still scrolling but no guiding.

The only thing I found to solve the issue was to launch the Calibration Assitstant again. I though the "restore calibration settings" was OFF but it was ON.

I am attaching two logs:

- Night Friday to Saturday: things were fine

- Night of Saturday to Sunday: guiding did not work from the beginning

https://openphdguiding.org/logs/dl/PHD2_logs_WjX3.zip

Many thabks for your support.

Best regards.

Eric Giraud.

[Bruce Waddington]

The guide logs show a somewhat different story than what you are remembering.  The same problem happened on both nights at the same sky pointing position.  And guiding didn't "stop" - it ran continuously but was completely unable to recover or control the huge tracking errors you had.  PHD2 tried multiple times to alert you to the problem, but you had chosen at some point in the past to suppress that alert. That said, it's hard to identify a specific source of the problem just from the data we have.  Here's a look at the events on the two nights - RA is in red, Dec is in green:

September 5:

September 6:

Notice the timestamps on the two different nights - very nearly the same - and the y-axis values to the left.  These are gigantic tracking errors.  When they occurred, PHD2 continued banging away trying to correct them but it was a hopeless situation.  If we measure the rate of displacement in these two cases, we see tracking errors of 186 arc-sec/sec and 166 arc-sec/sec.  Compare that to normal sidereal tracking which is 15 arc-sec/sec.  So even if the mount had stopped tracking altogether, it wouldn't have produced this result.  And of course, since you were running PPEC for RA guiding, all of this got baked into the model it was trying to build.  I think you probably have some substantial mechanical instability in your guiding assembly that is showing up in this sky location.  It could be the guide scope/camera moving around or it could be a cable that is pulling on the assembly, something along those lines. I suggest slewing the scope back to that location and looking very, very closely for something that is disturbing the guiding assembly or is not allowing the mount to track smoothly.  The pointing position of interest is side-of-pier west, Dec = 36 degrees, and RA 1.7 hours west of the central meridian (about 25 degrees)

Hope you can track it down quickly,

Bruce

[Eric Giraud]

Many thanks Bruce. 

I found the issue during daylight testing. It came from the USB cable connexion, on the mount side. With the large mouvements of the mount (like when changing target), there could be some loss of connection. I tried with a different cable, checked the robustness under mouvements, and all is perfect now.

Thanks again.

Best,

Eric. 

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[Bruce Waddington]

Glad you found it.  It's pretty important to have a systematic cable routing system because dangling cables can cause all kinds of problems.  For example, you might find that a cable "fix" for a particular pointing position won't always work depending on where the scope is when the slew begins.  

Cheers,

Bruce