Clearing Backlash Issue & High Guiding Error

[Arie]

Last night, when trying to start auto-guiding with PHD2 (v. 2.6.14), I found it trying to do a lot of Clearing Backlash steps (around 50), after which PHD2 often got disconnected from the device and the calibration was abruptly ended.

At one point, I switched to PHD2 (2.6.13dev7) and increased the calibration steps into 1,500ms. After these changes, there was a moment where PHD2 finally managed to start auto-guiding. However, the guiding error was quite high (the average error was around 4").

I wonder if anyone has any clue about the problem. Please find the log here.

Thanks.

[Brian Valente]

Arie

The basic problem is your mount is not responding well to calibration. Your logs show the unfortunate distinction among the worst of calibration results. Here is an example, RA in blue which appears not to return to the origin point in any straight line (note the west movements moving at 90 degree different direction(!) from the east. The dec (red) requires about 400% more steps than RA. So it seems there is something going on with your mount mechanically or possibly in the driver itself regarding rates. The mount does seem to respond to the communications in general. None of the 6 calibration runs produced an acceptable result, so until you get the calibration sorted out, you aren't going to get any good guiding results. It's probably worth a quick review and re-set up of your equipment, just to make sure obvious setup/mechanical problems are resolved.

 

The last calibration was quite surprising to see a large jump in the Dec angle, which also suggests something may be loose? I've never seen something quite like this 

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Bruce Waddington]

In order to work on this problem, I suggest doing a couple of things:

1.  Increase the guide speed in the mount driver up to 0.9x sidereal from your current value of 0.5x sidereal

2.  Use the Calibration Assistant as it was intended, not just as a quick way to slew the scope.  Use both the 'slew' and 'calibrate' buttons and follow all of the recommendations made by the tool.  Do this for all your calibrations.

3.  Do these tests manually, not with a session manager application banging away in the background.

If you can't get a calibration that's at least 'acceptable' to the Calibration Assistant, there's no point in trying to forge ahead with guiding.  At that point, you should use the star-cross test (Tools menu) in various parts of the sky in order to clearly demonstrate the mechanical problems with the mount.  Then use those images to work with the mount manufacturer to get more specific help.  In the meantime, you should ignore "recipes" you get on the forums regarding tweaking of PHD2 guiding parameters - those things are useless for your situation

Good luck,

Bruce