Calibration problems with AM5

[Keith Geissler]

I am having calibration issues with PHD2 on a mini pc attached to my rig.  My rig is an AM5, Apertura 6" Carbonstar Ritchey-Chetien, Askar OAG with asi174mm mini, Askar Filter drawer and ZWO 2600MC Pro.

When I attempt to run the calibration assistant, everything starts fine.  The west steps run well usually reaching the 25 pixels in about 12-13 steps.  When the east side runs, it takes 2-3 steps (i thought this should be the same amount of steps as the west steps).  Then it attempts to clear the blacklash.  I have seen this take up to 50-60 clears before it will move on.  At this point, when it "attempts to clear the backlash", the guide star doesn't even appear to move.  If it gets past this point,  the north steps either go normal (about 12-13 steps), the south then takes 2-3 steps like the east steps.  I then get a star lost message and calibration fails.

Last night while I was doing this, sometime the north steps would take 50 steps, while the pixels would go in opposite direction  (see the log files about 20:44), when it did complete, it would do its 2-3 south steps and loose the guide star again.

I also have and asiair with has a "lite" version of PHD2.  If i swap the mini pc for the asiair, its calibration finishes and guiding is fine.  Albeit with only 2-3 steps for south and east.

I have attached part of the log and some screenshots of my settings.  I also did an uninstall and reinstall of PHD2, but that didn't help.  Any help would be appreciated.

[Brian Valente]

Hi Keith

please use the built in log uploader to post a link to both your guidelog and your debug logs

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

Also please update to the latest dev release and use the calibration assistant, which will help by walking you through the errors

https://openphdguiding.org/development-snapshots/ 

Brian

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Brian Valente

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[Keith Geissler]

I have upload the log file.  Here is the link.  https://openphdguiding.org/logs/dl/PHD2_logs_CjHW.zip

I will also download the latest dev version

[Bruce Waddington]

Hi Keith.  You've got some pretty serious problems with the mount, so this isn't a PHD2 problem.  It's just that PHD2 has the tools and diagnostics to tell you how bad things are.  Take a look at a sample of the calibrations you've gotten, all of which can be visualized in the LogViewer or in real-time using the Tools/Review Calibration data menu item.  In these diagrams, RA is in red, Dec is in green.

There's no consistency here so the calibration results are poor and guiding will suffer.  The biggest problems appear to be with declination.  I think you've got a lot of static resistance on the Dec axis meaning the axis can't respond to guide corrections quickly, smoothly, and consistently.  This could come from an over-mesh of the gear system or by a large weight imbalance in Dec.  This is why most of the calibrations you did resulted in computed Dec guide rates that were substantially lower than 7.5 arc-sec/sec, which is the value programmed into the mount.  I think you should try running the PHD2 Star Cross test (Tools menu) to get a clear visualization of how your mount responds to guide commands vs. what is expected.

It is very important that you always use the Calibration Assistant even if you're frustrated with the poor results.  The CA does a lot of things to help you get good results, including automatically clearing Dec backlash for you.  I saw that you abandoned use of the CA after a while which was a bad decision.  Remember, the problem is with the mount, not the tools. You haven't told us what the payload is on the mount but are you operating within the photographic weight capacity of the mount?  When I see a profile name of "RC 2600", I have to wonder if you're trying to carry a large, heavy scope on the mount.

Beyond these fairly crippling problems with calibration, some of your other choices aren't likely to work well.  You need to create a dark library for use with the guide camera and you will need to use shorter guide camera exposure times.  These strain-wave mounts don't usually track very well by imaging standards, so they need to be guided with a fast cadence - try starting with 1-sec guide exposures.  If the shorter exposures result in a shortage of guide stars, you should take a hard look at the focus of the guide camera.  Some of your star HFD values look substantially too high to me.  Getting a critical focus requires some technique that gives you quantitative feedback on the the stars sizes - the User Guide section on the Star Profile tool discusses one approach to getting critical focus.  Finally, you should disable the 'star mass detection' on the guiding tab of Advanced Settings.

Good luck,

Bruce

[Keith Geissler]

Thanks for the info.  My scope is a carbonstar RC6.  It weighs 11lbs. The rest of the gear (OAG, Filter Draw and camera) might add another 3 - 4lbs.  So I am at 15lbs, which is under the 25lb limit of the mount.

I will look into the other suggestions and let you know.

[Keith Geissler]

Just weighed my rig, it is at 17lbs.  Weight limit of the AM5 (without counterweight) is 28lbs