Guiding Issue with EQ6-R Pro

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Jeff Sauck

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Sep 12, 2021, 5:22:40 PMSep 12
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Hello I'm having some guiding issues with my mount using PHD2.  I'm new to autoguiding and to PHD2 so I'm hoping it's just some setting I screwed up.  I can't seem to get better than about 1.75" RMS, and RA is twice as bad as DEC.

I am using a Celestron OAG with an Edge HD 8 native FL (the 0.7 Focal reducer has been hard to find) with ASI174mm mini so I know guiding at this FL is challenging but i haven't had issues finding and holding guide stars.

I keep getting an excessive DEC backlash error during calibration but I've checked the backlash on both axes and I cannot see any looseness in belts or in the worm gear.  The backlash chart does show about 7 pulses of backlash, I'm beginning to wonder if there is some stiction in the mount?


Thanks,
Jeff

bw_msgboard

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Sep 15, 2021, 10:13:40 PMSep 15
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Hi Jeff, sorry for the delay.  It looks like the mount is the problem, not something you've screwed up with the guiding parameters.  To start, the backlash test you did demonstrates pretty clearly that you have a lot of reversal delay in Dec - it takes over 3 seconds to reverse direction on the Dec axis and get any actual movement.  You can see that in the graph results - the "flat top" is what we're looking at:
 
 
Each of the data points represent a guide pulse of 500ms, so the reported delay value of 3.3 secs is pretty easy to see.  Unless you can fix this mechanically, it's going to be difficult to get good guiding results unless you switch to uni-directional Dec guiding.  This backlash problem also affects your calibrations unless you manually clear the backlash before the calibration begins.  You have to do this every time you calibrate.  With PHD2 looping camera exposures, use your hand-controller to move the mount north ('up' button)until you see the stars in the display clearly start moving.  Then start the calibration.
 
Next, look at the raw tracking performance of your mount in RA for the 14 minute session starting at 22:06 - this shows what the mount was doing with guiding corrections removed (RA in red):
 
 
You can see the long-period oscillation from the uncorrected periodic error but this is actually guided out reasonably well.  But look at all of the ragged, abrupt guide star movement that shows up in various segments of that curve.  Many of the excursions are both abrupt and large and these aren't going to be handled well by guiding.  This is why your RA performance is always much worse than Dec - and as it turns out, your worst-case results near Dec = 0 would be 35% worse than this. 
 
You should probably seek EQ-specific help on what you can do to improve on the mount behavior.  Other forums have more contributors with that sort of specific knowledge.
 
Good luck,
Bruce


From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of Jeff Sauck
Sent: Sunday, September 12, 2021 2:23 PM
To: Open PHD Guiding
Subject: [open-phd-guiding] Guiding Issue with EQ6-R Pro

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Bruce Waddington

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Sep 16, 2021, 12:06:14 AMSep 16
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There are some other operational points I forgot to mention.  You should be binning your guide camera at this focal length and disable star-mass detection (Advanced Settings/Guiding tab).  You should also always let PHD2 auto-select the guide star with multi-star guiding enabled.  The star you chose manually was saturated which reduces guiding accuracy.  When you change the binning level, build a new PHD2 profile so that all the guiding parameters are initialized correctly.  You can keep both profiles if you want to switch back and forth between binning and un-binned although there's no good reason to not bin with your setup.

Bruce

Jeff Sauck

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Sep 16, 2021, 10:42:08 PMSep 16
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Hi Bruce,

No worries thanks so much for the reply!  I have been somewhat concerned about the performance of the mount since I got it in March, it never seemed right to me but I thought it was in my head or something I was doing.  I've barely been able to get 30 second unguided subs without star trailing and occasionally I get these weird jumps in the mount where nothing was touched, no snagged wires, wind, etc, and I'd get these long star trails every 10 subs or so.  Fortunately it should still be under warranty so I'll need to give Skywatcher a call.  I did get noticeably better unguided results with some PEC training in the handset before I switched to EQMOD/PC control.  I'm contemplating doing PEC through EQMOD (permanent), then use the predictive PEC in PHD2 to see if I can get down to under 0.70" guiding.  However that might just be masking the root cause if there is some issue with the mount.

Again, appreciate your feedback,

Best Regards,
Jeff
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