Guiding Spikes... Any ideas?

[Tangoringo]

Hi folks,

Just wondering if I may tap in to the wealth of knowledge on this forum.

Ive been guiding recently with a ST80 scope and QHY5Lii but after a rush of blood to the head with one of those hard to resist FLO offers I thought I'd try a lighter weight WO 32mm unilock to ease the strain on my poor old belt modded HEQ5 Pro ( it was at the top end of its load capabilities with a WO Megrez 90/Eagle 4 and the ST80.) Its a tad on the small side with a 5.1"/pixel figure compared to my 1.4"/Pixel imaging ratio but its within the 4 advisory 'limit'.

Compared to the ST guide graph the WO graph looked great for sawing large lumps of 2 by 4 but the resulting images were still just as good but with the occasional blip ( coincidentally in both RA and Dec which is odd ) and the guide bullseye was pretty well defined apart from a small rogue cluster which you can see in the top L quadrant. Any thoughts as to possible causes? Ive checked for snags and nothing is apparent, I dont think the belt is slipping and it was a calm night for once. Any other ideas?

Log file here

https://openphdguiding.org/logs/dl/PHD2_logs_Ppsb.zip

( Please note in the log file the first two hours or so contained a lot of bu??ering about on my part due to an issue with platesolving and also a lot of tinkering with PHD settings to see if I could reduce the spikes. )

Any help all gratefully received.

Many thanks,

Ian

 

Edited February 23, 2022 by Tangoringo

[Tomatobro]

The polar alignment is out as all the DEC corrections are one way but I guess you know this already.  The DEC/RA large correction takes place just after the DEC is told to move. It looks like the mount tries to correct in DEC a few times and no movement takes place and then just after another correction the mount unsticks and moves. The same thing then repeats. You can just see the DEC move command (orange) before the RA and DEC move together.

 

[Tangoringo]

Thanks Tomatobro ( love that ). 

Does that look like a snag to you or maybe something needing a bit of lubrication on the innards? Something over/under tightened maybe?

Appreciate your thoughts on this. Thankyou. 👍🏻

[wimvb]

Here are the things that grab my attention. The moves in RA and DEC are always in the same direction at the same time. This makes me wonder, how good is your calibration? Whenever guiding missbehaves, I start with redoing the calibration. Something may have changed which I missed, and I want to rule out that calibration is no longer valid.

Second, you have a MinMo of 0.11 and 0.13, and this is also what your guiding shows as RMS. With your guiding scale of 6.5"/pixel (!! not 5.1 "/pixel), and MinMo of 0.11 pixels, the best guiding you can hope for is with an RMS of about 0.7" in RA and 0.8" in DEC, or more than 1" RMS total. Any smaller star movements are simply never dealt with. If your mount has even a small amount of stiction, this is amplified by the settings.

The guide graph is overall very noisy; how was your seeing? If you use a motorised autofocuser, you can tell from the reported fwhm/hfr values how good your seeing is. If seeing is bad, you should increase the MinMo values, so you won't chase the seeing. Also, with a guide exposure time of 1.5 seconds, you are definitely chasing the seeing. Try to increase this to 2.5 - 3 seconds and use multi star guiding. You use a large value for the aggression. Too much aggression can cause erratic behaviour. All these changes should help calm the graph down.

Try this remedy:

1. redo the calibration. Calibrate near the Meridian and close to the celestial equator (but at least 40 degrees altitude to minimise atmospheric disturbances).

2. run the guiding assistant (for at least one full worm period, preferrably two). Let the GA measure backlash.

3. Accept the settings suggested by GA, then guide for at least half an hour, preferrably longer.

After all this, examine the guide log.

[Tangoringo]

Hi Wim,

Thankyou so much for your detailed reply….plenty to look at that’s for sure.

Think you may be on to something with the minmo/stiction as I had just accepted the calibration figures blindly as I’d had a certain amount of agro during the setup. The changes I did make were maybe not targeted enough and ended up changing too much too soon…. especially if the seeing wasn’t helping. Between yourself and Tomatobro I’ve lots to explore but hopefully I have some clear skies over the next few nights to have a play. I may just have to accept the Uniguide experiment is just stretching it a bit too far.

Either way, Thankyou for all the advice and for taking the time to reply. It is really appreciated Thankyou.

ATB,

Ian

 

 

[alacant]

18 hours ago, Tangoringo said:

the resulting images were still just as good

 

1 hour ago, Tangoringo said:

I may just have to accept

+1.

Unless you're going to pull the mouut apart and clean, lubricate and adjust tolerances and as pretty and colourful as the lines on the graph may be, look at the images. Not the lines!

One thing you may want to try is -belt or no belt-, go RA east heavy.

Cheers

Edited February 24, 2022 by alacant

[michael8554]

Although your Log doesn't include a Calibration, it appears to have been okay - no error message, Orthog okay, and RA and Dec guide rates close to the mount setting.

But that Cal was done on the day before - did you do a new Cal on the 22nd ?

PA from the Guide Assistant run was good,  1.9arcmin.

There was an advisory to improve the guidescope focus.

But the identical RA and Dec moves suggest the Cal from the 21st didn't match the scope setup of the 22nd.

Follow wim's instructions.

Michael

[Tangoringo]

Thanks Michael,

I think what I may have done in haste is post the guide log from the early part of the session, not the one from the later part as I did download two I remember. The photo was taken after another calibration run but with similar results to the earlier part of the session. Apologies if this caused confusion. 

[Tangoringo]

…. and to follow on, hopefully I’ll have more time to troubleshoot tonight but thankyou again to everybody for the help and suggestions.

[rickwayne]

Are you using multistar guiding? Any reason not to?