Guiding issues (Over correcting)??

[stefa...@gmail.com]

Hello,

Maybe someone has a hint regarding a guiding issue. I can’t explain why the mount acts one day perfectly and other days totally weird. For example 3 days ago the guiding was perfect (eg Pic1)

and 1 day ago really bad again. The Weather/Seeing almost similar. Also guiding at the same object.

 Pic2

 

My setup is a EQ8R (permanent setup)
Scope is a C11 with Celestron OAG and a ZWO 174mini Guidecam 
My city is in a 4,5 Bortle Area with a SQM between 18.5-19.5.
I setup PHD based on Recommended_EQ8_Guide_Settings_Aug2021_C.xls.

 

Any Hint how to optimize the guiding?

Thx for any answer hint Guide logs attached

Debug-Log storded here due to size limit

https://drive.google.com/drive/folders/137pnhENkYkhqan_Ly3aN_IuSp9M0VtIL?usp=share_link

[steve]

"Any Hint how to optimize the guiding?"

Hi

These are very much 'works-for-us' recommendations after having the same mystery a while back.

- Adjust DEC backlash to prevent stiction over the whole 180º of movement.

- Guide DEC using Resist Switch

- Guide RA using PPEC with a fixed period of 198s

- Bin the guide camera.

I'm sure the software gurus will be able to provide more expert insight.

Cheers and HTH

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[stefa...@gmail.com]

Thx Steve for the Hint. Will try this

Br SK

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[Brian Valente]

Hi Stefan

You are using some exotic settings and algorithms for guiding. Is there a reason for that (such as z-filter for dec and very low aggression for RA)

Regarding the settings document you mentioned,  "Recommended_EQ8_Guide_Settings_Aug2021_C.xls"

where did you get this and can you send a copy?

That's not anything i'm familiar with

Brian

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Brian Valente

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[stefa...@gmail.com]

Hello Brian,

it' from a EQ8r-Group

https://groups.io/g/SkywatcherEQ8/message/5809

heres the Link to the xls wih the rec settings

https://www.dropbox.com/s/wmzv7pmsfber37j/Recommended_EQ8_Guide_Settings_Aug2021_C.xls?dl=0

All the best Stefan

[Rick Cohen]

I'm not an expert.  But in the PHD2logviewer, if you check the SNR checkbox, you'll see that the star SNR for the two nights are vastly different.

[Brian Valente]

  Hi Stefan

These suggested settings seem outdated and seem very specific to that person's experiences. They are from 2019 and updated in 2021. A lot has changed since then and we would not recommend some of the suggestions. I'm not saying it doesn't work for that person, but it's generally not a great place to start 

I suggest you start a new profile via the wizard and use default settings. 

Use the calibration assistant to achieve a good calibration and get confirmation (the log i reviewed did not have a calibration run nor a guiding assistant run)

then use the guiding assistant for a few minutes and follow its recommendations

That is a much better place to start

Your current settings are too slow to respond to your changes. Your mount also shows some stiction in RA. A low aggressiveness in RA is causing this problem to be worse

RA stiction 

Finally, the guidestar SNR is poor and quite variable. I suggest you increase your auto select SNR to 30 or higher (advanced settings, Guiding)

The yellow line (your guidestar) should exhibit much less noise and oscillation. Someone else suggested seeing conditions may be highly variable as well, which could certainly be the case.

Brian

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[steve]

Those settings are for the old eq8. IIRC, you have the eq8r.

Cheers

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[stefa...@gmail.com]

Hello Brian,

thx for the advice. Ill try this at next CS nght. Could you re-send the picture with the RA-sticktion? It somehow disapeared.

I have just one question regarding aggressivness. When there's an oscillation like in the picture below, isn't this overcorrection or too much aggressivness? At least thats my assumption and led to lowering the aggressivness

cs Stefan

[Brian Valente]

You can view the discussion on the web to get the picture again (link in the footer of all emails)

>>> When there's an oscillation like in the picture below, isn't this overcorrection or too much aggressivness?

If it was just one pulse, yes i agree, but you can see it's taking multiple guide pulses to reverse the direction, so it's not overcorrecting on one pulse. 

This behavior also makes me think there's something mechanically going on with your RA, possibly stiction

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[stefa...@gmail.com]

I see. Thx again Will check the tolerances on both axis. I only checked RA and it was without any tolerance, but not too tight. Therefor I took the belt from the wheel and moved the gear manually back and forth. But yes, with a chinese mass production there's always a good chance to have also mechanical issues.

My next mount will be a higher quality.

Cheers

Stefan