PhD guiding gone wonky

[Quatermass]

And by that I mean it was working just fine but now for some weird reason it only works correctly if I change the Dec guide command to south. It used to work fine in auto but the last few nights has decided to turn evil on me. I'm assuming it's polar alignment any one else had this issue or am I cursed?

[Gmx76]

Have you cleared calibration? I recalibrate near every time now and have a lot less guiding issues. 

[ONIKKINEN]

If you'll post your guide log it would be much easier to try and figure out what has gone wrong.

[Quatermass]

I did clear my calibration and went through the wizard again to start afresh haven't checked my guide log yet but so long as I change the Dec correction to south the guiding last night was fine which has me baffled thought it might be the cable at first but as it guided ok when set to south I guess the cable is fine. I read on the posts here that setting the Dec to south and making sure the polar alignment is spot on solved the Dec dropping off so my next port of call will be the polar alignment. I'm also considering getting a mini pc to avoid having three ten foot cables running from my shed extension to the roll off observatory. One day every thing will work flawlessly, yeah right and pigs will fly 🙄 

 

[michael8554]

"I read on the posts here that setting the Dec to south and making sure the polar alignment is spot on solved the Dec dropping off s"

Does not compute.

PA is never "spot on", so Dec will drift in one direction, not necessarily south.

Could be that on that particular night Dec was drifting north, so south-only guiding worked.

Which is a fix for Dec Backlash/Stiction.

Because any guide commands that cause Dec to swing over to the other Dec side will take the duration of the Dec Backlash to correct.

If your mount does have Dec Backlash/Stiction then on the night, track for a minute with guiding off and look which way Dec  drifts.

Then guide in the opposite direction, raise Dec Min Move a bit to stop Dec reversals.

The drift direction may change later on as you track across the sky.

Michael

Edited November 26, 2022 by michael8554

[newbie alert]

What mount is it?

Some mounts have really fluid axis so any really slight imbalance can throw it all out

Does it veer off both sides of the meridian, ie after the flip? If it guides ok with it guiding south does it go haywire after the flip?

How are you guiding? If pulse guiding you calibrate both sides of the pier

[Quatermass]

Thank you for the helpful advice my mount is a skywatcher eq5 mount with a 130pds and guide scope. I will do some more tests and get back to you on the results but this is the first time I have ever seen this when guiding and found it quite strange that making Dec move in south rather then auto got it guiding again also you need to know that I am dyslexic so not great with non visual instructions 

[Quatermass]

I got this message after calibration was done so I'm assuming my polar alignment is out again sigh I hate polar alignment 

[ONIKKINEN]

just post the log

[The Lazy Astronomer]

You seem to be making the assumption you have a polar alignment problem, but phd is giving you the 3 possible causes and you've discarded the other 2. Personally, I would think PA is the least likely cause unless you've made some recent change to how or where you set up. Like others have said, we need the log to make any conclusions. 

[Quatermass]

Ok  guys Here is the log from my last session as requested no chance of doing a polar alignment at the moment but as the mount is in a permanent position and had a very good polar alignment I am not keen to have to polar align it all over again. However I know have a full licence for sharp cap that came with my new camera so might try that out for polar alignment if that is the issue as it seems to have good reviews. Cheers QM

PHD2_GuideLog_2022-11-25_130955.txt

[newbie alert]

Take one thing at a time to eliminate the possibility of errors

Sharpcap is good, so yeah give that a go. .

Did it give you the calibration data such as this?

Where in the sky did you calibrate?

[michael8554]

Hi Quatermass

From the GuideLog, the guide rates are on the default "EQMOD ASCOM PulseGuide setting" of 1.5arcsec/sec:

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

Needs to be at least 7.5arcsec/sec

That very low rate made it difficult for PHD2 to correct guide errors.

And also caused Calibration to take 53 steps instead of about 12.

Cal included about 15 second worth of Dec Backlash, it's best to clear that before Calibrating, it's all in the Help files.

A PHD2 Guide Assistant run would have measured it for you and suggested a PHD2 Dec Backlash Compensation figure.

PA error was about 10arcmins, and was drifting south, which the PHD2 Guide Assistant run would have advised you of.

To correct a south drift you needed to guide north, not south !!

So the drift wasn't being corrected !!

I didn't see anywhere where "it only works correctly if I change the Dec guide command to south", all Dec your guiding was marred.

You Calibrated at Dec = 59.3 deg, it's best to Cal at near south and within 20 degrees of Dec = 0.

I suggest you have a good read of the PHD2 Help files, as you don't seem to know the basics.

Michael

[Quatermass]

Hi Michael

Thank you for taking the time to look at all that for me much appreciated. To be honest I have never really had any issues with PHD before certainly not like this so tended to just switch it on and let it do its thing. I will have good read through the help files as you suggest. Just to pick up on what you are saying,

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

Needs to be at least 7.5arcsec/sec

That very low rate made it difficult for PHD2 to correct guide errors.

The guide speed you are pointing out here is that the button next to the stop button you are talking about which I normally have set to 1.5?

To correct a south drift you needed to guide north, not south!!

So the drift wasn't being corrected!!

Ok I will try that next time this is what being dyslexic does to my thinking reversing the order of information which can be very frustrating at times.

You Calibrated at Dec = 59.3 deg, it's best to Cal at near south and within 20 degrees of Dec = 0.

Yes I should have done that I do normally but this time just wanted to get on with it before the clouds came in again.

Next clear night I will have another go and post the log file and take a few more notes if things don’t go to plan.

Again thank you for taking the time to look at all this it is much appreciated. QM

[Quatermass]

Ok Im confused now . Reading the help file it says this about the guide speed setting. 

5. Mount connection pane:  mount guide speed.  This is another area that seems to cause confusion.  The guide speed is a parameter set in the mount or in the mount driver, it's not something controlled by PHD2.  PHD2 never sets the mount guide speed, it only reads it.  It is usually expressed as a multiple of the sidereal rate and is typically in the range of 0.5x - 1x sidereal.  Despite what you may read elsewhere, it's usually best to use guide speeds in this range rather than much lower speeds.   Higher guide speeds can help to clear backlash more quickly and may help to overcome stiction problems.  If you say 'yes' to the connection option prompt, PHD2 will attempt to read the current guide speed from the mount.  If this fails for some reason, you'll need to enter the guide speed manually.  PHD2 uses this value to automatically set the calibration step-size and to aid in checking calibration results; but the guide speed information is not important for the actual guiding.  If you're using different guide speeds on the RA and Dec axes, enter the larger value.   If you really can't determine what the guide speed settings are in the mount, leave the setting at the default value of 0.5X.  This pane also has a checkbox regarding the presence of high-precision encoders in the mount.  These devices are sometimes included on expensive, high-precision mounts, and you are likely to know if you have them.  Most users will leave this box unchecked.

You mentioned this in your reply

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

Needs to be at least 7.5arcsec/sec

That very low rate made it difficult for PHD2 to correct guide errors.

So how do you change the guide speed??

[michael8554]

Hi Quaternass

I said:

EQMOD ASCOM PulseGuide setting"

It says EQMOD, so you won't find it in PHD2  :-<

Michael

[Quatermass]

Ah right thank you I will check that out in eqmod cheers 👍

[Quatermass]

Right now I get what your saying at first I thought it was a setting in PHD that controlled this. No joy tonight as the cloudy weather continues but soon as I get a clear patch again I will try all of the above and let you know how things go.

Guiding Rate The Pulse Guide Rate can be set between x0.1 to x0.9 of the nominal tracking rate at increments of 0.1 independently on each motor (RA or Dec). The rate sliders will determine how quickly the mount can move to correct a guiding error.

The EQMOD Project EQASCOM & Autoguiding Setting the rate “high” will cause the he mount will move much quicker in response to guiding pulses. This may seem desirable however if the error is small the guider will have to issue correspondingly short pulses. If the resulting pulse width is less than the 50ms minimum imposed by EQASCOM there could be an over correction. Set the Rate to low and corrections will take longer so there is more chance that the guider will always be chasing the error rather than correcting it.

[Quatermass]

A bit more investigation showed that the pulse guide settings in eqmod were set to a pulse of x0.10  much to low according to the recommended setting so will change that to x0.90 and looking back at my original setting screen shots from several months ago several things had got changed. Hopefully that will bring all back to working order again. Phd is a great bit of software and I have used it for years but when things go wrong it can be a real pain in the astro fingers crossed that all will go well just need the pesky clouds to go away now. I wouldn't have minded so much but having just spent a lot of dosh on a new camera PHD going wonky was the last thing I needed.

Will let you know how I get on 

[Quatermass]

Well Happy to say my guiding is back to normal again, realized after some investigations I had changed some settings when doing a new profile and messed things up also the advice given about my pulse guide settings was very helpful and corrected that so everything is behaving itself again. Sheesh this hobby can drive you nuts some times but then again I'm sure we have all been there pulling our hair out over some unticked box we forgot to check. Thanks for you help guys much appreciated as usual.