Continuing Autoguiding Woes with AZ-EQ5-GT

[Jim Smith]

I have been trying to get autoguiding working for several weeks now but without much luck. I often get a good calibration near the meridian and celestial equator and guiding at the same location usually starts off OK. But when I slew to my target it all goes horribly wrong.

I suspect that my mount is faulty as I have tried three different laptop to mount connection methods (EQDIR cable, USB A to USB B cable and ST-4) all with the same poor results. Last night I used my new 13.8V regulated mains power supply instead of a battery but that didn't help either.

I don't think PHD2 is the problem but I thought I would post here as an experienced hand might know what is going wrong.

Last night I used my usual Redcat 51 set-up with a WO 120mm guide scope and Altair GPCAM3 178C guide camera. I use SharpCap Pro, EQMOD and PHD2. Clutches tightened. No cable snags. Polar alignment (SharpCap) < 1 arcminute.

I have attached my log files.

At 4, I got a good calibration.

At 5, a few minutes of good tracking.

At 6, more good guiding followed by invoking Guiding Assistant.

At 7, 15 minutes of good guiding!

At 8, I think this was when I slewed to M16.

At 9, guiding on M16 starts OK but then the madness starts.

At 10, I tried PPEC...no good.

At 11, more PPEC...no good.

At 12, Lowpass started fairly well but things rapidly deteriorate.

I checked inside the mount this morning and the RA assembly looked fine with a reasonably tight belt and no axis wiggle.

If anyone has any ideas as to what I am doing wrong, I would be most grateful.

Jim

[Bruce Waddington]

Hi Jim.  Your problems are coming from things external to the mount - not guiding and not the mount drive system.  Here's one example (RA in red):

The typical source for something like this is the guide camera/guide scope moving around on its own.  You need to keep in mind the tiny measurement scales we're talking about here.  These huge 30 arc-sec movements are equivalent to a movement of the guide camera sensor by about 16 microns - about 1/3 the thickness of a human hair.  So you can't just assume or assert that everything is rigidly in place, not when you're dealing with these tiny amounts of movement.  It's possible that slewing the scope exerted enough indirect force on the guiding assembly to loosen something up.  I don't know how your guide scope is mounted or how you've routed your cables.  Thumb-screw mounting arrangements are prone to these problems and even the weight of hanging or dragging cables can contribute.  You should also confirm that polar aligning the mount didn't leave any of the alt-az adjustment points loosened.  You'll just have to track down and eliminate the source of this movement, wherever it is.

In the meantime, you've made a hash of the guiding parameters in a futile effort to make the problem go away.  No amount of guiding can do that.  You should start over with the PHD2 parameters by using the new-profile-wizard to create a new profile, then dump the old one.  Then leave the guiding parameters alone while you address the mechanical problems.  The good news is that there doesn't appear to be anything obviously wrong with the mount, so getting things sorted out should require only time, patience, and effort as opposed to repair costs.

Good luck,

Bruce

[Jim Smith]

Hi Bruce,

Thanks for your swift and detailed reply. It's good news that my mount seems OK. There doesn't seem to be any obvious source of the movement in the pier or alt-az bolts. I will try tonight with a minimum set-up with just the guide-scope. There will only be one moving cable...

Regards, Jim

[bw_m...@earthlink.net]

Why is that cable wound around the pier?  What’s going to happen when the scope is rotated all the way to the west and pointing near the meridian?  Many of your worst problems occurred in that area of the sky.  The dangling cable from the guide cable is also a bad idea – I think you should do some research and come up with a better cable routing solution. 

 

Hope you can track it down,

Bruce

 

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Jim Smith
Sent: Sunday, July 10, 2022 11:59 AM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Re: Continuing Autoguiding Woes with AZ-EQ5-GT

 

Hi Bruce,

 

Thanks for your swift and detailed reply. It's good news that my mount seems OK. There doesn't seem to be any obvious source of the movement in the pier or alt-az bolts. I will try tonight with a minimum set-up with just the guide-scope. There will only be one moving cable...

Regards, Jim

 

On Sunday, July 10, 2022 at 5:38:46 PM UTC+1 bw_m...@earthlink.net wrote:

Hi Jim.  Your problems are coming from things external to the mount - not guiding and not the mount drive system.  Here's one example (RA in red):

 

 

The typical source for something like this is the guide camera/guide scope moving around on its own.  You need to keep in mind the tiny measurement scales we're talking about here.  These huge 30 arc-sec movements are equivalent to a movement of the guide camera sensor by about 16 microns - about 1/3 the thickness of a human hair.  So you can't just assume or assert that everything is rigidly in place, not when you're dealing with these tiny amounts of movement.  It's possible that slewing the scope exerted enough indirect force on the guiding assembly to loosen something up.  I don't know how your guide scope is mounted or how you've routed your cables.  Thumb-screw mounting arrangements are prone to these problems and even the weight of hanging or dragging cables can contribute.  You should also confirm that polar aligning the mount didn't leave any of the alt-az adjustment points loosened.  You'll just have to track down and eliminate the source of this movement, wherever it is.

 

In the meantime, you've made a hash of the guiding parameters in a futile effort to make the problem go away.  No amount of guiding can do that.  You should start over with the PHD2 parameters by using the new-profile-wizard to create a new profile, then dump the old one.  Then leave the guiding parameters alone while you address the mechanical problems.  The good news is that there doesn't appear to be anything obviously wrong with the mount, so getting things sorted out should require only time, patience, and effort as opposed to repair costs.

 

Good luck,

Bruce

 

On Sunday, July 10, 2022 at 4:22:24 AM UTC-7 xz16thdre...@gmail.com wrote:

I have been trying to get autoguiding working for several weeks now but without much luck. I often get a good calibration near the meridian and celestial equator and guiding at the same location usually starts off OK. But when I slew to my target it all goes horribly wrong.

 

I suspect that my mount is faulty as I have tried three different laptop to mount connection methods (EQDIR cable, USB A to USB B cable and ST-4) all with the same poor results. Last night I used my new 13.8V regulated mains power supply instead of a battery but that didn't help either.

 

I don't think PHD2 is the problem but I thought I would post here as an experienced hand might know what is going wrong.

 

Last night I used my usual Redcat 51 set-up with a WO 120mm guide scope and Altair GPCAM3 178C guide camera. I use SharpCap Pro, EQMOD and PHD2. Clutches tightened. No cable snags. Polar alignment (SharpCap) < 1 arcminute.

 

I have attached my log files.

 

At 4, I got a good calibration.

At 5, a few minutes of good tracking.

At 6, more good guiding followed by invoking Guiding Assistant.

At 7, 15 minutes of good guiding!

At 8, I think this was when I slewed to M16.

At 9, guiding on M16 starts OK but then the madness starts.

At 10, I tried PPEC...no good.

At 11, more PPEC...no good.

At 12, Lowpass started fairly well but things rapidly deteriorate.

 

I checked inside the mount this morning and the RA assembly looked fine with a reasonably tight belt and no axis wiggle.

 

If anyone has any ideas as to what I am doing wrong, I would be most grateful.

 

Jim

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[Jim Smith]

That's the mount power cable. It lives on the pier. I unwind it and plug it into the power supply. It doesn't move when using the mount.

I will reroute the camera USB cable so that it can't tug on the camera.

Thanks again, Jim

[Jim Smith]

Well, that certainly made a difference. Thank you, Bruce. I attached the cable to the dovetail saddle with an elastic band so that any cable wiggling would affect the mount rather than the guide camera. Without any dangling cables and a fresh PHD2 set-up I slewed around the sky with abandon and auto-guided without problems.

I just need to try it with a telescope now. I had no idea that tiny forces on the scopes and cameras could wreak such mayhem.

Thank you again!

[bw_m...@earthlink.net]

It’s good to hear you’re making progress on this.  When the camera is sensitive to movements of a few microns, it doesn’t take much to create “big” guide star movements.

 

Good luck,

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