Unexpected mount movement


Alex
 

I had a strange hiccup in one of my subs last night and was wondering if anyone has a suggestion of what may have happened.  I was imaging the horse head nebula, and during one of the subs, it looks like the mount jogged a bit.  The mount is an 1100 with absolute encoders and I’m using a pointing model with APCC pro 1.9.11.  I’m not guiding.



This movement was about 2.4’ in dec.  Judging by the equal brightness of the double stars, it appears this happened right in the middle of the 2 minute sub.  Looking at the SGP logs doesn’t show anything amiss.  The sub immediately before and after look fine other than the later subs are shifted.  This happens around 20 minutes before the meridian flip, which occurred normally.

Here is the APCC log file.  The exposure happened from 5:04:40 to 5:06:40, so I'd imagine the jog happened around 5:05:40 or so.

https://www.icloud.com/iclouddrive/0zFY_hvutFstb4z8F1XYlgm0w#APCC-2021-10-12-015143

And here's the offending sub.

https://www.icloud.com/iclouddrive/0KLHzvpcidYyds0Ueh3g-rnrA#horsehead_120sec_1x1_-5C_gain_0_L_frame11





Roland Christen
 

RA is which way? Left to right perhaps?

Roland

-----Original Message-----
From: Alex <groups@...>
To: main@ap-gto.groups.io
Sent: Tue, Oct 12, 2021 2:08 pm
Subject: [ap-gto] Unexpected mount movement

I had a strange hiccup in one of my subs last night and was wondering if anyone has a suggestion of what may have happened.  I was imaging the horse head nebula, and during one of the subs, it looks like the mount jogged a bit.  The mount is an 1100 with absolute encoders and I’m using a pointing model with APCC pro 1.9.11.  I’m not guiding.



This movement was about 2.4’ in dec.  Judging by the equal brightness of the double stars, it appears this happened right in the middle of the 2 minute sub.  Looking at the SGP logs doesn’t show anything amiss.  The sub immediately before and after look fine other than the later subs are shifted.  This happens around 20 minutes before the meridian flip, which occurred normally.

Here is the APCC log file.  The exposure happened from 5:04:40 to 5:06:40, so I'd imagine the jog happened around 5:05:40 or so.

https://www.icloud.com/iclouddrive/0zFY_hvutFstb4z8F1XYlgm0w#APCC-2021-10-12-015143

And here's the offending sub.

https://www.icloud.com/iclouddrive/0KLHzvpcidYyds0Ueh3g-rnrA#horsehead_120sec_1x1_-5C_gain_0_L_frame11





--
Roland Christen
Astro-Physics


Roland Christen
 

Maybe the scope jogged a bit, or the camera assembly? Sudden shift of camera or optics or mirror shifting sideways will do this. Check all your mechanical connections. Did you check the APCC logs to see if anything is amiss? If it did not issue a move command then it may not be a mount movement since APCC keeps track of the mount position at all times.

Roland

-----Original Message-----
From: Alex <groups@...>
To: main@ap-gto.groups.io
Sent: Tue, Oct 12, 2021 2:08 pm
Subject: [ap-gto] Unexpected mount movement

I had a strange hiccup in one of my subs last night and was wondering if anyone has a suggestion of what may have happened.  I was imaging the horse head nebula, and during one of the subs, it looks like the mount jogged a bit.  The mount is an 1100 with absolute encoders and I’m using a pointing model with APCC pro 1.9.11.  I’m not guiding.



This movement was about 2.4’ in dec.  Judging by the equal brightness of the double stars, it appears this happened right in the middle of the 2 minute sub.  Looking at the SGP logs doesn’t show anything amiss.  The sub immediately before and after look fine other than the later subs are shifted.  This happens around 20 minutes before the meridian flip, which occurred normally.

Here is the APCC log file.  The exposure happened from 5:04:40 to 5:06:40, so I'd imagine the jog happened around 5:05:40 or so.

https://www.icloud.com/iclouddrive/0zFY_hvutFstb4z8F1XYlgm0w#APCC-2021-10-12-015143

And here's the offending sub.

https://www.icloud.com/iclouddrive/0KLHzvpcidYyds0Ueh3g-rnrA#horsehead_120sec_1x1_-5C_gain_0_L_frame11





--
Roland Christen
Astro-Physics


Alex
 

The scope jogged north in the DEC direction about 110 pixels, or about 2.4' at my image scale.  I'm using a 130GTX with a QuadTCC and QHY268M camera and everything is using screwed connections and seems tight.  I've never seen this kind of movement in my images before that didn't involve bumping the pier, but it was still 20 minutes from the meridian and the images after this look fine.  I'm not sure what in the optical train would suddenly shift.  I reviewed the security camera footage in the observatory and I did see any external movement on the scope like cables shifting or anything.

I didn't see anything obvious in the APCC log, but most of what's in there is greek to me.

Alex


Roland Christen
 

Any other software attached that could have given a command to move. Something that perhaps issued a dither command? Maybe Ray can take a look at your APCC log.

Rolando

-----Original Message-----
From: Alex <groups@...>
To: main@ap-gto.groups.io
Sent: Tue, Oct 12, 2021 5:21 pm
Subject: Re: [ap-gto] Unexpected mount movement

The scope jogged north in the DEC direction about 110 pixels, or about 2.4' at my image scale.  I'm using a 130GTX with a QuadTCC and QHY268M camera and everything is using screwed connections and seems tight.  I've never seen this kind of movement in my images before that didn't involve bumping the pier, but it was still 20 minutes from the meridian and the images after this look fine.  I'm not sure what in the optical train would suddenly shift.  I reviewed the security camera footage in the observatory and I did see any external movement on the scope like cables shifting or anything.

I didn't see anything obvious in the APCC log, but most of what's in there is greek to me.

Alex

--
Roland Christen
Astro-Physics


Ray Gralak
 

Hi Alex,

According to your log, during the interval you said the shift happened, there was only 0.4 src-seconds of movement in Dec and 0.04 sec (.6 arc-sec) movement of RA.

Dec coordinates:
0797942 2021-10-12 05:04:30.730: Debug, Command Thread, TX='#:GD#'|RX='-02*22:55.9#'
0807658 2021-10-12 05:06:51.730: Debug, Command Thread, TX='#:GD#'|RX='-02*22:55.5#'

RA coordinates
0797940 2021-10-12 05:04:30.698: Debug, Command Thread, TX='#:GR#'|RX='05:41:52.93#'
0807656 2021-10-12 05:06:51.698: Debug, Command Thread, TX='#:GR#'|RX='05:41:52.97

So, whatever caused the double image was not caused by the mount or APCC. Are you sure the scope was well-balanced, and the mount clutches were tight?

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Alex
Sent: Tuesday, October 12, 2021 3:21 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Unexpected mount movement

The scope jogged north in the DEC direction about 110 pixels, or about 2.4' at my image scale. I'm using a
130GTX with a QuadTCC and QHY268M camera and everything is using screwed connections and seems
tight. I've never seen this kind of movement in my images before that didn't involve bumping the pier, but it
was still 20 minutes from the meridian and the images after this look fine. I'm not sure what in the optical train
would suddenly shift. I reviewed the security camera footage in the observatory and I did see any external
movement on the scope like cables shifting or anything.

I didn't see anything obvious in the APCC log, but most of what's in there is greek to me.

Alex


Alex
 

The only software that I was using that talks to the mount is SGP.  I checked its logs, and there's nothing logged during the exposure at all.  Plus SGP's dither is on the order of a few pixels, not a hundred.

Alex


Ray Gralak
 

The only software that I was using that talks to the mount is SGP. I checked its logs, and there's nothing
logged during the exposure at all. Plus SGP's dither is on the order of a few pixels, not a hundred.
There were no commands to move the mount issued during the time interval you specified. Even if a command external to APCC were issued, it would have shown up in changed RA/Dec coordinates. The logical conclusion is that something external caused the move.

Given your equipment, a likely reason would be a clutch slip. The slip could have occurred because the clutch is not tight enough to overcome an imbalanced OTA or a cable tugging on the OTA.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Alex
Sent: Tuesday, October 12, 2021 4:01 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Unexpected mount movement

The only software that I was using that talks to the mount is SGP. I checked its logs, and there's nothing
logged during the exposure at all. Plus SGP's dither is on the order of a few pixels, not a hundred.

Alex


Alex
 

I guess it would have to be a clutch slip, if the mount's encoders don't show the movement.  I'll check the balance again.  I know it's not a cable tug or the like as I viewed the security camera footage of the scope at the time interval in question, and the cables are shown free and unencumbered. 

I currently switch between using the QuadTCC and the field flattener on the scope.  The reducer is mostly in the focuser while the flattener protrudes from the end of the focuser, so the balance point shifts when swapping.  Being a lazy guy, I've balanced in Dec somewhere between the two, so my Dec isn't perfectly in balance.  I've been doing that for while now and haven't noticed any adverse effects.  Is that a bad assumption?  Will swapping between the two affect my APCC model?  If it's a problem, i could see about perhaps adding a small counterweight to the front when swapping to keep it all in balance w/out having to move the scope in the dovetail.  What's the best practice when changing flatteners/reducers as far as balance and models is concerned?

Alex


Roland Christen
 

Balance isn't that important on the 1100 as long as the clutches are fully tight. You might want to check that all your bits and pieces of the dovetail system are fully tight.

Rolando


-----Original Message-----
From: Alex <groups@...>
To: main@ap-gto.groups.io
Sent: Tue, Oct 12, 2021 7:01 pm
Subject: Re: [ap-gto] Unexpected mount movement

I guess it would have to be a clutch slip, if the mount's encoders don't show the movement.  I'll check the balance again.  I know it's not a cable tug or the like as I viewed the security camera footage of the scope at the time interval in question, and the cables are shown free and unencumbered. 

I currently switch between using the QuadTCC and the field flattener on the scope.  The reducer is mostly in the focuser while the flattener protrudes from the end of the focuser, so the balance point shifts when swapping.  Being a lazy guy, I've balanced in Dec somewhere between the two, so my Dec isn't perfectly in balance.  I've been doing that for while now and haven't noticed any adverse effects.  Is that a bad assumption?  Will swapping between the two affect my APCC model?  If it's a problem, i could see about perhaps adding a small counterweight to the front when swapping to keep it all in balance w/out having to move the scope in the dovetail.  What's the best practice when changing flatteners/reducers as far as balance and models is concerned?

Alex

--
Roland Christen
Astro-Physics


ap@CaptivePhotons.com
 

So don't laugh too hard but…

 

Could a bird have landed on the OTA then took off?  While that's a big motion tracking wise, it is not really a big movement.  Whether that shifted it on the clutch or something on that OTA…

 

It looks like a one-time, sudden impulse.  A cable dragging would, I think, have occurred slower (and left more of a star trail).

 


Alex
 

I actually thought some sort of critter (bird, bat, whatever) might have been the issue, but the security camera showed squat.  

Alex


Andrea Lucchetti
 

May be if you overlap the frames you can understand if the star position after the event is restored in alignment with the previous frames or remains shifted. If it is recovered it is a transient effect. What do you think?

On Wed, 13 Oct 2021 at 02:33, Alex <groups@...> wrote:
I actually thought some sort of critter (bird, bat, whatever) might have been the issue, but the security camera showed squat.  

Alex


Alex
 

It remained shifted for the half dozen or sub subs until the meridian flip.  After the flip and platesolve, the correct centering happened.


Ray Gralak
 

Hi Alex,

It remained shifted for the half dozen or sub subs until the meridian flip. After the flip and platesolve, the
correct centering happened.
I think this supports the slipped clutch theory. The offset stayed until the plate solve after the pier flip accounted for the offset position.

-Ray

-----Original Message-----
From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Alex
Sent: Wednesday, October 13, 2021 2:43 PM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Unexpected mount movement

It remained shifted for the half dozen or sub subs until the meridian flip. After the flip and platesolve, the
correct centering happened.


 

Alex - 

were you guiding during this period, and if so can you provide the guidelog from that night?

I"m wondering if somehow it may have locked on to a different star, or something happened during dithering that caused it to do a major move within the guiding


Brian


Alex
 

Not a guiding issue as I'm not guiding.  Since the absolute encoders didn't log they detected any slew or directed movement, then Ray's theory of slippage of the clutch makes sense.  I'm not sure how the slipping happen.  I feel no slippage when I manually try and move the scope.  The clutch knobs were tightened using a hex key.  Maybe there was some movement elsewhere in the imaging train, but everything seems buttoned down.  I imaged all night last night with no problems, so unless it crops up again, I'm assuming it's just one of those mysteries.

Alex


Bill Long
 

It was not likely the mount. Lets assume for a second it is not the mount, what would be next on the list?

Drawtube moving would move the star on the frame as well. Have you looked at that? If so how? Do you have a laser you can put in the drawtube and flex the drawtube to see how much play is in it?


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Alex <groups@...>
Sent: Friday, October 15, 2021 8:07 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] Unexpected mount movement
 
Not a guiding issue as I'm not guiding.  Since the absolute encoders didn't log they detected any slew or directed movement, then Ray's theory of slippage of the clutch makes sense.  I'm not sure how the slipping happen.  I feel no slippage when I manually try and move the scope.  The clutch knobs were tightened using a hex key.  Maybe there was some movement elsewhere in the imaging train, but everything seems buttoned down.  I imaged all night last night with no problems, so unless it crops up again, I'm assuming it's just one of those mysteries.

Alex


Cheng-Yang Tan
 

There’s one other possibility: ground motion. 

On Friday, October 15, 2021, 10:09 PM, Bill Long <bill@...> wrote:

It was not likely the mount. Lets assume for a second it is not the mount, what would be next on the list?

Drawtube moving would move the star on the frame as well. Have you looked at that? If so how? Do you have a laser you can put in the drawtube and flex the drawtube to see how much play is in it?


From: main@ap-gto.groups.io <main@ap-gto.groups.io> on behalf of Alex <groups@...>
Sent: Friday, October 15, 2021 8:07 PM
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Subject: Re: [ap-gto] Unexpected mount movement
 
Not a guiding issue as I'm not guiding.  Since the absolute encoders didn't log they detected any slew or directed movement, then Ray's theory of slippage of the clutch makes sense.  I'm not sure how the slipping happen.  I feel no slippage when I manually try and move the scope.  The clutch knobs were tightened using a hex key.  Maybe there was some movement elsewhere in the imaging train, but everything seems buttoned down.  I imaged all night last night with no problems, so unless it crops up again, I'm assuming it's just one of those mysteries.

Alex