Dec tracking fails every 10 mins

[Santhosh Palani]

Hi,

For some reason, I can't get consistent tracking today. My calibration and polar alignment error looked okay. However, when I start tracking, Dec fails periodically. When I restart PHD2, tracking looks okay for another 10 min and again fails on the Dec axis. Any idea why this is happening? Thanks for your help.

https://openphdguiding.org/logs/dl/PHD2_logs_KR5t.zip

Best,

Santhosh

[bw_m...@earthlink.net]

Hi Santhosh.  Are you using the PHD2LogViewer to examine your results?  The reason I ask is that you are mistaken about what axis has the problem.  Your logs show the problems are in RA, usually looking like this (RA in red):

 

 

This isn’t caused by guiding.  The rate of the guide star excursion is about 6 arc-sec/sec so it doesn’t look like the mount has simply stopped tracking.  I think you need to investigate whether you’ve got a cable binding or pulling on the guide camera and whether the guide scope assembly is moving around on its own.  Here is some explanatory material on this sort of thing:

Large/Abrupt Guide Star Deflections

Most users eventually encounter situations where the guide star appears to make a large, abrupt excursion away from the lock-point.  The great majority of these problems arise from neither the mount nor PHD2's guide commands.  Instead, they usually come from unwanted mechanical movement in the gear that is riding on top of the mount, especially the guide camera/guide scope assembly.  This is especially true if the large deflections occur in declination because the Dec motor is normally idle except for executing the very short, relatively infrequent guide commands it receives.  The unwanted mechanical movement usually comes from several sources:

1. Tiny movements of the various components in the guiding assembly as a result of the changing gravitational forces while the mount tracks the target object
2. Dragging, binding, or snagging of cables, especially those that are connected to the guide camera
3. Wind gusts or less commonly, effects from camera filter changes, auto-focusing, or mirror movement
4. Use of mount features for backlash compensation - these should not be used with PHD2 guiding

Before rejecting these things as likely sources of  problems, think again about the tiny measurement scales and tolerances described in the previous section.  With many guiding set-ups, a movement of only 5 microns can create an apparent tracking error (guide star deflection) of over 6 arc-sec, the equivalent of many star diameters. Every mechanical interface, every set-screw, every movable element has the potential to shift or move on its own by these tiny amounts.  Even when cables have been routed in a purposeful way, they may bind or pull in certain sky positions or after a meridian flip.  Cable ties or ribbed plastic cable guides hare small protrusions that can briefly catch on stationary parts of the mount.  For large Dec deflections, it's easy to determine if these things are coming into play.  Just use the PHDLogViewer tool to zoom in on the time of interest and see if the deflection was immediately preceded by a correspondingly large guide command in the direction of movement.  In most cases, you will find this didn't happen.  It can sometimes happen at the beginning of a guide session if you're using PHD2 Dec backlash compensation, but those events should disappear quickly.  If the abrupt deflections occur in RA, the analysis is less straightforward because the RA motor runs continuously.  But even then, unusually large, randomly space deflections are more likely to arise from the sorts of mechanical problems described here than from errors in the RA drive system.

 

This was all happening from the west side of the pier, pointing at Dec = 30 and about 1.5-2 hours east of the celestial meridian and following a meridian flip.

 

Good luck,

Bruce

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[Santhosh Palani]

Thank you Bruce. Your explanation makes sense. I have always remembered RA as red but for some reason both in my PHD2 software as well as in PHD2logviewer Dec is denoted in Red, which is what caused the confusion. Images attached. 

Interestingly, later that night when I switched to the east side of the pier, I got good tracking (2.5hrs starting at 00:45:22) without any major issues. Log file below. Does that help identify which of the four potential issues you mentioned is more likely? Thanks

https://openphdguiding.org/logs/dl/PHD2_logs_FsUj.zip

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/001201d8b8b6%24aa163390%24fe429ab0%24%40earthlink.net.

[bw_m...@earthlink.net]

Those are just the default colors, you should change them to colors that make sense to you. I’ve always thought (R)ed is for (R)ight ascension makes sense but we can't change the defaults at this late date. Both the PHD2 UI and the LogViewer let you set custom colors.

I think your problems are likely down to either (1) or (2) in the list but we can't tell just from the guiding data. The side-of-pier dependency would cause me to look at (2) first, but it's a toss-up.

Bruce

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Santhosh Palani
Sent: Thursday, August 25, 2022 2:13 PM
To: open-phd...@googlegroups.com
Subject: Re: [open-phd-guiding] Dec tracking fails every 10 mins

Thank you Bruce. Your explanation makes sense. I have always remembered RA as red but for some reason both in my PHD2 software as well as in PHD2logviewer Dec is denoted in Red, which is what caused the confusion. Images attached.
Interestingly, later that night when I switched to the east side of the pier, I got good tracking (2.5hrs starting at 00:45:22) without any major issues. Log file below. Does that help identify which of the four potential issues you mentioned is more likely? Thanks
https://openphdguiding.org/logs/dl/PHD2_logs_FsUj.zip

On Thu, Aug 25, 2022 at 3:12 PM <mailto:bw_m...@earthlink.net> wrote:
Hi Santhosh. Are you using the PHD2LogViewer to examine your results? The reason I ask is that you are mistaken about what axis has the problem. Your logs show the problems are in RA, usually looking like this (RA in red):

This isn’t caused by guiding. The rate of the guide star excursion is about 6 arc-sec/sec so it doesn’t look like the mount has simply stopped tracking. I think you need to investigate whether you’ve got a cable binding or pulling on the guide camera and whether the guide scope assembly is moving around on its own. Here is some explanatory material on this sort of thing:
Large/Abrupt Guide Star Deflections
Most users eventually encounter situations where the guide star appears to make a large, abrupt excursion away from the lock-point. The great majority of these problems arise from neither the mount nor PHD2's guide commands. Instead, they usually come from unwanted mechanical movement in the gear that is riding on top of the mount, especially the guide camera/guide scope assembly. This is especially true if the large deflections occur in declination because the Dec motor is normally idle except for executing the very short, relatively infrequent guide commands it receives. The unwanted mechanical movement usually comes from several sources:

1. Tiny movements of the various components in the guiding assembly as a result of the changing gravitational forces while the mount tracks the target object
2. Dragging, binding, or snagging of cables, especially those that are connected to the guide camera
3. Wind gusts or less commonly, effects from camera filter changes, auto-focusing, or mirror movement
4. Use of mount features for backlash compensation - these should not be used with PHD2 guiding

Before rejecting these things as likely sources of problems, think again about the tiny measurement scales and tolerances described in the previous section. With many guiding set-ups, a movement of only 5 microns can create an apparent tracking error (guide star deflection) of over 6 arc-sec, the equivalent of many star diameters. Every mechanical interface, every set-screw, every movable element has the potential to shift or move on its own by these tiny amounts. Even when cables have been routed in a purposeful way, they may bind or pull in certain sky positions or after a meridian flip. Cable ties or ribbed plastic cable guides hare small protrusions that can briefly catch on stationary parts of the mount. For large Dec deflections, it's easy to determine if these things are coming into play. Just use the PHDLogViewer tool to zoom in on the time of interest and see if the deflection was immediately preceded by a correspondingly large guide command in the direction of movement. In most cases, you will find this didn't happen. It can sometimes happen at the beginning of a guide session if you're using PHD2 Dec backlash compensation, but those events should disappear quickly. If the abrupt deflections occur in RA, the analysis is less straightforward because the RA motor runs continuously. But even then, unusually large, randomly space deflections are more likely to arise from the sorts of mechanical problems described here than from errors in the RA drive system.

This was all happening from the west side of the pier, pointing at Dec = 30 and about 1.5-2 hours east of the celestial meridian and following a meridian flip.

Good luck,
Bruce

From: mailto:open-phd...@googlegroups.com <mailto:open-phd...@googlegroups.com> On Behalf Of Santhosh Palani
Sent: Wednesday, August 24, 2022 8:09 PM
To: Open PHD Guiding <mailto:open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Dec tracking fails every 10 mins

Hi,

For some reason, I can't get consistent tracking today. My calibration and polar alignment error looked okay. However, when I start tracking, Dec fails periodically. When I restart PHD2, tracking looks okay for another 10 min and again fails on the Dec axis. Any idea why this is happening? Thanks for your help.
https://openphdguiding.org/logs/dl/PHD2_logs_KR5t.zip

Best,
Santhosh
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[Santhosh Palani]

Thank you Bruce, will check the cables. Yes, I now changed the colors. 

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[Jeff snell]

All, 

I read through the thread.  I recently started having a very similar issue.  Sometimes in both Dec and Ra but usually only in Ra.  I was able to capture a couple of screenshots of the PHD2 guiding graph attached below.  The "poor guiding" jpg is an example of how the mount is tracking just prior to the excursion.  The other screenshot shows the actual excursion.  This issue started about three weeks ago.  Before then tracking very solid at less than 1.0 total RMS producing some beautiful imaging results.  Then all of a sudden I started getting excursions about every 10-15 minutes and usually end up losing at least a third of my subs to evident star trailing.  I have changed out the cable, double checked star focus through the 120mm guide scope, SNR is 23 on the guide star.  I've tightened everything I know to tighten.  I took the mount apart and checked/adjusted the worm gears.  I run APT in conjunction PHD2 and thought maybe there was some setting incompatibility with dithering which I will check tonight.  I am still experimenting but in the interim, does anyone have any thoughts on these pics and the attached PHD2 log?  Could it be the camera?  I have an iOptron GEM 28 and an iOptron iGuider scope and camera that had been performing perfectly.

Thanks for any advice or help in advance...

Jeff   

[Brian Valente]

Hi Jeff

I will give you a quick response, but if you're looking for more input, please start a new thread with your logs and question

It's pretty clear there is a significant and instant jump in RA about every 1200 seconds, like clockwork

these are not from guiding: they are fairly instant, quite large, and correct quickly

 

If I were a betting man, i'd guess that is your period for that mount or something close to it. Worth asking in the mount user forums or with ioptron

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[Jeff snell]

Thanks so much Brian.  This is a great help.  I figured it was a mount issue.  First time this has reared its head.

I appreciate the analysis!

Jeff

Sent from my iPhone

On Sep 2, 2022, at 7:56 PM, Brian Valente <bval...@gmail.com> wrote:



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