Backlash Graph

[Nicholas Kramer]

Anybody seen this type of graph and know possible causes? It starts to come back south after seemingly little backlash but then stops moving. I consistently get a graph like this after using guide assistant. I am running GA close to DEC=0 and Meridian. 

[bw_m...@earthlink.net]

There are a couple of possibilities but it would help to see both your guide and debug log files from this session so we have some context.

 

https://openphdguiding.org/getting-help/

 

Regards,

Bruce

 

From: open-phd...@googlegroups.com <open-phd...@googlegroups.com> On Behalf Of Nicholas Kramer
Sent: Wednesday, November 9, 2022 8:14 PM
To: Open PHD Guiding <open-phd...@googlegroups.com>
Subject: [open-phd-guiding] Backlash Graph

 

 

Anybody seen this type of graph and know possible causes? It starts to come back south after seemingly little backlash but then stops moving. I consistently get a graph like this after using guide assistant. I am running GA close to DEC=0 and Meridian. 

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[Nicholas Kramer]

It won't let me copy the link but Ive attached the zip files

[Bruce Waddington]

Hi Nicholas.  You've got an interesting mechanical problem with the Dec axis that isn't necessarily related to backlash.  Look at this calibration, done at a pointing position of HA = 0.39 hours, Dec = 37.3 (Dec is in green):

You can clearly see that the Dec axis stopped moving for a significant period of time during the calibration.  But then another calibration, done at a slightly different pointing position, didn't have the problem.  This one was done at HA = 1.74 hours, Dec = 8.8 :

So the scope was slewed west by about 15 degrees and south by 29 degrees.  But when you ran the Guiding Assistant at this second location and tried to measure the backlash, you encountered the same problem.  I think there are a number of possible things to look into:

1.  The cabling might be interfering with the ability of the scope/mount to move freely in Dec.

2.  A declination clutch might be too loose

3.  The scope might be significantly out of balance in Dec

4.  The Dec gear mesh might be too tight.  This can happen when someone has over-tightened it in an attempt to reduce backlash.  This is the problem I suspect most.

5.   There may be some accumulated crud somewhere in the Dec gear system - for example, a clump of hardened lubricant

Beyond all this, it looks like you have Dec backlash compensation enabled in the mount.  That's a bad idea for guiding and it should be disabled.  I think that's why the Guiding Assistant test showed an initial quick response to the south moves before it ran into this resistance problem.

Hope you can track it down fairly quickly,

Bruce

[Nicholas Kramer]

I appreciate all the input. Im really curious what's going on because this mount is new from factory just a few weeks ago and I have not made any kind of mechanical adjustments. In fact, I feel a slight amount of play in the DEC axis (the stuff everybody try's to adjust themselves). Additionally, I have not even attempted to set dec backlash compensation in the mount itself, I have heard that's a bad Idea and even just confirmed I don't have anything set. I will keep an eye on the cabling but feel Im fairly cognizant of it. Ive heard of people balancing the scope camera heavy but I have not tried this, I just try to balance as evenly as possible.  

I hope it's not some serious mechanical issue. Even though Im an engineer and fairly mechanically inclined, Id really like to avoid opening up the mount myself. 

[Nicholas Kramer]

Oh and the mount is an EQ6R Pro

[Brian Valente]

>>>Additionally, I have not even attempted to set dec backlash compensation in the mount itself, I have heard that's a bad Idea and even just confirmed I don't have anything set.

If you are guiding with PHD2 and auto backlash compensation, it is a bad idea to set 'in mount' backlash compensation. Generally it should be one or the other

you might try balancing camera-heavy for the calibration phase (assuming you are calibrating near Dec = 0 and at meridian)  and ensuring you bump the mount north prior to calibrating and see if the behavior Bruce demonstrated earlier disappears

To view this discussion on the web visit https://groups.google.com/d/msgid/open-phd-guiding/58669d5d-b093-418f-93ec-26f95affd6aan%40googlegroups.com.

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Brian 

Brian Valente

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[Bruce Waddington]

Unfortunately, it's never a surprise for a new mount to exhibit problems when first exposed to guiding.  Whatever QA is done on each assembled mount - if any is done at all - is never scrutinizing things at the measurement scales typical of guiding.  Beyond manufacturing and assembly errors, mounts can also be affected by shipping.  I think you should contact the mount manufacturer, show them the graph, and ask for advice.  I don't recommend trying to fiddle around with balance in the hope that the problem will just go away.  If the scope is reasonably well-balanced in Dec, it shouldn't show this kind of problem.

Several of your calibrations resulted in alert messages warning you of poor results.  Just forging ahead with a poor calibration is not a good plan, particularly when we can see the severity of some of the problems. 

Good luck,

Bruce

On Thursday, November 10, 2022 at 11:10:57 AM UTC-8 Nicholas Kramer wrote: