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Tracking problems after manual slew

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#1 descott12

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Posted 15 June 2019 - 02:49 PM

Hello All,
I posted a similar blurb a month or two ago regarding poor tracking with my Evo 8 that seemed to magically be fixed after a firmware update. Well, now I am not so sure that it had any effect. I am seeing similar issues again but with a slightly more limited scope.  I am hoping somebody has seen this before

1) I do a 3-star alignment with SkyPortal

2) I can then do gotos that are pretty accurate and track well

3) As soon as I do a manual slew with either SkyPortal or the HC buttons, tracking seems to be off. Actually, it seems to stop altogether and I keep having to nudge the scope mostly in azimuth to get my object reframed. It is an issue with stars or solar system objects.  When I check the HC for the tracking mode, it says the appropriate thing so I think it at least thinks it is tracking.

4) If I do another goto, it seems to start tracking again.

 

I know my balance is off but if that were the problem it shouldn't track well ever and it only goes bad after a slew.

 

Any ideas? Thanks in  advance.



#2 sg6

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Posted 15 June 2019 - 03:22 PM

May not be any use but as Skyportal appears to be a Celestron product and it will be related to the Skywatcher Synscan.

 

Just set up a wifi Synscan and for whatever reason the app defaulted to "Tracking Off".

Now sure if it tracked after a goto, I was just really checking I had managed to get it running. All I can specifically recall was that I aligned, did a goto, slewed by hand and at some time I noticed nothing moved and no sound, checked the menu and found the state of Tracking Off. Toggled it to On.

 

Just not sure when in the playing I noticed no movement.

 

So maybe check the settings.

If the Skywatcher one does it I suspect the Celestron one may copy.

Does seem odd that it has a default of Off. And not sure how persistant to toggle to On is.



#3 Michael_Swanson

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Posted 15 June 2019 - 06:30 PM

Hi Dave,

 

After you nudge it, does it seem to start tracking okay after that?  It sounds like your Evolution mount has an unusual amount of gear backlash.  This page of my website explains backlash and provides a method for adjusting the NexStar system's built-in backlash compensation:

https://www.nexstars...ds/Backlash.htm

 

Or, if you have my book, see page 132 for a slightly more accurate method (which also includes specific instructions if you have the StarSense hand control).  

 

If this "fixes" the problem, you might want to investigate why your mount has more backlash than is usual for an Evolution.

 

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
https://www.NexStarSite.com


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#4 descott12

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Posted 15 June 2019 - 10:12 PM

Hi Dave,

 

After you nudge it, does it seem to start tracking okay after that?  It sounds like your Evolution mount has an unusual amount of gear backlash.  This page of my website explains backlash and provides a method for adjusting the NexStar system's built-in backlash compensation:

https://www.nexstars...ds/Backlash.htm

 

Or, if you have my book, see page 132 for a slightly more accurate method (which also includes specific instructions if you have the StarSense hand control).  

 

If this "fixes" the problem, you might want to investigate why your mount has more backlash than is usual for an Evolution.

 

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
Author of "NexStar Observer List"
https://www.NexStarSite.com

Hi Michael, yes I believe you are correct about the backlash. Typically once I do a small slew, the tracking gets messed up. But as I sit here typing, Jupiter is dead center and I did nudge it a bit. So not quite sure. I will investigate. I have been meaning to get your books so now I have a good excuse! Thank you



#5 roykirk

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Posted 16 June 2019 - 09:37 PM

I'll have to read some more on this in Michael's book, because I'm getting the same thing.  I'll "goto" something like Jupiter for some astrophotography.  It's not perfectly centered enough, so I manually slew to get it centered for the camera.  Within about 10 seconds it moves out of the field of view.  If I manually slew back to center Jupiter once again, it will suddenly track properly.  Sounds like a "backlash" problem. 



#6 Michael_Swanson

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Posted 16 June 2019 - 11:27 PM

Oh yes, most definitely backlash.  From my book:

 

After a GoTo or when you use the arrows to manually center an object, this can cause

significant delay before the very slow tracking speed of the motors winds out the backlash

and the scope actually starts tracking the motion of the sky.

 

and

 

The delay caused by backlash is noticeable when using the arrow buttons to move in

the direction opposite of tracking.

 

 

How important is it to set up the backlash compensation settings?  You will find my discussion of this on the first page of "Required Hand Control Setup" on page 132.

 

Best regards,
Mike Swanson
Author of "The NexStar Users Guide II"
Author of "The NexStar Users Guide"
Author of "NexStar Observer List"
https://www.nexstarsite.com


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#7 whizbang

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Posted 21 June 2019 - 10:45 PM

If you adjust the backlash, will the firmware remember the adjustment from session to session?

 

Or, dioes the backlash have to be re-set each observing session?



#8 mclewis1

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Posted 22 June 2019 - 04:24 PM

It retains or remembers the settings ... at least until a Factory Settings reset or firmware reload/upgrade is done. So it's valuable to take the time to do the backlash compensation well, it makes a number of things better (goto's, tracking, centering and object, etc.)



#9 descott12

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Posted 22 June 2019 - 04:32 PM

I just set my backlash settings last night and it did help but it is hard to tell what values to use.  I set the values from 20 to about 70 based on a few CN posts. Does anybody know what the actual ranges are or what the various numbers mean. Celestron's documentation is pretty lame.

 

EDIT: by "various numbers" I mean what does a increment of 1 actually mean. It seems that ALT acts very different then AZM as well.


Edited by descott12, 22 June 2019 - 05:30 PM.


#10 Arctic_Eddie

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Posted 22 June 2019 - 05:20 PM

The range can be from 0 to some high number depending on how much clearance exists in the total gear train from the motor to the final gear. Each scope is different. About 8 years ago, another member and myself attempted to determine the value for arc-sec / backlash number but were unsuccessful. The value for my 6SE was about half of his 8SE even though they use the same mount. I remember the numbers being in the 5 - 10 range. Several procedures have been developed over the years but none are straight forward. It's best to do it in daytime using a textured wall at some distance. I used an apartment building wall and tracked a star that was apparently behind the building. You need to increase the number until the backlash seems to be minimal.

 

PS

I found my data from 2011. It was a test using my data and some from Midnight Dan. Here's an excerpt. The numbers are arc-minutes per backlash number, BLN. The angle comes from slowing slewing past a marker, light pole edge, in opposite directions and stopping to record the HC angular readout at the same point on the pole. A cross-hair eyepiece is needed. You can also use the edge of the view as the feature appears going one way and disappears going the other way.

 

"Sent 18 December 2011 - 04:23 PM
That is a strange result. You get AZ=0.5'/BLN and AL=2'/BLN. With the same motors and firmware, I get AZ=1'/BLN and AL=0.5'/BLN. Maybe it's more important to know the numbers for your particular mount so you can reset it later if the mechanics change."


Edited by Arctic_Eddie, 22 June 2019 - 06:12 PM.


#11 satellitespotter

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Posted 25 June 2019 - 06:50 AM

I had this problem with my old NexStar se mount and to fix it I just slewed the cope from side to side a few times and it would usually begin to track again, not high tech but it worked! As many people have already said, it's probably backlash.

Nick



#12 descott12

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Posted 25 June 2019 - 10:07 AM

The range can be from 0 to some high number depending on how much clearance exists in the total gear train from the motor to the final gear. Each scope is different. About 8 years ago, another member and myself attempted to determine the value for arc-sec / backlash number but were unsuccessful. The value for my 6SE was about half of his 8SE even though they use the same mount. I remember the numbers being in the 5 - 10 range. Several procedures have been developed over the years but none are straight forward. It's best to do it in daytime using a textured wall at some distance. I used an apartment building wall and tracked a star that was apparently behind the building. You need to increase the number until the backlash seems to be minimal.

 

PS

I found my data from 2011. It was a test using my data and some from Midnight Dan. Here's an excerpt. The numbers are arc-minutes per backlash number, BLN. The angle comes from slowing slewing past a marker, light pole edge, in opposite directions and stopping to record the HC angular readout at the same point on the pole. A cross-hair eyepiece is needed. You can also use the edge of the view as the feature appears going one way and disappears going the other way.

 

"Sent 18 December 2011 - 04:23 PM
That is a strange result. You get AZ=0.5'/BLN and AL=2'/BLN. With the same motors and firmware, I get AZ=1'/BLN and AL=0.5'/BLN. Maybe it's more important to know the numbers for your particular mount so you can reset it later if the mechanics change."

Thanks for all this. Definitely not a simple problem...



#13 descott12

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Posted 28 June 2019 - 12:31 PM

Hello all,

It just occurred to me that my tracking problem may at least be partially self-induced. I usually do a three-star alignment mostly just out of habit and the problem that I reported early was strictly a planetary problem.

 

I guess I assumed most of the perceived motion of a target was due to earth's rotation and that the planet's actual proper motion was negligible. But maybe that isn't true. Should I be using solar system tracking?  I also assumed that a three-star alignment was more accurate than a single point solar system alignment but maybe that assumption was a false.

 

Thanks



#14 Michael_Swanson

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Posted 28 June 2019 - 08:08 PM

Hello all,
It just occurred to me that my tracking problem may at least be partially self-induced. I usually do a three-star alignment mostly just out of habit and the problem that I reported early was strictly a planetary problem.

I guess I assumed most of the perceived motion of a target was due to earth's rotation and that the planet's actual proper motion was negligible. But maybe that isn't true. Should I be using solar system tracking? I also assumed that a three-star alignment was more accurate than a single point solar system alignment but maybe that assumption was a false.

Thanks


From Earth we cannot see the proper motion of the planets in real-time.

The single point solar system alignment is much less accurate than the 2 and 3 star alignments. It is designed for a quick startup where you are not concerned about GoTo and tracking accuracy.

Additionally, the 3 object SkyAlign only uses 2 of the objects to build the sky model. The 3rd object just helps to identify what 3 objects you pointed at.

Best regards,
Mike Swanson
Author of "The NexStar User's Guide II"
Author of "The NexStar User's Guide"
https://www.NexStarSite.com

Edited by Michael_Swanson, 28 June 2019 - 08:12 PM.


#15 descott12

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Posted 28 June 2019 - 09:38 PM

From Earth we cannot see the proper motion of the planets in real-time.

The single point solar system alignment is much less accurate than the 2 and 3 star alignments. It is designed for a quick startup where you are not concerned about GoTo and tracking accuracy.

Additionally, the 3 object SkyAlign only uses 2 of the objects to build the sky model. The 3rd object just helps to identify what 3 objects you pointed at.

 

Hey Mike,

Thanks for the clarification. So my assumptions were correct (for once!) I haven't had a chance to test my tracking much since I attempted to fix the backlash as you suggested. Hopefully my problem is solved.




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