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CGX mount Dec backlash

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#1 oshimitsu

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Posted 19 June 2018 - 04:24 PM

Just a quick opinion check. Is 4000ms of Dec backlash normal or acceptable on a cgx? I haven't had a chance to check and see if it's improved after adjusting the mesh but that's what it was this last session.

#2 Poconut

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Posted 19 June 2018 - 06:26 PM

Just curious, how did you come up with that measurement?



#3 oshimitsu

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Posted 19 June 2018 - 06:49 PM

That was what PhD gave me when running the measure backlash portion of the guiding assistant

#4 spokeshave

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Posted 19 June 2018 - 07:44 PM

Just a quick opinion check. Is 4000ms of Dec backlash normal or acceptable on a cgx? I haven't had a chance to check and see if it's improved after adjusting the mesh but that's what it was this last session.

It depends on your guiding rate. If you're guiding at 0.1x, it's probably not a lot of backlash and you could decrease it to 800ms by moving to 0.5x and 444ms by going to 0.9x. On the other hand, if your guide rate is 0.9x, that's a lot of backlash and probably indicative if an adjustment being needed.

 

Tim


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#5 oshimitsu

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Posted 19 June 2018 - 07:54 PM

It depends on your guiding rate. If you're guiding at 0.1x, it's probably not a lot of backlash and you could decrease it to 800ms by moving to 0.5x and 444ms by going to 0.9x. On the other hand, if your guide rate is 0.9x, that's a lot of backlash and probably indicative if an adjustment being needed.

Tim


How do is do that exactly? Is it an option i change in the hand controller or PhD itself ?

#6 spokeshave

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Posted 20 June 2018 - 07:55 AM

How do is do that exactly? Is it an option i change in the hand controller or PhD itself ?

It's an option in the HC. I don't know if the CGX is different, but on the CGE Pro: Menu --> Scope Setup --> Autoguide Rates. There, you can set the guide rates for RA and DEC. The number you enter is a percentage of sidereal. So, if you enter "10" that's 0.1x sidereal.

 

It is also important that you tell PHD2 what these rates are in the profile settings. 

 

 

Tim



#7 oshimitsu

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Posted 20 June 2018 - 08:02 AM

It's an option in the HC. I don't know if the CGX is different, but on the CGE Pro: Menu --> Scope Setup --> Autoguide Rates. There, you can set the guide rates for RA and DEC. The number you enter is a percentage of sidereal. So, if you enter "10" that's 0.1x sidereal.

 

It is also important that you tell PHD2 what these rates are in the profile settings. 

 

 

Tim

I was just about to reply. Mine says its 85 on both. I think I did a good job of adjusting the worm gear mesh so the next clear night I'm gonna head out and test it out. I plan on bringing tools with me to fine tune it if needed. Is it less likely to cause binding w/ the spring loaded mesh or do i still need to be careful of that?



#8 spokeshave

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Posted 20 June 2018 - 08:39 AM

I was just about to reply. Mine says its 85 on both. I think I did a good job of adjusting the worm gear mesh so the next clear night I'm gonna head out and test it out. I plan on bringing tools with me to fine tune it if needed. Is it less likely to cause binding w/ the spring loaded mesh or do i still need to be careful of that?

Jonathan:

 

Then that's a lot of backlash. At 0.85x sidereal, the mount is guiding at 12.75 arcseconds per second. If it takes 4 seconds (4000ms) to take up the backlash, that means almost an arcminute of backlash. Good luck with the adjustment. I hope it helps.

 

Tim



#9 oshimitsu

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Posted 20 June 2018 - 09:06 AM

Jonathan:

 

Then that's a lot of backlash. At 0.85x sidereal, the mount is guiding at 12.75 arcseconds per second. If it takes 4 seconds (4000ms) to take up the backlash, that means almost an arcminute of backlash. Good luck with the adjustment. I hope it helps.

 

Tim

Are you familiar with how the spring loaded worm gear mesh works? I don't want to cause any binding but it's my understanding that with it being spring loaded it helps to prevent that. The way I adjusted it was I completely backed out the screw that moves the worm gear out. I slowly tightened it until I found a tiny bit of play and then slightly moved it back in



#10 spokeshave

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Posted 20 June 2018 - 12:05 PM

I'm not familiar with the mechanism in the CGX, but there are a number of CGX users here. Hopefully someone else will chime in.

 

Tim



#11 fgraus

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Posted 20 June 2018 - 07:40 PM

You might want to also check the belt adjustment. If the belt is loose you will have more backlash. Just don't tighten it too much. Celestron doesn't give any information about how tight it should be. 



#12 oshimitsu

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Posted 20 June 2018 - 08:05 PM

I asked celestron about what the best way to do the gear mesh adjustment was and they told me not to do it.... I replied with "I paid too much money for this mount to be under performing and 4000ms of backlash is unacceptable"


Edited by oshimitsu, 20 June 2018 - 08:06 PM.


#13 Poconut

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Posted 21 June 2018 - 06:27 PM

I asked celestron about what the best way to do the gear mesh adjustment was and they told me not to do it.... I replied with "I paid too much money for this mount to be under performing and 4000ms of backlash is unacceptable"

Did they ask you to send it in for warranty repair or did you talk to your seller about swapping it out for another prior to adjusting it?

I'll have to check my backlash out sometime to see what it is.


Edited by Poconut, 21 June 2018 - 06:32 PM.


#14 bogg

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Posted 22 June 2018 - 02:00 PM

PHD reported a high backlash number for my CGX on a few calibrations, but it has always been quite different each time as well. When I check visually for backlash I can’t see any. As a result I don’t know what PHD is seeing. It does guide very well and I just ignore the number and let it do its thing. 



#15 glend

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Posted 22 June 2018 - 05:43 PM

You might want to also check the belt adjustment. If the belt is loose you will have more backlash. Just don't tighten it too much. Celestron doesn't give any information about how tight it should be. 

There was a post in one of the CGX threads about belt adjustment. Your right that Celestron does not publish anything on tuning the CGX. However, I do recall a Utube video made by another mount manufacturer that shows how much tension should be adjuested into their belt (which looked identical to the CGX belt), it might have been Software Bisque's video.

 

The crux of the video is that there needs to be a little bit of side play on the belt when you press on it in the middle of the run between the pulleys.  You don't want it so tight that it does not move, or so loose that it deflects close to the centerline.



#16 oshimitsu

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Posted 23 June 2018 - 01:20 AM

Celestron replied that I could send it in to be adjusted which I'm fine with but Lord knows how long it'll be out. O have vacation next month and I'm going to a dark sky park in Michigan :/ I was expecting a reply with a rma number today but didn't get one.
What tans my hide is why have instructions in the manual to do it yourself and then tell a customer not to adjust it yourself.

#17 oshimitsu

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Posted 23 June 2018 - 01:23 AM

PHD reported a high backlash number for my CGX on a few calibrations, but it has always been quite different each time as well. When I check visually for backlash I can’t see any. As a result I don’t know what PHD is seeing. It does guide very well and I just ignore the number and let it do its thing.


Mine clearly has backlash. It did 30 steps during the calibration and I think 10 of them were to clear the backlash. Maybe I expect too much from a 2000 dollar mount.
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#18 oshimitsu

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Posted 29 July 2018 - 03:00 AM

Update for anyone still following this thread.

 

Received the mount back from celestron backlash is 4000ms @ .86 sidereal. Which if I'm not mistaken is what I had before. Maybe thats the best this mount can get. Luckily if I turn on PHD's backlash comp and up it to 500ms it seems to make the dec corrections pretty responsive. Did a so so pec training last night and had it to 1" overall rms 



#19 Poconut

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Posted 30 July 2018 - 06:34 PM

Update for anyone still following this thread.

 

Received the mount back from celestron backlash is 4000ms @ .86 sidereal. Which if I'm not mistaken is what I had before. Maybe thats the best this mount can get. Luckily if I turn on PHD's backlash comp and up it to 500ms it seems to make the dec corrections pretty responsive. Did a so so pec training last night and had it to 1" overall rms 

How long did they have the mount for to do the "repair" ??



#20 glend

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Posted 30 July 2018 - 06:48 PM

There have been a number of discussions about worm spring adjustment, and some CGX mounts were found to be improperly adjusted from the factory, with the spring locked down tight. The CGX manual has a section on adjusting worm spring settings.  It's pretty easy to do, just two small hex screws to adjust. You can easily feel the spring working to push against the worm, you want a little movement, less than 1mm is fine, but it does need to have some movement.


Edited by glend, 30 July 2018 - 06:49 PM.


#21 oshimitsu

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Posted 30 July 2018 - 11:24 PM

How long did they have the mount for to do the "repair" ??


It was there for about a week. I can combat it with PHDs backlash comp I think. I just need to play around with it.

#22 oshimitsu

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Posted 30 July 2018 - 11:26 PM

There have been a number of discussions about worm spring adjustment, and some CGX mounts were found to be improperly adjusted from the factory, with the spring locked down tight. The CGX manual has a section on adjusting worm spring settings. It's pretty easy to do, just two small hex screws to adjust. You can easily feel the spring working to push against the worm, you want a little movement, less than 1mm is fine, but it does need to have some movement.


I understand the adjustment for the limit screw but not the actual mesh. Do I just let the worm make contact and then set the limit screw? I didn't think having the worm make contact was good but then again the spring will stop binding won't it?

#23 glend

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Posted 31 July 2018 - 04:12 AM

I understand the adjustment for the limit screw but not the actual mesh. Do I just let the worm make contact and then set the limit screw? I didn't think having the worm make contact was good but then again the spring will stop binding won't it?

The purpose of the spring is to maintain contact but allow the riding of irregularities without binding, so you need some movement to absorb the irregularies.  I don't know how to explain it more simply. If you have it screwed down so tight that there is no pull back then your binding. 



#24 oshimitsu

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Posted 31 July 2018 - 05:18 AM

What i mean is there are two screws. One controls the worm gears distance from the gear (cog or whatever it's called) the second screw limits the back motion for the spring. Loosening the one screw let's the spring push the worm into the teeth. If the worm is in complete contact as long as the limit screw is set to allow 1mm of play all is well in the world right?

#25 rgsalinger

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Posted 31 July 2018 - 08:30 AM

Well, I have to ask. What exactly are your guiding results? I think that before doing anything, see what your system produces in the way of images. Don't trust measurements over results.

Rgrds-Ross


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