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CGX Mount - "Stiff" Axes

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#1 selectedpixels

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Posted 10 September 2019 - 11:12 AM

I have a new CGX after owning and using a CGEM for several years.

 

I'm getting guiding results in the 1-1.5 arc sec rms, which is higher than what I could do with the CGEM.

 

One thing that I wonder about is that both axes, when not engaged (i.e. when balancing), are much "stiffer" than with the CGEM.  With the CGEM (particularly after a hypertune but also before) could just be "spun" around freely.   But with the CGX, they don't move freely like that.

 

Is this normal?   If not, are there adjustments that need to be made?

 

I've looked around at threads here and couldn't find anything that answered this directly.

 

Thanks.

 

Bob



#2 Lead_Weight

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Posted 10 September 2019 - 11:34 AM

Mine are pretty stiff too. Though, with a heavy scope, I am able to fairly easily achieve balance. With lighter scopes this poses a problem as they’re too light to counter the stiffness of the axis. I’ve also found that balance can effect the guiding quite significantly. One time I had guiding like you over the 1.0 range, and I rebalanced. The guiding improved by .5 on each axis.

 

I am however able to guide between .2-.7 typically. RA is always higher than DEC for me. PHD2 says this is backlash, and I’ve attempted to use the anti-backlash compensation with mixed results. I have to keep the settings pretty low.

 

There is a screw that can be adjusted (it’s detailed in other posts here on CN) to fix RA, and I’ve managed to adjust it some, but didn’t see any noticeable difference in my RA guiding. That’s probably not helpful to you now, but I suspect you’ll encounter this once you get your guiding/stiffness improved as it appears common amongst CGX mounts.



#3 droe

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Posted 10 September 2019 - 12:55 PM

My AVX is very stiff but there is no stiffness in my CGX. Not a problem I heard before with the CGX.



#4 RazvanUnderStars

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Posted 11 September 2019 - 10:06 AM

Lead_Weight, if I remember correctly, the PHD2 documentation recommends not using the mount's backlash compensation, intended for visual use use.

 

EDIT: for anyone reading this, the relevant excerpt is "Many mounts have settings for backlash compensation but these should not be used for guiding - they are typically intended for visual use where high precision isn't required.  Because the actual amount of compensation needed at any given time may depend on the pointing position and the mechanical load on the system, a fixed value will usually result in oscillations that never stabilize.  The backlash compensation implemented by PHD2 is adaptive, meaning that the compensation amount is adjusted up or down depending on the measured results." from https://openphdguidi...#Algorithms_Tab.


Edited by RazvanUnderStars, 11 September 2019 - 06:46 PM.


#5 EFT

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Posted 11 September 2019 - 02:39 PM

I haven't had too many CGX's through the shop at this point, but none had particularly stiff axes and I'm not too surprised considering the some of the internal changes from the CGEM.  I can however see the potential based on the ring gear housings.  In addition, there is a possibility for the internal cabling to cause some difficulty but I would say that it is generally not as consistent a problem as other possibilities for stiff axes.



#6 neaptide

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Posted 20 September 2019 - 07:26 AM

Both axis were very stiff on my CGX when I first got it. The fix for my particular mount was relatively easy. I took the clutch levers off and backed them off one notch and reinstalled them. It made a huge difference for me. I am able to properly balance the mount now and my guiding improved dramatically ~0.7"-0.6" with good seeing. I am assuming that the clutches were not disengaging fully even though the levers were moving freely. 

One word of caution is that I believe Celestron used LocTite or something like it on the screws securing the levers and with the cheap hardware they use it's easy to strip the screw head. 


Edited by neaptide, 20 September 2019 - 07:39 AM.

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#7 Lead_Weight

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Posted 22 September 2019 - 10:43 AM

Both axis were very stiff on my CGX when I first got it. The fix for my particular mount was relatively easy. I took the clutch levers off and backed them off one notch and reinstalled them. It made a huge difference for me. I am able to properly balance the mount now and my guiding improved dramatically ~0.7"-0.6" with good seeing. I am assuming that the clutches were not disengaging fully even though the levers were moving freely.
One word of caution is that I believe Celestron used LocTite or something like it on the screws securing the levers and with the cheap hardware they use it's easy to strip the screw head.


That’s awesome, and the first time I’ve seen someone post about this particular fix. I’m going to try it with my mount today.


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