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Celestron AVX RA axis issue

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#1 Matt_TN

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Posted 25 January 2015 - 12:48 PM

Hello Everyone.

 

I have been struggling with my Celextron AVX mount for sometime now. There seems to be a horrible RA PE. I have PE trained it several times. each time it appears to have no effect. below is the imaging setup I use. Also attached is a PHD log of my RA PE. Any help/ideas would be very helpful. With the current RA PE it is impossible to get any imaging done. I used celestrons PECTool's program to train the AVX mount. and PHD2 for guiding.

 

System setup:

 

> C8 edge
> Edge .7 FR
> Orion 50mm guide scope
> AVX mount
> SXVR-H9 CCD (http://www.sxccd.com/trius-sx9)
> starlight express lodestar (http://www.sxccd.com...star-autoguider)
>
> with the above setup, i get the below stats:
>
> Results:
> FOV: 21.70' x 16.21'
> Resolution: 0.94"/pixel
> Area: 351.8 sq'
> Focal length: 1422mm
> Focal ratio: f/7.0
> Total OTA weight = 22 pounds ish

 

Batch training graph.png

 

I have been in touch with celestron support, I hope they allow me to send the mount in for repair as it is still under warranty. However i know there are alot of experts on this forum so I thought I would ask for help here too.


Edited by Matt_TN, 25 January 2015 - 12:50 PM.


#2 ronpen

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Posted 25 January 2015 - 02:56 PM

My AVX developed a knock and tracking issues in the RA that I have been trying to sort out.  Maybe your problem can be related.  

 

First...  Under the RA covers are two spur gears.  The top one is attached to the worm gear drive shaft.  The bottom is attached to the drive motor.  If these spur gears are meshed to tightly they will cause the motor to speed up and slow down at tracking speed due to binding.  So I would check that first.  With the covers off in a quiet room you can hear it speed up and down and the motor start to labor when the mount is tracking.   There are three motor adjustment bolts to allow you to move the motor in and out to adjust the spur tightness..

 

Second... even if the spur gears are not binding your RA could still be speeding up and down, or even stalling and this could be a result of your top spur/worm gear engagement to the RA drive ring.  If you look up and behind the motor you will see two socket head screws and a small recessed allen head screw in the middle.  The allen head screw is a standoff screw that adjusts the housing depth holding the worm gear drive shaft.  If the worm gear drive shaft is held too tightly or is not level to the RA drive ring it can periodically stall the motor.  Or speed it up and down from the resistance, leading to bad tracking.   If it is too loose you will get a knock and bad tracking as well due to the gears skipping..  There is a fine balance to getting it just right.  I adjusted the middle recessed allen head screw to get things just right and then just barely snugged the two socket head screws.  Barely snugged means tightened them to just touch and no more..  The two socket head screws play off the middle allen to adjust depth.  This took me a few tries to get it right and about an hour once I figured it out.  I made these adjustments with my scope mounted and varied the positions to ensure it was correct.  There is flex in the mount so scope position matters IMO. On my AVX these adjustments are touchy so it takes a bit of trial and error..


Edited by ronpen, 25 January 2015 - 05:27 PM.

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#3 Goofi

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Posted 25 January 2015 - 04:02 PM

I'd suggest not opening the covers of the mount, not yet at least.

 

What does your guiding graph look like in PhD?  What is your RMS error?

Try running the mount without PEC. I found PEC didn't help improve guiding any for my mount.

 

Before looking at a hardware issue, honestly ask yourself if it could be operator error.

All of my issues with the mount have been operator error except one (power supply failed, it was under warranty and OPT swapped out my mount).

So start with yourself, and your setup.

 

Is the load balanced well - just slightly east heavy?

Are you polar aligned? Did you run the calibration routine (I do 2+2)?

 

Once you know your mount is polar aligned, calibrated, and the scope balanced ... run PhD calibration and get a fresh start.

Then, slew to a target about 45 degrees up in altitude, and just run your guider for 30 minutes.

That will give you a good look at what is actually happening in your guiding.

 

Do you still see the problem? If so, maybe your PhD settings aren't good; maybe your mount settings are off.
In other words, once you eliminate operator errors, then look at software configuration problems.

 

Only after eliminating all of those would I consider checking hardware. You can make things a lot worse messing with the hardware; far more so than software.

Plus, will Celestron still honor the warranty if you go messing with the gears?

 

A final question - have you ever had smooth guiding with the mount?


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#4 T1R2

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Posted 25 January 2015 - 10:10 PM

try turning off the PEC on the mount, it is for use without an auto guider for those that are accurately polar aligned with a drift alignment, it will work against the corrections trying to be made. use the PHD only.


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#5 Matt_TN

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Posted 25 January 2015 - 10:55 PM

@ Goofi,

 

I have answered your questions below.

 

Q: What does your guiding graph look like in PhD?  What is your RMS error?

A: The picture attached is the guide graph from PHD while I was guiding. RMS error was all over as you can see from the attached picture.

 

Q: Is the load balanced well - just slightly east heavy?

A: I used a pencil on a table and placed the telescope on the pencil to find the balance point then centered the scope in the saddle on the mount. Then I balance the scope on all axis in conjunction with the counter weight. I tried both balanced and east heavy while guiding.

 

Q: Are you polar aligned? Did you run the calibration routine (I do 2+2)?

A: Yes I had a good polar alignment. ALT was less than 1 arc min, AZM was less than 5 min. might be seconds? either way that was achieved on a first time go of a 2+4 calibration. My calibration routine is ALWAYS 2+4.

 

Q: " Then, slew to a target about 45 degrees up in altitude, and just run your guider for 30 minutes.

That will give you a good look at what is actually happening in your guiding.Do you still see the problem? If so, maybe your PhD settings aren't good; maybe your mount settings are off. "

 

A: "That will give you a good look at what is actually happening in your guiding."  What I saw is in the attached picture. I have slewed all over the sky and guided and always get the same results that you see in the picture. 

 

Q: have you ever had smooth guiding with the mount?

A: No. since moving into AP/guided I have never gotten smooth guiding. I always get exactly what you see in the picture. Before moving into AP, I just used EP's.

 

@ T1R2 & Goofi,

 

Next time I am out I will try guiding with PEC off. However it might be a few weeks before i can get back out, with work I am only able to get out on the weekends, and when weather decides to play nice.


Edited by Matt_TN, 25 January 2015 - 10:55 PM.


#6 Goofi

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Posted 25 January 2015 - 11:27 PM

Matt ... More questions. Did you run PEC while your autoguider was running? If so, that might be part of the problem. 
As I understand it, you want to record the uncorrected error, so PEC can correct it.

 

But, as I said I don't use it and have no problems guiding.

(Yeah, I know ... I image at 420mm focal length, a lot easier to guide).

 

The graph is showing your RA axis not correcting right away ... it's taking 2 minutes for the RA corrections to stop the "down" error,

and then another 2 minutes before it starts correcting.  That's either really bad backlash or your settings are not good in PhD.

I find the LightVortex tutorial pretty good at getting your settings close, which leads me to believe its something else.

 

Back to your PEC correction.  The graphs are showing an error of 3" peak-to-peak... that's really good for an AVX (or any mount).

So some guiding/correcting is happening. This makes me think you had your autoguider turned on, sending corrections to the mount.

If so, and you're using that curve for your PEC curve, you're PEC is not going to compensate for your RA axis errors, but for your guiding errors.

Those are not nearly as repeatable (seeing, flexure, etc).

 

Next time you can image, try it without PEC. Just use the autoguider and nothing else. 

I think you'll get a smoother graph - maybe set your RA aggressiveness a little higher.

 

If you really want to use PEC, record a curve with the actual guide pulses turned off (PhD has a setting for this, in the 'brain').

What you'll get is your mount's periodic error, without guiding corrections interfering. 



#7 T1R2

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Posted 25 January 2015 - 11:42 PM

yes, make sure your anti-backlash settings are high enough

 

try them at different settings, for photographic guiding you might need a higher setting.

 

RA positive +20 or +50

RA negative +20 or +50

Dec positive +20 or +50

Dec negative +20 or +50

 

they should be the same but sometimes can differ a little, somewhere between these settings should be good. 



#8 Matt_TN

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Posted 26 January 2015 - 07:20 PM

@ Goofi,

 

Q: Did you run PEC while your autoguider was running?

A: Yes the autoguider was running while training the PEC. The reason I trained with the auto-guiding on (AKA tracking a star) is because in the celestron "PECTool" program it states the following -- "With an auto-guiding CCD camera - Find the worm index, then auto-guide on a star. Train while auto-guiding to record the corrections." You stated that we want to record with auto guiding off?

 

- You stated " The graph is showing your RA axis not correcting right away ... it's taking 2 minutes for the RA corrections to stop the "down" error,

and then another 2 minutes before it starts correcting.  That's either really bad backlash or your settings are not good in PhD."

 

- My response: Per celestron tech support they instructed me to PEC train the mount with anti-backlash turned off. PHD setting were at default. I tinkered with them some but it had no result on the graph as shown.

 

 

- You stated: "The graphs are showing an error of 3" peak-to-peak... that's really good for an AVX (or any mount)."

 

-My response: I dunno how that can be really good for an AVX as I cant go more that 10-15 second exposure with out getting star trails/blurring of the image. Also I have a friend with a very similar setup, C8, AVX, SSG, 50mm guide scope, FR 6.3, and a canon 600D. He showed me his logs from PHD and they are SMOOTH!!!, find the smoothest part of the DEC line in my graphs and that is how his DEC and RA lines are for hours at a time. Either way, how could "...error of 3" peak-to-peak... that's really good for an AVX..." be good if I cannot image more that 10 sec subs?

 

- You stated: "This makes me think you had your autoguider turned on, sending corrections to the mount.

If so, and you're using that curve for your PEC curve, you're PEC is not going to compensate for your RA axis errors, but for your guiding errors."

 

- My response: That is correct my auto-guider was on and tracking a star. I did that per the instruction from celestrons "PECTool". The instructions read as follows : "With an autoguiding CCD camera - Find the worm index, then autoguide on a star. Train while autoguiding to record the corrections."

 

 

- You stated: "Next time you can image, try it without PEC. Just use the autoguider and nothing else."

 

- My response: I will do that, However the very first time I ever attempted to image, I got graphs exactly as shown in the picture. This was before I ever knew what PEC was or for that matter turned on, but I will try it just to rule it out.

 

- You stated: "If you really want to use PEC, record a curve with the actual guide pulses turned off (PhD has a setting for this, in the 'brain').

What you'll get is your mount's periodic error, without guiding corrections interfering."

 

- My response:  I will try this as well.

 

@ T1R2

 

You stated: " yes, make sure your anti-backlash settings are high enough"

 

My response: Celestron tech support said not to PEC train with anti-backlash. But for the record I have PEC trained the mount with anti backlash, it made zero difference, I got exactly what you see in the attache image. once celestron support heard that I PEC trained with anti-backlash on they said not too because it interferes with getting a true PEC.

 

I would also like to thank all for being willing to help in this issue. Thank you so much. When I finally get the AVX working or give up and buy another mount. I'll be sure to share the images.

 

-Matt

 

 

 



#9 ronpen

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Posted 27 January 2015 - 09:39 AM

Well my guess is you may be chasing your tail trying to figure this out via software.

 

Indoors in a quiet room listen to your RA with all of your equipment set up the way it would be outside.  Do a quick align and then go to different stars and track in different positions.  You don't need to guide just have all of your equipment mounted. Track unguided and listen closely for a number of minutes (15-30 or so).  Listen to see if the motors sound labored, slowing and then speeding, or if they sound as though they are stalling and then starting again.  If so there's your answer.  Then you will need to figure out why... gearing as explained above, power supply sagging, etc.


Edited by ronpen, 27 January 2015 - 09:48 AM.


#10 Matt_TN

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Posted 27 January 2015 - 06:43 PM

@ Ronpen,

 

ok, I will try. I'll report back when it is done.! Thanks for the idea.

 

-Matt



#11 FirstC8

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Posted 31 March 2016 - 08:56 AM

Any update?

I have never used PHD LAB tool, not familiar with how the look at them.

But it appeared to me there might be hardware issues because the large errors are not the usual PE pattern and they are large under guide pulses.

But even at the "smooth" RA sections the jumps are severe compared to DEC line. Such errors are random and PEC can not smooth them out. They will cause elongated stars during long exposures.

But I am surprised this is happening with the Orion Mini guider, at FL=160mm I believe. Was the guide scope rigidly secured?

I see the same kind of excessive random jumps in my RA line no PHD configurations, or different weight balance combinations could cure.

But I guide with an OAG at FL=2,030mm, the errors are greatly amplified. From what have I read, AVX is simply not made to guide at such long FL.

However with the mini guider? If it were me I would call it a defective mount and get it replaced or repaired by Celestron.

Even if the issues are resolved, the mini guider will still be operating at the threshold when the main scope FL is at 1500mm. Flexture will bite and long exposures will be difficult.


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