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How do I PEC a CGX?

Astrophotography Celestron Mount
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#1 ted_barnes

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Posted 28 November 2021 - 10:59 AM

Hello all,

 

I have a one year old CGX mount carrying an Orion 190mm Mak-Newt (only 20 lbs) with a ZWO ASI-294MC-P, and PHD2 guiding (ASCOM connection to base of HC = hand controller). Normally I do stacks of short frames using Sharp Cap, which gives excellent results. Recently I started trying long single exposures of up to 30 mins, and discovered that my stars are badly smeared in RA. PHD2's GA confirms that I have large RA peak-to peak motion, of like 50 arcsecs, in these images.

 

I have read that this is likely due to worm gear error (478 sec period on a CGX), and periodic error corrections (PEC) can be stored in mount memory using PEC. (In the HC, PEC is under Menu > Utilities > PEC.) However I can't find any instructions for actually doing (and checking) PEC on a CGX. My downloaded manuals tell me to look elsewhere, e.g. under Astrophotography, but they don't say where.

 

Can anyone suggest instructions for running PEC on a CGX (presumably using the HC), or even better discuss their personal experiences?

 

I tried just running it on the HC but there is no visible improvement in star images. 

 

A recent image (single exposure, 16 mins) that shows the problem is attached.

 

Thanks!

 

 

ted_barnes

 

 

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#2 scopewizard

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Posted 28 November 2021 - 04:09 PM

The best way it to use the mount USB, connected to a laptop running CPWI. Start PHD2 connect to CPWI via Ascom. Start guiding a start South around 0 Declination. In CPWI, go to mount settings and look for PEC. Check the manual for all available features. When everything is stable and guiding is good, select the Train PEC and let it run until is done. Select to have it on on start.

 

The PEC data is in the mount but if you only use the HC, you need to turn PEC on every times you start the mount. It will not be automatic on power up.

 

With CPWI, it will turn it on when the program connects to the mount if selected to do so in CPWI. I don't use my HC as I rarely do visual. BTW, you do not need PEC for visual.


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#3 ted_barnes

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Posted 28 November 2021 - 06:26 PM

Thanks scopewizard I will try CPWI. Much appreciated! I seldom (almost never) do visual either.



#4 schellaj

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Posted 29 November 2021 - 10:04 AM

Hey Ted,

 

Just a couple of things regarding using PEC on the CGX (or CGX-L):

 

    1: recording the PE using the hand control or CPWI only records 1 period of the worm. So any seeing effects, wind gusts, etc will also get recorded. Not great for when using PEC afterwards,

    2: It is better to record at least 5 periods worth of data to average out the above effect. On can use PECtool (an old program that takes some effort to even get to work on most modern computers) or PemPro which costs a bit of money (~$150) which will also allow you to upload an averaged PEC curve to the mount.

    3: Celestron only allows 89 data point on the PEC curve to be stored.  This means a correction every 5.4 seconds.  This can be a significant correction on a  mount with potentially +-10-20" of PE.  This makes it less effective than it could be with a finer resolution on the PEC curve.

 

When I had my CGX, I used a PEC curve generated by PemPro and my PE went from +- 8" down to +-4-5" and PHD2 took care of the rest fairly well. My guiding was typically about 0.6-0.7" in RA.  There is a 8.9s (about 1" amplitude) oscillation and a 34.3s (about 2") oscillation in the CGX related to the gear system that does not get corrected very well that limits how well the guiding will work.  Again,  finer resolution on the mounts PEC curve would help.

 

Celestron has been talking about better PEC ability for these mounts for years now, but has not put any resources into addressing this.  I was part of the beta tester group for CPWI but Celestron stopped being active with it before the last CPWI software release.  Frustrating.

 

So basically, using a 1 period recording for PEC will show little benefit.  I think PHD2s PPEC algorithm will give you better results. Best results would be an averaged PEC curve with PPEC in PHD2 (just from my experience.

 

I had a mid-quality CGX mount that took a bit of energy to keep running well. Some lucky people get great mounts from Celestron, some get terrible ones, so it's difficult to know what experience you will have.

 

I've attached a plot of the PE (corrected for drift) that was measured by PHD2 and by PECtool to show the kinds of oscillations one can expect with these mounts (and why a 5.4s/correction PEC curve has difficulties with it).

 

Hope this helps,

 

Jason

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#5 Stephen2016

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Posted 02 December 2021 - 03:06 PM

Very interesting read schellaj

 

 

 

Can anyone suggest instructions for running PEC on a CGX (presumably using the HC), or even better discuss their personal experiences?

 

ted_barnes

I invite you to read my reply on this post: https://www.cloudyni...?hl= cgx#8208l=

I haven't even got the mount outside yet because i need to wait for the sprockets, belts, bearings (the 2 motor assembly ones: 2x5x2.5 and 5x8x4) to come in. I also noticed that the RA is quite stiff from factory in my heated garage at 23 celsius, so i believe that after some time and in colder temperatures, the very bad grease Celestron uses will get thicker and stiffer. On my DIY hypertuned CGEM, when i would pull the counterweight bar horizontally and let it go, it would rock at least 11-12 times before it would stop moving. https://www.facebook...215631537331765

My CGX-L fresh out of the box does not even rock once. 

I'm trying very hard to get any schematics or documentation on disassembling the CGX-L in order to adjust , sand and polish the whole assembly, remove the effin crappy Celestron grease and relube everything with lithium grease. So far no luck...


Edited by Stephen2016, 02 December 2021 - 03:14 PM.


#6 gcardona

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Posted 02 December 2021 - 03:23 PM

If you're guiding, why doesn't this take care of your PEC? It should. Maybe you should do a PHD2 Guiding Assistant run to tweak your settings.


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#7 scopewizard

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Posted 02 December 2021 - 04:18 PM

Hey Ted,

 

Just a couple of things regarding using PEC on the CGX (or CGX-L):

 

    1: recording the PE using the hand control or CPWI only records 1 period of the worm. So any seeing effects, wind gusts, etc will also get recorded. Not great for when using PEC afterwards,

    2: It is better to record at least 5 periods worth of data to average out the above effect. On can use PECtool (an old program that takes some effort to even get to work on most modern computers) or PemPro which costs a bit of money (~$150) which will also allow you to upload an averaged PEC curve to the mount.

    3: Celestron only allows 89 data point on the PEC curve to be stored.  This means a correction every 5.4 seconds.  This can be a significant correction on a  mount with potentially +-10-20" of PE.  This makes it less effective than it could be with a finer resolution on the PEC curve.

 

When I had my CGX, I used a PEC curve generated by PemPro and my PE went from +- 8" down to +-4-5" and PHD2 took care of the rest fairly well. My guiding was typically about 0.6-0.7" in RA.  There is a 8.9s (about 1" amplitude) oscillation and a 34.3s (about 2") oscillation in the CGX related to the gear system that does not get corrected very well that limits how well the guiding will work.  Again,  finer resolution on the mounts PEC curve would help.

 

Celestron has been talking about better PEC ability for these mounts for years now, but has not put any resources into addressing this.  I was part of the beta tester group for CPWI but Celestron stopped being active with it before the last CPWI software release.  Frustrating.

 

So basically, using a 1 period recording for PEC will show little benefit.  I think PHD2s PPEC algorithm will give you better results. Best results would be an averaged PEC curve with PPEC in PHD2 (just from my experience.

 

I had a mid-quality CGX mount that took a bit of energy to keep running well. Some lucky people get great mounts from Celestron, some get terrible ones, so it's difficult to know what experience you will have.

 

I've attached a plot of the PE (corrected for drift) that was measured by PHD2 and by PECtool to show the kinds of oscillations one can expect with these mounts (and why a 5.4s/correction PEC curve has difficulties with it).

 

Hope this helps,

 

Jason

You do have a problem which to me appear to be too much worm pressure on the main gear. Typical adjustment made by Celestron. I properly adjusted the motor and spring assemblies on both RA and Dec. Guided I get 0.3 to max 0.5 on a average night temperature down to -8c. I balance my setup as perfect as possible and only do polar alignment with SharpCap pro, plate solve the target as required. I have done 180s exposure unguided with my GT71 with no star drift in the image. I have no backlash on either axis.

 

One way to know if axis springs are too tight is to monitor the amperage on the mount (scope setup and balanced) while slewing at the max speed of 4°. You should get below 1 amps with both axis going.

With my WO 132mm and setup (total 25 lbs), my average is 700 ma +/- 50 ma. Tracking alone is around 325 ma. Nothing plug in to the mount except USB3 to minipc and power.



#8 Kevin Ross

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Posted 02 December 2021 - 05:30 PM

If you're guiding, why doesn't this take care of your PEC? It should. Maybe you should do a PHD2 Guiding Assistant run to tweak your settings.

Guiding corrects the error after it has already happened. PEC prevents the error in the first place.


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#9 gcardona

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Posted 02 December 2021 - 05:42 PM

Guiding corrects the error after it has already happened. PEC prevents the error in the first place.

Yes, but if your guide settings are good, the guider should correct before the PEC is noticeable.



#10 Kevin Ross

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Posted 02 December 2021 - 05:46 PM

Yes, but if your guide settings are good, the guider should correct before the PEC is noticeable.

I agree. But I prefer to have my autoguider just taking images every 4-6 seconds and just gently nudging the mount back on track, rather than every 2 seconds trying to fight the PE.


Edited by Kevin Ross, 02 December 2021 - 05:46 PM.


#11 ram812

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Posted 02 December 2021 - 09:55 PM

Not to butt in...BUT(😁) is that PECtool even still available? I had it on a laptop that passed away years ago and can't seem to find an affordable multi-pass training program. If I recall, you can even remove drift though it's been so long...😯

TIA, CS, Ralph

#12 Kevin Ross

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Posted 02 December 2021 - 10:41 PM

I thought PECTool only worked with EQMod-capable mounts (Sky-Watcher and Orion). I didn't think it worked with Celestron mounts.

 

Nevermind, I was thinking of PECPrep, not PECTool. My bad.

 

PEMPro (which is what I use) has a free trial, that allows you to collect 30 minutes of data to be smoothed out, which is usually enough, at least to get an idea if PEC will help or not for your mount.


Edited by Kevin Ross, 03 December 2021 - 03:44 AM.

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#13 freestar8n

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Posted 03 December 2021 - 02:34 AM

PECTool can still be downloaded and installed, and will work for cgx and cgx-l, but it may take particular settings so that it installs on Windows.

 

In addition, you may need to install NexRemote in order to send pulseguide corrections from an autoguider while also having PECTool track those corrections.

 

CPWI will train PEC, but it only handles one period of the worm.  In contrast, PECTool will let you train and average many turns of the worm and upload the average to the mount.

 

PECTool can be found at https://www.celestro...anuals-software

 

NexRemote can be downloaded here: https://www.celestro...pages/nexremote

 

It's all fairly old software now, but it does work and it's what I use to train my cgx-l.  After training I then use CPWI for PEC correction - and it uses the model stored in the mount by PECTool.

 

Frank


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#14 schellaj

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Posted 03 December 2021 - 09:37 AM

PECTool can still be downloaded and installed, and will work for cgx and cgx-l, but it may take particular settings so that it installs on Windows.

 

In addition, you may need to install NexRemote in order to send pulseguide corrections from an autoguider while also having PECTool track those corrections.

 

CPWI will train PEC, but it only handles one period of the worm.  In contrast, PECTool will let you train and average many turns of the worm and upload the average to the mount.

 

PECTool can be found at https://www.celestro...anuals-software

 

NexRemote can be downloaded here: https://www.celestro...pages/nexremote

 

It's all fairly old software now, but it does work and it's what I use to train my cgx-l.  After training I then use CPWI for PEC correction - and it uses the model stored in the mount by PECTool.

 

Frank

I agree with Frank here, except I did not use NexRemote at all (just guided with PHD2 while using PECtool).  

 

AN additional note is that PECtool needs to run in "compatibility mode" when running on an OS later than Windows 7.

 

Jason


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#15 freestar8n

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Posted 03 December 2021 - 04:23 PM

I agree with Frank here, except I did not use NexRemote at all (just guided with PHD2 while using PECtool).  

 

AN additional note is that PECtool needs to run in "compatibility mode" when running on an OS later than Windows 7.

 

Jason

Yes - I forgot that if you guide with the st4 port of the mount then you don't need to use NexRemote.  But if you use normal ASCOM guiding and send pulseguide commands into the mount, you need to have both PECTool and the autoguide software talking to the mount at the same time.  I know that NexRemote will let you do that, but I'm not sure if there is another way.

 

Did you use the st4 inputs, or some kind of ASCOM hub?

 

Frank


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#16 schellaj

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Posted 03 December 2021 - 05:00 PM

I honestly can't remember. I think I went thru the hand control for phd2, but I know it was a pain in the butt to get everything talking together.

Once the connections were sorted out, it all worked fine.

Jason

#17 scopewizard

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Posted 03 December 2021 - 06:28 PM

CPWI is the replacement for NexRemote and works with PecTool the same way.

 

The sequence is to use the HC and plug USB in HC and laptop, turn mount on and using HC set time location and align.

Turn PECTool on and connect, might be com3 or others, mine is com5.

 

Plug USB cable in CGX mount and in laptop USB, turn CPWI on and connect via USB.

PHD2 connect to ASCOM CPWI.

Go South and where you can get stars at Dec 0°, in HC set PEC recording on,

In PECtool, set the batch, maybe 5, seek index, when all settled PHD2 guide on, start the batch when guiding is good.

Ok, you can figure out the rest.


Edited by scopewizard, 03 December 2021 - 06:32 PM.

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#18 freestar8n

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Posted 04 December 2021 - 12:23 AM

CPWI is the replacement for NexRemote and works with PecTool the same way.

 

The sequence is to use the HC and plug USB in HC and laptop, turn mount on and using HC set time location and align.

Turn PECTool on and connect, might be com3 or others, mine is com5.

 

Plug USB cable in CGX mount and in laptop USB, turn CPWI on and connect via USB.

PHD2 connect to ASCOM CPWI.

Go South and where you can get stars at Dec 0°, in HC set PEC recording on,

In PECtool, set the batch, maybe 5, seek index, when all settled PHD2 guide on, start the batch when guiding is good.

Ok, you can figure out the rest.

Interesting - I'll try that next time.  That does make sense it would work.  That is much simpler if you don't need to install and use NexRemote.

 

Thanks,

Frank



#19 DennisR

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Posted 05 December 2021 - 01:28 PM

OK....   Do you have to do this using the Hand Control ??  Can it be done remotely?   I am setting up the CGX-L at a remote site and plan on operating all over the Internet.  I didn't plan on having a hand control connected and using CPWI to run the mount?  

 

Dennis



#20 scopewizard

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Posted 05 December 2021 - 03:36 PM

OK....   Do you have to do this using the Hand Control ??  Can it be done remotely?   I am setting up the CGX-L at a remote site and plan on operating all over the Internet.  I didn't plan on having a hand control connected and using CPWI to run the mount?  

 

Dennis

This is the only two ways so far that I have found. Using the hand controller or installing NexRemote (never tried it) to connect to PECTool.

NexRemote , not 100% sure can only connect to HC.

 

To use CPWI, when PECTool is connected to HC, then you can start CPWI, connect to USB on the CGX mount. PHD2 will then connect to CPWI and guide.

 

On mine I connect to my minipc on the mount and remote operate the process.

 

I guess the next time you go to your obs scope, connect the HC and USB cable to PC. Do the process remotely when needed. The HC will not affect using CPWI remotely if it is connected directly to the mount.


Edited by scopewizard, 05 December 2021 - 03:36 PM.


#21 freestar8n

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Posted 05 December 2021 - 04:24 PM

OK....   Do you have to do this using the Hand Control ??  Can it be done remotely?   I am setting up the CGX-L at a remote site and plan on operating all over the Internet.  I didn't plan on having a hand control connected and using CPWI to run the mount?  

 

Dennis

This is just done once to generate the curve. For playback you can just use cpwi. 
 

frank



#22 scopewizard

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Posted 05 December 2021 - 06:01 PM

This is just done once to generate the curve. For playback you can just use cpwi. 
 

frank

I believe he wants to do multiple PEC curves using average which is much better than just one with CPWI. I do the average of 6 and upload to the mount. I use CPWI to turn on PEC and the mount will use the uploaded 6 curve average.



#23 freestar8n

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Posted 06 December 2021 - 03:42 PM

I believe he wants to do multiple PEC curves using average which is much better than just one with CPWI. I do the average of 6 and upload to the mount. I use CPWI to turn on PEC and the mount will use the uploaded 6 curve average.

Yes that's what I have been describing.  To record and average you need PECTool in combination with autoguiding.  That can be done with PECTool plus either NexRemote or CPWI (the latter I have never tried).  But that recording session only needs to be done once with the two things operating together.  Once the batch run is complete and you load the averaged curve into the mount, the PEC can be played back without PECTool.

 

Without PECTool all you can do is a recording of a single worm period with CPWI alone - and I don't recommend that.

 

Frank



#24 ted_barnes

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Posted 06 December 2021 - 03:51 PM

Hello all, thanks for the many valuable suggestions regarding PEC and improving guiding on a CGX! I have been able to implement some of the suggestions.

 

I recently contacted Celestron Technical Support, and they (also) suggested using PECTool 1.0.18, and included a helpful 4 pp writeup about doing PEC corrections dated 3 Aug 2021:

 

celestron.com/blogs/news/using-pectool-to-improve-tracking-and-guiding-in-celestron-mounts-best-practices

 

I followed their suggestions, it all worked. Their link to the "Prolific USB to Serial Driver for Windows" was essential in getting PECTool to connect to my CGX through the HC.

 

Once connected I was able to run "Batch Training," and then stored an avg of 6 PEC runs in the mount. My curve looks rather like the last figure in the Celestron notes. I also confirmed that the mount had PEC=0.0 as its previous data.

 

I also followed several CN contributors' suggestions and dnloaded CPWI, and was able to use ASPA to vastly improve my polar alignment. (I can't see Polaris from my usual location.)

 

Finally I just rediscovered phdlogview, which is a great help in rechecking past PHD2 guide logs visually.

 

So, I am making great progress (I think), but am not there yet, a few more iterations are needed. Many thanks to the CN people for their suggestions.

 

ONE QUESTION:

 

Can someone tell me how I enforce the use of the PEC data that I have now stored in the CGX mount when guiding? (I use PHD2.) e.g. Is "PEC on" or somesuch specified in the PHD2 guide log?

 

ted_barnes



#25 scopewizard

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Posted 06 December 2021 - 04:36 PM

You have to turn it on in CPWI under mount settings. It will be turned on every time you start CPWI. You can use the hand controller but will have to turn it on every power up. I never have my HC on the mount when imaging.


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