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old_eyes

Help needed guiding iOptron CEM60EC

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Once again I used the Pleiades as a convenient test target.

This is the guiding trace I ended up with:

167556644_191203Guiding.png.96b3cbac8124ef2b5db3cd2f1e906bf7.png

Comparing that with the equivalent image from 01/12 the RA error is reduced and the DEC error increased.

 

Original FirmW

Beta FirmW

RA RMS

4.04”

1.74”

RA Peak

12.24”

5.39”

DEC RMS

0.60”

1.03”

DEC Peak

1.92”

3.59”

 

Not dreadful, but not what I was hoping for. However, I don't know to what extent the failed calibration is a factor.

With the clouds rolling in I took one 300 sec exposure. Debayered, stretched, cropped and reduced in size:

19_10_05_300sCsmall.png.e7b43d94994ee640fa4f6ca06a050ff0.png

At least the stars are roughly round although smeared out by a combination of poor focus and the symmetrical wobble in both RA and DEC.

I don't think I can make much more progress until I can find a way of getting a good calibration with PHD2 or an alternative guiding programme that will calibrate.

 

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On 03/12/2019 at 16:50, fwm891 said:

Just a mad thought but you have set the commander software to 'sidereal' not lunar or solar rates? Just seems that whatever your doing regardless of exposure the results look similar - hence the wrong guide rate thought...

I checked - set sidereal. Thanks for the suggestion. Finger troule is still a possible explanation 🤔

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I would not waste too much time like I did. I think your copy has some of the highest oscillation ever seen with a recent model cem60ec. You should get a new copy.

For your reference, my copy has a 1-2" peak to peak oscillation at the know SDE period of 5.4 seconds. Yours appears to have similar but at a much higher peak. This could be due to encoder issues. And according to iOptron it's a factory only fix. In other exam experience sending to their factory for fix has been problematic, with long waits and unsure results (some folks have received them back with nothing fixed). It is the reason why I haven't sent mine back yet because I am have no return policy to fall back on, and it would cost me hundreds to ship the mount to them for a roll of the dice.

So if you just got this mount. It is time to exercise your return policy.

Edited by cotak

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Would you say this is due to the drive, the driver, PHD2, or maybe the way all three interact?

Thought I'd got a fair handle on PHD2 problems, but this one is unique. 

Michael 

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It's the encoder.

The reader alignment to the ring has to be precise or it'll cause more problems than it solves. Realignment is not advisable at home per iOptron support.

 

All this is under the SDE topic threads on CN.

Edited by cotak

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I was thinking of "upgrading" to this mount but this thread has given me serious concerns.  

Perhaps I will look elsewhere.

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23 minutes ago, wornish said:

I was thinking of "upgrading" to this mount but this thread has given me serious concerns.  

Perhaps I will look elsewhere.

Other people have had great success with it; that is why I chose it. And it seems that you can have a Friday afternoon example with any mount. For me the test is not whether something can go wrong, that is always true, but how they handle the customer when there is a problem. We shall see.

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1 hour ago, old_eyes said:

Other people have had great success with it; that is why I chose it. And it seems that you can have a Friday afternoon example with any mount. For me the test is not whether something can go wrong, that is always true, but how they handle the customer when there is a problem. We shall see.

Hi,

I'm the CEM60EC user who submitted some of the log files to OzAndrewJ in that thread on CN, and previous to that in another CN thread related to the CEM60EC.

Firstly, and most importantly, if the log analysis is showing a high level of SDE deviations then it's highly unlikely this can be fixed through firmware changes / PHD settings.

The beta firmware has tamed my over-corrections / oscillations completely.  The calibration is still odd every time, as seen in the CN thread, but the guiding is improved.

image.png.559ab6dd6779401e8644d308f09b36a3.png

This was the last run from 29/11, calibrated with 4s exposures to try and give the mount a chance to fully move before the next pulse was sent.  It didn't quite work, you can see I have more RA pulses than DEC pulses to get to the same distance, but the guiding was acceptable. you just need to drop back the aggressiveness a bit.  You'll see from the very sparse corrections in the graph below (7 RA corrections in a 400s time span) that the mount is almost running unguided and this is how it should be with this mount.  The mount should only be correcting for drift caused by polar alignment, refraction effects etc so be sure to set a reasonably loose MinMo for RA.

Setup was: Tak FSQ85 at 332mm focal length, guided with an OAG / Lodestar.

Screenshot_20191129_201508.thumb.jpg.08060616e8675d7f86d6ef3b16c2bf35.jpg

I'm guiding with 4s exposures and the following algorithms;

X guide algorithm = Hysteresis, Hysteresis = 0.000 <--- this is important
Y guide algorithm = Resist Switch

I see you have backlash compensation enabled, did GA suggest you do this?  My GA runs have always said that I have negligible backlash and not to enable it.

 

Cheers,

Ian

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On 03/12/2019 at 12:00, old_eyes said:

 

1829563392_Recommendedguidesettings.png.5b82b3e0c8031832097cedbca0d6c160.png

 

On 03/12/2019 at 12:20, old_eyes said:

 

383458357_MainCameraGuide.png.c18e2e52709d0dd6a5b611d4e4cc1100.png

 

The first graph shows a typical response from the pre-beta firmware; a large amount of drift in RA in one direction.

The second graph shows the oscillation problem of the pre-beta firmware; the majority of corrections are in one direction, but a tiny pulse the other way results in a huge over correction.

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1 hour ago, michael8554 said:

Note starflyer's RMS and Peak values are in pixels, not arcsecs. 

Michael 

Well spotted, not sure when I changed that, here's the log analysis from the same evening.

image.thumb.png.e35615b243356d25fda20cf2a5d8d1e7.png

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@Starflyer Thanks for the information. Your guiding is now much better than mine. You note that calibration is still difficult. Does PHD2 accept the calibration or does it complain about the different guiding rates on the two axes?

I have read the CN threads, but I have not yet fully understood them. There are so many suggestions for the root cause, and so many differnet solutions that have worked for different people that I find it hard to see where the consensus lies. I will keep working away at it.

Just to note that the second graph of mine you quote was a slightly weird run when I was using the main scope and camera as the guide system to eliminate the mounting of the guiodescope as a source of the problem. It answered that question, but I would not trust it as an indication of how the guide system is working.

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1 hour ago, old_eyes said:

@Starflyer Thanks for the information. Your guiding is now much better than mine. You note that calibration is still difficult. Does PHD2 accept the calibration or does it complain about the different guiding rates on the two axes?

I have read the CN threads, but I have not yet fully understood them. There are so many suggestions for the root cause, and so many different solutions that have worked for different people that I find it hard to see where the consensus lies. I will keep working away at it.

Just to note that the second graph of mine you quote was a slightly weird run when I was using the main scope and camera as the guide system to eliminate the mounting of the guiodescope as a source of the problem. It answered that question, but I would not trust it as an indication of how the guide system is working.

PHD complains about the calibration, I confirm it and tell it to use it.  The only difference from a 'good' calibration is that PHD will now issue a slightly bigger pulse that it should do, this is easily overcome by decreasing the aggression slightly.

I can see you loaded the beta firmware, did you force a re-calibrate on the encoder?  This is an important step after a firmware update.

From the firmware page;

"To calibrate the encoder: 1) Turn off the mount; 2) Hold number "2" on the hand controller, then turn the mount power on, keep holding the #2 key until the calibration started automatically; 3) After the mount stopped, turn off the mount, and turn on again."

Happy to help you try and resolve this if I can, try another run or two and post back with questions, logs etc.

 

Cheers,

Ian

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29 minutes ago, Starflyer said:

PHD complains about the calibration, I confirm it and tell it to use it.  The only difference from a 'good' calibration is that PHD will now issue a slightly bigger pulse that it should do, this is easily overcome by decreasing the aggression slightly.

I can see you loaded the beta firmware, did you force a re-calibrate on the encoder?  This is an important step after a firmware update.

From the firmware page;

"To calibrate the encoder: 1) Turn off the mount; 2) Hold number "2" on the hand controller, then turn the mount power on, keep holding the #2 key until the calibration started automatically; 3) After the mount stopped, turn off the mount, and turn on again."

Happy to help you try and resolve this if I can, try another run or two and post back with questions, logs etc.

 

Cheers,

Ian

Ian,

Thanks for the clarification. I don't think I am going to fix the problem with a slight reduction in aggression.

Yes I did force a recalibration of the encoder.

I will wait for another clear night (nothing in the forecasts for the next week unfortunately, but there may be some short spells or partially clear skies I can use) and retry with hysterisis set low, exposure long and play with aggression if I get a chance. I will also repeat the unguided experiment to get a handle on underlying RA error.

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You can gather data to determine the level of the SDE errors even if you don't have a full clear night.  It's probably worth doing this sooner rather than later to help determine whether you do have an SDE problem with your copy of the mount.

Calibrate as normal and then perform a Guiding Assistant run of five minutes with very short exposures, say 0.5 seconds.  Gather the PHD2 guide and debug logs and post them to in that thread on CN and OzAndrewJ or another helpful soul will analyse them for you.

As you probably know by now it helps to calibrate with a relatively long guide exposure, I've settled at 4 - 5 seconds.

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