Problem with new iOptron CEM120EC2, DEC guiding results

[Sean McCully]

Hi,

I recently got a CEM120EC2, and have been using it for unGuided imaging on my RASA 11. I wanted to try guiding so I put on a 70mm Guide scope with a QHY163M attached with a ZWO Ring Holder. I am not entirely sure if any of the issues I am seeing in the DEC guiding could be related to Differential Flexure as the ring doesn't fit firmly around the QHY163m it does allow the camera to slide back and forth. But I wanted to get feedback from PHD developers on the issue, as I have shared the results with other who are suggesting it could be due to DEC backlash or something with how PHD handles iOptron mounts. The DEC axis does have an encoder, and I selected the encoder option when creating the profile in PHD.

Thanks,

Sean

[Brian Valente]

Hi Sean

Looking at your guidelogs, you haven't yet logged a good calibration, and without that you aren't going to get any reasonable guiding results. 

so we can only look at your calibrations right now

Here's a good calibration (example, not yours) - note 90 degrees separation between the axis, and fairly uniform consistent spacing of the calibration exposures, along the line of the axis:

Here are your calibrations

you also had two that looked nearly identical (although they were exposed at 500ms which is too short for guiding, but we'll get to that):

I think the most telling part of your guidelog is the unguided portion which is quite unusual:

This shows only the mount's performance, no guiding pulses at all. as soon as you turn on the guiding assistant, the DEC moves almost 125" quite linearly for about 50 seconds

Then it tops off

then DEC moves about 65" in the opposite direction at about the same rate as previous

then it is solid as a rock for the remainder of the 

My best guess is this isn't DEC backlash, i think there is something fundamentally wrong here. It may just be a setting somewhere, but a mount on its own, without any input at all, doing that kind of movement is imo a non-starter.

I don't see anything (yet) that would suggest DEC backlash is a problem, but only because you haven't gotten far enough to see if in fact that's an issue. You have encoders, so backlash appears not to have been measured in the guiding assistant results, PHD probably assumes it's a non-issue because of an encoder mount.

Your DEC guidescope mounting certainly sounds problematic, and could explain some of the issues you see in your calibrations, but cannot explain the above unguided results. 

I suggest you share that specifically with ioptron or the ioptron user group and see what they say

Brian

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[Brian Valente]

Sean

PS - i neglected to revisit the topic of your exposure time.

you really want to be in the 2-4 second range for guiding. 1/2 second is too short.

it appears from the unguided run your mount has a periodic error of about 4" - but that could be due in part to poor calibration and the orthagonality issues mentioned previously

it's worth asking ioptron about this as well, since encoder mounts should effectively eliminate your periodic error

On Sun, Aug 2, 2020 at 7:21 PM Sean McCully <seanm...@gmail.com> wrote:

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[Sean McCully]

Thanks Brian,

I didn't do any guiding because the calibration results were soo, well suggesting something is fundamentally wrong. The main reason, I initially suspected the camera, is because I've put in maybe ~> 40 - 60 hours in this mount since I got it which has all been unguided and I've not had any issue with any of the pictures I've been able to take that were not due to something else. So the mount appears to be performing very well unguided, but the guiding results show something isn't right. I suspect I will need to contact iOptron.

The short exposures were used because it was being suggested on another Forum that you want to capture short exposure to try and detect SDE (Sub Division Error) with the encoders. 

I suspect that the initial movement after starting the Guiding Assistant, has to do with the wild swings in DEC from the error in Calibration. But I am not certain either, since I have not seen any wild movements like that when just Slewing, and unguided captures. 

Thanks 

Sean

On Sunday, August 2, 2020 at 8:26:12 PM UTC-7, Brian Valente wrote:

Sean

PS - i neglected to revisit the topic of your exposure time.

you really want to be in the 2-4 second range for guiding. 1/2 second is too short.

it appears from the unguided run your mount has a periodic error of about 4" - but that could be due in part to poor calibration and the orthagonality issues mentioned previously

it's worth asking ioptron about this as well, since encoder mounts should effectively eliminate your periodic error

On Sun, Aug 2, 2020 at 7:21 PM Sean McCully <seanm...@gmail.com> wrote:

Hi,

I recently got a CEM120EC2, and have been using it for unGuided imaging on my RASA 11. I wanted to try guiding so I put on a 70mm Guide scope with a QHY163M attached with a ZWO Ring Holder. I am not entirely sure if any of the issues I am seeing in the DEC guiding could be related to Differential Flexure as the ring doesn't fit firmly around the QHY163m it does allow the camera to slide back and forth. But I wanted to get feedback from PHD developers on the issue, as I have shared the results with other who are suggesting it could be due to DEC backlash or something with how PHD handles iOptron mounts. The DEC axis does have an encoder, and I selected the encoder option when creating the profile in PHD.

Thanks,

Sean

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[Brian Valente]

Hi Sean

>>>I suspect that the initial movement after starting the Guiding Assistant, has to do with the wild swings in DEC from the error in Calibration.

At that point, nothing from PHD is in play, including the calibration. this is just letting the mount run without any input

so calibration etc. is not a factor in that performance. that's just straight mount

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[Sean McCully]

Right, so I think because there was all this excesses movement in DEC from the bad calibration the mount was still trying to overcorrect the guiding movements. But, again I am not 100% sure either.  

Any suggestions, on how to possibly narrow down the root cause here or best way to show iOptron that there is a problem? Or eliminate the camera as the problem?

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[Brian Valente]

Hi Sean

>>>>Right, so I think because there was all this excesses movement in DEC from the bad calibration the mount was still trying to overcorrect the guiding movements. But, again I am not 100% sure either.  

I'm fairly sure that isn't the case, but again this is the mount operating on its own over the course of many minutes, so I can't see how any prior input from PHD would have any impact on the mount

If you want to eliminate the guidescope, i'd recommend switching to your imaging camera and scope and just do an unguided run similar to what you did before

that would eliminate any issues related to guidescope setup

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[Sean McCully]

Thanks Brian,

I am trying to use the main Camera to test the mount in PHD2, but getting some errors.

1. Trying to connect to ASCOM QHYCCD-Camera Main, it shows as no camera found, even though ive already connected and disconnected from the camera in Maxim DL.

2. After using the ASCOM QHYCCD-Camera-Guide to connect to QHYCCD QHY600 camera, PHD is throwing an System.OutOfMemory Exception when trying to image. 

Sean

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[Brian Valente]

Hi Sean

that's a huge pixel camera!

you might try binning 2x and using subframes, or both

if that's still too much, maybe bin 3 or 4?

It will lessen the resolution, but should still be enough resolution to show the issues

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[Sean McCully]

Thats a good point, I'll see if I can give the binning a try tomorrow then.

What I ended up doing was putting the QHY178m on the 70mm Guide scope with a losmandy guide rings to stabilize it. I ended up getting a good calibration, but the DEC started to oscillate after a minute of decent guiding. To me this seems like its definitely the camera, considering I had the QHY163m on the 70mm Guide scope yesterday and could not get a good calibration and now I can get a good calibration but DEC is still oscillating. And while PHD was reporting oscillation in DEC axis of +5 arc minutes, I was able to capture an image with Maxim with round stars. So I think it's probably just Differential Flexure. But it until I put my EdgeHD with an OAG on, I can try my main camera to try and validate. 

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[Sean McCully]

P.S.

The RA motor started to stall out at 700 seconds or so during the Guiding Assistant which caused the RA start to drift. 

[Brian Valente]

>>> The RA motor started to stall out at 700 seconds or so during the Guiding Assistant which caused the RA start to drift. 

RA stalls during tracking? that sounds worth talking to ioptron about

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[Sean McCully]

Certainly, the first time I have seen something like that happen as well. I was pretty far past the zenith. I think the way the iOptron mounts work is usually the belts/gears need to be tighten but I should ask them about it.

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[Bryan]

Sean

I have a iOptron ieq45 that I have used use for outreach for several years, but not for imaging; so I have no sense of its guiding performance.  I do know that over time (several months with 4-6 events per month), the belt stretched enough to throw off GoTos by 10-15 degrees.  While I have no data to quantify error in tracking, I reckon there is some.  I purchased an idler pulley kit designed to keep the tension on the belt, but after 3 years, I had to replace the belt.  Still a good mount for visual when the belt is tight, both in terms of GoTos and tracking.

It is an older and different technology than the iOptron CEM series, but both have belt drives.

Bryan

On Monday, August 3, 2020 at 8:24:17 AM UTC-6, Sean McCully wrote:

Certainly, the first time I have seen something like that happen as well. I was pretty far past the zenith. I think the way the iOptron mounts work is usually the belts/gears need to be tighten but I should ask them about it.

On Mon, Aug 3, 2020 at 7:14 AM Brian Valente <bval...@gmail.com> wrote:

>>> The RA motor started to stall out at 700 seconds or so during the Guiding Assistant which caused the RA start to drift. 

RA stalls during tracking? that sounds worth talking to ioptron about

On Mon, Aug 3, 2020 at 12:12 AM Sean McCully <seanm...@gmail.com> wrote:

P.S.

The RA motor started to stall out at 700 seconds or so during the Guiding Assistant which caused the RA start to drift. 




On Sunday, August 2, 2020 at 7:21:53 PM UTC-7, Sean McCully wrote:

Hi,

I recently got a CEM120EC2, and have been using it for unGuided imaging on my RASA 11. I wanted to try guiding so I put on a 70mm Guide scope with a QHY163M attached with a ZWO Ring Holder. I am not entirely sure if any of the issues I am seeing in the DEC guiding could be related to Differential Flexure as the ring doesn't fit firmly around the QHY163m it does allow the camera to slide back and forth. But I wanted to get feedback from PHD developers on the issue, as I have shared the results with other who are suggesting it could be due to DEC backlash or something with how PHD handles iOptron mounts. The DEC axis does have an encoder, and I selected the encoder option when creating the profile in PHD.

Thanks,

Sean

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[David Kerber]

That sounds a little bit like what I was seeing when I had backlash
compensation set in my handset: PHD would start oscillating shortly
after guiding started (probably when it had to make its first reversed
adjustment). Once I turned off backlash compensation, the oscillation
went away.

> image.png
>
> it's worth asking ioptron about this as
> well, since encoder mounts should
> effectively eliminate your periodic error
>
> On Sun, Aug 2, 2020 at 7:21 PM Sean
> McCully <seanm...@gmail.com> wrote:
>
> Hi,
>
>
> I recently got a CEM120EC2, and have
> been using it for unGuided imaging on
> my RASA 11. I wanted to try guiding so
> I put on a 70mm Guide scope with a
> QHY163M attached with aZWO Ring Holder

> <https://astronomy-imaging-camera.com/product/new-holder-ring-for-asi-cooled-cameras78mm-diameters>.

> <https://groups.google.com/d/msgid/open-phd-guiding/cd88e8b2-3882-40af-b90b-adab501eea5co%40googlegroups.com?utm_medium=email&utm_source=footer>.

>
>
>
> --
> Brian
>
>
>
> Brian Valente
> portfolio brianvalentephotography.com

> <http://brianvalentephotography.com>

>
> --
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>
>
>
> --
> Brian
>
>
>
> Brian Valente
> portfolio brianvalentephotography.com

> <http://brianvalentephotography.com>

>
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[Ross Walker]

Hello Sean,

I have the 120EC2 so perhaps I can offer you some advice. The EC2 has encoders so it should never be guided at a rate of 0.5s due to limitations in the firmware. The advice you received for using 0.5 second exposure was never intended in any way for guiding or calibration; it should only be used for measuring star movement while the mount is operating *unguided* via Guiding Assistant. The mount's SDE is at a period of 3.3 seconds, so to accurately measure its magnitude you need to use an exposure rate of much less than 3.3 seconds. Your use of 0.5s exposures plus other latency (image download time etc.) has resulted in a sample rate of around 1.4 samples per second so your guiding assistant results are good enough to measure your mount's SDE magnitude: 0.2 arc-sec RMS. That is a very good figure for this mount so you should have no concerns with SDE affecting your images even at long focal length.

As to the recommended rate of exposures for guiding this mount (or any of the iOptron encodered mounts for that matter), I'd recommend not going any faster than say 3 second exposures, otherwise you may experience instability in either or both RA or Dec, especially large dec oscillations. A bug in the firmware results in the likelihood of PhD sending new guide commands before previous guides commands have been fully executed (isGuiding bug), so the mount need ample time to fully execute guide commands, and 3+ second exposures provide that. For the same reasons, calibration should also be done using around 3+ second exposures for accurate calibrations.

I think once you change your exposure rate to say 4 seconds, you'll start to see much better calibrations and a mount that behaves quite differently to what you've been previously experiencing.

Cheers,

Ross

[Sean McCully]

Thanks Ross,

The logs I uploaded from 08/02 show a guide run and calibration with 3 second exposures. There appears to be still some issues with DEC oscillating. I am hoping this has to do with differential flexure in the guide camera/scope. So I will keep these recommendations in mind when i try guiding with my main image camera tonight.

Sean

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[Ross Walker]

Sorry I missed that guide log. I don't believe I have seen a Dec oscillation like that with such a low frequency, and I don't think the oscillation has anything to do with diff flexure because, if so, you would probably be seeing it affect RA too.

What firmware are you currently using Sean? If you haven't tried upgrading or downgrading the firmware yet, I suggest you give that a try. I'm currently using V1903 and I've head several users give the thumbs up to V1907, but in the end iOptron's CEM120 firmware is a dog's breakfast so you may need to try several before finding one that works with your mount.

[Brian Valente]

>>> iOptron's CEM120 firmware is a dog's breakfast 

I have to admit never hearing that phrase before. What does it mean?

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[Ross Walker]

A dog's dinner (or breakfast)

noun: dog's breakfast

1. INFORMAL•BRITISH

   a poor piece of work; a mess.

Sean, just realised you have been posting on CN.

[Brian Valente]

ah thank you. British humor ;)

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[Sean McCully]

I only upgraded the firmware to the latest when setting up the mount for the first time required by iOptron commander.

HC V2: 200110

Main: 191120

RA: 190820

DEC: 190820

Hopefully, I can test with my main imaging camera, which should help rule out any flexure in the Guidescope imaging train.

[Ross Walker]

Well that might be the problem then. If my memory serves me correctly, several users on the now defunct CEM Mount User Forum tried V1911 and even a later firmware and had many problems with them, so they moved back to firmware V1907xx. Not sure if those problems included Dec oscillation, but it may be worth a try downgrading to one of the V1907 firmwares (one of which works well, the other not so well). Maybe Andrew has analysed examples of guide logs under V1911 firmware?

[Sean McCully]

I've attached Logs from last night, imaged with QHY600 main imaging camera on my RASA 11. The images were binned, and then subframe selected.

The calibration was sort of fine, but there was some strangeness with DEC. There was some large DEC movement right after calibration, then during the Guiding Assistant Run and Backlash test PHD was unable to move the star back to starting position. 

After Guiding Assistant run, and a few minutes of good guiding the once PHD started to make large DEC corrections the DEC started to Oscillate. It seems strange, because I don't see this kinda of movement from the mount itself when imaging. It would seem that after slewing there would be also some DEC oscillation that would show in images that were captured right after slewing which is done when plate solving with Maxim. 

I ended up changing the PHD DEC algorithm to ResistSwitch, first with FastSwitch disabled. Which still showed DEC oscillations, then with FastSwitch enabled, DEC guiding was fine. Although, it seemed liked there were very few DEC corrections, with aggressiveness at 80% which actually doesn't seem to be an inherent problem. 

Later, I put the GuideScope back on with the 178m attached to GuideRings and tried a calibration with ResistSwitch. But there was still very large DEC oscillations.

So, my conclusion is that there was Differential Flexure with the GuideScopes but that there seems to be perhaps some tweaking that needs to be done from the defaults for PHD based on the DEC encoders. 

I am still using the default firmware (i.e. latest). 

[bw_msgboard]

Hi Sean.  I think the backlash test was telling you there’s something pretty seriously wrong with how the mount behaves in Dec.  Here’s what that looked like:

 

 

As you probably know, it should look something like this:

 

 

The red points show consistent moves *north*, in your case using guide pulses of 1.1 sec.  You can your mount actually moved *south* for about 4 seconds before finally starting to move in the right direction.  So the mount/firmware isn’t even close to “doing what it’s told” for guiding.  I really don’t see much point in trying to somehow work around this sort of problem, I think it would be better to talk to iOptron and get the underlying problem fixed.

 

Sorry you’re having all this trouble,

Bruce

 

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[Sean McCully]

Thanks Bruce,

That actually makes sense, and something i can send to iOptron. 

Sean

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[Sean McCully]

I wanted to provide an update here, after the last message I contacted iOptron and they gave a few suggestions. The two notable ones were to tighten the DEC axises gears, and try the firmware Ross suggested. iOptron provided the firmware, and I still wanted to try with my EdgeHD 11 with OAG before switching over to the firmware suggested. 

So last night I finally put on the EdgeHD 11, and almost none of the issues that were being seen previously were present. The one notable issue was that the Calibration run showed large backlash in DEC. Otherwise guiding was rock solid the entire night generally around 0.4" < 0.5". I've attached the guide logs, the debug logs were too large for attachment so below is a dropbox link. 

PHD2 Debug Logs

PHD2 Guide Log

I was not expecting this result, and wonder if this means that more or less all the behavior I was seeing before had to with differential flexure or was the mount really not behaving well with the RASA 11 itself. Images taken with the RASA 11 unguided were always optimal, so is there differential flexure even in the main image train? Not sure, but I am pretty happy with the results with my EdgeHD. Though if I can get that total RMS down a little bit lower would be even better. 

[MountainAir]

Hello Sean,

I was reading your old post about the CEM120EC2 in the forums.  I have been troubleshooting my CEM120EC2 for almost a month now and am about to send it back.  In troubleshooting this with Ross and quite a few other folks on Cloudy Nights, I've had issues with DEC backlash being as high as 3.4 seconds in PHD (though at hand controller speed 1, I see reversals in ~0.5 seconds in the camera).  My star cross tests look almost entirely one-sided.  I was also getting some truly horrible DEC oscillations but I chalked that up to me being a PHD2 newbie, and I was eventually able to work around that behavior.

I've reviewed ALL the "EC" related posts in this forum and plan to try the recommendations on the next clear night... but since I'm almost out of time before I need to send the mount back, I wanted to ask if you are still happy with your results with this mount.  Did you ever get it serviced/upgraded by iOptron?  Any guidance you could offer would be HUGELY appreciated!

Thanks!

[Sean McCully]

Hi,

I would be interested to know what your work around was? Before beginning, I should note that my imaging setup includes the use of a Starlight Xpress AO, and this does change a lot on how PHD sends guide pulses. 

There are a couple of things worth noting, i would not say i am 100% happy with my CEM120EC2 but it does perform well enough and aside from going out to spend $15k on an AP mount i don't think i could really do much better. Also, iOptron Support has always been extremely helpful though, with both my CEM60EC and 120. I think the guiding issues with PHD and iOptron is probably not as one sided as sometimes it's made out to be. So when i raised the issue with iOptron after i first purchased my mount, this is what iOptron suggested.

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Could you check whether the DEC physically has backlash when the motor reverse direction, and how much? You may remove the DEC cover and expose the belt, set slew speed at 1X, using hand controller up/down key to slew/reverse the motion, see how long the belt take to reverse after an arrow key is pressed. Whether adjusting the belt tension help?

http://www.ioptron.us/Support/CEM120_DEC_Belt_Tension_ADJ.pdf

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Follow Up Message:

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Backlash is irrelevant to encoder. Spring loaded gear is no backlash design, however, it requires proper gear mesh and belt tension.  500 ms, or 0.5 s, backlash is actually not bad, it should not cause large error in guiding. Besides backlash, gear stiction might result the same error as backlash.

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Ive also found that properly balancing both Axises can have a pretty big effect on guiding as well. After just tightening the belt tension which had probably gotten loose maybe during shipping, i saw some pretty big improvements. Getting the gear mesh correct is probably a little dependent on what you are putting on top of the mount as well but equally important. Ive taken the mount apart a few times now, and as such have gotten pretty familiar with how all of it fits together. Dont be afraid to disassemble the entire thing, it does help to understand how everything works. It may help to make sure that there are no loose cables or anything. When doing a guiding calibration in PHD, my RA and DEC axis start to look like two parallel lines that's really what you should expect with proper polar alignment and the encoders working properly. 

See some instructions:

http://www.ioptron.us/Support/CEM120_GearTensionADJ.pdf

http://www.ioptron.us/Support/CEM120_Board_Replacement.pdf

http://www.ioptron.us/Support/CEM120_DEC_Belt_Tension_ADJ.pdf

https://www.ioptron.com/v/Support/CEM120_RA_WormReplacement.pdf

https://www.ioptron.com/v/Support/CEM120_DECWorm_ADJ_REPL.pdf

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[MountainAir]

That's some great response, Sean, thank you!

Regarding my oscillation issue:  On first-light I tried KStars/Ekos's internal guider, since that's what I used successfully in the past.  RA and DEC were balanced east-heavy and back-heavy by a small amount (later tried exact balance to no real difference).  That experienced a large oscillation in DEC with this mount (right off the chart), and since the internal guider is not as configurable I decided to try PHD2.  That had the same oscillation.  Guiding Assistant said anywhere from 2.4 to 3.4s DEC backlash.  I could not feel any in the mount head, but when I adjusted the gear mesh it did seem adjusted out too far.  That reduced the backlash to 1.4 or so.  The belts were tight.  So in software, I ended up changing to the ResistSwitch algorithm and ended up with 50% aggression and minMove .30 in both axes, with 10% hysteresis in RA.  This wasn't the result of tuning, it's just what I settled on while trying to stop the oscillations (in reading through this forum, it seems these settings were just a shot in the dark).  With those settings, I rarely got oscillation but when it did happen, I'd have to adjust the MaxMove from 2500 to 250 or even 50 to get it to settle down, then I could increase it again.  That's far from ideal, but if I just let it oscillate it just didn't seem to calm down even after several minutes.

Please note that this profile does have the setup wizard checkbox for "DEC axis has high resolution encoder (some high-end mounts)" selected.  I'm not exactly sure what that does, and I have not tested without it.

Thanks for your comment about the issues with this mount probably not being as one-sided as they seem.  There's a lot of scuttlebutt online about this mount and PHD2 just not behaving properly.  I understand there's a near-infinite number of combinations of main cam, guide cam, focal length, mount characteristics, encoder resolution, etc. that all factor into those PHD2 settings, but I'm on a mission to find the best possible combination of PHD2 settings (for my setup at least) and then publish them as a "Start somewhere here" recommendation for CEM120EC2 owners.  I'm frequently told to guide with something else, but I don't want to change my entire automation software suite just to work with some external guiding software.  I'm sure PHD2 can handle it if we can just figure out a good set of settings for this particular mount (since it does seem to require SOME adjustment).

One of the issues we came across is that PHD2 sends a guide pulse, the mount doesn't apply it immediately or applies it with a delay or applies it too slowly, then says it's done when it's in fact still moving.  PHD then starts the next guide exposure while the mount is still moving (because the driver lied to it), and results suffer -- presumably this is part of the DEC oscillation problem.  I'm still trying to work though that with iOptron, but this has been in the forums for a couple years now.

[Sean McCully]

Well, I would start with tightening the belt in the DEC axis, and trying the procedure iOptron lays out for determining if there is actual backlash. The belt may feel tight to the touch but you may find it can be I improved. I used a crowbar to get the gear

Belt as tight as possible.

Regarding PHD settings, I've found that if I reduce the Guiding Rate to 0.25X, I can reduce guide exposures to 2-3 seconds which is really because the AO device does better with faster exposures.

Regarding the guide algorithm, I use Hysterisis on both axis's and usually keep it below 40%, Hysteris at 5% and min move small 0.16 to 0.35.

Sean

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