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Erratic guiding spikes with CEM40EC-NUC

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#1 grayzork

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Posted 16 September 2021 - 05:14 PM

Hello all. I received this new CEM40EC-NUC mount in August and have seen these guiding anomalies from the beginning. I am operating the mount with the ASIAIR Pro.  I have similar guiding problems when using my EdgeHD8 f/10 with a 162 mm FL guide scope or the Redcat51 with a 120 mm guide scope.  The PA works fine and the mount performs GOTOs very well and after plate solve it responds to syncing as expected. The guiding calibration seems to be fine.  However when guiding, the log shows intermittent large correlated spikes in both RA and DEC whenever the DEC guiding mode is either AUTO, N or S.  If DEC guiding is OFF then the RA tracks very well but the DEC drifts as expected. 

 

I am in the process of trying to return this to B&H Photo since iOptron tech support has not responded to multiple help requests.  Any suggestions would be greatly appreciated. Thanks for reading.

 

Attached files:

 

1) Guide log starting at 21:36 with DEC mode set to AUTO  then changed to OFF at about 21:42.

 

2) Guide log starting at 00:59 with DEC mode set to OFF

 

Screen Shot 2021-09-16 at 2.09.19 PM.jpg

Screen Shot 2021-09-16 at 2.11.10 PM.jpg



#2 rgsalinger

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Posted 16 September 2021 - 05:26 PM

Attach the actual guide log and post a picture of the entire system. If the error is not periodic in nature then cabling is often the problem. Have you tried an actual drift alignment? The polar scope with these mounts is often not correctly mounted. Lots of threads about this here. That would not cause spikes like the ones you are showing.

 

I'd want to see really tidy cabling and a no wind night on an absolutely stable base - not a wood deck or soft soil - to be sure that it's the mount and not the environment.  

 

To get help from iOptron, I hope that you've used email. They will almost never respond to phone calls. I've owned the brand for years and email has always worked really well. 

 

Rgrds-Ross


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#3 grayzork

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Posted 16 September 2021 - 06:21 PM

Thanks Ross. I can see why the environment could lead to problems. However, I'm sure that is not the case here since turning DEC mode to OFF completely solves the issue. I have gone through this over multiple nights and have seen the same problems.  I have emailed iOptron twice and had the sales manager also ping them with no result. I think they might be getting inundated with tech requests. It's a shame because I really like the mount other than this *important* issue.

 

Frank

 

Attached File  PHD2_GuideLog_2021-09-10_213309.txt   430.9KB   5 downloads

 



#4 rgsalinger

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Posted 16 September 2021 - 07:06 PM

You calibrated the guiding system at 57 degrees DEC. That's a bad idea. Calibrate it once per night at the intersection of the meridian and the celestial equator. I doubt that's the problem here but you will get better guiding usually because the calibrated speed will be more accurate. I'm really bothered by the calculated guide speed being so low. It just looks wrong to me even at DEC 57. I would also never guide a mount with 95 percent aggression. That's can easily lead to oscillations in the RA axis if you have mediocre seeing.

 

When you turned off the DEC guiding the mount fell off pretty fast. That means to me that something is wrong with the polar alignment. I would check by doing a PHD assisted drift alignment. It's possible that your guide camera is not orthogonal to the mount. I think that's part your problem - your PA is way off and calibrating so high in DEC is exacerbating the issue in the other axis. 

 

One final thing to check is the power supply. Make sure that the mount is getting a full 12 volts under load. Bad power can cause all sorts of nonsense when guiding.

 

Overall, if you are confident about your cabling and you've checked the the polar scope is orthogonal with the mount axis, it looks like a bad mount.

 

I'm just bothered by the correlation between the DEC axis movements and the RA axis movements. When I get stuff like that it's always environmental and not the mount.

 

Rgrds-Ross



#5 grayzork

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Posted 16 September 2021 - 08:51 PM

Ross, Thanks for all your suggestions. I don't think the guide camera was aligned to the mount axes. I was wondering about that but assumed the guiding software would take it into account properly. I can try another session with the camera aligned.

 

I am pretty sure my polar alignment was well within 2 minutes. I am not using the polar scope but plate solving and rotating around the RA axis.  ... I can see why non-optimum PA could lead to larger RMS guide deviations but I don't see how it could cause these spikes.

 

The correlated spikes are very interesting. As you suggested, the obvious source of the correlation would seem to be environmental. Other than that, I cannot imagine how guide-pulsing the DEC motor could influence the RA motor.  



#6 OzAndrewJ

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Posted 16 September 2021 - 08:55 PM

Gday Frank

 

Interesting plot :-)

I 80% agree with Ross that its something mechanical in your DEC,

as when i plot the pulses sent vs the final position, they all indicate no loss of position,

ie the pulses sent exactly matched the excursions, but what is really weird

is how slowly the error manifests itself, and how similar it was in magnitude..

Its almost as if there is a backlash type effect where "something" can wobble at times

and this wobble gives a local RA and DEC error

I dont think its cable snag related, as in most cases, when it occurs, you get pretty much

identical excursions in RA and DEC  ( hence my "something is loose" idea )

Your comment ( and data ) agrees that it doesnt happen when DEC guiding is OFF

so that semi scuttles that idea.

One other low probability guess

I did note it appears ( in most cases ) to occur on the first DEC reversal after a while

Does the mount itself have some form of internal DEC lash settings that can apply on reversing ???

 

Andrew Johansen Melbourne Australia



#7 grayzork

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Posted 17 September 2021 - 09:23 AM

Thanks Andrew,
I have been trying to digest your comments. I am not sure I understand your last idea about the effect mostly occurring after DEC reversal. I have noticed that with DEC mode AUTO the excursions are sometimes anti-correlated (section starting 00:30) and have not found a systematic reason. The ASIAIR guiding is based on PHD but they have a very automated control interface that does not allow for the detailed settings available running stand alone PHD. I am using a Mac and have PHD2 but have not been able to use it for lack of the INDI driver. I guess I will be spending some time getting that working.

 

Screen Shot 2021-09-17 at 6.59.32 AM.jpg



#8 rgsalinger

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Posted 17 September 2021 - 11:02 AM

I think I'd return the mount and get another one. If that one gives you the same result then I'm really wondering about the use of an ASI Air with an encoder mount. Why anyone would create a hacked version of PHD is beyond my comprehension. I thought that PHD was open source and all that you needed to do was to port the code. If the developers can't even do that then I'm not impressed with their skill set. I'd love to see PHD on your Mac running natively, but at this point, if you can return it, that would be my advice.

Rgrds-Ross



#9 OzAndrewJ

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Posted 17 September 2021 - 06:28 PM

Gday Frank

I am not sure I understand your last idea about the effect mostly occurring after DEC reversal.

If you turn off the RA trace and look at the DEC, you can see the pulses being sent.

What i noted is that when a new DEC pulse swapped from N to S or S to N  ( after being stable for a while ),

the "effect" started. I call it an effect as it takes such a long time to manifest, and includes RA.

 

"are sometimes anti-correlated"

I dont understand. Allthey show is at a given point in time BOTH axes start moving oddly

Have attached a full trace for the end of the night showing the path the guide pulses would have run in theory.

This trace looks like a classic DEC "back lash", ie it always swings between 2 settings.

The problem is you never normally see this in RA, and your RA is showing it.

No idea why.

Andrew Johansen Melbourne Australia

Woofs.jpg


Edited by OzAndrewJ, 17 September 2021 - 06:43 PM.


#10 rgsalinger

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Posted 17 September 2021 - 06:55 PM

That's why I keep thinking that using a hacked up version of PHD running in a black box appliance with a third party driver with an encoder mount might be asking for trouble. Very few AsiAir owners are going to have high resolution encoders on their mounts. The manual for the air pro doesn't say much about where the drivers come from, what mounts have actually been tested, etc.

 

Now it still looks to me like some kind of binding/drag issue. I'd still return the mount. I have to wonder about the software being used with an EC mount written by a third party. Could this be something absurd like dithering gone wild? Or RA guiding turned off? Or some PEC issue? 

 

Rgrds-Ross



#11 grayzork

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Posted 18 September 2021 - 06:44 AM

Good morning Andrew,

 

By anti-correlated I mean the simultaneous RA / DEC glitches sometimes have odd parity rather than even, i.e. +/- rather than +/+.

 

I have been marveling at your plot and wondering about the program that generated it. What is it? All I have is "phdlogview" (Mac version). The integration of the guide pulses is useful.  Thanks for your interest in my problem.



#12 grayzork

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Posted 18 September 2021 - 06:49 AM

Good morning Ross, 

 

I am trying to return the mount. I have tried a couple times to email iOptron about this. Even their sales manager tried to ping them for me with no response.  I wonder what's going on over there.  You must read a lot of the posts here - have you ever  seen an issue like this that was not due to the outside environment?

 

Frank



#13 OzAndrewJ

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Posted 18 September 2021 - 04:37 PM

Gday Frank

 

By anti-correlated I mean the simultaneous RA / DEC glitches sometimes have odd parity rather than even, i.e. +/- rather than +/+.

You need to understand that they are just arbitrary directions, and dont always tell the truth.

The fact both move at the same time is certainly odd but the +/- vs +/+ etc isnt.

Many ASCOM drivers are non compliant when it comes to the DEC axis "direction"

so it might be part of that with your mount.  ( for the pulses sent plot )

At the end of the day, your plot shows both axes move a set distance away from lock

then move the same distance back, it it oscillates between 2 positions.

The big question is why.

 

I have been marveling at your plot and wondering about the program that generated it.

Its something i wrote for myself, as no other app allows plotting of a whole session in one hit.

Also, i dont always like the way PHD plots data ( for error analysis ),

as it leaves stuff out and "adjusts" other stuff in a way i dont like ( ie converting RA/DEC using bad cals ).

By doing my own plot, i can look at the data in many different ways

and as such, can see trends that the shorter plots dont show.

 

Andrew Johansen Melbourne Australia


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#14 rgsalinger

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Posted 18 September 2021 - 05:50 PM

I remain very skeptical of both the environment and the software. First, I'd like to see a picture of the setup as I mentioned earlier. I keep thinking that something must be dragging or pinching. Sorry.

 

Second, as far as I know, the AsiAir gets it's drivers from Indi. I looked at the Indi driver site and did not see that the 40EC was supported. None of the mount drivers there are written by iOptron and there's no ASCOM to insure driver compliance. I may have some of this wrong because I don't use an AsiAir Pro so................. I would carefully research the mount driver that's being used and post on the AsiAir forum and the Indi forum to see if there are others using EC mounts with the ASI Air Pro. 

 

https://www.cloudyni...ith-asiair-pro/ may be probative of the matter at hand. 

 

I just had one of these events last week with my CEM120EC2. We were dialing in the flattener for my AP155 refractor. We were using a Bahtinov mask to check the the corners to see if they were in focus when the center was in focus by moving the mount around. The scope was pointed at the zenith. Suddenly both axes jumped several arc seconds. The it happened again. After the third time I went out to the observatory to look. Since I had just set up the scope for temporary use, I had not done a really good cabling job and one of the cables was contacting the pier. I fixed it. 

 

Rgrds-Ross


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#15 grayzork

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Posted 18 September 2021 - 06:36 PM

I don't have a photo of the setup on 9/10 when I had the Redcat 51 on the mount. Here is a photo of the setup with the EdgeHD8 SCT a few nights later. I began the guiding with DEC in AUTO but observed the glitches so switched to DEC OFF and everything went well after that. It does look like the AstroZap heat shield cable is slightly dragging on the mount. But, again, no problems with DEC mode OFF.

 

IMG_4704.jpg



#16 rgsalinger

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Posted 18 September 2021 - 09:25 PM

I'm really confused about your software setup when using the mount as pictured. You aren't using a PC but I don't see the AsiAir Pro either. Is it obscured in some manner? Using the AP you should only have two cables going to the AP - one for power and one for USB. You also need a USB cable to the mount, of course but that should come from the AP and you need a separate power cable to the mount as well. 

 

You also posted what appears to be PHD running on a Mac in your first post where you had jumps as well.  I wish I could help more but I don't own an ASIAir.  It's unclear to me what mounts are actually supported by the box. I could not find any evidence (a list) of mounts with encoders that would be supported. I think, overall, that this is some kind of software issue because you are using an unsupported driver. To resolve anything like that you need to make sure that the AP developers affirm that your mount is supported and that someone has tested it.

 

I can't say for sure (picture isn't 3d), but the way you have that system cabled is asking for trouble of the sort that you are getting - jumps.

 

FWIW, with the AP there's no reason at all to be using an ST4 cable. Now that I see the system, I realize that's why you chose to calibrate at +57 DEC rather than at the equator. You just use the USB port on the mount and drive it with a USB port on the AP.

 

Generally, you can't use a guide scope with an SCT and get nice round stars from long exposures. I can see that you have the reducer in the system and that may help the results but I wouldn't ever try it that way. 

 

If your cabling is no better when using the redcat then I suspect you will have trouble guiding. However, the fact that the guiding is good with DEC corrections turned off must mean that there is some other problem. I'm still thinking some kind of software issue - that's all that there can be that would magically clear up with no DEC guiding. So, I have to ask, how did you turn off the DEC guiding? 

 

If there's a local club around your area you should join and get someone to give you a second pair of eyes. Still, if you can get a replacement and it works fine, then it's the mount for sure. 

 

 

Rgrds-Ross 



#17 grayzork

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Posted 19 September 2021 - 09:35 AM

Hello Ross,

 

In the pic there is a white ethernet cable going to the AAP.  The AAP includes a driver for CEM40. In the guiding module one can select the DEC mode -  either AUTO, North, South or OFF.   I don't think the driver needs to worry about the encoder. I would not expect the firmware to even allow any outside interaction with it. I have seen many people report problems with SDE from their encoders and asking for a way to turn it off. I believe iOptron has said it can't be done. My cousin is running a CEM26EC with the AAP and it works fine which is one reason I went for the EC option in the first place. That was before I started reading about the SDE problems.  I believe your CEM120EC2 has different higher end encoders than the ones my mount has.

 

I just now received the RMA form from B&H so the mount is going back. Now I have to decide what to replace it with.

 

Thanks again for all your suggestions. 

Frank



#18 Kevin_A

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Posted 23 September 2021 - 04:29 PM

Did you ever try something simple like loosening the dec mesh? My mount had erratic dec guiding like yours and it turns out worm gear stiction was causing it to ignore constant correction pulses then rapidly overcorrect…then guide nice for awhile then do it all over again. I loosened the mesh and no more erratic dec. worth a try.



#19 grayzork

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Posted 25 September 2021 - 09:38 AM

Thanks Kevin. That's an interesting suggestion. I did check the belt tension on both motors but never looked at the gear mesh. I've never understood what would lead to the correlation in the RA and DEC glitches. I assume the glitches you observed were only in RA. Was that the case? 



#20 Kevin_A

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Posted 27 September 2021 - 09:15 PM

Thanks Kevin. That's an interesting suggestion. I did check the belt tension on both motors but never looked at the gear mesh. I've never understood what would lead to the correlation in the RA and DEC glitches. I assume the glitches you observed were only in RA. Was that the case? 

Mine was mostly on dec. ran great 90% of the night with erratic jumps in dec with plenty of corrections the an overshoot past midpoint then back to midpoint and great guiding. Happened randomly every 5-15 minutes. Sometimes ra was erratic but more jagged than anything. With these mounts it is a fine line between backlash and stiction on the worms. I am going to try a heavier scope as sometimes lightweight scopes suffer more from stiction and i may have to alter the mesh per scope i use.



#21 Kevin_A

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Posted 27 September 2021 - 09:19 PM

Usually when both ra and dec jump in tandem it is from a snag or star issue as mine only does that when there is that type of issue. Mine was just for a single axis at a time. Have you tried guiding with phd2 on a laptop? Maybe it is the asiair pro and not mount related.


Edited by Kevin_A, 27 September 2021 - 09:22 PM.

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#22 Kevin_A

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Posted 04 October 2021 - 12:00 PM

Found an article that was posted for cem26 and gem28 that may explain similar issues some are having on their mounts…

https://www.ioptron....nAdjustment.pdf



#23 grayzork

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Posted 04 October 2021 - 02:26 PM

Kevin,  First of all, thanks for keeping this issue in mind and the last two posts. I was out of town and missed the previous one. I would have liked to run stand-alone PHD2 from my Mac laptop but I wasn't able to get the INDI driver. It is a moot point now since I returned the mount and B&H Photo graciously gave me a full refund. I have ordered the CEM40-NUC (no encoder this time) and will see how it works with the ASIAIR. I plan to post my results here.

 

The pdf document from iOptron is interesting. It is good to know how to operate on the mount internals. I wonder how you are able to access the "For iOptron Internal Use Only" documents and what other interesting docs they might have.  It seems like the problem there is due to "stiffness" in the axle bearing.  Both RA and DEC manual rotations were extremely smooth and easy in my mount - unlike my Celestron CGX mount.  It is very unsatisfying to not solve this problem.



#24 Kevin_A

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Posted 04 October 2021 - 06:29 PM

Kevin,  First of all, thanks for keeping this issue in mind and the last two posts. I was out of town and missed the previous one. I would have liked to run stand-alone PHD2 from my Mac laptop but I wasn't able to get the INDI driver. It is a moot point now since I returned the mount and B&H Photo graciously gave me a full refund. I have ordered the CEM40-NUC (no encoder this time) and will see how it works with the ASIAIR. I plan to post my results here.

 

The pdf document from iOptron is interesting. It is good to know how to operate on the mount internals. I wonder how you are able to access the "For iOptron Internal Use Only" documents and what other interesting docs they might have.  It seems like the problem there is due to "stiffness" in the axle bearing.  Both RA and DEC manual rotations were extremely smooth and easy in my mount - unlike my Celestron CGX mount.  It is very unsatisfying to not solve this problem.

If the bearings are too loose you can feel slight rocking in the dec plate when you push n pull on opposite corners or rocking on the end of the counterweight shaft…. and if bearings are too tight you feel stiction or what feels like you are turning and it is not smooth, more like rolling a plate on top of marbles. How i got this document…. A very nice guy passed it on to me! 



#25 rgsalinger

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Posted 04 October 2021 - 08:27 PM

I think that you're chasing ghostsflowerred.gif . I think that you need to look carefully at how the rig is cabled. It takes virtually no pressure at all - snagging, pushing, pulling - on just one cable to cause the guiding to go off even with the best of mounts. I think that if you clean up the cabling with a quality USB hub and some form of better power distribution then your problem with go away. It may well be a bad mount but geting clean cabling will be useful even if you get a replacement. 

 

Rgrds-Ross


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