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iOptron CEM40 - strange guiding fault

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Notice that each instance of "going crazy" corresponds to a moment when the guide star snr crashes to zero. My guess? Clouds (or tree branches, etc).
1 year 9 months ago #83425

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Hmmm. I just looked more closely at the first screenshot. There are obviously stars, and the guider is locked on, yet the Guide SNR is reported as zero.

That's really weird. But I think it points in the direction of a software problem, not a mount problem.
1 year 9 months ago #83426

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I actually do remember SNR going to zero and back (like #3 in my second picture) in the last couple of months or so.
But I do not remember which mount was it. Stopping/restarting guiding did help as far as I remember.
It's either software or cables, I guess.
-- Max S
ZWO AM5. RST-135. AZ-GTI. HEQ5. iOptron SkyTracker.
TPO RC6. FRA400. Rokinon 135 and other lenses.
ZWO ASI2600MC. D5500 modified with UVIR clip-in filter.
ZWO ASI120MM Mini x 2. ZWO 30F4 guider. Orion 50mm guider.
ZWO EAF x 2.
1 year 9 months ago #83427

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I looked through my analyze logs.
I had those SNR down to zero oscillations in the end of April when I was at a dark site with an RST-135 mount.
It was extremely windy then. So it's similar but not relevant since the night in question was quiet and clear (clouds appeared at 00:40).

I looked at the guiding history of my CEM40 (which I started to use on May 19).

I started to use it in my front yard with cables from RST-135.
The guiding was perfect for three nights.
Before the fourth night I fed a USB3 cable through-the-mount and tested it again in my yard - the guiding was great.
I used a thick generic USB3 cable.

So I thought everything was fine and moved CEM40 to the permanent location on my garage roof to replace the HEQ5.
Used the HEQ5 set of cables this time. Fed a flat ZWO USB3 cable through-the-mount.

First two nights at the permanent location the guiding was great.
Next two nights the DEC would occasionally run away pretty badly.
The third night (two nights ago) I tidied up cables and didn't have DEC run-aways any more but started to have these strange DEC/RA oscillations after dither.

So, I suspect that the USB3 cable which is fed through the mount is causing some resistance/pull and is causing problems.

Removed that cable. Will route the cable outside the mount and test when the weather is good.
Oh, boy... I hate what IOptron did with the "G" version of the mount...
Useless iGuider. Not usable trough-the-mount cable management.
-- Max S
ZWO AM5. RST-135. AZ-GTI. HEQ5. iOptron SkyTracker.
TPO RC6. FRA400. Rokinon 135 and other lenses.
ZWO ASI2600MC. D5500 modified with UVIR clip-in filter.
ZWO ASI120MM Mini x 2. ZWO 30F4 guider. Orion 50mm guider.
ZWO EAF x 2.
Last edit: 1 year 9 months ago by maxthebuilder.
1 year 9 months ago #83428

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Hey Max,

I had the mount out last night but did not notice any "crazy" oscillations like you experienced. Very windy but still managed sub arc 0.7 arc sec guiding. The only problems I had were from the failure to park after polar aligning. Pressing "go to home" returned the mount to the park position but I think it seems that one needs to tell EKOS that it is parked by setting the parking in "site management tab" otherwise it cannot calculate and perform an automated flip it seems. So just another thing to remember to do. It would be nice if the mount parked after doing PA though :).
Due to the extraordinary cloudy weather over the last few months this is the first time I have been able to get the mount under the skies. Hope it lasts!

Cheers
1 year 9 months ago #83448

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So, I removed the flat ZWO USB3 cable from the through-the-mount channel and routed it outside the mount.
Aesthetically it doesn't look bad at all.

Testing the setup right now.
Guess what? Everything is going great.
Meridian flip went smoothly.
Guiding is better than ever. And it's getting better as it gets darker. (10:40pm right now).
Just a more or less flat line without any run-aways or oscillations. Around 0.5" RMS total.
Cloudless and quiet night. But the Moon is there. Bortle 8.

So, that flat but still thick/stiff USB3 cable was making too much disturbance in the through-the-mount channel.
Problem solved. Shame on iOptron. The through-the-mount cable management worked a generation ago.
Finally my CEM40 is working well. Hope it will stay this way.

-- Max S
ZWO AM5. RST-135. AZ-GTI. HEQ5. iOptron SkyTracker.
TPO RC6. FRA400. Rokinon 135 and other lenses.
ZWO ASI2600MC. D5500 modified with UVIR clip-in filter.
ZWO ASI120MM Mini x 2. ZWO 30F4 guider. Orion 50mm guider.
ZWO EAF x 2.
Last edit: 1 year 9 months ago by maxthebuilder.
1 year 9 months ago #83464
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Hey Max,

Guess what. I have just had the crazy oscillations that you reported. The mount was guiding fine up to the meridian flip. The mount flipped as expected then automatically re-aligned, re-focused and re-calibrated the guiding. All this appeared to go OK. The first image was taken then after the first dither the oscillations in RA stated. This eventually responded to reducing aggression in RA in the guiding options and reducing prediction ratio to 0.1 (from 0.5). This settled it down but then after the next dither it started up again so I tried reducing the max adjustment down to 0.1 from the default. This seemed to help but the next dither off it went again albeit less dramatic. Eventually I changed to one pulse dither and this seemed to stop it. Maybe it was unable to reach the set dither after the flip so the one pulse does not have a set target dither amount. I didn't have time to explore if setting all the other changes back to how they were would make a difference but I will try next time. I might leave one pulse dither on from now on though. If your oscillations occur again try just changing to one pulse dither as it seemed to have the greatest effect of all the changes that I made. Out of interest I have also noted that the SEP focus algorithm does not seem to detect any stars so I have reverted to gradient. Have you noticed anything similar?

Cheers
1 year 9 months ago #83495

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Do you have a screenshot (or log) to share? "Crazy oscillations" could have many different causes. Max's were quite specific - for some reason (maybe usb related?) the guide algorithm lost the ability to lock onto the star (SNR went to zero).
1 year 9 months ago #83537

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Hi Ron,Thanks for the interest. Unfortuanately I did not take any screen shots and the weather has closed in again. I have attached the guiding logs. Everything was fine until the meridian flip which on the logs is line 2145. The guider did a recalibration but at the next dither it takes much longer to complete the dither. The oscillation were in RA mainly. During this period I was making on the fly changes to RA aggression and predictive components. The next few dither had a similar prolonged adjustment period then the settling to normal post dither behaviour coincided with the change to one pulse dither. After which I ran out of time. I dont remember any issues with loss of SNR etc but the guiding log is the only log I have. I will need a bit more time to explore if this behaviour repeats.
Cheers
Mike

File Attachment:

File Name: guide_log-...2-08.txt
File Size:196 KB
1 year 9 months ago #83552
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I had several sessions since that weird guiding experience (and I had some other strange guiding issues).
Everything was working fine without any issues.
As I mentioned before my problem was related to a USB3 cable fed through the mount.
Once I removed that cable and routed it outside the mount all guiding problems that I had disappeared.
With no clouds and no wind I get around 0.5" RMS total which is pretty good in my books.
-- Max S
ZWO AM5. RST-135. AZ-GTI. HEQ5. iOptron SkyTracker.
TPO RC6. FRA400. Rokinon 135 and other lenses.
ZWO ASI2600MC. D5500 modified with UVIR clip-in filter.
ZWO ASI120MM Mini x 2. ZWO 30F4 guider. Orion 50mm guider.
ZWO EAF x 2.
1 year 9 months ago #83558

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Hi Mike,

It looks to me like that 2nd calibration failed in some way. The mount appears to have not moved at all during the first West step and it winds up thinking that the RA only moves at 1.7 arcsec/second. So, when it sends a correction to the RA that correction is way larger than really necessary. So it overshoots, then overcorrects in the other direction and you are off to the races.

Why the new calibration after the flip? Are you using ST4 for guiding?
1 year 9 months ago #83571

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Hi Ron,
Thanks for looking at the log. Your analysis is very valuable. I am guiding with ASI120 using a OAG via the mount not ST4.
I have always recalibrated after a flip but have never had this oscillation issue afterwards. I don't want to over-react about this as it has only happened on the one night. I will just monitor the situation once the weather improves and I can get out under clear skies. It may be just a one off issue related to the failed calibration. I was not monitoring the re-calibration in real time but I will when I retest. If it appears to be a persistent issue I will start another thread as it now appears different to Max's problem.
Cheers,

Mike
Last edit: 1 year 9 months ago by Spartacus. Reason: Extra info
1 year 9 months ago #83577

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