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iOptron CEM40 - strange guiding fault

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  • Thank you received: 69
Hello,
I am new to iOptron mounts.
Acquired an CEM40G just over two weeks ago.
Used/tested it for 5-6 nights.
It works great on average but gives me surprises now and then which I never had with my HEQ5.

I am shooting with it right now. The guiding is pretty good at about 0.5" RMS total.
However, just randomly after a dither, both RA and DEC would go into some wild oscillations.
This happened two times over one hour. I never in three years saw such a behavior with my other mounts.

I stopped/restarted guiding and it was good again.
Any thoughts?
Thanks!
Max S.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
Last edit: 3 months 2 weeks ago by maxthebuilder.
3 months 2 weeks ago #83407
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Hi
I have the CEM40G and have never seen this behaviour but I have heard that PEC can interefere and can lead to problems. Just check that you have PEC turned off.

Cheers
iOptron CEM40G, SharpStar CF90IIApo with Moonlight focuser, ASI294MCpro, ASI120MM-S, DIY MyFocuserPro2, RPi4 8Gb 480SSD running KStars/Ekos/Indi under Ubuntu Mate 22.04, DIY flat box
Skywatcher Flextube 12" Dob, Meade LX75 8SCT, Skywatcher NEQ6Pro

3 months 2 weeks ago #83413

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I have PEC disabled in CEM40 driver.
I do use GPG in the guider settings.
Max S.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
3 months 2 weeks ago #83421

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Hey Max,

I might be able to get my scope out tonite as the weather is starting to clear after months of cloudy skies. So I should be able to see if I get the same problem. A few months ago the CEM40 driver was causing connection problems but a change to the V3 driver sorted things. I thought that V3 was the same but go figure :). I'll let you know how it goes.
Cheers
Mike
iOptron CEM40G, SharpStar CF90IIApo with Moonlight focuser, ASI294MCpro, ASI120MM-S, DIY MyFocuserPro2, RPi4 8Gb 480SSD running KStars/Ekos/Indi under Ubuntu Mate 22.04, DIY flat box
Skywatcher Flextube 12" Dob, Meade LX75 8SCT, Skywatcher NEQ6Pro

3 months 2 weeks ago #83422

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I used the mount 6-7 nights so far.
Last night was the only night I saw this behavior.
But this happened four times in three hours...

Max S.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
Last edit: 3 months 2 weeks ago by maxthebuilder.
3 months 2 weeks ago #83424
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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).
3 months 2 weeks 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.
3 months 2 weeks 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.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
3 months 2 weeks 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.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
Last edit: 3 months 2 weeks ago by maxthebuilder.
3 months 2 weeks 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
iOptron CEM40G, SharpStar CF90IIApo with Moonlight focuser, ASI294MCpro, ASI120MM-S, DIY MyFocuserPro2, RPi4 8Gb 480SSD running KStars/Ekos/Indi under Ubuntu Mate 22.04, DIY flat box
Skywatcher Flextube 12" Dob, Meade LX75 8SCT, Skywatcher NEQ6Pro

3 months 2 weeks 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.

RPI 4 B (4Gb) with SMate
Askar FRA400, TPO RC6, Nikon D5500 full spectrum (with IDAS D1 clip-in filter).
ASI2600MC Pro
ZWO ASI120MM Mini on ZWO 30F4
ZWO ASI224MC-S on Orion 50 mm f/3.2
ZWO EAF x 2
SW AZ-GTi
SW HEQ5
RST-135
iOptron CEM40G
Last edit: 3 months 2 weeks ago by maxthebuilder.
3 months 2 weeks 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
iOptron CEM40G, SharpStar CF90IIApo with Moonlight focuser, ASI294MCpro, ASI120MM-S, DIY MyFocuserPro2, RPi4 8Gb 480SSD running KStars/Ekos/Indi under Ubuntu Mate 22.04, DIY flat box
Skywatcher Flextube 12" Dob, Meade LX75 8SCT, Skywatcher NEQ6Pro

3 months 2 weeks ago #83495

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