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DEC going nutts

iOptron CEM70-NUC ZWO ASIAIR Plus ZWO ASI120MM Mini Guiding Troubleshooting
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enta avatar
enta avatar
Hello everyone!

I'm at a point where I run out of ideas what to do and I hope someone can help me.

My Gear:
CEM 70, ZWO everything with AsiAir, EAF, 120mm mini, ES ED 127mm

I have a journey of tracking problems behind me and it just won't stop.

So it started with ma RA going mad every like 5 minutes with peaks up to 4"
I decided to 3D balance my rig with little weights to a point where I'd say it's optimal.

I calibrated my guiding and started imaging.
At first it performed incredibly good with .25-.3" rms
Then after 10minutes DEC started to go up and down in symmetrical waves getting worse and worse until it peaked at 1.5"
I stopped and decided to do a PA again.
PA was on point with 4" error

I went to my target again, it tracked nicely for like 15 minutes and suddenly DEC started to get wavy again and didn't stop.
It's so weird to me, that it suddenly just goes south.

My Setup is very sturdy on solid ground, leveled, 3D balanced, sn cables pulling, superb seeing, no clouds, no moon, no nothing.

One thing that is weird, my mount is losing connection to the asiair every now and then, seems like a few people have this problem, new cable is on its way.
I doubt it's the cable but who knows.
I checked that everything is tight and nothing is moving, because the only thing I can think off that would start a behavior like that is something moving slightly in the DEC axes but I doubt it.

I have no idea what to try now, 4 nights of frustration and sleep deprivation.

If you have any idea what might be the issue, please let me know.

CS
Sascha
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andrea tasselli avatar
andrea tasselli avatar
I can only suggest that all is likely due to poor autoguiding parameters. I'd switch to nina if you could. Or at least use the "brain" in PHD2 and see its suggestions.
enta avatar
enta avatar
But would't paar parameters have an effect on the autoguiding right away and not after 15min.?
I heard that suggestion before tho, might spend a night with my laptop and try with nina to see if it corrects the error.
Frédéric Ruciak avatar
Frédéric Ruciak avatar
Hi, 
have you checked that the RA and DEC axis are smooth,without any binding even soft one on 360 or at least 180°? This could trigger something like the mount slowing down and then the autoguiding is sending pulses to compensate but the mount passes the binding point and overshoots. Just an hypothesis
Frédéric
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Brian Puhl avatar
Brian Puhl avatar
I would rule out bad gear mesh first.   It sounds to me like your declination gear is rolling over a tooth and having a hard time doing it because it's not meshed properly.    Remember, RA gear is constantly turning.  DEC gear only turns to correct.   The more accurate your PA is, the less often you will see it.

I dealt with it on my EQ6, and it was a very fine line between where the gear was too tight and too loose.
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Andreas Zeinert avatar
Andreas Zeinert avatar
If you use PhD2 try to reduce agressivity on Dec correction and move to switch resist to avoid overcorrection. I had a similar problem and this fixed it. Of course other origins of the issue are possible. It is also useful to calibrate on a target around zero declination.
enta avatar
enta avatar
Brian Puhl:
I would rule out bad gear mesh first.   It sounds to me like your declination gear is rolling over a tooth and having a hard time doing it because it's not meshed properly.    Remember, RA gear is constantly turning.  DEC gear only turns to correct.   The more accurate your PA is, the less often you will see it.

I dealt with it on my EQ6, and it was a very fine line between where the gear was too tight and too loose.

Hi Brian, I had those RA problems and tightended the mesh a little, it's a possibility, I will losen it a little next time I have CS.
Thank you.
Andreas Zeinert:
If you use PhD2 try to reduce agressivity on Dec correction and move to switch resist to avoid overcorrection. I had a similar problem and this fixed it. Of course other origins of the issue are possible. It is also useful to calibrate on a target around zero declination.

I will try that as well, had different varieties of agressivness, didn't seem to do much for dec, but it had great impact on ra.
enta avatar
enta avatar
Guys, I finally found the bug.
After weeks of pain and suffering my setup is finally guiding properly!
In the End it turns out it was the shitty ZWO standard cable.
I replaced it with a high quality one and suddenly it guides like a champ.

It guides so good I'm actually sceptical about the whole thing, hope it's not just a fluke.
Anyway, I had 2 nights of expectionally good guiding and I couldn't be happier.



tbh this is as good as it gets , but even overall it barely goes over .3"
Worst case scenario it goes a little over .5"
Over the whole night my tracking had an average of .34" which is more than good enough for my setup.

Thanks for your help and suggestions.

CS
Sascha
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Nick Grundy avatar
Nick Grundy avatar
Sascha, I had a similar gremlin with my CEM70 awhile back. I would get very strange/large oscillations in DEC that didn't seem to correlate to anything. I ended up shipping the mount to Ioptron support to have them go through. They did some testing and ended up finding a loose axle that needed some fine adjustment. It did cost to ship the mount, but the work itself was under warranty. It's back to .5" rms nightly now. 

Hoping yours is fixed, but let me know if you see it again and I can share my notes

CS
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