Cem40: RA jumps around in 5-7 mins - Forums

Topic starter

Sep 2, 2021

I started having this issue where it seems the mount jumps a bit every 5-7 minutes. It happens quite consistently. I can see that in my auto guider view, the stars move at the same time I see a jump in RA error. I use ASIAIR for my captures, guiding etc.

I have started having this problem very recently with ioptron cem40 ever since I upgraded my telescope. The lighter one (WO GT71) never had this problem. The newer scope is 12 lbs and I use two counterweights. It is still well within the weight limit (stated at 40 lbs). My total weight should be less than 20-22 lbs.

I use ZWO OAG for auto guiding. Checked for cable snags, etc and everything is in order. I use a 2” ZWO filter wheel and a ASI1600mm pro camera. My guide cam is ASI174mm mini.

I am wondering if there are any known issues with cem40 that become more evident with heavier load.

any suggestions, experiences welcome 😊

Engaging

Björn Arnold

Sep 2, 2021

Hi Kapil,

I‘m running my CEM40 with a similar load than you do and don’t believe to have the issue you mention. Although, if you could be a bit more specific on the issue that would help:
By 5-7 minutes, do you mean it happens regularly but sometimes after 5 and sometimes after 7 minutes or do you *estimate* the periodicity to be within the interval of 5-7 minutes?

Do you have a guide graph so we could see how it looks?

The CEM40 has a worm period of 400 seconds and it might be that the worm gear is causing it. When I am guiding with PHD2 I have seen sometimes some more sudden RA changes but nothing I would call a jump. The PPEC algorithm for RA does wonders on this to compensate the worm irregularities.
I wouldn’t simply recommend turning this on before you have made sure that the gear is fine.

There’s a series of possible causes and I would recommend some test to narrow it down:
Does it appear if you go back to the lighter gear?
Does it appear on a specific pointing direction?

Björn

Helpful Insightful Respectful Engaging

Sean McCully

Sep 2, 2021

I have seen a problem like this with the EC version of my CEM60, iOptron recommended cleaning the encoder it worked like a charm. I would contact iOptron, they probably can tell you exactly what is wrong.

That said, Its possible somethings is maybe wrong with the RA Gear tension or possibly something in the Worm Gear causing a problem.

Concise Supportive

Kapil K.

Topic starter

Sep 2, 2021

Björn Arnold:
Hi Kapil,

I‘m running my CEM40 with a similar load than you do and don’t believe to have the issue you mention. Although, if you could be a bit more specific on the issue that would help:
By 5-7 minutes, do you mean it happens regularly but sometimes after 5 and sometimes after 7 minutes or do you *estimate* the periodicity to be within the interval of 5-7 minutes?

Do you have a guide graph so we could see how it looks?

The CEM40 has a worm period of 400 seconds and it might be that the worm gear is causing it. When I am guiding with PHD2 I have seen sometimes some more sudden RA changes but nothing I would call a jump. The PPEC algorithm for RA does wonders on this to compensate the worm irregularities.
I wouldn’t simply recommend turning this on before you have made sure that the gear is fine.

There’s a series of possible causes and I would recommend some test to narrow it down:
Does it appear if you go back to the lighter gear?
Does it appear on a specific pointing direction?

Björn

Hi Bjorn, thanks for your reply. I think 400 s sounds just about right. I don’t have a guide graph as ASIAIR used phd2, but I don’t see where I can access the graph. It occurs every single time. It also doesn’t seem to be direction related. I tried 3 targets and each had the issue. Just that I never saw this issue with my lighter scope mounted. I have been working with this scope for 6+ months and it so far has worked like a charm. This issue though is pretty annoying and pretty much renders it useless for exposure beyond a couple mins.

Kapil K.

Topic starter

Sep 2, 2021

Sean McCully:
I have seen a problem like this with the EC version of my CEM60, iOptron recommended cleaning the encoder it worked like a charm. I would contact iOptron, they probably can tell you exactly what is wrong.

That said, Its possible somethings is maybe wrong with the RA Gear tension or possibly something in the Worm Gear causing a problem.

Thanks Sean. How do you clean the encoder? Is it a mechanical thing or a setting somewhere?

Well Written Respectful

Björn Arnold

Sep 2, 2021

Hi Kapil,

Do you actually have the CEM40 with Encoder? The standard version just runs with its steppers without any position feedback.

I don't know anything about the ASIAIR. Usually PHD2 does create a log for each instance that's started. This can be viewed with tools like phd2logviewer. Maybe you can access the file storage on the ASIAIR?

If there is really a sudden jerk on the axis it might be the worm spring tension or the worm has either dirt or some damage. However, before to worry one should analyze more carefully what's going on.

Björn

Helpful Concise

Sean McCully

Sep 2, 2021

Do you have the Encoder version? iOptron can provide a PDF on how to clean, but you dab a cotton tip in alcohol and gently run across the encoder. If you dont have the Encoder, or even if you do its worthwhile to check the RA gear tension and Worm Gear for debris.

Concise Supportive

AstroLion

Sep 2, 2021

The ASIAir creates a PHD2 Guide Log file. You can find it in the folder named "log" along with the Autorun Log file. The PHD2 guide log file is a text file and can be read when the standard phdlogbiew application.

Concise

Kapil K.

Topic starter

Sep 2, 2021 · Edited: Sep 2, 2021

Thanks folks. I don’t have the encoder version (I suspect that is appended by EC). Mine is the regular cem40. I will check the phd2 log based on @AstroLion’s suggestion.

SemiPro

IOTD Staff

Sep 2, 2021

This definitely sounds like a mechanical issue within the gear system. It probably managed to say hidden when the payload was smaller, or perhaps it was the bigger payload that finally broke the camels back so to speak. It's like a car ya know? One day you try to start it up and something is just wrong after being fine for so long. If it's not too spooky for you, I'd open 'er up and take a look.

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