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CEM25P problem with DEC movement

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45 replies to this topic

#1 niccoc1603

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Posted 25 January 2019 - 07:08 PM

I have received the mount in December and only used a couple of times, never hit or rocked the DEC saddle while the worm gear was engaged.

 

Now suddenly I have DEC motor hanging when slewing south
 

The problem only happens in this position.
I can't notice any damage on the saddle teeth.

 

I uploaded a few videos here

https://drive.google...vEXMRPv_upJ4Gyr

 

Any ideas?

 

Thanks



#2 petert913

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Posted 25 January 2019 - 08:32 PM

I have no answers for you, but as an iOptron mount owner, I must say I am concerned by all the reports of issues with their

whole line of go-to mounts.   I am starting to regret moving away from my trusty AVX.


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#3 gotak

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Posted 25 January 2019 - 08:47 PM

Plenty of avx issues too like dead motor boards etc.

How did you set your the tension knobs? All the way in or do you have it backed off a bit?

From the video I would suggest you see what the grease and ring in that area looks like. Could be something simple like a foreign object on the ring gear.

Edited by gotak, 25 January 2019 - 08:49 PM.


#4 rkinnett

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Posted 25 January 2019 - 08:49 PM

@petert913, I've had no end of problems with my zeq25 as well.

 

Are you balancing your OTA precisely?  If it's not well balanced then you might be overloading the stepper motors, in which case the motors would skip steps without sounding overstressed.  I don't know if or how the cem25 detects and reacts to the motors skipping; the mount might not report it at all.  If your belts were slipping then you would definitely notice the extra noise.

 

It could also be a low voltage problem.  Try to find a bigger (higher amp rating) 12V supply or battery.

 

Edit: watched the videos; you're right, seems to be a function of output position, but the worm gear teeth look clean, so either imbalanced or a problem with the worm itself.  Maybe try realigning the worm:  https://www.youtube....nuGQNYS8&t=709s


Edited by rkinnett, 25 January 2019 - 09:00 PM.


#5 SteveInNZ

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Posted 25 January 2019 - 09:23 PM

The noise is the stepper motor dropping out (the stepper equivalent of a stall) and when it's occurring is typical of that you'll see with an unbalanced mount. If the tension knob is a bit too tight, it becomes more susceptible to imbalance as it's using more torque to overcome the worm friction, leaving less to cope with the imbalance.
The noise isn't causing any harm but the mount doesn't know that it didn't move as far as it commanded, so it's now lost it's star alignment.

 

If you loosen the clutches and unlock the mount and move the OTA to the position that the noise occured, you'll probably find that it won't stay there. You need to rebalance so that the OTA will stay in any position with the mount unlocked. If you want to have an easterly bias, balance it first and then add a known imbalance.

 

Steve.



#6 niccoc1603

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Posted 26 January 2019 - 12:50 AM

Unbalanced mount was my first thought. So I remove the OTA entirely, and you can see from one of the video that the stall happens even with nothing on the saddle, but still at the same position

#7 niccoc1603

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Posted 28 January 2019 - 12:33 AM

Just for the record, I was able to solve the issue.

A while back iOptron provided a procedure to tension DEC motor belt that greatly reduced backlash.

Apparently the tensioning also applied too much pressure on the gear when the worm was engaged and caused the motor to stall at a certain position during DEC rotation.

Also, since the belt tensioning moved the motor a bit outward, the motor body was pushing a bit on the plastic cover and this caused further pressure to be applied on the gear.

I did the followings:
- 3D printed a new cover that leaves enough room for the motor body
- loosened the tension screw 1/2 turn when the worm is engaged

the motor does not stall anymore.

I made a PHD2 calibration test to check if backlash is still under control and it was positive

Thanks to iOptron support very quick and effective
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#8 tkottary

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Posted 28 January 2019 - 01:50 AM

I have issues with DEC on my CEM25p too. Does not stall like yours but there is little to no movement on south. Dither on dec never settles, PHD2 GA says large backlash. 

Tried the procedure listed  in PDF, hopefully it fixes some issues.(waiting for clouds to clear )



#9 Gvs

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Posted 28 January 2019 - 04:06 AM

Can't say about the CEM25. Though on the IEQ30, experienced a similar issue. After opening the DEC casing, the end cap off the servo in question had slipped and it caused the problem. Once properly fitted, everything worked like a charm.

#10 SteveInNZ

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Posted 30 January 2019 - 04:04 AM

Thanks for reporting back with your solution.

 

Steve.



#11 tkottary

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Posted 06 February 2019 - 01:39 PM

So I was able to test last night ; no improvements in dec! Also noticed after the worm is engaged and tension screw is tightened ,(released1/4 turn) I can still move the dec head slightly like a play. Is that expected?

#12 OldManSky

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Posted 06 February 2019 - 02:22 PM

No, that's not expected.  If you tighten the tension screw a bit more, does the play go away?  And if the play goes away, does that improve the dec action?

I only back mine off of "full tight" about 1/8 turn.  That results in little/no backlash in DEC, smooth motions in both RA/DEC, and quiet operation.



#13 tkottary

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Posted 06 February 2019 - 03:04 PM

No even with the fully tightened  knob, there is some slight play with dec head. There was no change in backlash  it still remained as is. I guess have to send this back for inspection.

 

I bought this used from CN, so hopefully they will respect the warranty?



#14 OldManSky

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Posted 06 February 2019 - 04:10 PM

It sounds like some adjustment may be necessary to get the DEC axis fully engaged.  Or it could possibly be something more...

Have you tried the "tuning" outlined in the video linked in rkinnett's message above?



#15 tkottary

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Posted 06 February 2019 - 04:40 PM

Sort of . Removed the dec saddle , shaft . Loosened the motor and tightened it back. I’ll add a video later.
Sorry OP didn’t mean to hijack your thread

#16 niccoc1603

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Posted 09 February 2019 - 03:22 AM

What is your measured backlash?

#17 tkottary

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Posted 09 February 2019 - 11:08 AM

It was whopping 2870ms last time I ran GA.  I am curious to know how much time it takes to settle in DEC.  iOptron sent me another detailed PDF to try but I am not positive its going to help. 



#18 Gvs

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Posted 10 February 2019 - 09:17 PM

What's the total weight with out the mount and counterweights?



#19 tkottary

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Posted 11 February 2019 - 02:46 AM

it is this setup, less than 6.9lb 

ZWO Machine

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#20 Gvs

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Posted 11 February 2019 - 05:17 AM

Backlash seems excessive for that payload.

You must have some component in the drive that is not properly secured.

With an 8" SCT + guider + cameras total weight of ~18lbs, backlash on an IEQ30 didn't exceed 1/4 of what you have.

Keep in mind, IEQ30 uses servos not steppers. CEM models use stepper motors, so the behavior is different.

Edited by Gvs, 11 February 2019 - 05:22 AM.


#21 daw316

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Posted 11 February 2019 - 09:37 AM

I have CEM25 which was a factory conversion of my ZEQ25.  I also have a lot of Dec "slop".  Could you share the iOptron pdf? 

 

Thanks!

 

>>It was whopping 2870ms last time I ran GA. 

>>I am curious to know how much time it takes to settle in DEC. 

>>iOptron sent me another detailed PDF to try

>>but I am not positive its going to help.



#22 StarMike8SE

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Posted 11 February 2019 - 10:17 AM

Yes, I would like to see the PDFs as well.  Mine will guide good for a while then I will get these big jumps on the guiding graph which seems like something needs adjustment



#23 tkottary

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Posted 11 February 2019 - 11:44 AM

This is what tech support responded:

 

If you are handy enough, you may remove the worm bracket and check if the worm or hinge is over tightened.

http://www.ioptron.c...Instruction.pdf



#24 StarMike8SE

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Posted 11 February 2019 - 01:49 PM

That is odd, those are the instructions to convert a zeq25 to a cem25



#25 tkottary

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Posted 11 February 2019 - 02:35 PM

Yes, basically they are asking to me dismantle and see if there are any obvious issues with the hardware.




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