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Mount gears barking when starting/stopping

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#1 Arringar

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Posted 12 June 2019 - 10:05 PM

I'll keep this short, mount brand and model probably do not matter much in this case because most are designed much the same; worm and worm wheel.  But what are the potential causes for a mount's gears to bark when starting and stopping (mostly stopping in this case)?  And moreover, what can be done to correct it?



#2 Jerome Ni

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Posted 12 June 2019 - 10:15 PM

If the sound is merely a bit louder than slewing, then it is expected, as least for Atlas/Sirius kind of mount.

 

And I think mount model does matter here as different mount has different designs(i.e. gearboxes vs belts etc.), and this abnormal behavior can mean different things to different mounts.

 

Try slewing the mount 360 degrees in both directions for both axis. If you also hear abnormal/uneven sounds during this, it is likely that the worm is too tight...


Edited by Jerome Ni, 12 June 2019 - 10:20 PM.


#3 Arringar

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Posted 12 June 2019 - 11:34 PM

The mount is a CEM60. It is in fact a bit louder than slewing as you said. The mount hasn’t always done this. It has been used gently, never stressed or overloaded. The gear meshing is just right, not too loose or too tight (which is really easy to tell with these mounts). If it is loosened to the point of being a tiny bit sloppy the barking sound stops but that’s not surprising.

I’m going to regrease the worm and wheel with some Aeroshell 64 (33ms) and see if there is any improvement. It only happens on the dec axis gear, the RA is perfectly normal.

#4 Der_Pit

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Posted 13 June 2019 - 09:04 AM

Ha, reading the subject I suspected the CEM already...  because mine also has that slightly different sound at start and end of slewing.  You can change/eliminate it by changing the gear meshing, but then usually (for me) it's to tight for proper slewing the full range....

The mount is brand new, so no experience regarding changes over time (so far).



#5 WadeH237

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Posted 13 June 2019 - 09:55 AM

I'll keep this short, mount brand and model probably do not matter much in this case because most are designed much the same; worm and worm wheel.  But what are the potential causes for a mount's gears to bark when starting and stopping (mostly stopping in this case)?  And moreover, what can be done to correct it?

Mount brand and model actually matter a whole lot in this case.

 

Even before reading your subsequent posts, I suspected that you have a CEM60.  I was chatting with the owner of an astronomy shop just a couple of days ago about all kinds of mounts.  When we were talking about the CEM60 and its clutch arrangement, he said that if the adjustment is off a little, it will make a sound like you've described.

 

Since I've never actually used a CEM60, I won't make any suggestions for doing the adjustment (I'm sure that other people will do so, now that we know that you have a CEM60).  I will say that I think that it's harmless.



#6 Der_Pit

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Posted 13 June 2019 - 10:10 AM

Well, the usual explanation for the noise is the stepper motor getting 'stuck' (not having enough torque to move), which leads to loss of steps and, as a consequence, pointing errors.

 

I cannot tell if during ramp-up for slewing it does loose steps, or whether it is a different cause (it could also be resonant oscillations of something when the stepper sweeps through the respective frequency band).

 

I'm quite sloppy with pointing model anyhow, rellying on plate solving for final positioning, so I didn't feel the need so far to investigate it further.

The good thing in any case is that noise from stepper being stuck / losing steps does not cause any harm :D



#7 555aaa

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Posted 13 June 2019 - 10:41 AM

There is a resonant mode in worm wheels (the large gear) that is pretty easy to excite and it will make a loud whining sound.
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#8 Spikey131

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Posted 13 June 2019 - 11:05 AM

Mine only make noise when out of balance 



#9 Arringar

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Posted 14 June 2019 - 02:31 AM

Well, the usual explanation for the noise is the stepper motor getting 'stuck' (not having enough torque to move), which leads to loss of steps and, as a consequence, pointing errors.

 

I cannot tell if during ramp-up for slewing it does loose steps, or whether it is a different cause (it could also be resonant oscillations of something when the stepper sweeps through the respective frequency band).

 

I'm quite sloppy with pointing model anyhow, rellying on plate solving for final positioning, so I didn't feel the need so far to investigate it further.

The good thing in any case is that noise from stepper being stuck / losing steps does not cause any harm laugh.gif

 

I appreciate everyone's helpful feedback.  This was very enlightening and has given me some ideas of things to try.  It is merely a mild annoyance, it causes no actual issues and the mount tracks very well.  I consistently get ~0.40-"0.55" total tracking error, so I can't complain about it too much, I just don't like to hear it.




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