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Counterbalanced mounts and Payload Capacity

Astrophotography Beginner Equipment Mount
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#1 unbreakable goose

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Posted 03 December 2021 - 09:32 PM

Hi all, I have a bit of a theory based question that I am just curious about.

If a mount is perfectly counterbalanced on all its axis, then there is no net torque on any of the mounts axis i.e I think any perfectly counterbalanced mount should have an effective payload of 0 kg.

So from this understanding, any mount should have no max payload capacity, provided it is perfectly balanced.

This however is not the case, as all mounts do have a payload capacity.


Where is the gap in my understanding of the physics/Operation of the mount?

Thanks for your time!
Clear skies!

#2 sellsea

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Posted 03 December 2021 - 09:44 PM

There is bending stress and flexure in the counterweight shaft.  A setup that requires heavy weights needs a larger diameter shaft so that the shaft does not flex elastically.  The bearings in the RA shaft have their limits for smooth operation without wearing.


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#3 junomike

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Posted 03 December 2021 - 09:52 PM

The work (motor) require to stop/start 10lbs at each end (20lbs total) is a lot less then what's required to start stop 30lbs at each end (60lbs total).

 

Inertia and momentum can be  motor killers if over-worked.


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#4 mrlovt

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Posted 03 December 2021 - 09:52 PM

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#5 unbreakable goose

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Posted 03 December 2021 - 10:17 PM

There is bending stress and flexure in the counterweight shaft.  A setup that requires heavy weights needs a larger diameter shaft so that the shaft does not flex elastically.  The bearings in the RA shaft have their limits for smooth operation without wearing.


I didn't think about the mechanical stress on the mount itself

Thanks for the response!

#6 unbreakable goose

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Posted 03 December 2021 - 10:19 PM

The work (motor) require to stop/start 10lbs at each end (20lbs total) is a lot less then what's required to start stop 30lbs at each end (60lbs total).
 
Inertia and momentum can be  motor killers if over-worked.


I suspected it was related to the intertia, but wasnt 100% sure

Thank you!


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