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Balancing Ioptron CEM: per axis or with both axis free?

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#1 meegja

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Posted 11 July 2020 - 03:35 AM

Yes, another question ;)

I have the Ioptron CEM25EC mount. And for balancing an Ioptron CEM mount I see/read that it is done for each axis separate: first balancing DEC, lock it, then balance RA axis.

But I am used to check the balance with both axis free: when moving the RA axis from one end to the other (so 180 degrees), the DEC axis should stay (almost) stable on it's own axis, constantly pointing in the same direction as where the counterweight is.

And when the movement of the RA axis is stopped (in any position), it should stay in that position and the DEC axis in it's position.

For me this is logical: the whole system is in balance, no matter the positions and the strain on the motors is also balanced. But when each axis is balanced separate, there is no "real" balance: when the RA axis is moving, the DEC will become more unbalanced when the RA axis angle increases and the strain on the motor will also increase because of that.

And that is no theory: I tried separate balancing per axis and then, when moving by hand with both axis free, indeed the DEC will go out of balance then when the RA axis is moving.

 

So, am I crazy? Is there something I am missing?



#2 PaulE54

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Posted 11 July 2020 - 06:45 AM

I have a CEM40. I've not tried it "one axis at a time".

 

I unlock both axes, and balance so that whatever position I have in RA and Dec, the scope stays pointing wherever I point it at.

Moving the scope in RA should not cause any movement in Dec. And vice versa. 

 

So I agree with your approach and your logic. 

 

Paul



#3 OldManSky

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Posted 11 July 2020 - 10:37 AM

You can do it either way.  The thing is, when actually trying to move things (DEC attachment plate or RA counterweight), it can be very awkward to do if both axes are spinning freely.  So the idea of starting with one axis free and the other locked, so that you can more easily move the things that need to be moved, makes sense in that light.

You can then unlock both axes, and move it freely, to check the balance.


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#4 meegja

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Posted 11 July 2020 - 10:57 AM

I have a CEM40. I've not tried it "one axis at a time".

 

I unlock both axes, and balance so that whatever position I have in RA and Dec, the scope stays pointing wherever I point it at.

Moving the scope in RA should not cause any movement in Dec. And vice versa. 

 

So I agree with your approach and your logic. 

 

Paul

Good to hear :) And yes, it's indeed logic.

 

You can do it either way.  The thing is, when actually trying to move things (DEC attachment plate or RA counterweight), it can be very awkward to do if both axes are spinning freely.  So the idea of starting with one axis free and the other locked, so that you can more easily move the things that need to be moved, makes sense in that light.

You can then unlock both axes, and move it freely, to check the balance.

Yes, that's what I do: I do a pre-balance per axis and then both unlocked. The RA-axis is 8 out of 10 times fine then already, so it's a matter of checking the balance with both axis unlocked, lock them, adjust scope on DEC, unlock both, balance, and so on.

In my case it helps that I have a short scope plus I am a tall guy, so lots of arm length to hold things :)

I am just a but surprised that in every video or description, only the balance per axis is mentioned and not the real balance of the whole set-up.



#5 Jarno

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Posted 11 July 2020 - 11:33 AM

The secret to successful analysis of a problem is to reduce it to as little variables as possible, preferably one. In your case the problem is "What's the perfectly balanced position of my scope?" so I would definitely do it per axis. If scope and counterweight are in perfect balance they should remain so regardless of DEC axis rotation and the same applies for the scopes front-rear balance. If balance changes with rotation then there's an off-center mass somewhere: finder scope, focuser with heavy eyepiece, etc. Thankfully, perfect balance isn't always desirable. If the mount has to work against a slight imbalance that takes the slack out of the gears so they're constantly engaged. I wouldn't worry about a slight imbalance.

 

Jarno


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#6 meegja

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Posted 11 July 2020 - 02:21 PM

The secret to successful analysis of a problem is to reduce it to as little variables as possible, preferably one. In your case the problem is "What's the perfectly balanced position of my scope?" so I would definitely do it per axis. If scope and counterweight are in perfect balance they should remain so regardless of DEC axis rotation and the same applies for the scopes front-rear balance. If balance changes with rotation then there's an off-center mass somewhere: finder scope, focuser with heavy eyepiece, etc. Thankfully, perfect balance isn't always desirable. If the mount has to work against a slight imbalance that takes the slack out of the gears so they're constantly engaged. I wouldn't worry about a slight imbalance.

 

Jarno

Slight imbalance doesn't bother me :) And yes, indeed a bit of tension on the gears here too.
It was really just the question of why only per axis balancing is mentioned in articles and videos and not a complete set-up balance check. It's just the small trouble of checking balance with both axis disengaged. For me it's a bit of a contradiction that that isn't checked but at the same time going banana's over something like cable management :)



#7 Jarno

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Posted 11 July 2020 - 05:36 PM

It's just the small trouble of checking balance with both axis disengaged. For me it's a bit of a contradiction that that isn't checked but at the same time going banana's over something like cable management smile.gif

 

Probably for the same reason why I still level my tripod before polar-aligning: it's not really necessary but it's a lot easier if adjustments in one axis don't affect the other axis. I do one direction at a time but afterwards I do check balance with both axis free. But if you really like a challenge, try balancing a side-by-side setup in all directions at once... grin.gif

 

Jarno


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#8 meegja

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Posted 11 July 2020 - 06:46 PM

Probably for the same reason why I still level my tripod before polar-aligning: it's not really necessary but it's a lot easier if adjustments in one axis don't affect the other axis. I do one direction at a time but afterwards I do check balance with both axis free. But if you really like a challenge, try balancing a side-by-side setup in all directions at once... grin.gif

 

Jarno

Mmmm, I think that I kindly decline that offer :)




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