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Equipment Discussions >> Mounts

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zombie1210
sage


Reged: 12/26/09

CGEM counterweight question *DELETED*
      #5220678 - 05/13/12 06:04 PM

Thanks guys

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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM counterweight question new [Re: zombie1210]
      #5220721 - 05/13/12 06:32 PM

Hi!
Congrats on the new mount!
Personally i would use also a second one even if i could balance with the 1st one at the very edge of the shaft.I would preffer to keep the counterweights closer to the axis so to keep the lever smaller.It could help in case of wind if you have vibrations.
Just my thought.


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zombie1210
sage


Reged: 12/26/09

Re: CGEM counterweight question new [Re: Mike X.]
      #5220746 - 05/13/12 06:50 PM

I'm thinking I will get an additional 11 pounder.

Is there a "formula" for how much weight? Like 75% of the weight of the scope, or something like that?


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gmartin02
scholastic sledgehammer
*****

Reged: 04/11/05

Loc: Santa Clarita, CA
Re: CGEM counterweight question new [Re: Mike X.]
      #5220881 - 05/13/12 08:24 PM

Quote:

Hi!
Congrats on the new mount!
Personally i would use also a second one even if i could balance with the 1st one at the very edge of the shaft.I would preffer to keep the counterweights closer to the axis so to keep the lever smaller.It could help in case of wind if you have vibrations.
Just my thought.



I actually find the reverse to be true - I use a longer counter weight shaft (from Criterion Machine Co) - even though it is longer, the moment is the same, and I do not experience any increased vibration problems with wind or at the end of slews.

The advantage of a longer counter weight bar is that you can put less overall weight on the mount, which is always better (as long as it does not increase vibration). My fully loaded rig, which consists of a Orion 110ED mounted on an ADM side by side saddle with an Orion ST120 used as the guide scope only requires 18.5 pounds of counterweights (11 lb CG-5 weight + 7.5 lb Sky View Pro weight - both fit the CGEM counter weight bar).

I do not recommend putting extra weight on the bar just to keep the weights closer to the RA axis. This will add unnecessary vertical load on the mount (and RA bearings) which will degrade performance.

I did extensive experimentation with short & long counter weight bars with a C11 on my CG5 (AS-GT) mount with different weight configurations (don't try this at home kids - definitely overloaded but functional). With the shorter counter weight bar, I needed 33 pounds of counter weights to balance the C11. With the longer counter weight bar I only needed 18.5 pounds of counter weights to balance the scope. With the longer bar & less weight, the motors were noticeably quieter and the damping time at the end of slews actually decreased vs. the stock arrangement.

I don't know how much weight you will need with your Meade 10", but I am guessing an extra 11 lb should do it with the stock weight & bar. Hopefully someone else here has tried it.

Good luck,
Greg


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RTLR 12
Post Laureate
*****

Reged: 12/04/08

Loc: The Great Pacific NorthWest
Re: CGEM counterweight question new [Re: zombie1210]
      #5220924 - 05/13/12 09:07 PM

Here's a site that will help you...

Stan

http://www.robincasady.com/Astro/WeightCalc.html


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zombie1210
sage


Reged: 12/26/09

Re: CGEM counterweight question new [Re: gmartin02]
      #5220936 - 05/13/12 09:15 PM

Quote:

Quote:

Hi!
Congrats on the new mount!
Personally i would use also a second one even if i could balance with the 1st one at the very edge of the shaft.I would preffer to keep the counterweights closer to the axis so to keep the lever smaller.It could help in case of wind if you have vibrations.
Just my thought.



I actually find the reverse to be true - I use a longer counter weight shaft (from Criterion Machine Co) - even though it is longer, the moment is the same, and I do not experience any increased vibration problems with wind or at the end of slews.

The advantage of a longer counter weight bar is that you can put less overall weight on the mount, which is always better (as long as it does not increase vibration). My fully loaded rig, which consists of a Orion 110ED mounted on an ADM side by side saddle with an Orion ST120 used as the guide scope only requires 18.5 pounds of counterweights (11 lb CG-5 weight + 7.5 lb Sky View Pro weight - both fit the CGEM counter weight bar).

I do not recommend putting extra weight on the bar just to keep the weights closer to the RA axis. This will add unnecessary vertical load on the mount (and RA bearings) which will degrade performance.

I did extensive experimentation with short & long counter weight bars with a C11 on my CG5 (AS-GT) mount with different weight configurations (don't try this at home kids - definitely overloaded but functional). With the shorter counter weight bar, I needed 33 pounds of counter weights to balance the C11. With the longer counter weight bar I only needed 18.5 pounds of counter weights to balance the scope. With the longer bar & less weight, the motors were noticeably quieter and the damping time at the end of slews actually decreased vs. the stock arrangement.

I don't know how much weight you will need with your Meade 10", but I am guessing an extra 11 lb should do it with the stock weight & bar. Hopefully someone else here has tried it.

Good luck,
Greg




I will probably show my lack of physics knowledge here, but doesn't moving the weight further away, on a longer shaft, still make the same "effective" weight? Sort of like moving forward or backward on a teeter totter?

I don't see how it would have any effect on the motors if the effective weight is the same.


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Stew57
Carpal Tunnel
*****

Reged: 05/03/09

Loc: Silsbee Texas
Re: CGEM counterweight question new [Re: zombie1210]
      #5221049 - 05/13/12 10:37 PM

the advantage to me is total weight on the tripod. the CGEM tripod is already a weak link.

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gmartin02
scholastic sledgehammer
*****

Reged: 04/11/05

Loc: Santa Clarita, CA
Re: CGEM counterweight question new [Re: zombie1210]
      #5221253 - 05/14/12 01:57 AM

Quote:

I will probably show my lack of physics knowledge here, but doesn't moving the weight further away, on a longer shaft, still make the same "effective" weight? Sort of like moving forward or backward on a teeter totter?

I don't see how it would have any effect on the motors if the effective weight is the same.




You are correct about the effective weight around the RA axis (angular mass, or more correctly the moment of inertia around the axis of rotation), so in an environment without gravity everything would be equal.

Since there is gravity where we use our mounts, the downward force of gravity is a second force that affects the mounts rotational movement. This force is "pushing down" on the bearings of both the RA and Dec axes, putting both radial and axial load on the bearings, depending on the orientation of the axes at any given point in time.

Radial & axial load can be conceptualized by thinking about a wheel bearing on an automobile wheel. The radial load is the weight of the car pushing down on the bearing, and the axial load is the sideways (thrust) force on the bearing when the car goes around a corner.

Putting more weight on the counterweight shaft doesn't increase the load on the Dec axis, but it does increase the load on the RA axis. Radial load is generally a more significant factor than axial (thrust) load because a radial load is not pushing on all of the bearings with the same force - at any given moment in time more of the radial load force is acting on the single bottommost bearing.
Even though bearings are rated for a certain weight, putting more weight on the bearings will decrease their performance. They probably won't wear out any faster, but more load means the bearings have to work harder even though the moment of inertia around the axis of rotation is the same.

Additionally, some people (like Mark) like to increase the load on the tripod to make it more stable, but putting more weight on the counterweight bar is not the right way to do this - the advantage gained by putting more load on the tripod is offset by the increased load on the bearings. The correct way to do this is to hang a weight from the center support underneath the EQ head, or even better, to improve the bracing on the legs, like using something like the TPIAstro leg braces, or a pier (portable or permanent).

Greg


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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM counterweight question new [Re: gmartin02]
      #5221354 - 05/14/12 06:39 AM

Quote:

Quote:

Hi!
Congrats on the new mount!
Personally i would use also a second one even if i could balance with the 1st one at the very edge of the shaft.I would preffer to keep the counterweights closer to the axis so to keep the lever smaller.It could help in case of wind if you have vibrations.
Just my thought.



I actually find the reverse to be true - I use a longer counter weight shaft (from Criterion Machine Co) - even though it is longer, the moment is the same, and I do not experience any increased vibration problems with wind or at the end of slews.

The advantage of a longer counter weight bar is that you can put less overall weight on the mount, which is always better (as long as it does not increase vibration). My fully loaded rig, which consists of a Orion 110ED mounted on an ADM side by side saddle with an Orion ST120 used as the guide scope only requires 18.5 pounds of counterweights (11 lb CG-5 weight + 7.5 lb Sky View Pro weight - both fit the CGEM counter weight bar).

I do not recommend putting extra weight on the bar just to keep the weights closer to the RA axis. This will add unnecessary vertical load on the mount (and RA bearings) which will degrade performance.

I did extensive experimentation with short & long counter weight bars with a C11 on my CG5 (AS-GT) mount with different weight configurations (don't try this at home kids - definitely overloaded but functional). With the shorter counter weight bar, I needed 33 pounds of counter weights to balance the C11. With the longer counter weight bar I only needed 18.5 pounds of counter weights to balance the scope. With the longer bar & less weight, the motors were noticeably quieter and the damping time at the end of slews actually decreased vs. the stock arrangement.

I don't know how much weight you will need with your Meade 10", but I am guessing an extra 11 lb should do it with the stock weight & bar. Hopefully someone else here has tried it.

Good luck,
Greg




Mine was just a thought and personal prefference.I'm complettely open to any suggestions and ideas!
I just thought that having a shorter lever and the mass concentrated near the axis would produce the same desired effect as the force applied would be identical to the force applied if the mass would be further away to the shaft...but less susceptible to external factors that could produce vibrations.

Maybe i am mistaken but..if the setup is well balanced the force needed by the motors to move the axis is minimal.
In theory..as the load is not supported by the motors...using 2 counterweights or 1 counterweight to balance the scope should not change anything...right?

I do understand your point about vertical load...and i must say i dont find it wrong at all.
I'm just thinking that...if the mount is rated for an X amount of load excluding counterweights...i guess the parts that support the total load (OTAs and Counterweights) should be designed to support X+X(counterweights)...virtually with no problems..no?(specially if we keep the total load under the max one as we tend to do in AP)

Edited by Mike X. (05/14/12 06:41 AM)


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EFT
Vendor - Deep Space Products
*****

Reged: 05/07/07

Loc: Phoenix, AZ
Re: CGEM counterweight question new [Re: zombie1210]
      #5221684 - 05/14/12 11:11 AM

You will probably need more than one counterwieght. However, keep in mind that you can use counterwieghts from the CG5, LXD55/75 and many Vixen mounts on the CGEM. They are usually lighter than the standard CGEM counterwieght but they can be obtained used for much less (if you don't already have some around).

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gmartin02
scholastic sledgehammer
*****

Reged: 04/11/05

Loc: Santa Clarita, CA
Re: CGEM counterweight question new [Re: EFT]
      #5221800 - 05/14/12 12:18 PM

Hi Mike,

The motors wont be working harder in either case, but in the case of the heavier counter weight load closer to the RA axis, you are still putting more force on the bearings, decreasing their performance. Even though a mount has a particular load rating, it will perform better with less load. Again, for radial loads, a significant amount of the weight is born by the bottommost single bearing at any point in time (or by the 2 bottommost bearings when down is in between 2 bearings). That's a lot of weight on that one tiny little bearing.

This of course assumes that there is not a vibration problem.

I think the best thing to do is to experiment, which is what I did with my CG5 as I said above. I got better performance with less weight and the longer counter weight bar. You could try it both ways - use your single weight farther out, and 2 weights closer in. Listen for the motor noise during full speed slews and see if there is a damping time difference at the end of slews and while focusing with a high power eyepiece in both cases. Also look for vibration in both cases - hey, you could even set up a fan on high blowing on the counterweight shaft and see if the vibration is different in either case.

Final thought - for visual observing in your case it probably won't matter either way, because you are still under the mounts rated capacity, but remember one thing about Celestron mounts: they don't conservatively rate the load capacity of the mount like some of the "premium" mount manufacturers do, so you don't even want to get close to the mounts rated capacity - lower weight is always batter (assuming no vibration.)

Some time in the future I may try to generate PE test curves with PEMPro for a long light counterweight config vs a short heavy counterweight config to see what the results are, but not this weekend - I am going eclipse watching in Nevada

Greg


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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGEM counterweight question new [Re: gmartin02]
      #5221890 - 05/14/12 01:07 PM

Hello Greg, thank you for the input regarding the counterweight near the axis!I'll keep it in mind!
Yes..i rigured that out about the stated load as soon as i started photography a few years ago
I keep it around 24-25 lbs with the cg5..usually less if i have windy night.The focal lentghs i sually shoot are between 500 and 945mm.No more than that...and at 945mm i must admit i preffer an off axis guider to reduce weight.
Thanks again for the suggestions!


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mrlovt
member
*****

Reged: 09/08/12

Loc: Smyrna, TN
Re: CGEM counterweight question new [Re: gmartin02]
      #5565049 - 12/10/12 10:50 PM

Quote:


Some time in the future I may try to generate PE test curves with PEMPro for a long light counterweight config vs a short heavy counterweight config to see what the results are, but not this weekend - I am going eclipse watching in Nevada

Greg



I would love to see the results of some real testing on these configurations with a loaded CGEM, especially as they relate to AP guiding and mechanical wear. I may pick up an extension and compare, but someone with more experience (Greg ;-) could sort things out more efficiently!

I'm running a 10" LX200 with finder and guidescope on the CGEM's stock short shaft. My concern with extending the counterweight shaft has been vibration. I'm less concerned about a breeze than about dampening from gotos, focusing, etc.

Even more important: stress on the mount! If the bearing acts as a fulcrum, then force on the bearing would be the same in either configuration (short lever, heavy weight <vs> long lever, light weight). Wouldn't the same be true for the gears? Total weight on the tripod is another story, but as I said, my primary concern is identifying the configuration that provides the least stress on the mount.

OK Greg, we're awaiting your results!

~~Aaron


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