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CGEM - Longer Counterweight bar or extra weight?

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#1 rsraney

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Posted 27 February 2011 - 04:33 PM

I'm looking to pick up an additional 7 to 11 pounds for counterweight for my CGEM and I keep seeing adds for longer counterweight bars. What is the breaking point between putting on a longer counterweight bar instead of stacking additional weights? Is there a greater advantage to leverage and while making your swing radius larger?

I currently have 37 lbs on top along with the 17 lbs counterweight under it. To be equal on top and bottom, I would need exactly 37 lbs at equal distance? I believe that would be about 9" from the polar scope?

I have the following atop the CGEM, again POOR Thing!

17 lbs - 17lb counterweight (Under it)
_2 lbs - ADM upgrade pack DUAL-CGEM-SAD and knobs
21 lbs - Orion 8" Astrograph with Orion rings
_1 lbs - ADM Guide Scope rings 120mm with LDX bar
_7 lbs - Orion 100mm guide scope. (will be exchanged for a 60mm)
_1 lbs - Meade DSI Pro on 100mm guide scope
_1 lbs - TeleVue PLU-1106 Paracorr Coma Corrector - Universal
_1 lbs - Orion StarShoot Pro V2.0 CCD
_2 lbs - Standard cables, USB x2, power to StarShoot, and heater(s)
_1 lbs - Telrad, 16 years old and still kicking

I find with the 100mm on top the the CGEM starts jumping during a mov along the RA. But when I duct taped' 10 lbs of additional weight to the existing 17lb, the CGEM seemed to be humming along contentedly.

I do plan to replace the 100mm guide scope with a small kwikguider or something half the weight. But at 7+1 lbs it's very light

Hints or Tips would be great.

#2 skybsd

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Posted 27 February 2011 - 05:04 PM

Hello,
If you're still running on a tripod, my preference would be to get an additional counterweight rather than a longer counterweight shaft.

Shorter shaft = shorter moment arm on your tripod.

Come to think of it.., I'd go this way even if it were on a pier, too.

Regards,

skybsd

#3 bbbri

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Posted 27 February 2011 - 08:35 PM

I went with the extra weight.

#4 Adam E

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Posted 27 February 2011 - 08:46 PM

I have a 6 inch extension on my CW shaft.

I have imaged with the same payload balanced with more weight closer to the mount head and with less weight farther away from the mount head. I have never found any notable difference in my mount's ability to guide and track accurately.

So, from my experience, more weight / less length or less weight / longer length is mostly a user preference sort of thing. I haven't seen any real world difference in the performance of the two different means to an end.

#5 avarakin

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Posted 27 February 2011 - 09:48 PM

I went with extension bar when I mounted 10" 40lb reflector on top of my LXD75.
I think that extension bar is a better solution because it reduces overall weight of the system thus reduces friction in bearings. As far as "moment of force" is concerned - it is the same for both options because "moment of force" of the scope to be compensated is the same no matter what.


Alex

#6 Cliff Halliwell

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Posted 27 February 2011 - 11:20 PM

The key disadvantage of a longer counter-weight bar is the increased risk of whacking your head against it! :foreheadslap: That said, when I move around my mount now my head tells me (from experience) to move like a Ninja -- very slowly -- for that reason. More seriously, although whacking a head against a counter-weight is serious, in a small observatory like a SkyPod a longer counter-weight shaft confines you even more, although the business end is the other side.

#7 avarakin

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Posted 27 February 2011 - 11:34 PM

The key disadvantage of a longer counter-weight bar is the increased risk of whacking your head against it! :foreheadslap: That said, when I move around my mount now my head tells me (from experience) to move like a Ninja -- very slowly -- for that reason. More seriously, although whacking a head against a counter-weight is serious, in a small observatory like a SkyPod a longer counter-weight shaft confines you even more, although the business end is the other side.

Never thought this would be a problem of longer CW shaft because in my case I would more worry about my foot getting hurt by the extended shaft :grin:

Alex

#8 rsraney

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Posted 28 February 2011 - 07:25 PM

After all the responses here on CN forums, and on the CGEM Yahoo mailing list, I decided to go with adding an 11 lb Orion Atlas Counter weight. I had to pop out a little plastic centering loop inside the counter weight, but it still fits smoothly on the CGEM weight bar.


1) it's much cheaper than the extra long counter weight bar from ADM.

2) For some odd reason the 6 or 10 inch extension looks like it could be a possible a shifting point. Not that I've had experience with this or similar items. I bet it's great and might even be better than adding more weight. It still just makes me twitch.

3) I live 20 minutes from an Orion Telescope store and could pick up the weight for tonight.


Thank you for all the suggestions.

#9 eric_zeiner

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Posted 01 March 2011 - 06:31 AM

Hello,
If you're still running on a tripod, my preference would be to get an additional counterweight rather than a longer counterweight shaft.

Shorter shaft = shorter moment arm on your tripod.

Come to think of it.., I'd go this way even if it were on a pier, too.

Regards,

skybsd


Exactly!






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