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Old 05-08-2021, 10:12 PM
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Stonius (Markus)
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Formula for counterweights?

I'd like to calculate how much weight I'll need to add the the back end of my Dob to counterweight my eyepieces to maintain balance.



Is there a formula for figuring out how much weight to add to one side of a see-saw with a length x and fulcrum at position y that will achieve balance?


Like, a see-saw 1m long, where the fulcrum is at, say 33.333cm and the weight on the long end is 1kg. Will it require 2kg on the shorter end to counterbalance it? 4kg? I've no idea what the mathematics are here. I'm sure some long-bearded greek guy figured it out 2,000 odd years ago, but I don't know his name or the name of the theory he invented.


Many Thanks


Markus
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Old 05-08-2021, 11:36 PM
raymo
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If the distance from the pivot point to your eyepiece is for example 1200mm,
and the counterweight[s] will be mounted for example 400mm the other side
of the pivot point, then the counterweight[s] will need to be 3x the weight of the eyepiece, because the eyepiece is 3x as far from the pivot point as the weight[s] are, and yes, simple answer to your question, 2kg. Put simply, however many times further the eyepiece is from the pivot point than the weight[s] are, is how many times heavier the weight[s] have to be.
raymo

Last edited by raymo; 05-08-2021 at 11:43 PM. Reason: more text
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Old 06-08-2021, 05:03 AM
Top_oz (Tim)
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The moments around the pivot point need to sum to zero.

A moment is the centre of mass x distance from pivot.

So 1kg x 1m clockwise - 0.5kg x 2m anticlockwise = 0 and would be static.

The sign you give to each direction is arbitrary but you must be consistent.

Where this will get tricky if you want to be super accurate is friction at the pivot(ignore it) and the COG of your various masses but you should be able to get into the ballpark fairly easily.

Last edited by Top_oz; 06-08-2021 at 05:14 AM.
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Old 06-08-2021, 05:52 AM
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mura_gadi (Steve)
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Hello,

As suggested already, it is mass X distance from the pivot points. The main thing to remember is the rough ratio, 1kg on the focuser is 6.5kg on the base sort of thing. That actual ratio is dependent on a large range of factors based on your scope.

You'll end up needing a lot of separate weights if you work it at each optical setup weight. So think about variable weight setups like a sliding weight, chains and hooks on the base etc. You should be able to mark off chains links or slide points for each ep later to make setting up easier.


Steve

Last edited by mura_gadi; 06-08-2021 at 06:12 AM.
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Old 06-08-2021, 07:15 AM
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Stonius (Markus)
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Ah, thank you so much guys! That makes total sense!


Markus
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Old 06-08-2021, 07:18 AM
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Rainmaker (Matt)
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A x B divided by C = D

A is distance in cm from pivot to focuser centreline
B is extra weight of eyepiece
C is distance in cm from pivot to where you want to attach the counterweight
( in the opposite direction )
D is weight of counterweight

P.S. Assuming that your scope already balances with at least one of your eyepieces, then you need to work on the difference of the weight of that eyepiece and the heavier ones...... but realistically a scope should not be that sensitive to changes unless you're going from a small plossl to a N31T5
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Old 06-08-2021, 09:16 AM
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RB (Andrew)
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Quote:
Originally Posted by Stonius View Post
I'm sure some long-bearded greek guy figured it out 2,000 odd years ago, but I don't know his name or the name of the theory he invented.


Many Thanks


Markus
Yes Markus (Stonius), it was my great, great, great grandfather, Andreas Studakopoulos, who figured it all out.
The name of the forumla in Greek roughly translates to-
Momentous Fulcrumanus Heavyweightous Simplicitiosus.

RB
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Old 06-08-2021, 10:12 AM
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Stonius (Markus)
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Quote:
Originally Posted by RB View Post
Yes Markus (Stonius), it was my great, great, great grandfather, Andreas Studakopoulos, who figured it all out.
The name of the forumla in Greek roughly translates to-
Momentous Fulcrumanus Heavyweightous Simplicitiosus.

RB



Ah yes, I think I've heard of him. Didn't he invent the automatic field rotator one day over a spannakopita, 1,600 years before Gallileo invented the telescope? Impressive chap. Before his time, some might say. ;-)
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Old 06-08-2021, 12:03 PM
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RB (Andrew)
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Quote:
Originally Posted by Stonius View Post
Ah yes, I think I've heard of him. Didn't he invent the automatic field rotator one day over a spannakopita, 1,600 years before Gallileo invented the telescope? Impressive chap. Before his time, some might say. ;-)
That's the one !

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Old 13-10-2021, 03:19 PM
Reilly1502 (Reilly)
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I'm actually glad I stumbled upon this thread, I was just guessing but I can actually rest assured now I was relatively close
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  #11  
Old 13-10-2021, 04:51 PM
astro744
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I use this https://www.meade.com/tube-balance-w...tml#additional

on my Lightbridge 16” in addition the the Farpoint weights. I found that when I add a Paracorr with heavy eyepieces I needed some sort of variable weight system. Works well with just one weight. I mounted it on top of the lower tube assembly and slightly on the opposit side of the eyepiece to offset any lateral out of balance that would put more weight on one altitude bearing than the other.

Last edited by astro744; 13-10-2021 at 04:58 PM. Reason: Added link.
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