Re: [ATM] How to find Centre of Gravity of an existing telescope

[dave w <daze39@earthlink.net>]

Bruce MacDonald wrote:

> Thanks, Dave,
> The base/tube assembly balances side-to-side and front-back quite
> nicely just about exactly on the centre of the azimuth bearing, so
> that much I know.  The centre of the az bearing is just about exactly
> the centre of the OTA when the tube is vertical, and the tube
> more-or-less balances unless I add an extremely heavy eyepiece.  I've
> never had the need to use weight to balance the tube.
> 
> So in two planes, I'm fine -- the balance piont is known, and in the
> correctl place.
> 
> What I'm having difficulty with is how high above the ground is the
> centre of mass.  I'm fairly certain that it is well below the altitude
> axis, since the base is much heavier than the tube, and the tube sits
> quite high on the base.
> 
> 
> Years ago, in high school physics -- or maybe even in university, we
> had to find the CoG of an irregular mass by suspending it from a
> ringstand by various points, and plotting the vertical lines.  I can't
> see myself hanging my precious telescope from the ceiling!


You could try something like the following, which should have the same effect
(no strings attached)...

Find a flat panel about as large as the base of the mount - something like a
sturdy piece of plywood, light enough that it weighs much less than the scope
but stiff enough to resist flexing. Place the scope on this with a piece of 2"x2"
lumber under the front edge of its mount, so the whole scope is tilted back
just a bit relative to the plywood, and find the balance point with a rod
underneath as I described before. Mark (or note) the position of the vertical
line from the position of the rod up the side of the scope with the whole
business balanced level.

Now do the same thing with the 2x2 under the back of the mount, so the scope
is tilted forward a bit, and again note the position of the vertical line.

The height at which the two lines intersect should be the vertical position
of the center of gravity.

-dave w


_______________________________________________
ATM mailing list http://www.atmlist.net/