Balancing a GEM that's not level

[W. eWatson]

My GEM has gotten a little cranky recently, and I thought I'd check the
balance. Dec is just fine anywhere. I balanced the RA on the east side,
and it was just fine, then checked it on the west. It was not steady.
Looking at the RA axis from north, I'd move the weight arm to about 4
o'clock. It would rotate down to 6 o'clock in 5-6 seconds. I don't see
an serious imbalance from equipment mounted on the OTA. The only item
that's not aligned the N=S position of the OTA is a view finder. I doubt
it weighs more than one pound. Possibly this is a leveling problem?
Comments?

[William Hamblen]

Leveling the tripod would have no effect on balance.

To balance a telescope you have to get the center of gravity of the
moving parts at the intersection of the polar axis and the declination
axis. Weights offset from the center of the telescope that can't be
balanced by moving the telescope back and forth will drive you nuts.

Bud

[W. eWatson]

Definitely. Perfection is not possible.

However, it seems to me the specific problem described would contribute
to the imbalance in the case cited, or be a major players. Gears and
motors would likely rule the day to make it work, if it's not a major
imbalance.

[Chris.B]

On Sep 2, 2:48 am, "W. eWatson" <wolftra...@invalid.com> wrote:
> On 9/1/2010 2:05 PM, William Hamblen wrote:
>
> > On Wed, 01 Sep 2010 10:22:26 -0700, "W. eWatson"

> > <wolftra...@invalid.com>  wrote:

What weight arm?

Did you rotate the OTA between balance tests? Radial balance of a
*rotatable* OTA is highly desirable. Even if it only means that you
occasionally rotate the tube in its rings accidentally on set-up. Or
do so routinely to make the eyepiece position more comfortable/
accessible. A small weight (or weights) attached to the tube on the
*opposite side* to the focuser and/or finder, will help to
counterbalance the out-of-balance moments around the OTA axis and
thence to the RA axis. Since the attached weight(s) are permanent the
OTA need only be balanced once. i.e. Longitudinally when setting up
from scratch. Later OTA rotation should no longer affect RA balance.
If you look at the problem from a very simplistic point of view:
Rotation of the OTA *at present* is like sliding small counterweights
up and down a shaft fixed at right angles to the RA shaft. If you do
not rotate your OTA then burn this message. ;-)

[W. eWatson]

It's not a portable system. It sits on a fixed pad. I haven't changed
the OTA position in years.