Re: ATM Center of gravity of semicircular elevation bearings

["Albert Highe" <ahighe@ix.netcom.com>]

Tom,

I've been thinking about this post. Its not clear to me that the solution
for this problem is to offset the bearings. The elevation bearings will
rotate the mass around the axis defined by the centers of the two bearing
circles. If the mass of the scope is centered on this axis, there is no
off-balanced mass from the scope. No problem. However, as you point out, if
the bearings are semicircles, then the center of mass of the bearings is not
centered on the rotation axis. If the bearings are offset so their COG
coincides with the COG of the OTA, then the COG of the total scope +
bearings is offset from the axis of rotation. This would seem to be worse
than the starting location. Since the COG of semicircular bearings is not on
the axis of rotation, I don't see how offsetting the bearings can help At
best, offsetting the bearings will allow the OTA + bearings to be balanced
at only one elevation.

In practice, I would guess that the bearings weigh much less than the scope.
Is this really a problem? If so, the only solution I see is to make the
bearings as light as possible or to add mass to compensate for the missing
half of the bearing circles.

Albert

----- Original Message -----
From: Tom & Lou Krajci <krajcit@3lefties.com>
To: <scope-drive@egroups.com>; <atm@shore.net>
Sent: Sunday, August 13, 2000 1:12 PM
Subject: ATM Center of gravity of semicircular elevation bearings


>
> I've recently been doing some math to figure out the location of the
center
> of gravity of semicircular elevation bearings (assuming the are solid, no
> cutouts, etc.).  Since my integral calculus is not what it used to be, I
> approximated the solution in a spreadsheet, slicing up the bearing's shape
> into 100 narrow strips to approximate the circle.
>
> I ended up with this answer:  the C/G is located at approximately 42.5% of
> the radius.  Does this sound about right?
>
> This piece of info is helpful to those wanting to precisely balance their
> design of a motorized big dob that moves on sheet metal and roller
bearings.
> (If you move on teflon and formica you can ignore this extra math/analysis
> in your balance calculations.)
>
> Tom Krajci
>
>