From: "Good, Donald" 
To: "'Bodor, Murray'" , atm{at}shore.net
Reply-To: "Good, Donald" 


Does the same thing happen when you run the platform in reverse (west to
east)?  If it happens in the first 1/3 in this direction, then you may have
a platform bearing binding, or out of round or mis-aligned RA circle, or
mis-aligned support roller.  If it tracks ok for the first 2/3, as before
and then starts to labor, you may be right about the CG.

Disengage the drive roller from the RA circle (or disengage the reduction
gear from the drive roller if the drive roller is also a support roller)
and see how hard it is to push the platform from stop to stop by hand.  If
the platform strongly wants to swing back toward center, it is a CG
problem. Can you move the scope further north on the platform without
affecting its stability?  This would bring a low CG closer to the polar
axis.

If it gets hard to push in one direction only, or both directions, but will
stay when released, it is most likely one of the other mentioned problems.

-----Original Message-----
From: Bodor, Murray [mailto:bodor.murray{at}aquila.com]
Sent: Friday, January 24, 2003 12:23 PM To: atm{at}shore.net
Subject: ATM Equatorial platform - balance



Hi,

Another question for you equatorial platform experts (you were so helpful
last time!).

The platform top, north and (single) south bearings are complete, the whole
thing moves quite smoothly with very little friction. Now I am in the
process of connecting my 5V 0.9 deg stepper to a 500:1 gearbox output
to a rubber drive roller. I mounted this arrangement on a piece of .5"
x 2" x 4" plywood, and attached
a spring and turnbuckle to the end to control the tension of the roller
pressed against the sector. I
wanted to avoid making the drive roller a north support bearing. My circuit
supplies power to the half-stepped motor through a 5W resistor.

When I mount my scope on the platform, snug up the roller and run the
circuit, the platform moves
quite effortlessly for the first 2/3 of the range of motion. Then it starts
to labor, with the drive roller starting to slip. If I tighten up the
tension on the roller more, the motor begins to stall out. I suspect that
the balance is off just enough so that the motor is trying to lift the
scope in the last 4" of travel. I am at 51 degrees N. lat.

What causes this? Is it because the true COG of my scope is too far below
where the polar axis intersects? Anyone have any tricks on correcting this?

Thanks in advance,
Murray

--- BBBS/NT v4.00 MP