RE: ATM Equatorial platform - balance

["Bodor, Murray" <bodor.murray@aquila.com>]

That did the trick..moving the box south by about 3 inches makes the platform much easier to move.
 
I just put some pictures of it up at: http://www3.telus.net/muz/astronomy/platform.html
 
Thanks for the advice
Murray
 
 

	-----Original Message----- 
	From: Nils Olof Carlin [mailto:nilsolof.carlin@telia.com] 
	Sent: Sat 2003-01-25 3:26 AM 
	To: atm@shore.net 
	Cc: 
	Subject: Re: ATM Equatorial platform - balance
	
	



	Bodor, Murray asked:
	
	> 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?
	
	If you disconnect the roller, and move the platform by hand through
	the intended range, you should get an idea of how the balancing is, or
	if there is some other cause of friction. You can try move the rocker
	box a bit south to see if this improves the balance - there ought to
	be some position where the whole assembly balances, even if you must
	lengthen the platform top to accommodate it.
	
	Nils Olof