Subject: Rotator analysis
From: "Shawn Callahan" <[email-masked]>
To: "'Morag Hastie'" <[email-masked]>, <[email-masked]>, <[email-masked]>, "'John Glaspey'" <[email-masked]>, "'Ricardo Ortiz'" <[email-masked]>, <[email-masked]>
Cc: "'Faith Vilas'" <[email-masked]>, "'Dusty Clark'" <[email-masked]>, <[email-masked]>
Date: Mon, 14 May 2007 17:24:46 -0700

A full model of the rotator shows the 850 lbs Maestro counterweight is just
not heavy enough to damage the MMT rotator bearing in normal operation. I
ran several models  with a variety of ever more abusive loading of the
rotator. The full report is attached and is also in SiteScape.
 
I finally ended up applying the full 850 lbs to a 33-inch "JT-wrench". This
simulates the entire weight of the counterweight being applied to a single
bolt in the rotator flange. Even in this extreme case the margin of safety
(the ratio of the bearing yield strength to the maximum stress) is around
50. The material of the outer race directly under the wrench still had a
margin of safety greater than 10. The impressive strength of the bearing is
due to the large size and  use of VERY strong steels.
 
I  then looked at the stripping strength of the 3/4" tapped holes in the
instrument rotator flange. Each of these bolts can easily hold over 40,000
lbs.
 
Dusty says the friction damping of the bearing is high enough that the
weight of MAESTRO and counterwieght will not affect the rotator servo.
 
However, while I was on the MAESTRO tour I saw the roll-over fixture.This
fixture uses two 4" diameter pivots. Be sure to put down a plate under the
fixture before rolling the instrument. Without the plate the 2500 lbs weight
of the instrument (?) causes a shear stress in the plywood floor of 240 psi.
This is right at the shear limit of the floor plywood in the direction of
the plies. 
 
Be safe all,
 
Shawn Callahan
System Engineering Coordinator
MMT Observatory
520-621-7649 Office
520-954-6619 Cell
"When you have learned what an explanation really is you can then go on to
more subtle questions." Richard Feynman