From: "Mel Bartels" 
To: 
Reply-To: "Mel Bartels" 


from http://astro.tsuniv.edu/eng_t13_fea.html

>>>
We considered both friction-coupled wheels and steel-cable-coupled capstan
drives. The latter reduce somewhat the problems of contact forces in the
drive system, and we and our lead consultant from Tenn Tech visited
Sagebrush Technology in Albuquerque, a company that makes such drives, on
Sept. 19, 1996. We eventually decided to use friction coupled wheels
because cable drives stiff enough for our telescope would have been
inconveniently large. We also decided to use Compumotor AC servo motors to
drive the axes, specifically DM1015B's, which cost about $5200 each. The
moderate peak torque delivered by these units (11 lb-ft) make it easier to
control contact forces in the drive (700 lbs per drive cylinder), but we
will consequently use six of these motors, two for altitude and four for
azimuth. The minimum number of motors would be three in any case, one for
altitude and two for azimuth separated by 180 degrees to avoid a so-called
palm-tree instability (Bruce Truax-private communication).
<<<

Anyone know what palm-tree instability is?

Mel Bartels

--- BBBS/NT v4.01 Flag-4