[alma-config]Re: transporter

[David Woody]

It appears to me that a large emphasis for the
transporter design has been to avoid driving
over the pads.  This leads to a very challenging
design problem.  It looks like the pistons
in the design concept I saw will have forces
in excess of one million pounds when lifting
the antenna off the pad or out of the back
of the transporter.  Lateral stability also 
looks problematic at the peak of the lifting
stroke.  

Large numbers of ganged wheels
work well for distributing loads on flat paved
roads, but it is difficult to build a suspension
system that does a good job of distributing 
the load on kinds of roads ALMA is likely
to have.  A lot of construction and maintenance
costs can be saved if the transporter can
use less than perfect roads, if only at
slow speeds.

I thought driving over the pads was explicitly
part of the pad design specifications.

A cantilevered lifting vehicle will actually
exert about four times more local ground force 
than a vehicle that surrounds the antenna
and drives over the pad.  It is the local
ground pressure that dictates the number and
size of the tires and the road bed design near the 
pads.  All existing reconfigurable arrays 
I am aware of have transporters that drive
over, or at least straddle, the pads.  This
has not caused any problems that I am 
aware of.  

********************************************
| David Woody                                   
| Assistant Director of Instrumentation 
| Owens Valley Radio Observatory     
| Caltech                                              
| P.O. Box 968, Big Pine, CA 93513   
| phone 760-938-2075ext111             
| dwoody at ovro.caltech.edu              
********************************************
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