Newsgroups: comp.robotics
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From: lynwood@csn.org (Lynwood H. Wilson)
Subject: Positioning w/DC motors
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Date: Fri, 19 Aug 1994 02:17:10 GMT
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I'm looking for advice on using DC motors with encoders to position
a heavy object in several axes.  The straightforward approach seems to
be to use servos or steppers, but I am investigating the idea of using
cheaper motors and computing power instead.  The device already has a
computer that won't be doing anything during the positioning.  The 
mechanical part of the job is shaping up nicely, and position sensing
doesn't seem too hard.  The object weighs several hundred pounds, and 
must be positioned within about 0.001 inch.  The problem as I (naively)
see it seems to come down to how small an increment of rotation can I
reliably get from a 1/4 hp (or so) motor.  Can't gear it down too far
'cause I need to move fairly fast in another part of the cycle.
I'd appreciate some advice from anyone with experience in this area,
even if it's a recommendation to forget it.
Thanks very much,
Lynwood Wilson
lynwood@csn.org
P.S. It strikes me that I am unduly restricting the question.  What I
really want to know is this:  Given computer power and the positioning
problem, how can I save money on the hardware cost of the device by
spending on the software, spend up front to reduce the unit cost of
the device?
Thanks
Lynwood

