Subject:
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Limit Switches without using sensor inputs
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 12 Jan 2001 21:28:45 GMT
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Original-From:
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Pete Sevcik <sevcik@flash=nospam=.net>
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Perhaps the biggest problem with Mindstorms is having only 3 sensor
inputs. Using sensor inputs to control motor positioning is often a
waste of valuable resource. Industrial automation has long used the
concept of limit switches to control positioning. I think this concept
can be applied to Lego Robotics. There are many cases of hand, arm, or
steering mechanism movement that can be controlled without using an RCX
input.
The basic idea is to have a switch turn off motor power directly,
without going through a RCX sensor input. This stops to motor
mmediately, and sets the position accurately. When the RCX program
starts with known position, it can move small distances simply by
controlling the motor "on" time. Most of us have tried positioning by
"on" time, and have had limited success. The problem is that small
errors build up over many cycles of back and forth motion. A limit
switch will remove these small errors on each cycle, preventing their
buildup.
Unfortunately, the Lego sensor switch is not suitable as a limit
switch. It does not have normally closed contacts, and has too much
internal resistance. However, there are a large number of "microswitch"
style switches on the surplus market, that are very suitable as limit
switches. With some simple plastic cutting, and simple soldering, you
can build your own limit switch.
If you are interested, follow the link below for a discussion of theory,
and directions on how to build your own limit switch.
http://home.flash.net/~sevcik/limit.htm
--
Pete Sevcik sevcik@flash.net
Techno-stuff Robotics
http://www.flash.net/~sevcik/
Robotics for FUN !
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