Newsgroups: comp.robotics
Path: cantaloupe.srv.cs.cmu.edu!das-news2.harvard.edu!news2.near.net!howland.reston.ans.net!ix.netcom.com!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: Ideas for position sensors?
Message-ID: <nagleD3Lyu6.ur@netcom.com>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <3h5sc4$353@pith.uoregon.edu>
Date: Tue, 7 Feb 1995 02:27:42 GMT
Lines: 28

ben@chinook.uoregon.edu (Ben Marcotte) writes:
>Our lab has been working on Miniboard based robots and we're now at the 
>point where we'ld like to add some position sensors so we can get some 
>feedback on what the real effect a motor operation has had.  However, our 
>system is supposed to model a biological system and as such has the 
>following contrains:
>	1) Sensors must be analog.
>		This also means no stepper motors!
>	2) Must have small amount of inertia/physical resistance when 
>		changing position.
>	3) Must have a low or zero spring constant.  (i.e. turning the 
>motor off should not cause the structure to return to, or start to 
>return to, it's original position).

     LVDT transducers are good, although they seem to cost more than
they should.  

     If you can't afford LVDTs, consider something using a variable density
filter and an LED-detector pair.  Look at page 131 of Digi-Key catalog
951 for the Quality Technologies interrupter modules. These are $1.75
each.  Use one whose detector can be operated in its linear range.
Make a circular variable density filter by printing a suitable dot
pattern on paper, photographing it, and making a black-and-white slide of it.
Mount the slide film on a plastic disk, fit a shaft, and you're in business.

					John Nagle

					John Nagle
