Newsgroups: comp.robotics
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From: heinz@focus-systems.on.ca (Heinz Wolter)
Subject: Re: Using a pot for position feedback -- good idea?
Message-ID: <D36yzG.Fx5@focus-systems.on.ca>
Organization: Focus Automation Systems Inc.
References: <3g63cg$b0v@nntp.Stanford.EDU> <1995Jan26.165643.164433@zeus.aix.calpoly.edu>
Date: Mon, 30 Jan 1995 00:06:51 GMT
Lines: 22

In article <1995Jan26.165643.164433@zeus.aix.calpoly.edu> csheel@harp.aix.calpoly.edu (Catherine Anne Sheel) writes:
>In article <3g63cg$b0v@nntp.Stanford.EDU> Andrew Huibers <andy@risk.stanford.edu> writes:
>>
>>I want to be able to accurately set a rotary position over about 1
>>turn... since I need high torque (can't use a stepper) I was thinking
>
>
>Sounds like a perfect application for an optical encoder.  With a quadrature
>encoder driver, you can get 512 count resolution from a 128 line encoder.
>If it's a really good 128 line encoder, you can even get 512 count accuracy.

Don't throw away that stepper motor! You can use it as a cheap encoder!
Ok, not a great encoder, but a cheap, sturdy one. A 200 step stepper
will give you quadrature out at 50 steps/rev. Just put some load resisors
and zener limiters on the "outputs" and feed it to some schmidtt triggers...
voila, instant poor man's encoder. Or you could try for some surplus encoders..
Unless the pot is of good quality, you may have noise. You will certainly
have wear and tear. Pot's are commonly used on most RC servo units for feed
back.

heinz

