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From: rick@ameristar (Rick Spanbauer)
Newsgroups: comp.robotics,comp.lsi,sci.electronics
Subject: Re: velocity sensing for robotic joints
Message-ID: <1990Aug9.224721.5683@ameristar>
Date: 9 Aug 90 22:47:21 GMT
References: <1990Aug7.205751.21206@ecf.utoronto.ca> <19481@well.sf.ca.us>
Organization: Ameristar Technology, Inc
Lines: 16

In article <19481@well.sf.ca.us> nagle@well.sf.ca.us (John Nagle) writes:
>Remember to use an enclosed variable capacitor with a grounded, conductive
>case, so that the readings aren't affected by nearby moving conductive
>objects.
>					John Nagle

John, I've got a couple of noisy var caps in my antenna tuner I would like to 
introduce you to ;-).   The mechanical coupling to the variable element
seems to have worn, resulting in noise when the shaft is rotated.

Anyways, using capacitance to close the loop seems a reasonable solution.  
Check out the July 1990 Issue of Sky & Telescope for an application that 
uses a differential capacitative measurement to control the mirror in the
Keck telescope.  Neat idea!

					Rick Spanbauer