Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!agate!library.ucla.edu!news.ucdavis.edu!bunsen!nelsonk
From: nelsonk@bunsen.cs.ucdavis.edu (Karl Nelson)
Subject: Re: Shaft encoders for DC gearmotors (micromouse)
Message-ID: <CLK8M8.24F@ucdavis.edu>
Summary: rebutal against mounting encoders out of loop
Keywords: shaft encoders, DC motors, micromouse
Sender: usenet@ucdavis.edu (News Guru)
Organization: University of California, Davis
X-Newsreader: TIN [version 1.2 PL1]
Date: Mon, 21 Feb 1994 05:58:55 GMT
Lines: 23

Tony Campbell wrote that he felt the best approach of mounting the
shaft encoders was on a seperate wheel to avoid slipping.  This may
help prevent measurement errors resulting from the slippage of the
drive wheels.  However, this comes at a major danger.  If the drive
wheels slip or skip the shaft encoder will not read any information
about the speed of the wheel.  As a result the shaft encoders will be
worthless for controlling the DC motor!  Without a accurate reading
the feedback loop will probably "blow up" and send the wheel to either
max or min speed.  When the wheel catches the mouse will go spiralling
into a wall!  Furthermore if there is more than one motor being
controlled, the extra wheel will not be at the same place as the drive
wheel so it will get a combination of both wheels.  This is bad
because the information is dificult to seperate and it dependance
changes with turning.  Therefore, it is better to mount shaft encoders
on wheel shaft (or somewhere in the drive assembly) for control.
Another wheel may be added as Tony suggested for distance measurement,
if wheel slip is a big concern.  But that really is just an added
complexity.

  --- Karl Nelson
      UC Davis Engineering student


