Newsgroups: comp.robotics
Path: brunix!news.Brown.EDU!agate!howland.reston.ans.net!europa.eng.gtefsd.com!library.ucla.edu!news.ucdavis.edu!judy.ucdavis.edu!ez007738
From: ez007738@judy.ucdavis.edu (tawen mei)
Subject: Re: Shaft encoders for DC gearmotors (micromouse)
Message-ID: <CLFqEB.y5@ucdavis.edu>
Sender: usenet@ucdavis.edu (News Guru)
Organization: University of California, Davis
X-Newsreader: TIN [version 1.2 PL2]
References: <2jqrgs$3sp@zip.eecs.umich.edu> <1994Feb16.182911.9623@feline.uucp> <2jvtq7$a12@bigboote.WPI.EDU>
Date: Fri, 18 Feb 1994 19:34:59 GMT
Lines: 45

Tony L. Campbell (campbell@bigwpi.WPI.EDU) wrote:
: In article <1994Feb16.182911.9623@feline.uucp>,
: Kelly Gray <gray@feline.uucp> wrote:
: >I'm working on building a micromouse myself, and have found an excellent
: >source of small optical encoders for position sensing. Find an old, dead
: >mouse, and use the encoders from that. The mouse I have has two encoders,
: >mounted on a shaft with a small roller. I plan to mount the encoders on
: >the micromouse so that the roller rides on the top of one of the drive 
: >wheels. This should give me a very accurate measurement of the movement
: >that that wheel has made.
: >
: >It shouldn't be too difficult to mount the encoders so that they can sense
: >the movement of a motor. If nothing else, mount them so that the roller
: >rides against one of the gears.
: >-- 
: >
: ><o_o>    Kelly Gray
: >         gray@feline.uucp (preferred)
: >         gray@admin.humberc.on.ca

: I'm yet another micromouse builder, and I'm not sure you'd want to
: mount the encoders to the drive wheels.  Drive wheels are more prone
: to slipping due to the driving forces.  Coupling the shaft encoders 
: to these wheels may cause your corrupt the accuracy of these measurements.

: A strategy considered by my group puts the shaft encoders on separate
: wheels that do nothing but sense position.  As these wheels do nothing
: but roll with the mouse, their chance to slip is less.  I know of at
: least two other mice that use this idea, but since ours doesn't seem
: to work yet :) I don't really know the magnitude of the slippage problem.

: -- 
:    -00-   | Tony Campbell       \    //  |]| || Senior, Mechanical Engineering
:   __)(__  | campbell@wpi.wpi.edu_\/\//___|___||_Worcester Polytechnic Institute
:  /*____*/ |  "I wish a robot would get elected President.  That way, when he 
: ^  _||_ ^ |   came to town, we could all take a shot at him and not feel 

There's nothing wrong coupling shaft encoders on the wheels.  When your
wheel loses traction or locks, you might consider aborting this run, since
losing traction or locking wheels will provide only inferior performance. 
Extra wheels doesn't justify the performance gain.  Real cars with
traction control and anti-lock braking system doesn't have extra wheels,
they mount shaft encoders (electro-magnetical, not optical) directly on
the wheel bearing. 

