Subject:
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Re: Autonomous Robot
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 3 Aug 2000 14:56:49 GMT
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Viewed:
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1135 times
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I explored the use of a single rotation sensor to make a robot drive
straight here:
http://www.oreillynet.com/pub/a/network/2000/05/22/LegoMindstorms.html
You can use a differential to take the difference of the two motors'
output; if the motors are not moving at the same speed, you'll see some
movement on the rotation sensor.
My conclusion was that dead reckoning alone is not enough--you should
periodically calibrate with another navigation technique, like using
landmarks.
Jonathan
Juergen Stuber wrote:
>
> Hi Mario, Mauro,
>
> "Mario Ferrari" <mario.ferrari@edis.it> writes:
> >
> > Some free thoughts about this topic:
> >
> > 1) With a differential drive setup, you could use two rotation sensors both
> > for navigation between landmarks, and for collision detection: when the
> > wheels are supposed to rotate (motor on) but don't, you know you are against
> > an obstacle. Very simple but effective. You now can use the third sensor
> > port for a light sensor bound to landmark detection.
>
> I tried to get away with a single rotation sensor on a
> differential drive (put it on one of the output), assuming
> that I one motor is not moving I could deduce total
> movement. Unfortunately the turning motor drifts slightly
> on forward/backward motion, so the thing is not going
> straight.
>
> > 2) A grid of tape on the floor works very well as
> > artificial landmark. Use different color for the
> > horizontal and vertical lines, so you're sure of what kind
> > of line you crossed.
>
> I have a natural landmark in the form of a checkered kitchen
> floor, I'd like to try that for navigation. It's a little
> more complicated I guess.
>
> > 3) A different landmarking approach could be using a laser beam to query
> > some base stations (if you're open to use a non-Lego laser pointer). The
> > idea is you have a roating laser pointer connected to a motor and a rotation
> > sensor (multiplied to increase resolution). When the robot wants to
> > calculate its position, it stops and starts slowly rotating the laser beam.
> > The base stations have a light sensor positioned at the same height of the
> > laser beam. When the light sensor gets hit by the laser light, it reads
> > almost 100% and the base station transmit an IR message to say "got it".
>
> Almost 100% is an understatement, a laser really saturates a
> light sensor. The problem is hitting it in the first place,
> I found that next to impossible to achieve. I'd rather go
> for some strobe lights (good for identification by rhythm),
> or maybe halogene lights, with the light sensor on the robot
> like scanbot in Dave Baum's book. I also tried candles
> once, but they are to dim, they can be seen only from a
> short distance, on the order of 10cm.
>
> Jürgen
>
> --
> Jürgen Stuber <stuber@loria.fr>
> http://www.loria.fr/~stuber/
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Message is in Reply To:
 | | Re: Autonomous Robot
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| Hi Mario, Mauro, (...) I tried to get away with a single rotation sensor on a differential drive (put it on one of the output), assuming that I one motor is not moving I could deduce total movement. Unfortunately the turning motor drifts slightly on (...) (24 years ago, 3-Aug-00, to lugnet.robotics)
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