Subject:
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Re: Navigation using landmarks (Was: Re: lasers and RCX)
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 26 Jun 2002 09:07:37 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail.netSAYNOTOSPAM>
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Reply-To:
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sjbaker1@airmailIHATESPAM.net
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Viewed:
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967 times
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Mauro Vianna wrote:
> "Steve Baker" wrote:
>
> > I looked into several patterns. What would be ideal would be something which
> > you could drive across along any straightline path and get back your direction
> > and position from the pattern of dark and light.
> >
> > It seems rather unlikely that such a pattern could exist - but I havn't
> > finished thinking about it yet.
>
> Somebody in this list already tried a pattern with 4 colors. If you can
> have all your floor covered with squares with 4 distinct colors, you can
> detect your aproximate position and direction. Unfortunatelly that won't
> work for me. I don't want to build a big mat or redecorate my apartment. :)
I don't want to cover the entire floor - just place a *few* of these
things on the floor as landmarks. The idea is that the robot would
run over one of these things, figure out exactly where it is (both
position and heading) - and then use dead-reckoning to get close enough
to the next landmark to re-sync itself. If it ever missed a landmark, it
could detect that it had driven too far without finding it and do some
kind of spiral search to find it.
> I already built the robot (wheelchair style) with 2 rotation sensors.
> Although it seens very precise to move in a straight line, sometimes it
> changes its direction by a few degrees. It looks like one of the rotation
> sensors is losing some counts. Some people already reported this kind of
> problem. I'll debug to be sure. I may need to change the gears to reduce the
> rotation sensor speed. The problem is that I will lose precision as well.
Probably you need to INCREASE the speed that the sensor rotates. I found
that the range 50 to 300 RPM was the most reliable range for the sensor:
http://www.sjbaker.org/steve/lego/rotation_sensor.html
...but still, you can't expect perfection. Wheels slip, their radii are
never *exactly* the same, there are imperfections in the surface you
are driving on, there is whiplash in your gear train.
Try to accellerate your robot smoothly up to speed - sudden starts and
stops can cause excessive wheel slippage. It goes without saying that
if you run into a solid object at speed, your wheels will slip for
a while. You can use a non-contact sensor (the IR port has been used
as a rangefinder - with mixed success) - or perhaps a large, bendy bumper
to detect imminent collision with enough time for a controlled stop.
----------------------------- Steve Baker -------------------------------
Mail : <sjbaker1@airmail.net> WorkMail: <sjbaker@link.com>
URLs : http://www.sjbaker.org
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