Subject:
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Re: THOUGHTS on mapping with Lego Robot ( added to searching walls)
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 27 May 2003 23:41:17 GMT
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Original-From:
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[chammers@xaosnet.]AvoidSpam[com]
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Viewed:
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2565 times
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Hmmm.. if you had two RCX's you could do a polar co-od's trick. Place a
spool of white wire with black markers every inch on the robot and a use a
light sensor to count the number of black sections that have gone by. Use
a rotation sensor on the base station to get the angle of the wire and
transmit it to the rover.
Might have to use a strip rather than a wire to get it wide enough for the
light sensor to see it, plus you have to tension it if you go backwards. A
true angle sensor would be nice too, maybe use touch sensors to calibrate
the readings. (place them under the swing arm at 180 degrees apart so 0
and 180 depress one of the touch sensors.)
On Tue, 27 May 2003, Steve Baker wrote:
> Bill Blackmer wrote:
>
> > What I want to do is take a five foot by five foot square, put random items
> > in the square, MAP THE SQUARE AND OBSTACLES and run our dog robot around the
> > course and never have it stop. I do not want to do obstacle avoidance (that
> > is much easier) I want to build a map and work from it.
>
> It's very difficult because all of the 'dead reconing' methods out there are
> approximate and accumulate errors.
>
> If you drive your robot 10 feet in a straight line, your software will probably
> by 'off' by maybe a half inch, after 20 feet, you'll be off by an inch...after
> an hour of driving around, you could be just about anywhere! Turning is
> worse still - if you drive around a zig-zag course for 10 feet, you'll probably
> be off by many inches in position and tens of degrees in heading.
>
> You need some way for the robot to (at least periodically) do a check on
> some absolute position to reset it's internal position indicator.
>
> > To do this, we have acquired several HiTechnic Sensors (these sensors are
> > much more accurate then the Lego sensors - Compass, Ultrasonic and Infrared
> > Range Sensors); and we have created several statistical averaging and
> > correction algorithms, etc.
>
> But things like wheel slip, slop in the gear train, small errors in the
> diameters of wheels, the fact that the Lego rotation sensors sometimes
> gain or lose a 'count' (especially when moving slowly)...all of these
> things conspire to make this a completely intractable problem.
>
> There are things you can do to lessen the problems - but *some* inaccuracy
> is certain to occur and if the "dog" robot doesn't periodically know with
> some precision exactly where it is, the errors will build up with alarming
> speed (ESPECIALLY when the robot turns).
>
> One idea that might work would be to have a 'kennel' for the dog - with
> a funnel-like entrance and an interior that *exactly* fits the shape of
> the robot. If the dog returned to the kennel every so often, the funnel
> would point it into the kennel even if it's navigation was off by a bit
> and the tight fit inside the kennel would allow the robot to reposition
> it's internal navigation coordinates to be EXACTLY where the 'kennel'
> is known to be. There are other ways to achieve the same effect - a
> barcode placed on the floor, navigation lights placed around the arena,
> etc.
>
> ---------------------------- Steve Baker -------------------------
> HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
> HomePage : http://www.sjbaker.org
> Projects : http://plib.sf.net http://tuxaqfh.sf.net
> http://tuxkart.sf.net http://prettypoly.sf.net
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