Subject:
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Re: Some questions that relate to an idea I am thinking about
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 20 Sep 2002 12:48:58 GMT
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Viewed:
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878 times
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lego-robotics@crynwr.com (Chris 'Xenon' Hanson) wrote:
> Mike Thorn wrote:
> > I think what you want is a 4-wheel-steering car; or better yet, a
> > tricycle - one motor for drive, one motor for steer. If you don't
> > want to paint your ceiling, stand the RCX up with the IR port to the
> > sky and you're set.
> >
> > 4WS wouldn't be as easy and it wouldn't have as great a turning
> > radius, but it's a more interesting design, IMHO.
>
> I've always wondered about the possibility of a non-steerable drive
> system
> powered by one motor output, with a large 'foot' that could descend
> from the center of the bot to lift the wheels/treads off the ground
> (pneumatics?) and a third output controlling a motor that would rotate
> the foot clockwise or counterclockwise (thus counterrotating the bot
> counterclockwise or clockwise relative to the ground), and driving a
> rotation sensor to moderately precise measured turns could be
> executed.
>
> Challenges:
> Strength of lifting apparatus
> Strength and stability of 'foot'
> Weight/balance of bot (so it is stable while it is raised and
> turning)
>
> Has anyone done anything like this? It would seem to allow you to
> build a
> very strong rigid drive system that could still execute precise tight
> turns. It could not turn 'on the move' unfortunately, but it would be
> a good system for a move-scan-plan-move robot that could get itself
> out of tight corners.
I have built a robot based on this architecture. I used it to attend a
contest where the robots had to cover a distance, touch a wall, rotate
and come back as precisely as possible to the starting point. I don't
have a page on my site for this robot yet, but I just copied a few
pictures of it in a temporary folder:
http://www.marioferrari.org/temp/DCP_1281.JPG
http://www.marioferrari.org/temp/DCP_1287.JPG
http://www.marioferrari.org/temp/DCP_1299.JPG
http://www.marioferrari.org/temp/DCP_1301.JPG
http://www.marioferrari.org/temp/DCP_1304.JPG
As rotation sensors were not allowed, the measurement of the covered
distance was based on a light sensor facing a pulley with black & white
1x1 round plates on it. This worked very well.
It actually used a mechanical stop to control its rotation, as Steve
suggests. It was very precise: typical error on the longest distance - 5m
+ 5m - was less than 5cm. It was not the most precise robot, thoug: it
ranked second after Paolo Masetti's one, which was simply unbelievable!
Ciao
Mario
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