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 00:56:31 GMT
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Original-From:
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Steve Baker <sjbaker1@airmail/IHateSpam/.net>
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Reply-To:
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sjbaker1@airmail+stopspammers+.net
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Viewed:
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611 times
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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.
I thought of trying this in order to get precise 90 degree turns WITHOUT
using a sensor of any kind. The idea would be to have mechanical endstops
preventing the 'foot' from rotating more than 90 degrees in either direction
with some kind of clutch or slipping belt drive. Then the robot could turn
in multiples of 90 degrees by rotating the foot all the way over to one
end-stop, lowering it, then rotating in the opposite direction until it hit
the other endstop.
With a bit of mechanical cleverness, I bet you could make the foot raise or
lower using the same motor as you use to turn it - which would give you
precise rotation without a sensor and using just one motor output.
Then I got to thinking about making the end-stops be less than 90 degrees
apart (eg 45 degrees) so the robot could turn accurately through smaller
angles.
> Challenges:
> Strength of lifting apparatus
> Strength and stability of 'foot'
> Weight/balance of bot (so it is stable while it is raised and turning)
It seemed to me that the plate that makes up the foot can be '+' shaped and
stick out between the wheels of a 4 wheel bot. if you only need 90 degree
rotations. Otherwise, a roughly circular foot that just fits between the
wheels when it's retracted should be OK.
Anyway - I never did build it - it was just one of those thought experiments
that never turned into anything.
----------------------------- Steve Baker -------------------------------
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