Subject:
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Non-pivoting free wheels (was Re: odometry (was Re: Homing with the IR Tower)
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 3 Aug 1999 19:34:02 GMT
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Viewed:
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1397 times
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You'll have a very hard time making a ball-and-socket design bear a load and
turn without lots of friction. Putting wheels between the ball and the socket
just brings us back to the problem that we were trying to avoid by not having
wheels.
A much better solution that will definitely accomplish what you want is 1/3 of
a Killough platform. This is a pair of balloon tires that are free to rotate on
two axes (via a rotating mount) and geared to each other so that the primary
axles of the two wheels are always at a right angle, but coplanar. Here are two
good pictures of the design:
http://www.net-info.com/~dcarlson/images/kmrp3.jpg
http://carol.wins.uva.nl/~leo/lego/killough.html
There are two balloon tires, and only one touches the ground. You'll have to
omit the motor in your model so the wheels turn freely on both axes.
I also want to point out that the full Killough platform with three pairs of
wheels is also rather nice for many other reasons, the main one being that you
can move in any direction without turning, or in fact you can turn while moving
without changing your direction of movement. This makes for much better
maneuverability and flexibility and is also pretty darn fun to watch. However,
it wouldn't be that great for odometry because it's difficult to travel in a
perfectly straight line.
- Robert Munafo
In lugnet.robotics, Erik Steffl writes:
> [...]
> it looks like the good free wheel should do its 'wheeling' equally
> well in each direction. therefore it should be a ball. the design should
> look like this:
> [...]
> there should be something between the holder and the ball so that the
> ball can rotate freely (few wheels would do the trick).
>
> if did was not clear enough - it is something like a computer mouse
> ball, only it is supported, not hanging (so it is where the mouse ball
> is but it is of the same construction as trackball ball).
> [...]
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Message has 1 Reply:
Message is in Reply To:
 | | Re: odometry (was Re: Homing with the IR Tower)
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| I haven't done any 'bot yet but I have been thinking about this problem. and here's the result: it looks like the good free wheel should do its 'wheeling' equally well in each direction. therefore it should be a ball. the design should look like (...) (25 years ago, 31-Jul-99, to lugnet.robotics)
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