Subject:
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Re: 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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Wed, 4 Aug 1999 18:30:01 GMT
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Viewed:
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2217 times
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I was asked via E-mail where to get the balloon tyres. They are listed in the
Shop-at-Home catalog as item 5282:
http://www.lugnet.com/pause/search/?query=5282
I just ordered some from here in the United States and they were $6.00 per
package. Each package includes two tyres and two wheels (hubs) that the tyres
fit on.
If you just want to support weight with a free wheel (the original purpose I
was replying to) then one pair of these tyres is all you need.
Also, on the general topic of linear wheels, it isn't necessary to use balloon
tyres if you're willing to use more than two real wheels per linear wheel
structure. The idea is to make sure one wheel is touching the ground at all
times. If you use more wheels, each wheel can be thinner. Instead of two wheels
offset by 90 degrees, you can use three wheels offset by 60 degrees, four
wheels offset by 45 degrees, or five wheels offset by 36 degrees. All are easy
to accomplish with LEGO gears. There will always be a bit of up-and-down
variation as you go from one wheel to another but for most robotics
applications that should be acceptable.
More wheels is also the only way to make a linear wheel assembly with higher
clearance, for negotiating rough terrain. However, using more wheels also
causes more variation in wheelbase. Depending on which wheel is touching the
ground at any given moment, the point of contact moves which means the whole
structure has to be far away from your center of gravity or else the robot will
tip over. If you want to handle rough terrain you should probably be using tank
treads, an insect walker design (like
http://userpages.itis.com/jvwillou/legorob1.htm) or a fancy suspension like the
Mars rover (http://mars.jpl.nasa.gov/MPF/rovercom/images/sojrov2.jpg).
- Robert Munafo
LEGO: TC+++(8480) SW++ #+ S-- LS++ Hsp M+ A@ LM++ YB64m IC13
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