Subject:
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Re: Mechanical question
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Newsgroups:
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lugnet.robotics
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Date:
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Mon, 26 Jul 1999 22:53:27 GMT
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Original-From:
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Laurentino Martins <lau@mailSPAMLESS.telepac.pt>
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Viewed:
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966 times
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At 22:01 26-07-1999 Monday , Laurentino Martins wrote:
> At 20:55 26-07-1999 Monday , Dennis Clark wrote:
> > In lugnet.robotics, Jon Shemitz writes:
> > > I've been puzzling over this one, and I still don't really understand
> > > it: Why can a bot with tank treads do a turn in place, while a bot with
> > > four wheels geared together so that the front and back wheels on each • [snip]
> > > Or is it that the wheeled version is concentrating all the sideways
> > > force at four points, while the treaded version is spreading the same
> > > force over a much larger area?
> >
> > You are close here. Tank steering is often called "skid" steering because
> > tank tracks are optimized for traction parallel to direction travelled and
> > have little traction in a tangent direction. A look at the tread pattern
> > will show you why. You only need a skid a little to get the steering to
> > work, and on a high grip surface (carpet) even your tank tracks will strain
> > when trying to turn. Wheels on the other hand are OPTIMIZED to NOT allow
> > sideways motion at all, watching all those Goodyear tire commercials has
> > convinced me of that!
>
>
> I don't know the other LEGO tracks, but the CyberMaster tracks confirm
> everything you said. They look like this (fixed font):
>
> | ----|
> |---- |
> |---- |
> | ----|
> | ----|
> |---- |
> |---- |
> | ----|
> | ----|
> |---- |
>
> Also, they are deeper in the center than in the edges.
>
> I'm positive that they where designed to let the track be dragged sideways
> without much effort, while the pattern is clearly designed for front/rear
> traction.
Add on:
Also important in all this is the distance the tracks are apart. The further apart the less friction they have, since the radius is larger.
Same happens with wheels.
Laurentino Martins
[ mailto:lau@mail.telepac.pt ]
[ http://www.terravista.pt/Enseada/2808/ ]
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 2 Replies:
 | | Re: Mechanical question
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| (...) Why is this? The further apart they are, the greater r*cos(theta) is going to be for any given theta. Seems like that would make for more turning resistance, not less. (25 years ago, 27-Jul-99, to lugnet.robotics)
| | | Re: Mechanical question
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| (...) I'll try to explain this with an ASCII picture, but I'm make no promises about the quality... Please use a fixed font (as you always should in newsgroups) Legend: #### - Lower part of the track (the part that touches the ground). OOOO - Inner (...) (25 years ago, 27-Jul-99, to lugnet.robotics)
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Message is in Reply To:
| | Mechanical question
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| I've been puzzling over this one, and I still don't really understand it: Why can a bot with tank treads do a turn in place, while a bot with four wheels geared together so that the front and back wheels on each side always move together can not? My (...) (25 years ago, 26-Jul-99, to lugnet.robotics)
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