offset differential steering

Common wheeled robot differential steering uses 2 wheels directly opposite each other, usually through the center of the base so that the robot can
rotate in place.
What would happen if the wheels are offset, i.e. the wheels are on motors that are mounted alongside of each other, rather than end to end? Is this a viable method of movement? Anyone try this or have any references? Thanks.
Marcus
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Marcus wrote:

Some people have reported trying it -- because the design of their robot required it -- and it seems to work. I have not seen any scientific studies on whether there are any advantages or disadvantages.
-- Gordon
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Thanks for the input, Gordon. Logically it should work, but I'm far from sure it will be that easy.
Marcus
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    --FWIW during the heyday of Battlebots someone dreamed up the "Meltybrain" controller for predictable steering regimes on spinning two-wheeled robots. Maybe one of these would help?
--
"Steamboat Ed" Haas : Before the last "election"
Hacking the Trailing Edge! : a fifty was a twenty...
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You are asking about two wheels that are parallel, but not both perpendicular to an imaginary line passing through their centers. I believe that this is essentially the same as the case where you have crooked wheels. So if one wheel is forward to the other and both wheels turn at the same rate of speed, my guess is that the system will tend to drift to the side of the forward wheel. The wider the bot, the less pronounced the effect.
Gary

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Bronson Silva did it back in '03 at RoboMaxx with Bob, the micro sumo bot. (http://www.robotdirectory.org/details.cfm?cat=1&id 8) As I remember, Bob moved about just fine.
I have been trying it with Tiny, which measures smaller than micro- but larger than nano-size. It does indeed turn to one side, but I think one of my motors is slightly less powerful than the other:
http://robotguy.net/tiny1.jpg
http://robotguy.net/tiny2b.jpg
http://robotguy.net/tiny3b.jpg
http://robotguy.net/tiny4b.jpg
The biggest problem I have had is that every time someone looks at it they ask "Did you know your wheels are crooked?"
I am molding several new chassis for Tiny this week and getting more motors probably next week. I hope to build 5 of these for a "swarmlet". If you are interested in the results, keep an eye on my blog (http://robotguy.net/blog ).
-Robotguy http://robotguy.net/blog
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snipped-for-privacy@comcast.net wrote:

If mechanical system has center of (rotational) symmetry and both wheels have the same velocity but opposite direction drift is impossible: in symmetric system all directions are equals, no preferred directions exists.
But both wheels MUST SLIDE relative to ground; the bigger wheel axis eccentricity - the bigger sliding. It have at least two negative effects:
- more power consumed (because sliding required power)
- rotating on the inclined ground accompanied by sliding down (inclination destroyed symmetry :-)
So big eccentricity is obviously harmful.
Nick

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