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Originally Posted by M. Krass
I've always imagined and wanted the opportunity to design and build, for anyone who's interesested (hint, hint, nudge, nudge), a six-wheel drivetrain that keeps them all at a single height, but uses omniwheels on the four corners. It seems like that's a simple solution for enhancing traction in the robot's direction of travel while minimizing additional friction in turning.
I'd be surprised if another team has not yet tried this method, though nothing springs to mind.
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Team 40 used that method this year.
I seem to remember them turning pretty well.
Now for some editorializing:
In order to push competitively in this competition, one needs as much tractive force available as possible.
Tractive Force = Wheel Coeff. x Normal Force
Normal Force is limited to the weight of the robot (and whatever the robot is able to pick up. In order to maximize Tractive Force, we want our wheels/treads/whatever to have the MAXIMUM coefficient of friction possible. (Many teams use high traction belting, or pneumatic tires).
Here is the kicker -- I have NEVER seen an omni wheel that can compete with straight up, high traction wheels when it comes to coefficient of friction. So... if you use omni-wheels on your robot, you are "wasting" normal force. You have weight sitting on "low" traction wheels, and have decreased your tractive force.
The GREAT thing about the 6WD configuration, is that it allows the robot to turn like crazy, but ALL the robot's normal force is sitting on driven, high traction wheels. It's the best of both worlds! Turning + Pushing!
Note: Casters pose the same problem. If you have weight resting on "non-driven wheels" you're shooting yourself in the foot again, when it comes to pushing matches.
For more information about WHY the 6WD, lowered middle wheel configuration turns better... check out Chris Hibner's turning whitepaper. He's got GOLD in there:
http://www.chiefdelphi.com/forums/pa...le&paperid=222
It's physics,
John