Quote:
Originally Posted by Andrew Lawrence
That is correct, but in most cases* an all-omni drive would just render you powerless against your opponents since you have almost no traction. A traction + omni mix, a butterfly drive, or drop down casters fixes this by adding an area of high friction to rotate around while the low friction spins out of the pin.
*Ellen Green and 33 are exempt from this
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Not quite, the exact reason why 33 is able to get out of friction pins is because with all omni's you are not applying any resistant force back against the robot that's pushing you which greatly reduces the friction between bumpers. Increased friction causes the opposing robot to "lock" onto the side of your robot and if they just keep driving forward they get pulled in whatever direction you drive. On the other hand, with a low amount of friction between bumpers your robot doesn't apply enough force to rotate the robot pinning it, and simply slips off the side of the pin instead of locking bumpers with them.
Omni's are the best thing in the world for getting out of a friction pin, you just drive forward and you slide right off of them. Traction wheels are only good for pushing in the direction of travel and resisting pushing (relatively isotropically). You can only spin your wheels forward and backward, so they're really only good for applying force in that direction, and a high coefficient of friction in all directions makes you a little but harder to push sideways (although this advantage tends to have very little application and is generally more disadvantageous than advantageous).
For maneuverability on the field, and getting around defense, the ideal wheel for most FRC games (specifically this year and last year) would be an omni wheel with a very high CoF in the direction of rotation, and very low CoF perpendicular to their direction of rotation.
A similar effect can also be achieved by making your bumpers out of butter.