Physics of T-boning

[DampRobot]

T bones occur when the usual dynamic of friction in FRC is switched. Usually, friction between the ground and the wheels is static, or rolling, and the friction between bumpers is dynamic (as robots slide off each other, etc). When the bumper-bumper friction becomes static, and the wheel friction of the robot being defended becomes dynamic, then theres a T bone pin going on.

The pinned robot can't escape because they can't move sideways relative to the defending robot (because the bumper friction outweighs the sliding friction on the tires) and it can't move forwards of backwards relative to the pinning robot because it's wheels don't move that way. Its wheels are in constant dynamic friction because it is being pushed from the side, so it's always sliding (whether or not it's wheels are rotating). As soon as the pinned robot stops getting pushed sideways, it can usually get out of the pin.

Interestingly, one of the things we look for in tread (low sideways COF) which makes it easy to turn makes it particularly difficult to get out of T bone pins. We found VersaWheels were just terrible in this regard this year.