From VEX Wiki
One of the most common types of drivetrain is known as a skid steer drivetrain, which may also be referred to as a tank drive. A skid steer drivetrain consists of two independent sets of powered wheels (or treads), one on each side of its chassis. By running the sides of the drivetrain at different speeds, it is possible to steer the robot in arcs. This drivetrain is also capable of a zero-radius turn (it will spin in place) if the sides are run at the same speed in opposite directions. Much of this discussion focuses on skid steer drivetrains.
