US Patent 8214970 Wheel system with lifter apparatus

A wheel system includes a frame, a wheel rotatably mounted to the frame, and a lifter. The lifter defines a first end and a second end. The first end of the lifter is pivotably mounted to the frame, and the second end of the lifter defines a contact surface. The contact surface of the lifter is adapted to establish initial contact with a vertically disposed obstacle, and thereafter the lifter is configured to pivot about the first end such that the wheel is lifted and translated over the vertical obstacle.