In this paper we examine the nature of a gymnastic maneu ver, the forward flip, and describe how a planar biped run ning machine executes it. To perform a flip the machine runs forward, thrusts with both legs to jump while pitching the body forward, shortens the legs to tuck once airborne, untucks in time to land on the feet, and then continues running. The control system produces these actions and the resulting flip by issuing a prespecified pattern of actuator commands to the actuators in conjunction with a set of control algorithms used for normal running. When all components of the system are working properly, the machine executes nine out of 10 flips successfully.
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