English: Video of the Passive-Dynamic Robot: The robot takes two consecutive walks down the ramp. A robot wrangler first launches the robot, to give it proper initial conditions. The robot then proceeds down the ramp with a passive-dynamic gait, arising from the natural interactions between the limbs and gravity. To restore energy lost at the heel-strike collision the machine walks down a ramp, using gravitational potential energy during each stride in a manner similar to a glider. The knees are held in place by suction cups during stance, but otherwise swing freely. The hips swing freely throughout gait. Arms are rigidly attached to the contralateral legs, and counteract the angular momentum of the legs. Developed by Steve Collins, Martijn Wisse, and Andy Ruina at Cornell University