FULL, R.J.: Stability and maneuverability in sprawled posture, legged locomotion.

Legged animals bounce up and down and side to side as they run. Species that differ in leg number and posture run stably like sagittal and horizontal plane spring-mass systems. Preflexive mechanisms at the level of legs permit passive, dynamic feedback that can reject rapid perturbations before sensor-based reflexes and thereby simplify control. A greater number of widely spaced, compliant legs potentially in contact with the substrate provide for robust, dynamic self-stabilization. Legs of sprawled posture runners produce lateral and opposing ground reaction forces, since these vectors tend to minimize joint moments by aligning along the leg axially. Front legs tend to decelerate the body, while rear legs only accelerate the center of mass. All legs tend to push away from the body. Differential leg function in sprawled posture runners not only permits greater stability, but also greater maneuverability. Maneuvers can require minor neuro-mechanical alterations to straight-ahead running. A small change in force production can generate turning and climbing without large changes in leg kinematics. A greater number of widely spaced, compliant legs potentially in contact with the substrate provide for greater maneuverability because of an increased opportunity to shift the center of pressure. Legged animals appear to manage energy in a way that works with their natural dynamics. Principles from sprawled posture runners are being used to inspire the design of highly mobile, autonomous physical models � robots. Supported by DARPA/ONR N00014-98-1-0747 and ONR N00014-98-1-0669.