Force-based motion editing for locomotion tasks

This paper describes a fast technique for modifying motion sequences for complex articulated mechanisms in a way that preserves physical properties of the motion. This technique is relevant to the problem of teaching motion tasks by demonstration, because it allows a single example to be adapted to a range of situations. Motion may be obtained from any source, e.g., it may be captured from a human user. A model of applied forces is extracted from the motion data, and forces are scaled to achieve new goals. Each scaled force model is checked to ensure that frictional and kinematic constraints are maintained for a rigid body approximation of the character. Scale factors can be obtained in closed form, and constraints can be approximated analytically, making motion editing extremely fast. To demonstrate the effectiveness of this approach, we show that a variety of simulated jumps can be created by modifying a single key-framed jumping motion. We also scale a simulated running motion to a new character and to a range of new velocities.