Projection based whole body motion planning for legged robots
This addresses the challenge of efficient whole-body motion planning for legged robots, particularly in handling contact switches without explicit models, though it appears incremental as it builds on existing optimization methods with a novel projection technique.
The paper tackles dynamic motion planning for legged robots by formulating a trajectory optimization problem using a compact dynamics model that projects rigid body dynamics to remove contact forces while accounting for their effects, enabling tractable solutions without explicit contact models; results include dynamic motions like rearing and stepping on a hydraulic quadruped robot, with reduced problem size for faster computation.
In this paper we present a new approach for dynamic motion planning for legged robots. We formulate a trajectory optimization problem based on a compact form of the robot dynamics. Such a form is obtained by projecting the rigid body dynamics onto the null space of the Constraint Jacobian. As consequence of the projection, contact forces are removed from the model but their effects are still taken into account. This approach permits to solve the optimal control problem of a floating base constrained multibody system while avoiding the use of an explicit contact model. We use direct transcription to numerically solve the optimization. As the contact forces are not part of the decision variables the size of the resultant discrete mathematical program is reduced and therefore solutions can be obtained in a tractable time. Using a predefined sequence of contact configurations (phases), our approach solves motions where contact switches occur. Transitions between phases are automatically resolved without using a model for switching dynamics. We present results on a hydraulic quadruped robot (HyQ), including single phase (standing, crouching) as well as multiple phase (rearing, diagonal leg balancing and stepping) dynamic motions.