title: Kinematic primitives for walking and trotting gaits of a quadruped robot with compliant legs.
abstract: In this work we research the role of body dynamics in the complexity of kinematic patterns in a quadruped robot with compliant legs. Two gait patterns, lateral sequence walk and trot, along with leg length control patterns of different complexity were implemented in a modular, feed-forward locomotion controller. The controller was tested on a small, quadruped robot with compliant, segmented leg design, and led to self-stable and self-stabilizing robot locomotion. In-air stepping and on-ground locomotion leg kinematics were recorded, and the number and shapes of motion primitives accounting for 95% of the variance of kinematic leg data were extracted. This revealed that kinematic patterns resulting from feed-forward control had a lower complexity (in-air stepping, 2-3 primitives) than kinematic patterns from on-ground locomotion (νm4 primitives), although both experiments applied identical motor patterns. The complexity of on-ground kinematic patterns had increased, through ground contact and mechanical entrainment. The complexity of observed kinematic on-ground data matches those reported from level-ground locomotion data of legged animals. Results indicate that a very low complexity of modular, rhythmic, feed-forward motor control is sufficient for level-ground locomotion in combination with passive compliant legged hardware.
authors.affiliation: Biorobotics Laboratory, École Polytechnique Fédérale de Lausanne Lausanne, Switzerland.
authors.forename: Alexander T
authors.initials: AT
authors.lastname: Spröwitz
authors.affiliation: Biorobotics Laboratory, École Polytechnique Fédérale de Lausanne Lausanne, Switzerland.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Ajallooeian
authors.affiliation: Biorobotics Laboratory, École Polytechnique Fédérale de Lausanne Lausanne, Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Tuleu
authors.affiliation: Biorobotics Laboratory, École Polytechnique Fédérale de Lausanne Lausanne, Switzerland.
authors.forename: Auke Jan
authors.initials: AJ
authors.lastname: Ijspeert
keywords: central pattern generator; entrainment; locomotion patterns; motion primitives; passive leg compliance; principal component analysis; quadruped robot; walk and trot