A Cockroach-Like Hexapod Robot for Natural Terrain Locomotion.

Abstract : This report describes progress over the last six months in three areas: robotics, physiology and modeling. The posture controller for Robot III was found to be robust to large disturbances and modeling errors. It was discovered that the 48 valves controlling the robot have dissimilar outputs by as much as 30%. We had initially assumed that the valves were similar and used one model for all of the valves. This dissimilarity caused the magnitudes of some control torques to be 30% less than desired. The middle legs, which typically bear much of the load, were particularly affected. Despite this the posture controller worked well in rejecting large disturbances. We have now experimentally modeled all of the valves and implemented the models in the controller. In our initial work with Robot Ill walking, the robot's posterior swayed when legs were lifted in the transition to swing. In cockroach rear legs, the coxa-femur joint and femur-tibia joint typically move in-phase with the same magnitude. We designed the robot with 3 degrees of freedom (DOF) in case all 3 were found to be important. We have now reduced them to 2 DOF by disconnecting the femur-tibia actuators and kinematically coupling the C-F and F-T joints using a parallel four-bar mechanism. This causes the joint coupling observed in the animal and reduces swaying of the robot's posterior as it walks.