Controlling Fast Height Variation of an Actively Articulated Wheeled Humanoid Robot Using Center of Mass Trajectory

Abstract

Hybrid wheel-legged robots have begun to demonstrate the ability to adapt to complex terrain traditionally inaccessible to purely wheeled morphologies. Further research is needed into how their dynamics can be optimally controlled for developing highly adaptive behaviours on challenging terrain. Using optimal center of mass (COM) kinematic trajectories, this work examines the nonlinear dynamics control problem for fast height adaptation on the hybrid humanoid platform known as Aerobot. We explore the dynamics control problem through experimentation with an offline trajectory optimisation (TO) method and a task-space inverse dynamics (TSID) controller for varying the robot's height. Our TO approach uses sequential quadratic programming (SQP) to solve optimal 7th order spline coefficients for the robot’s kinematics. The nonlinear Zero Moment Point (ZMP) is used to model a stability criterion that is constrained in the TO problem to ensure dynamic stability. Our TSID controller follows motion plans based on using task jacobians and a simplified passive dynamics model of the Aerobot platform. Results exhibit fast height adaptation on the Aerobot platform with significantly differing results between the control methods that prompts new research into how it may be controlled online.