Catching flying balls with a mobile humanoid: System overview and design considerations

A ball catching scenario with the mobile humanoid Rollin' Justin is presented. It can catch up to two simultaneously thrown balls with its hands, reaching a catch rate of over 80%. All DOF (degrees of freedom), i.e., the arms, the torso, and the mobile platform, are used for the reaching motion and the system works completely wirelessly using only onboard sensing. The task is demanding because of the necessary precision in space (<; 2cm) and time (<; 5ms) as well as its realtime character due to the short flying time (<; 1s). Fast perception, a good catching strategy and whole body path planning and control are important, but their tight interplay enabled by an appropriate system architecture is essential. The system overview presents the design considerations for extending Justin's versatility to this highly dynamic task. The key is not to radically change one component of the system but to do well-considered upgrades on all architectural levels, be it sensors, algorithms or middleware.