Abstract:
This thesis focuses on designing and controlling a dynamically stable shape-accelerating dual-arm mobile manipulator, the Carnegie Mellon University (CMU) ballbot. The CMU ballbot is a human-sized dynamically stable mobile robot that balances on a single spherical wheel. We describe the development of a pair of seven-degree-of-freedom (DOF) humanoid arms. The new 7-DOF arm pair have human-like kinematics, a large bimanual workspace, and the strength to carry a 20 kg payload. As part of this thesis, the pair of strong and lightweight arms are integrated into the CMU ballbot. To the best of our knowledge, this robot configuration is the first and only of its kind. The underactuated ballbot class of robots presents unique challenges in planning, navigation, and control; however, it also has significant advantages over conventional mobile robots. The new multi-DOF arms add to the existing complexities of ballbots.

The ballbot is inherently unstable and requires careful coordination between the upper and lower body to maintain balance while performing manipulation tasks. This thesis demonstrates that this new configuration for mobile manipulation can be controllable over a wide envelope of possible configurations. Two different control strategies are presented: (i) a decoupled lower and upper body control strategy where the balancing controller compensates for the arm movement while the arms react to the body motion; and (ii) an optimal whole-body planning and control strategy that considers the entire kinematics and centroidal dynamics of the system in a single formulation. The controllers are implemented and evaluated on the CMU ballbot.

We also present experimental validation of the implemented controllers on the CMU ballbot. Experiments include station-keeping, precise end-effector control, payload lifting, and loco-manipulation tasks.

Thesis Committee Members:
Ralph Hollis, Chair
Nancy Pollard
Oliver Kroemer
Patrick Wensing, University of Notre Dame

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