Rock-and-Walk Manipulation: Robotic Object Transport through Passive Dynamic and Quasistatic Manipulation

We present a novel robotic manipulation capability for transporting an object on the ground in a dynamic and nonprehensile manner. The object is manipulated to rock from side to side repeatedly; in the meantime, the force of gravity enables the object to roll along a zigzag path that is eventually heading forward. We call it "rock-and-walk" object manipulation. Our work is motivated by an interesting question in archaeology, how the giant rock statues of Easter Island (known as "moai") were transported several hundred years ago, and a recent demonstration done by archaeologists that it is possible to "walk" the statue by repeated rocking. We examine the kinematics, statics, and dynamics of the rocking motion to understand how the state of the object evolves and how to control the robot to connect individual rocking motions into a stable gait of the object. Our rock-and-walk object transport technique is implemented in multiple robotic settings: 1) one robot arm with an end-effector that can cage the object, 2) two robot arms to interact with the object via cables, and 3) an aerial robot with the caging end-effector. A set of experiments demonstrate successful rock-and-walk object transport under a range of terrain conditions.