Steering Control of an Active Tether Through Mass Matrix Control

The smaller the robot the easier it is for it to access voids in a collapsed structure. Yet, small size brings a host of problems due to resource constraints. One of the primary constraints on small robots is limited motive power to surmount obstacles and rough terrain. We are developing a small reconfigurable robotic system with various add-on modules to provide bulk motive force adaptable for different scenarios. The difficulty in adding modules with unsteerable motive force to generic host robots stems from directing the energy in the proper direction in a general way. This paper investigates modulating the non-isotropic Cartesian mass matrix of a robot, in contact with the ground, to passively steer the acceleration resulting from a motive force module. A robot in contact with the ground in a statically stable configuration is a parallel chain mechanism. We dynamically model the robot itself as an augmented object supported by multiple serial chain mechanisms to ground. In this paper, we develop the Cartesian mass matrix of the TerminatorBot robot by summing the dynamics component of each individual serial chain using the operational space formulation. A map is built of the resulting Cartesian acceleration vectors as a function of the robot's configuration. Desired acceleration vectors are mapped backwards from Cartesian space to configuration space, allowing the controller to assume a stance for the robot that will result in the desired motion.