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PublicationDynamic Rolling for a Modular Loop Robot(2006-07-01) Sastra, Jimmy; Chitta, Sachin; Yim, MarkReconfigurable modular robots use different gaits and configurations to perform various tasks. A rolling gait is the fastest currently implemented gait available to a modular robot for traversal of level ground. In this work, we analyze and implement a sensor-based feedback controller to achieve dynamic rolling for a 10 module loop robot. The controller exploits the dynamics of the system to build up momentum in each step by specifying a desired global shape for the robot at touchdown. Energy is input into the system both by raising the height of the center of mass of the robot and moving the position of center of mass with respect to the ground to maximize the moment arm due to gravity. Using simulation and experimental results, we show how the desired shape can be varied to achieve higher terminal velocities. Through simulation, we also show rounder shapes have lower specific resistance and are thus more efficient. PublicationControl of Locomotion with Shape-Changing Wheels(2009-05-01) Mellinger, Daniel; Kumar, Vijay; Yim, MarkWe present a novel approach to controlling the locomotion of a wheel by changing its shape, leading to applications to the synthesis and closed-loop control of gaits for modular robots. A dynamic model of a planar, continuous deformable ellipse in contact with a ground surface is derived. We present two alternative approaches to controlling this system and a method for mapping the gaits to a discrete rolling polygon. Mathematical models and dynamic simulation of the continuous approximation and the discrete n-body system, and experimental results obtained from a physical modular robot system illustrate the accuracy of the dynamic models and the validity of the approach.