High-torque spherebots


Imagine a robotic amphibious assault requiring a vehicle that can be released near a shoreline, self-propel near the sea surface towards the shore, submerge and self-propel near the sea floor through the surf zone, then move up onto the beach, over sand, rocks, vegetation, barbed wire, and even up stairs.  The only robotic vehicle one can imagine that could survive such a mission profile is a (sealed, buoyancy-controlled) spherebot, which doesn’t have any external moving parts that can get snagged or gunked up.  Traditional (“pendulum-driven”) spherebots are, in effect, small wheeled rovers tucked inside lightweight spherical shells; when the rover drives up one side of the shell, the system center of mass shifts ahead of the contact patch with the ground, and a component of the acceleration due to gravity goes to torque the vehicle.  There is a fundamental performance limitation associated with the amount of torque that this class of vehicle can produce.  Our spherebot design (iceCube) overcomes this limitation with an entirely different actuation strategy, leveraging reaction wheels or control moment gyros (CMGs) to gradually build up and store a large amount of angular momentum within the spherebot, then quickly transmitting this angular momentum onto the frame of the spherebot, either by applying a brake to the reaction wheel, or gimbaling the CMG array appropriately, thus providing a robust mechanism for generating significantly more torque than possible with other spherebot designs.

© 2017 by Thomas Bewley