KRITTER - A Novel Wheel-on-Limb Robot for Training Planetary Rover Suspension Control

Current planetary rover systems rely on purely passive suspension mechanisms which, while simple, greatly limit their mobility capabilities. As areas of interest to planetary science communities shift to more difficult to navigate terrain, new classes of rovers are required which, in turn, require new supporting autonomy capabilities. Articulated suspension systems, which use actively controlled joints, are emerging as an alternative means of supporting rover motion in rough terrain. Wheel-on-limb rovers, which combine high-degree-of-freedom manipulators with wheels, are popular in prototype rover systems as a flexible means of combining driving with articulated suspension and walking motion for rough terrain traversal. To date, the autonomous control of these systems has been limited to manually created gaits and motion types, preventing them from fully using their dexterity and limiting their use for completing real exploration missions. This paper describes KRITTER, a novel wheel-on-limb robot design to be used as a research platform for flexible, multi-modal control of planetary rovers. The system is designed to allow for flexible walking and driving motion, using limbs as legs for quasi-static walking or as articulated suspension for driving or hybrid motion. The system’s manipulator-based suspension allows KRITTER to mimic the suspension systems of other vehicles or use novel mobility modes to navigate difficult terrain. Electromechanical hardware for the system is detailed and is used as the basis for generalized kinematic control of wheel-on-limb systems. A general control scheme for commanding the system is described, enabling custom suspension control policies to position individual limbs while maintaining continuous wheel-ground contact.