WaLTER: A Wheel and Leg Tumbling Expedition Robot

For effective operation in challenging outdoor environments, mobile unmanned robots face stiff and competing demands including payload capacity, driving speed, range, as well as the ability to traverse rough terrain. To address these issues we introduce the hybrid wheel-leg quadrupedal robot WaLTER. WaLTER utilizes a unique combination of continuously rotating distal leg joints, actuated wheels, and a roll body DOF to efficiently drive on flat ground and effectively tumble over stairs and difficult, broken terrain. We developed an intuitive teleoperation scheme and employed deep reinforcement learning as proof of concept control techniques for the novel morphology. To test its capabilities, we constructed a multi-body simulation in MuJoCo and a 2.1 kg physical prototype for experimentation on traversability and energy economy. Our testing demonstrated the ability to traverse rougher terrain relative to larger-wheeled counterparts and reliable stair-climbing while maintaining a 4 km range on a 24.4 Wh battery (COT: 1.21).