Ravi Balasubramanian Legless Locomotion: Computer Science and Engineering, University of Washington, A Novel Locomotion Box 352350, Seattle, WA 98195-2350, USA Technique for Legged
[email protected] Alfred A. Rizzi Robots Boston Dynamics, 614 Massachusetts Avenue, Cambridge, MA 02139, USA Matthew T. Mason Robotics Institute, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213-3890, USA Abstract Our interest in the problem arose from experiments with a hexapod robot in uneven terrain. The robot, RHex (Saranli et We present a novel locomotion strategy called legless locomotion that al. 2001) (see Figure 1), has a simple design where each singly allows a round-bodied legged robot to locomote approximately when actuated compliant leg can rotate around its “hip”. While this it is high-centered. Typically, a high-centered robot is stuck since the design, inspired by a cockroach, offers significant mobility, robot’s legs do not touch the ground. Legless locomotion uses the legs RHex can be easily trapped when it becomes high-centered, as a reaction mass to set up oscillatory body rotations which when as there is no contact between its legs and the ground. The coupled with ground contact gradually translate the robot. Legless only possible means of locomotion when the robot becomes locomotion’s continuous dynamics differs from previously studied lo- high-centered is to use the dynamic effect of swinging the legs, comotion methods because of the simultaneous interaction of gravity- where the legs act simply as a reaction mass (see Extension 1). induced oscillations, a configuration-dependent system inertia, and However, the question of how the robot should swing its legs to non-holonomic contact constraints.