Locomotion Strategies and Mobility Characterization of a Spherical Multi-legged Robot


Mobile robotics has seen a wide variety of mechanisms and strategies for motion in diverse terrain. Some robots employ rolling, some use legs for walking, some can hop, and some are capable of multiple of these modes. In this paper, we present the latest Robotic All-Terrain Surveyor (RATS) prototype as a unique design that can emulate a variety of locomotion modes by virtue of its geometric design and type of actuation. The novel robot has a spherical body the size of a soccer ball with 12 legs symmetrically distributed around its surface. Each leg is a singleDOF pneumatic linear actuator, oriented normal to the spherical body. Thorough investigation of this prototype’s mobility and actuation behavior has demonstrated the feasibility of tipping, hopping, and prolonged rolling locomotion by altering the actuation patterns of its legs. Here we summarize the experimental results of this characterization and present an understanding of the system’s performance limitations in an effort to draw insight for controlling its movements. We also discuss the effectiveness of RATS mobility strategies for varied terrains in light of initial testing on flat surfaces. INTRODUCTION Planetary exploration and locomotion has historically been the domain of wheeled robots. Such platforms may be stable and reliable, but there are serious drawbacks when these robots ∗Address all correspondence to this author. FIGURE 1. RATS IS A 12-LEGGED PNEUMATIC ROBOT DESIGNED FOR MULTI-MODAL LOCOMOTION. must maneuver through rough, uneven terrain with obstacles. As a result, there has been strong interest in recent years to develop robots that combine other forms of mobility to better handle diverse terrain. The Robotic All-Terrain Surveyor (RATS) is a new approach 1 Copyright c © 2010 by ASME to the hopping robot concept. It is a spherical robot designed for multiple modes of locomotion using its 12 single-DOF pneumatic piston legs. The robot is powered by a high-pressure tank at its center and its piston legs are evenly spaced and oriented radially, normal to the surface of the sphere. RATS is unique in its diverse modes of locomotion resulting from these simple actuators. The robot has demonstrated ability to hop for obstacle avoidance and execute discrete tipping/walking. Simulation results indicate high-speed rolling/running is possible using more rapid, closed-loop sequencing of leg actuations. Its round shape makes rolling more efficient, and the symmetry inherent in the RATS design means there is no “right-side-up.” It has no need for self-righting mechanisms or procedures, because the robot is stable and equally capable of motion regardless of its initial orientation. To understand the advantages of the RATS mobility system, this paper first reviews other examples of robot mobility with similarities to individual traits of RATS. We then present a description of the novel design of the RATS mechanism and analyze its mobility characteristics. The physical behavior of the system has been explored through a series of trials and experiments. The results of this testing illuminate the strengths and deficiencies of the prototype design and provide insight for the development of control strategies for mobility. We also present some initial locomotion testing performed on flat terrain and discuss the effectiveness and appropriate application of the various RATS locomotion modes based on these results.

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@inproceedings{Wagenknecht2010LocomotionSA, title={Locomotion Strategies and Mobility Characterization of a Spherical Multi-legged Robot}, author={Bryan Ellis Wagenknecht}, year={2010} }