Tetraflex: A Multigait Soft Robot for Object Transportation in Confined Environments

Unstructured environments call for versatile robots with adaptable morphology that can perform multiple goal-directed actions including locomotion in confined spaces, environmental mapping, object retrieval and object manipulation. In response to these challenges, we present the Polyflex design concept for fabrication of modular, soft truss robots and demonstrate its varied capabilities in a tetrahedral robot (Tetraflex). Tetraflex is composed of six pneumatically actuated bellows joined at four points by rigid nodes. By extending or contracting the bellows, Tetraflex is capable of large size and shape change, and rolling, crawling and bounding gaits. Furthermore, Tetraflex is able to roll onto and engulf objects then subsequently transport them with the crawling gait. The rolling gait discretises Tetraflex's locomotion into predictable steps on a triangular grid, simplifying odometry and allowing the use of path planning to attain a desired position. The size of rolling step can be changed at any time by dynamically varying the size of the robot. The crawling and bounding gaits enable Tetraflex to move in smaller incremental steps or through narrow passages (80 mm wide). The maximum speed was attained with a bounding locomotion gait at 19.6 mm/s (0.15 body lengths per second, or BL/s). Rolling locomotion attained between 15.6 and 19.4 mm/s (0.12–0.15 BL/s), and crawling 7.8 mm/s (0.06 BL/s). The rolling gait was the most accurate gait, achieving 2.3% linear deviation. The flexibility and versatility of Tetraflex in morphology, locomotion and object transportation demonstrates its suitability for deployment in a wide range of environments and for applications including surveying, search and rescue, and remote sample collection.