Bistable Steering Mechanism for Enhanced Control in Soft Toroidal Robots

Navigating confined and complex environments, such as pipes, biological tissues, and collapsed debris, has remained a challenge for conventional robotic systems, which often struggle with maneuverability and adaptability. Soft toroidal robots offer a promising alternative, with a compact and lightweight toroidal shape that allows continuous movement without requiring bulky external equipment. However, the lack of a steering mechanism has limited their applicability in dynamic and complex terrains. To overcome this, we developed a steering mechanism that leverages the bistable characteristics inherent in the toroidal structure to enable curvature formation. By adjusting the position of the tail within the structure, the robot can change its direction of bending, enabling flexible and responsive steering. To achieve this bistable behavior, we utilized the orthotropic properties of ripstop nylon fabric, reducing the robot's bending stiffness and enhancing its steering capabilities. Through theoretical modeling and experimental validation, we identified key design parameters, such as optimal operating pressure and steering device length. The proposed soft toroidal robot, with a diameter of 70 mm and a total length of 400 mm, achieves 1-degree of freedom (DOF) steering by exploiting this bistable deformation. Our experiments demonstrated its ability to navigate a T-shaped pipe and climb vertically in confined spaces, achieving a maximum curvature of 13.4 m^-1. These findings highlight the potential of soft toroidal robots for maneuvering through both confined and open environments with enhanced adaptability and efficiency.