Eversion Robotic Mechanism with Hydraulic Skeletonto Realize Steering Function

For rescue or endoscope applications, snake-like robots have been extensively studied to access and explore confined spaces, such as small-diameter holes or complicated debris. Among them, eversion robot which can evert their flexible surface membrane to extend, exhibit high-mobility performance, even in fragile or soft ground, because they can move without friction or slippage. However, the steering mechanism of these flexible robots require a rigid environment or complex mechanisms to maintain their curved shape. In this study, we realize a long eversion robot with a selectable extension direction and with a retractable function using an 'unsealed' liquid-driven system that takes advantage of a high-density liquid. It comprises a container whose upper-part is open, an eversion robot, and a hollow steering mechanism inserted within the robot. The theoretical analysis of the steering is presented, and the generated friction and required tension under several conditions are measured. Experimentally, we determine the minimum diameter of the steering mechanism, which can minimize friction and enable retraction. The inner tubular mechanism can be operated independently during eversion of the outer membrane structure; therefore, the steering mechanism can be replaced with other structures, such as cameras and inspection sensors.