Soft robots mimic mantis shrimp’s punch and flea’s leap for added power

A research team has taken inspiration from principles found in nature and developed the “hyperelastic torque reversal mechanism” (HeTRM), which enables robots made from rubber-like soft materials to perform rapid and powerful movements. This study is published in Science Robotics, and the researchers were led by Professor Kyu-Jin Cho from Seoul National University’s Department of Mechanical Engineering.

The mantis shrimp delivers a punch at speeds of up to 90 km/h to break its prey, while the flea can jump to heights exceeding 200 times its body length. Professor Kyu-Jin Cho explained, “The secret behind these organisms’ ability to generate powerful forces with their soft bodies lies in the ‘torque reversal mechanism,’ which enables the instantaneous switching of rotational force direction applied by muscles to their limbs.

“Our research team previously developed flea-inspired robots capable of achieving high jumps both on land and water; and this latest study is particularly significant as it is an advancement that achieves powerful performance in soft, rubber-like structures.”

According to the research team, the core principle of the developed hyperelastic torque reversal mechanism lies in leveraging the characteristics of soft hyperelastic materials, which rapidly stiffen as they compress. The team developed upon their discovery that when compression is concentrated on one side of a flexible joint, it reaches a critical point where the stored energy is released instantaneously. They explained that even with a simple structure that connects a tendon and motor to a flexible joint, repetitive and powerful bending motions could be realized, just like the cilia found in nature.

The research team expanded this principle and demonstrated various practical applications. The soft gripper utilizing the developed principle can instantly catch falling ping-pong balls, while other applications include a robot that crawls over rough terrain like sand with strong propulsion and a robot that rapidly wraps around objects like an octopus tentacle, showcasing fast and powerful movements. Furthermore, they demonstrated a mechanical fuse that is triggered when the structure encounters unintended external forces exceeding a certain threshold.

Co-first authors of the research Wooyoung Choi (currently at Naver Labs) and Woongbae Kim (currently at the Korea Institute of Science and Technology) explained, “The instant wrapping of slap bracelets is driven by a rapid transition between two stable states, known as snap-through. While many efforts have been made to mimic this behavior, we introduced a novel approach by leveraging material properties rather than structural designs.”

Professor Kyu Jin Cho expressed his optimism about the research, stating, “This technology will expand the horizons of soft robotics design and applications.”