A groundbreaking study has led to the development of the “hyperelastic torque reversal mechanism” (HeTRM), a new approach that allows robots made from soft, rubber-like materials to perform rapid and powerful movements. Published in Science Robotics, this research was led by Professor Kyu-Jin Cho from Seoul National University’s Department of Mechanical Engineering. The study draws inspiration from nature, specifically the remarkable abilities of the mantis shrimp and flea, known for their extraordinary power and speed despite their soft bodies.

The mantis shrimp is famous for delivering punches at speeds of up to 90 km/h to break through prey, while the flea can leap to heights exceeding 200 times its body length. According to Professor Cho, the secret behind these organisms’ ability to generate such powerful forces lies in the “torque reversal mechanism,” which allows for the rapid switching of rotational force direction applied by muscles to their limbs. This discovery has now been adapted into the field of soft robotics.

Previously, Professor Cho’s team developed flea-inspired robots capable of achieving high jumps on land and water. The latest development marks a significant advancement, enabling soft, rubber-like structures to generate powerful performance.

The key to the hyperelastic torque reversal mechanism is the use of soft hyperelastic materials that stiffen rapidly when compressed. The team found that when compression is applied to one side of a flexible joint, it reaches a critical point where the stored energy is released instantaneously. With a simple structure that connects a tendon and motor to a flexible joint, the robot can achieve repetitive, powerful bending motions similar to the natural cilia found in many organisms.

The research team has demonstrated several practical applications of HeTRM. A soft gripper, based on this principle, is capable of instantly catching falling ping-pong balls. Other applications include a robot that can crawl over rough terrain like sand, utilizing strong propulsion, and a robot that mimics the rapid wrapping motion of an octopus tentacle around objects. The team even demonstrated a mechanical fuse that activates when the robot encounters unintended external forces that exceed a set threshold.

Co-first authors Wooyoung Choi, now at Naver Labs, and Woongbae Kim, currently at the Korea Institute of Science and Technology, explained that their innovation in this field involves leveraging material properties rather than relying solely on structural designs. “The instant wrapping of slap bracelets, driven by a rapid transition between two stable states known as snap-through, is a behavior that many have attempted to mimic, but our novel approach uses material properties to achieve this function,” they explained.

Professor Cho expressed optimism about the future of this research, saying, “This technology will expand the horizons of soft robotics design and applications, paving the way for more versatile and efficient soft robots.”

By Impact Lab