Shrimp and fleas are inspiring the latest generation of robotics as a team of researchers is employing soft, rubbery materials to generate powerful motion.
Professor Kyu-Jin Cho, Director of the Soft Robotics Research Center at the Seoul National University College of Engineering, led the team in developing the “Hyperelastic Torque Reversal Mechanism (HeTRM).” The new mechanism is the latest development in a long line of bug-inspired robots.
Tiny Creatures With Great Power
While the tiny creatures may often escape human notice, mantis shrimp and fleas carry incredible power for their size. A mantis shrimp kills its prey with a 90 km/h punch, while a flea can jump 200 times its body length. It’s no wonder that these incredible creatures inspire scientists and engineers to imitate their construction.
“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,” Cho explained.
“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.”
Hyperelastic Properties Come To Robotics
Hyperelastic materials are the core element of the “Hyperelastic Torque Reversal Mechanism,” with which Cho’s team worked. Leveraging the material’s ability to stiffen as it compresses, the team discerned that the compression concentrates on one side of a flexible joint until reaching a critical threshold where all the stored energy is instantly released. A simple structure connecting a motor to a flexible joint can create powerful repetitive motions resembling cilia.
“As I analyzed this phenomenon, I discovered that such structural transitions operate similarly to how cilia function in nature. The cilium is a structural design found in nature that uses phase transitions to produce efficient and repetitive movements,” Cho said.
“Inspired by this natural design, I realized that applying the principles of cilia to soft robotics could enable the creation of new types of motion without complex mechanisms. This discovery became the foundation and motivation for initiating this research.”
Showcasing The Future Of Robotics
In practical demonstrations, the research team evidenced expanded applications of this principle. One of their real-world examples was a soft gripper capable of instantly catching falling ping pong balls. In another example, they developed a robot capable of traversing challenging terrain like sand.
Additionally, one robot displayed the ability to wrap itself around objects, similar to the behavior of an octopus tentacle. Finally, they showed a mechanical fuse that trips when a structure encounters a certain amount of unexpected pressure.
“Our robot is made of soft, stretchy materials, kind of like rubber. Inside, it has a special part that stores energy and releases it all at once—’BAM!’—to make the robot move super fast,” Cho commented. “It works a bit like how a bent tree branch snaps back quickly or how a flea jumps really far. This robot can grab things like a hand, crawl across the floor, or even jump high, and it all happens just by pulling on a simple muscle!”
Next Steps for Robotics
With proof of concept in hand, Cho envisions expanding the applications of this tech in new directions, including other scales and environments. To facilitate these new dimensions, a major focus area will be enhanced performance analysis. The analysis will involve sophisticated modeling of shear stress and finite element analysis, which models how a product will physically react to forces like heat and vibration.
“In addition, we will enhance the practicality by applying HeTRM to larger systems or complex multi-joint soft robots, and also the efficiency and durability of the mechanism will be improved through performance optimization of hyperelastic materials and utilizing multiple materials,” Cho added.
“Furthermore, we encourage other researchers to actively incorporate nonlinear dynamic mechanisms, such as snap-through, into soft robotic designs. Such approaches will play a crucial role in developing energy-efficient and multifunctional soft robotic systems.”
The paper “A Hyperelastic Torque-Reversal Mechanism for Soft Joints with Compression-Responsive Transient Bistability” appeared on February 06, 2025, in Science Robotics.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.