Light-Powered Soft Robots Can Keep Jumping Without Ever Being Reset

Engineers at North Carolina State University have developed a teardrop-shaped soft robot that can keep jumping under infrared light without needing to be reset between leaps. The design, described in a paper in the Proceedings of the National Academy of Sciences, demonstrates a new mechanism for self-resetting jumping behavior in soft robotics.

"This 'ring leaper' design is very simple," said Jie Yin, corresponding author and professor of mechanical and aerospace engineering at NC State. "We use torsion to store elastic energy and then release that energy all at once. And the nature of the design means that it does not need to be reset between jumps. It resets itself." The robot is made from a liquid crystal elastomer ribbon shaped into a teardrop, with a thin V-shaped aluminum tube attached at one end. Infrared light causes the ribbon's surface to contract, making it rotate; the stiff V forces it to twist progressively tighter until the stored energy releases all at once, snapping the V down and launching the robot into the air before it returns to its original shape and repeats the cycle.

A simple change to the angle of the V-shaped end determines how the robot moves, said Fangjie Qi, the paper's first author and a postdoctoral researcher at NC State. A 120-degree angle makes the robot crawl forward, a 90-degree angle makes it jump forward, and a 50-degree angle makes it leap vertically. Adding a small amount of weight to the rounded end can also improve jumping distance by shifting the robot's center of mass, similar to a swimmer leaning forward off a starting block. Infrared light intensity must be strong enough to trigger jumping but not so strong that it causes erratic, unpredictable movement.

In proof-of-concept tests, the teardrop-shaped robots successfully leaped across slopes and hurdles and moved over grass, sand, rocks and mulch. The researchers are not proposing an immediate practical use for the design. "There are no immediate applications for this work, but it's a fundamental advance that is worth exploring for potential use in environmental navigation, swarm robotics, and unstructured terrain navigation," Yin said.