Imagine a tiny robot that does not need a motor, battery, gears or complicated electronics to jump. Shine infrared light on it, and it can repeatedly leap into the air, land, return to its original shape and jump again—all without needing an external mechanism to reset it.
That is the remarkable behavior demonstrated by researchers at North Carolina State University (NC State), who have developed teardrop-shaped soft robots capable of crawling, jumping forward or even leaping vertically depending on their shape.
The research, published in the Proceedings of the National Academy of Sciences, introduces a simple but powerful mechanism for creating self-resetting jumping motion in soft robots. Although the technology is still at the proof-of-concept stage, it could eventually contribute to robots designed to move across difficult and unpredictable environments.
A Robot That Uses Light Instead of a Motor
The new robot, described as a “ring leaper,” has an unusually simple structure.
It is made from a ribbon of liquid crystal elastomer, a soft material that can change shape when exposed to heat or light. The ribbon is formed into a teardrop-like loop. At one end, researchers attach a thin aluminum tube bent into a V shape.
When infrared light shines on the robot, something interesting happens.
The surface of the soft ribbon contracts. Because of the robot's shape and the rigid V-shaped component, the ribbon cannot simply roll around in one place. Instead, the contraction causes the ribbon to rotate and twist.
As the twisting continues, the robot stores elastic energy.
Think of it like twisting a rubber band. The more you twist it, the more energy becomes stored inside it. Eventually, the rubber band wants to release that energy. The ring leaper works on a similar principle.
But instead of slowly releasing the stored energy, the robot suddenly releases it when the twisting reaches a critical point.
The Secret Behind the Jump
The V-shaped aluminum tube plays a crucial role.
As the soft ribbon twists tighter, the rigid V prevents the robot from simply rotating without producing useful movement. The increasing twist continues to store energy until the system becomes unstable.
At that moment, the stored energy is released almost instantly.
The V-shaped section snaps downward and strikes the surface beneath the robot. That sudden impact pushes against the ground and launches the entire teardrop-shaped robot into the air.
The robot then lands and returns to its original configuration.
Most importantly, it is already prepared for another jump.
As long as infrared light continues to illuminate the robot, the ribbon contracts again, the structure twists, energy builds up and another jump occurs.
This makes the system self-resetting.
Jie Yin, professor of mechanical and aerospace engineering at NC State and corresponding author of the research, describes the concept as a simple design that uses torsion to store elastic energy and release it all at once. Because of the robot's geometry, the structure automatically resets after each jump.
That eliminates the need for a separate motor or mechanical reset system.
One Small Design Change Can Completely Change Its Movement
One of the most interesting findings is that researchers can control how the robot moves by changing just one geometric feature: the angle of the V-shaped tube.
This seemingly small modification produces dramatically different behaviors.
When the V has a wide 120-degree angle, the robot does not jump. Instead, it primarily crawls forward.
Reduce the angle to 90 degrees, and the robot begins jumping forward.
Reduce it further to approximately 50 degrees, and the robot can leap almost vertically upward.
In other words, the same basic robot can perform three different types of movement simply by changing its geometry.
This is particularly interesting for soft robotics because traditional robots often require different mechanisms, motors or control systems to achieve different types of movement.
Here, mechanical design itself determines the robot's behavior.
Adding Weight Can Make the Robot Jump Better
The researchers also discovered that the robot's performance can be improved by making another relatively simple change.
By adding a small amount of weight to the rounded end of the teardrop, they could alter the robot's center of mass.
This helped produce a more powerful and stable forward motion.
The principle is similar to what happens when a swimmer prepares to dive. Moving the body's center of mass forward can influence the direction and stability of the movement.
For the robot, carefully positioning its mass can help it travel farther and more reliably after each jump.
This demonstrates how seemingly simple physical properties—shape, stiffness and mass distribution—can strongly influence the behavior of a soft robot.
Infrared Light Has to Be Carefully Controlled
Light intensity is another important factor.
The infrared light needs to be strong enough to activate the liquid crystal elastomer and trigger the robot's motion. But increasing the light intensity too much is not necessarily better.
According to the researchers, excessive infrared intensity can make the robot jump erratically and travel in unpredictable directions.
This means that controlling the energy input will be important if these robots are eventually developed for practical applications.
Rather than simply turning the light up as much as possible, future systems may need carefully controlled illumination to produce predictable movement.
Testing Across Difficult Surfaces
The researchers tested the robots in several challenging environments.
The teardrop-shaped robots were able to move across slopes and hurdles, as well as different types of natural surfaces.
Their demonstrations included environments containing grass, sand, rocks and mulch.
This is significant because uneven natural terrain can be extremely difficult for conventional wheeled robots.
Wheels work well on smooth and predictable surfaces, but rocks, loose sand, vegetation and obstacles can interfere with their movement. A robot capable of jumping over obstacles or changing between crawling and leaping could potentially have an advantage in such environments.
The ring leaper's movement is also generated through the interaction between its soft body and the surface beneath it, rather than through conventional wheels or legs.
Could This Lead to Autonomous Swarms?
The researchers emphasize that there are currently no immediate applications for the technology. It is still a fundamental research project.
However, its unusual movement mechanism could be valuable for future soft robotic systems.
One potential area is environmental navigation.
Small robots could eventually be designed to move through natural environments where conventional robots struggle. Instead of carefully calculating a route around every obstacle, a jumping robot might simply leap over certain barriers.
The technology could also be interesting for swarm robotics. Large numbers of simple, inexpensive robots could potentially work together to explore an environment.
Because the ring leaper does not require a conventional motor-driven jumping mechanism, its simple architecture could potentially make it attractive for applications where minimizing mechanical complexity is important.
Another possibility is unstructured terrain navigation, where robots need to operate across surfaces that are uneven, loose or filled with obstacles.
A Small Robot With a Big Lesson
Perhaps the most important aspect of this research is not the jumping itself.
The work demonstrates how mechanical design can replace complex control systems.
Instead of using motors, sensors and software to tell a robot exactly when and how to jump, researchers designed the robot so that its physical structure naturally creates the desired behavior.
Light provides the energy. The soft material converts that energy into motion. The geometry stores the energy through twisting. And the structure releases the energy automatically when a critical point is reached.
Then the robot resets itself and begins the cycle again.
That simplicity could become an important idea in the future development of soft robots.
The ring leaper is still far from becoming a practical field robot. Researchers will need to improve its control, reliability, efficiency and ability to navigate complex environments.
But the experiment demonstrates an intriguing possibility: robots do not always need complicated machines to perform complicated movements. Sometimes, carefully designed materials and geometry can do much of the work themselves.
And in this case, all it takes to keep the tiny robot jumping is a continuous beam of infrared light.
Reference:
A self-resetting soft ring for autonomous, continuous leaping in unstructured environments, Proc. Natl. Acad. Sci. U.S.A. 123 (35) e2607940123, https://doi.org/10.1073/pnas.2607940123 (2026).
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