A small frog-like robot has demonstrated a surprisingly powerful way to move: storing energy in flexible elastic rods and releasing it in sudden snaps.
Researchers from the UCLA Samueli School of Engineering and the University of Michigan have developed a robotic movement system that allows a compact robot to hop, flip, swim and travel across different surfaces without relying on large, powerful motors.
The study, published in Science Advances, shows how carefully designed elastic rods can act like mechanical springs, storing energy slowly and releasing it rapidly when they suddenly change shape.
A Simple Rod With a Powerful Trick
The key idea behind the robot is surprisingly simple.
When an elastic rod is bent and its ends are rotated, the rod stores mechanical energy as it becomes deformed. As the bending and twisting continue, the rod eventually reaches a critical point.
At that moment, instead of continuing to deform gradually, the rod can snap into another shape.
This sudden change releases some of the stored energy in a short burst.
The researchers discovered that the exact geometry of the rod determines how this energy is released. Some shapes deform smoothly, while others undergo a rapid snapping motion.
That difference is important because a sharp snap can produce a much stronger movement than the slow motion of the motor that caused the deformation.
The research was co-led by Khalid Jawed, an associate professor of mechanical and aerospace engineering at UCLA Samueli, and Xiaonan (Sean) Huang, an assistant professor of robotics at Michigan.
Turning Small Motor Movements Into Powerful Motion
Traditional small robots often face a major engineering problem: motors become less powerful as robots get smaller, while batteries and other components also have limited space and weight.
The snapping mechanism offers a different approach.
Instead of asking a motor to produce a powerful movement directly, the motor slowly winds up the elastic rod. The rod stores the energy, and when it reaches its critical configuration, the stored energy is suddenly released.
In other words, the motor does the slow work, while the elastic structure produces the rapid burst.
This could be particularly useful for miniature robots where adding a larger motor would increase weight and consume more power.
Unlike conventional beams or rigid structural components, these elastic rods can simultaneously experience bending, twisting and compression. This allows them to undergo large three-dimensional deformations.
The researchers also found that a helical rod can be created from a naturally straight rod simply by moving and rotating its ends with a motor.
That makes the mechanism relatively simple to build and potentially adaptable to different robot designs.
Researchers Predicted the Snap Before Building the Robot
Before creating the frog-like robot, the team developed computer models to understand how elastic rods behave under different combinations of bending and twisting.
They then tested those predictions using physical rods that were repeatedly deformed with a robotic arm.
The experiments helped the researchers identify the conditions under which the rods would snap sharply rather than deform gradually.
These findings became the design rules for the robot's snapping mechanism.
Once the researchers could predict when the rods would snap, they could carefully synchronize the motion with the robot's movement.
The result was a compact robot powered by helically shaped elastic rods acting as snap actuators.
A Small Robot That Can Move Across Six Surfaces
The prototype was only 11 centimeters long and weighed about 98.2 grams.
Despite its small size, the robot was tested on six different surfaces:
Wood
Cloth
Acrylic
Leather
Grass
Sand
The snapping robot moved faster than a comparable robot using rigid legs on all six surfaces.
On wood, it reached a peak speed of about 3.21 body lengths per second.
Across all six surfaces, it averaged approximately 2.46 body lengths per second.
The rigid-legged version averaged only about 0.79 body lengths per second.
The difference was particularly noticeable on cloth and grass, where the rigid-legged robot nearly stopped while the snap-powered robot continued moving.
This suggests that the flexible snapping mechanism can help small robots deal with surfaces where conventional rigid legs struggle.
The Robot Can Also Jump and Backflip
The elastic rods do more than help the robot move forward.
Because they can release energy very quickly, the mechanism can launch the robot into the air.
Researchers demonstrated repeated backflips, showing that the stored elastic energy can be directed into different types of movement.
This is important because jumping and flipping require rapid bursts of force. Producing those movements continuously with a small motor would be difficult, but an elastic structure can store energy and release it almost instantly.
The same basic robot was also modified for movement in water.
Researchers attached thin, flexible fins to the robot, allowing it to swim at approximately 0.5 body lengths per second.
It could turn and navigate around obstacles, even when wind disturbances affected its movement.
Testing the Robot in More Complicated Environments
The team also tested the robot in a sandbox containing rock obstacles.
Researchers remotely controlled the robot as it moved through the uneven environment.
They also combined the robot with light sensors to demonstrate autonomous steering, showing that the mechanical system could potentially work together with relatively simple sensing and control.
This points toward a broader idea in robotics: instead of solving every movement problem with software, sensors and powerful motors, researchers can sometimes build useful behavior directly into the robot's mechanical structure.
Why the Snapping Mechanism Matters
One of the most interesting aspects of this research is that the robot's performance comes partly from its geometry.
The researchers found that the shape of the elastic rod, rather than simply its physical size, determines whether it will snap sharply or deform gradually.
That means similar design principles could potentially work at different scales.
In the future, such mechanisms could be useful for robots that need to be extremely small while still producing fast and powerful movements.
Jawed explained that the approach could potentially help create robots only a few millimeters wide, where small motor movements are converted into much larger bursts of mechanical motion.
The concept could also reduce the need for continuously operating high-power motors.
A New Direction for Small Robots
The frog-like robot demonstrates how mechanical structures can function almost like an additional source of power.
The motor slowly stores energy in the elastic rods. The rods then release that energy rapidly, producing movement that would otherwise require a more powerful motor.
The experiments showed that this approach can support fast ground locomotion, jumping, backflips and swimming, while also allowing the robot to handle multiple types of terrain.
The researchers believe the broader opportunity is to design robots where the mechanics themselves perform part of the work normally handled by motors and complicated control systems.
For future small robots, that could be an important advantage. Instead of making the motor bigger, engineers may be able to make the robot's structure smarter.
The study, titled “Geometry-controlled instability pathway selection in elastic helices enables fast, efficient robotic locomotion,” was published in Science Advances in 2026. The research was led by teams from UCLA and the University of Michigan, with contributions from researchers at Vassar College and Newcastle University.
Reference: Dezhong Tong et al, Geometry-controlled instability pathway selection in elastic helices enables fast, efficient robotic locomotion, Science Advances (2026). DOI: 10.1126/sciadv.aeh2779
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