In a recent study published in Advanced Science, researchers introduced a small, soft robot that looks deceptively simple—a closed ring made of liquid crystal elastomers (LCE). But don’t let its appearance fool you. This autonomous robot can crawl along three-dimensional tracks, climb steep inclines, carry loads far heavier than itself, and even weave through complex paths like spirals or knotted threads. And it does all of this under a constant beam of infrared (IR) light—no external control systems required.
Study: Aerial Track‐Guided Autonomous Soft Ring Robot. Image Credit: Fangjie Qi, NC State University
At the heart of its motion is a clever trick inspired by aerial tram systems. The robot flips itself over repeatedly, and thanks to its twisted structure, this motion is converted into forward movement using principles from screw theory. It’s a compact, elegant design that solves a long-standing challenge in soft robotics: navigating complex environments with precision, using only passive materials and a single, unchanging energy source.
Why 3D Navigation Is So Hard in Soft Robotics
Soft robotics has made impressive strides in mimicking biological motion, crawling, inching, swimming, but achieving reliable movement in 3D space remains tricky. That’s because soft materials, while flexible and safe, are difficult to control. Directing them along complex paths often requires elaborate, real-time actuation systems, which undermines the very simplicity and adaptability that make soft robots attractive.
Some systems have drawn inspiration from nature or mechanical transport—think plant tendrils or cable cars—by following predefined tracks. But until now, soft robots have typically required precise, time-dependent stimuli like moving light or magnetic fields to stay on course, and even then, they’ve mostly been limited to flat surfaces or simple curves.
This LCE ring robot changes the game by autonomously following intricate 3D paths with nothing more than steady IR illumination.
How it Works: Turning Flips into Forward Motion
The robot starts as a ribbon of twisted LCE, which is then bent into a loop and bonded at the ends. When exposed to infrared light, one side of the ribbon heats up more than the other, creating a thermal gradient that generates torque. This torque causes the ring to flip over itself, continuously rotating around its centerline.
Now, here’s where the twist pays off—literally. When the ring is curled once around a suspended thread, that flipping motion is converted into linear travel along the track. The behavior is similar to how a screw moves through a surface: rotation becomes translation.
Several factors influence how well the robot moves—its twist direction (chirality), the angle and direction of incoming light, and the physical interaction between the ring and the track. The most efficient motion occurs when the light hits the ring perpendicularly, the ring is positioned at an optimal distance from the IR source, and just a single loop is wrapped around the track.
One of the robot’s biggest strengths is how well it adapts to different tracks. It can move across surfaces of varying materials and diameters, from steel wire to human hair to plastic tubing. While friction affects speed, smoother surfaces make for faster travel—the robot keeps moving even when facing obstacles like knots or sharp bends.
It also hauls weight impressively well. While heavier loads do slow it down, the robot can carry more than 12 times its own mass. And since its motion is entirely driven by light, it doesn’t need feedback systems or corrections to handle slopes, curves, or even shifting tracks in 3D space.
What Sets it Apart
Compared to other soft robotic systems, the LCE ring robot offers a few standout advantages:
- True 3D mobility: It can travel in and around complex, three-dimensional geometries, not just along flat paths.
- Predictable trajectories: Following a fixed track eliminates the randomness often seen in free-moving soft robots.
- Simplified actuation: With only constant IR light required, the system avoids complex stimulus timing or control circuits.
All of this points to real-world potential. This type of robot could be especially useful in confined or unpredictable environments—inside the body for medical applications, in industrial systems with narrow channels, or in remote locations where traditional actuation isn’t feasible.
Final Thoughts
This study presents a creative solution to a difficult problem: how to get soft robots to move reliably through 3D space without sacrificing simplicity. The LCE ring robot is compact, self-contained, and surprisingly capable, turning a basic flipping motion into a reliable crawling behavior across a wide range of conditions.
It’s a reminder that sometimes, elegant mechanics paired with smart material design can go a long way—even without motors, sensors, or software.
Journal Reference
Qi, F., Zhou, C., Qing, H., Sun, H., & Yin, J. (2025). Aerial Track‐Guided Autonomous Soft Ring Robot. Advanced Science. DOI:10.1002/advs.202503288. https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202503288
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