Caterpillar Robot with Built-In Steering System Crawls Easily Through Loops and Bends

Soft robots often face challenges in being guided effectively because adding steering mechanisms typically reduces their flexibility by increasing rigidity. Now, a team of engineers has combined ancient paper folding techniques with modern materials science to develop a soft robot that can easily navigate through mazes by bending and twisting. The new design integrates the steering system within the robot’s structure, effectively overcoming previous limitations in guiding the robot.

The new robot was created by engineers at Princeton University (Princeton, NJ, USA) and North Carolina State University (Raleigh, NC, USA) out of modular, cylindrical segments featuring an origami form called a Kresling pattern. These segments are designed to operate both independently and as part of a larger assembly, contributing collectively to the robot's mobility and directional control. The Kresling pattern enables each segment to twist into a flat disk and then return to its cylindrical shape, a motion that is fundamental to the robot's crawling and turning abilities. By partially folding part of a segment, the engineers can induce a lateral bend, and through a series of such small bends, the robot is able to change direction while advancing. This new system allows the robot not only to crawl forward and reverse but also to lift objects and assemble into longer formations. Its ability to assemble and split up on the move enables the robot to function either as a single entity or as part of a swarm.

Image: The robot`s segments can flatten and extend into cylinders (Photo courtesy of Princeton)

One of the most complex parts of this project was developing a mechanism that could control the bending and folding movements necessary for the robot's propulsion and navigation. The solution came from researchers at NC State University. They utilized two materials—a liquid crystal elastomer and a polyimide—that react differently under heat, shrinking or expanding respectively. These materials were integrated into thin strips positioned along the creases of the Kresling pattern. Additionally, each fold was equipped with a thin, stretchable heater made from a silver nanowire network. By passing an electrical current through the nanowire heater, the control strips are heated, causing the materials to react and create a fold due to their different rates of expansion. The amount of current and the specific materials used in the control strips are carefully calibrated to precisely manage the robot’s folding and bending, thus directing its movements and steering. The current version of the robot moves somewhat slowly, but the researchers are focused on enhancing speed in future iterations. They also plan to explore various shapes, patterns, and instabilities to further refine both the speed and steering capabilities of the robot.

“We have created a bio-inspired plug-and-play soft modular origami robot enabled by electrothermal actuation with highly bendable and adaptable heaters,” said Princeton engineer Glaucio Paulino. “This is a very promising technology with potential translation to robots that can grow, heal, and adapt on demand.”

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Princeton University
NC State University