Snakelike robot made with Kirigami

Snake-inspired robot wriggles without rigid parts

Image credit: Ahmad Rafsanjani/Harvard SEAS

Researchers at Harvard University have created and tested a robot which moves with a snake-like motion, using a variation of origami to grip and slide across the ground.

While some robots – such as Honda’s ASIMO or Boston Dynamics’ BigDog – have legs like us and our favourite companion animals, this type of motion is inappropriate in many situations. When exploring a disaster zone or crawling inside machinery, for instance, it is more beneficial for robots to move like low-slung worms or snakes.

Snakes use their scales to grip the ground and propel the body onwards – a type of motion known as friction-assisted locomotion – allowing them to slither faster than 6m/s, swim and climb trees.

Inspired by this versatile motion, a team of engineers at Harvard’s John A. Paulson School of Engineering and Applied Sciences have developed a serpentine robot capable of moving without the use of rigid parts.

The shape and arrangement of a real snake’s scales are vital when it comes to propelling itself forwards. The researchers created their own version of a snake’s scales using Kirigami, a variation on origami which uses cuts and folds to create 3D ornaments with sheets of paper.

The engineers started with a flat plastic sheet, which they sliced in various ways – with triangles, circles and trapezoids – using a laser cutter. They wrapped this sheet around a tube-like actuator, which uses air to expand and contract. They packed a small power supply into its tail.

When the robot extends its body, its cuts pop out of the sheet, transforming it into a textured surface which grips the ground. When the robot contracts, these cuts are flattened and the robot shifts forwards.

“There has been a lot of research in recent years into how to fabricate these kinds of morphable, stretchable structures,” said Dr Admad Rafsanjani, first author of the study detailing the development of the robot.

“We have shown that Kirigami principles can be integrated into soft robots to achieve locomotion in a way that is simpler, faster and cheaper than most previous techniques.”

The researchers tested the soft, serpentine robot on Harvard’s campus, and found that trapezoidal cuts – which approximately resemble snake scales – allow for the robot to move with longer motions.

“We believe that our Kirigami-based strategy opens avenues for the design of a new class of soft crawlers,” said Professor Katie Bertoldi, senior author. “These all-terrain soft robots could one day travel across difficult environments for exploration, inspection, monitoring and search and rescue missions, or perform complex, laparoscopic medical procedures.”

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