Soft robots: Pasta-shaped device with no moving parts can navigate through mazes

A soft robot made from a twist of rubber can harvest heat energy and use it to roll across a variety of surfaces and even escape mazes

By Matthew Sparkes

A soft robot with no motors, batteries or computers can roll over a range of surfaces and escape simple mazes by harvesting heat energy and turning it into motion.

Jie Yin at North Carolina State University and his colleagues created a spiral-shaped device from a narrow rectangle of rubber-like material impregnated with liquid crystals. When placed on a surface heated to at least 55°C, the areas of the robot touching the surface warm up and expand, while others remain static. This causes a twisting motion that rolls the device along at speeds up to 3.8 millimetres per second.

Although the robot has no computational ability, it can achieve relatively complex tasks such as navigating mazes. When the soft robot reaches an obstacle, its orientation is slightly changed and it will occasionally be able to continue moving. Failing that, it will continue to push against the obstacle until the tension in the device changes, causing it to quickly change shape from an arc in one orientation to an arc in the opposite orientation. This causes it to roll away in the opposite direction.

These two abilities mean that when placed in a maze it will continually change direction when meeting obstacles, bumping from surface to surface, eventually finding its way out despite lacking any intelligent control.

In tests, the soft robot was able to roll over smooth surfaces as well as sand and pebbles. It could even cope with gentle slopes such as sand dunes at an angle of 15 degrees to the horizontal. The 12-centimetre-long, 0.36-gram robot was also able to push a 0.3-gram aluminium cylinder along.

Yin says that the capabilities of these soft robots are limited by “materials intelligence” – the different ways that newly discovered materials can react to stimuli like heat or light – and “structural intelligence”, which is the way that inanimate designs can be made to take advantage of those reactions to create complex behaviours.

“Without both of them, it will not work,” he says. “This guy’s not like a robot, but his performance is like a robot. We show that with only a simple twist you can already achieve such interesting things. And if you make this guy more complex, like a more complex 3D structure, I believe it can encourage more advanced capabilities.”

Yin believes that the technology could be used to create cheap robots that can explore environments and take sensor readings, and that they could even be made on the microscopic scale for use within the human body.

Journal reference: PNAS, DOI: 10.1073/pnas.2200265119