Twisted soft robots self-navigate mazes

The soft robots, developed by researchers at North Carolina State University and the University of Pennsylvania, are made of liquid crystal elastometers in the shape of a twisted ribbon resembling translucent rotini. 

Jie Yin, associate professor of mechanical and aerospace engineering at NC State and corresponding author of a paper on the work, said that the robots demonstrate a concept called ‘physical intelligence’, meaning structural design and smart materials are what allow the robots to navigate various situations as opposed to computational intelligence.

The team explained that when the ribbon is placed on a surface that is at least 55°C (131°F), which is hotter than the ambient air, the portion of the ribbon touching the surface contracts, while the portion of the ribbon exposed to the air does not. This induces a rolling motion in the ribbon, and the warmer the surface, the faster it rolls.

“This has been done before with smooth-sided rods, but that shape has a drawback – when it encounters an object, it simply spins in place,” said Yin. “The soft robot we’ve made in a twisted ribbon shape is capable of negotiating these obstacles with no human or computer intervention whatsoever.”

According to researchers, the ribbon robot does this in two ways. First, if one end of the ribbon encounters an object, the ribbon rotates slightly to get around the obstacle. Second, if the central part of the robot encounters an object, it ‘snaps.’ The snap is a rapid release of stored deformation energy that causes the ribbon to jump slightly and reorient itself before landing.

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The ribbon may need to snap more than once before finding an orientation that allows it to negotiate the obstacle, but ultimately it always finds a clear path forward, researchers said.

Yin added that in this sense, it’s much like the robotic vacuums that many people use in their homes, except the team’s soft robot draws energy from its environment and operates without computer programming.

“The two actions, rotating and snapping, that allow the robot to negotiate obstacles operate on a gradient,” said Yao Zhao, first author of the paper and a postdoctoral researcher at NC State. “The most powerful snap occurs if an object touches the centre of the ribbon. But the ribbon will still snap if an object touches the ribbon away from the centre, it’s just less powerful. 

“And the further you are from the centre, the less pronounced the snap, until you reach the last fifth of the ribbon’s length, which does not produce a snap at all.”

The team conducted multiple experiments demonstrating the robot’s capability of navigating a variety of maze-like environments. They also demonstrated that the soft robots would work well in desert environments, showing capability to climb and descend slopes of loose sand.

Yin said this provides new insights into how soft robots can be designed to harvest heat energy from natural environments and autonomously negotiate complex, unstructured settings such as roads and harsh deserts.