Caterpillar-like soft robot showcases great mobility skills

A soft robot that can move forward, backwards and dip under narrow spaces, imitating caterpillars, has been developed by researchers at North Carolina State University.

The caterpillar-like robot developed by the North Carolina researchers could offer a new approach to locomotion for soft robotics.

The caterpillar-bot’s movement is driven by a novel pattern of silver nanowires that use heat to control the robot’s bending, allowing users to steer its movements in either direction.

“A caterpillar’s movement is controlled by local curvature of its body – its body curves differently when it pulls itself forward than it does when it pushes itself backward,” said Yong Zhu, a leader of the research. 

The team drew inspiration from the caterpillar’s biomechanics. The robot uses its nanowire heaters to control a curvature similar to that of the animals, which allows it to copy the way it moves.

The robot is made of two layers of polymer, which respond differently when exposed to heat: the bottom layer shrinks, or contracts, while the top one expands. The polymer layer also has a pattern of silver nanowires embedded in it, which includes multiple lead points where researchers can apply an electric current and control which sections of the nanowire pattern heat up. 

The finding is significant to the field of robotics, as developing soft robots that can move in two different directions is a significant challenge. 

“The embedded nanowire heaters allow us to control the movement of the robot in two ways,” Zhu said. “We can control which sections of the robot bend by controlling the pattern of heating in the soft robot. And we can control the extent to which those sections bend by controlling the amount of heat being applied.”

The researchers demonstrated that the caterpillar bot’s movement could be controlled to the point where users were able to steer it under a very low gap – similar to guiding the robot to slip under a door. In essence, the researchers could control both forward and backward motion as well as how high the robot bent upwards at any point in that process.

“We demonstrated that the caterpillar bot is capable of pulling itself forward and pushing itself backwards,” said Shuang Wu, the first author of the paper. “In general, the more current we applied, the faster it would move in either direction.

“However, we found that there was an optimal cycle, which gave the polymer time to cool – effectively allowing the ‘muscle’ to relax before contracting again. If we tried to cycle the caterpillar-bot too quickly, the body did not have time to ‘relax’ before contracting again, which impaired its movement.”

This approach to driving motion in a soft robot is highly energy efficient and could prove highly significant in the future of robotics. 

The researchers’ next step is to make the process even more efficient by integrating this approach to soft robot locomotion with sensors or other technologies for use in various applications, such as search-and-rescue devices.

The scientists’ findings were published in the paper ‘Caterpillar-Inspired Soft Crawling Robot with Distributed Programmable Thermal Actuation‘, published in the journal Science Advances.

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