New soft robots can be used to navigate and map unknown environments

The robots, coined as twisted ringbots, are made of ribbon-like liquid crystal elastomers that are twisted and then joined together at the end to form a loop. 

When the robots are placed on a surface that is at least 55^oC, 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; the warmer the surface, the faster the robot rolls. 

The twisted ringbot also spins along its central axis, and as it moves forward it travels in an orbital path around a central point, essentially moving in a large circle. However, if the twisted ringbot encounters a boundary – like the wall of a box – it will travel along that boundary. 

In a statement, Fangjie Qi, first author of the paper and a Ph.D. student at NC State, said: "Regardless of where the twisted ringbot is introduced to these spaces, it is able to make its way to a boundary and follow the boundary lines to map the space’s contours. 

“We were also able to map the boundaries of more complex spaces by introducing two twisted ringbots into the space, with each robot rotating in a different direction. This causes them to take different paths along the boundary. And by comparing the paths of both twisted ringbots, we’re able to capture the contours of the more complex space.” 

These robots are examples of devices whose behaviour is governed by physical intelligence, meaning their actions are determined by their structural design and the materials they are made of, rather than directed by a computer or human intervention. 

Researchers were able to fine-tune the behaviour of the twisted ringbot by engineering the geometry of the device. For example, speed can be influenced by varying the width of the ribbon, or the number of twists in the ribbon. 

“In principle, no matter how complex a space is, you would be able to map it if you introduced enough of the twisted ringbots to map the whole picture, each one giving part of it,” said Jie Yin, corresponding author and an associate professor of mechanical and aerospace engineering at NC State.  

“And, given that these are relatively inexpensive to produce, that’s viable.” 

“Soft robotics is still a relatively new field,” said Yin. “Finding new ways to control the movement of soft robots in a repeatable, engineered way moves the field forward. And advancing our understanding of what is possible is exciting.” 

The research was supported by the US National Science Foundation, and the paper, 'Defected Twisted Ring Topology For Autonomous Periodic Flip-Spin-Orbit Soft Robot' will be published in Proceedings of the National Academy of Sciences this week.