Cleverly scurrying “Spirelli robots”

They look like transparent Spirelli pasta – but they are soft robots with amazing abilities. © Yao Zhao

They have neither control technology nor batteries: researchers have developed ingeniously simple soft robots that can only navigate through complex environments using their so-called physical intelligence and energy from the environment. The Spirelli noodle-like structures made of a twisted strip of liquid-crystal elastomer move in a directed manner on warm surfaces and can even wriggle out of mazes. The principle could benefit the development of new concepts in robotics, say the scientists.

They should be able to cope with special environmental challenges and complete missions independently: research teams around the world are currently working on robots with many different characteristics and for different areas of application. A special division is the so-called soft robotics: Instead of hard structures, developers use soft materials to produce robots with “soft” and flexible properties. They are also usually controlled by humans or by means of electronics based on integrated data processing.

Material and structure instead of complex technology

But the navigation capabilities of the soft robots, which the researchers led by Jie Yin from North Carolina State University are now presenting, are not based on external steering or integrated software. “Our designs demonstrate a concept called physical intelligence. This means that the structure and smart materials allow the soft robot to navigate in different situations, as opposed to computational intelligence,” explains Yin. The concept of their development seems correspondingly simple: their soft robots are twisted ribbons made of liquid crystal elastomer material that look like transparent Spirelli noodles.

The secret of their ability to move lies in the strong reactions of the plastic material to temperature differences: If you place one of the structures on a surface that is at least 55 degrees Celsius warm, the parts of the twisted ribbon that touch the surface contract due to the heat. The elevated parts, which are only exposed to the cooler air, remain unchanged. The scientists explain that these processes then trigger dynamics that lead to a directed rolling movement of the structure. The warmer the surface, the faster the robot will wriggle forward. “Similar things have been shown for smooth-sided sticks, but this simple shape had the disadvantage that the object just rotates in place when it encounters an obstacle,” says Yin. “The soft robot that we made in the form of a twisted ribbon, on the other hand, is able to avoid such obstacles without human or computer intervention.”

“Brainless” clever on the go

According to the researchers, the “Spirelli robot” achieves this in two ways: When part of the structure encounters an object, it can turn sideways to move around the obstacle. Second, there is a kind of snapping effect when the middle part of the robot hits an object. By continuing to move with partial obstruction, it accumulates deformation energy, which can then be discharged abruptly. This causes the robot to jump slightly, which also allows for a new orientation. In this way, he can finally get back on track and continue his way through an obstacle course.

The scientists used various experiments to show what the concept can achieve. The robots were therefore able to move over differently structured surfaces – including granular surfaces. They were even able to overcome sandy obstacles with an incline of up to 15 degrees. The physical intelligence was particularly evident when used in labyrinth systems: The simple structures could only find their way to the exit without help thanks to the material and the structural design. “The principle is similar to the autonomous vacuum cleaner robots that many people use at home,” says Yin. “Only that the soft robot we developed draws its energy from its environment and does not require computer programming”.

As the team concludes, the concept is more than a curious gimmick: “The system is interesting and fun, but more importantly, it provides new insights into how we might design soft robots capable of absorbing heat energy.” from natural environments and move autonomously in complex, unstructured environments such as roads and harsh deserts”. says Yin.

Source: North Carolina State University, professional article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2200265119

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