Snake locomotion inspires search and rescue robots

Snakes are very capable of slithering up trees, rocks and shrubbery and by studying how these serpents move, Johns Hopkins engineers have created a snake robot that can nimbly and stably climb large steps. The team's new findings are published in Journal of Experimental Biology and Royal Society Open Science.

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"We look to these creepy creatures for movement inspiration because they're already so adept at stably scaling obstacles in their day-to-day lives. Hopefully our robot can learn how to bob and weave across surfaces just like snakes," said Chen Li, an assistant professor of mechanical engineering at The Johns Hopkins University and the papers' senior author.

Previous studies had mainly observed snake movements on flat surfaces, but rarely in 3D terrain except for on trees, said Li, and don't account for real-life large obstacles such as rubble and debris that search and rescue robots would have to climb over.

Li's team first studied how the variable kingsnake, a snake living in deserts and forests, climbed steps in Li's Terradynamics Lab.

"These snakes have to regularly travel across boulders and fallen trees; they're the masters of movement and there's much we can learn from them," Li said in a statement.

Li and his team ran a series of experiments, changing step height and the steps' surface friction to observe how the snakes contorted their bodies in response to barriers.

They found that snakes partitioned their bodies into three sections: their front and rear body wriggled back and forth on the horizontal steps like a wave while their middle body section remained stiff to bridge the large step. The wriggling portions, they noticed, provided stability to keep the snake from tipping over.

According to JHU, as the snakes got closer and onto the step, the three body sections travelled down each body segment. As more and more of the snake reached the step, its front body section would get longer and its rear section would get shorter while the middle body section remained roughly the same length, suspended vertically above the two steps.

If the steps got taller and more slippery, the snakes would move more slowly and wriggle their front and rear body less to maintain stability.

After analysing their videos and noting how snakes climbed steps in the lab, Qiyuan Fu, a graduate student in Li's lab, created a robot to mimic the animals' movements.

At first, the robot snake had difficulty staying stable on large steps and often wobbled and flipped over or got stuck on the steps. To address these issues, the researchers inserted a suspension system into each body segment so it could compress against the surface when needed. After this, the snake robot was said to be less wobbly, more stable and climbed steps as high as 38 per cent of its body length with a nearly 100 per cent success rate.

Compared to snake robots from other studies, Li's snake robot was speedier and more stable than all but one, and even came close to mimicking the actual snake's speed. One downside of the added body suspension system was the robot used more electricity.