The robot was inspired by the mantis shrimp, which has a powerful appendage capable of shooting toward its prey at about 60 miles per hour.
Mantis shrimp wield appendages so powerful they can impale snail shells, split open human thumbs and even shatter aquarium glass.
To decipher how these ocean predators deliver such deadly strikes, scientists created Ninjabot, an ultrafast underwater robot that mimics the shrimp’s striking motion.
The robot could shed light on how a striking shrimp produces a water bubble phenomenon called cavitation. Understanding that mysterious process could spur the development of ultrafast vessels and new materials that reduce drag underwater.
“They’re really amazing animals,” said Sheila Patek, an associate professor of biology at Duke University who studies the connection between evolution and the physics of animal movements. “For a really long time, actually since I started working on this system, I was interested in building models of how they do it.”
Before striking, the mantis shrimp bends its appendage. Milliseconds later, the appendage shoots toward the prey at about 60 miles per hour. That cavitation phenomenon created can generate shock waves powerful enough to erode boat propellers, but it’s also poorly understood.
Patek collaborated with Suzanne Cox, a PhD student in organismic and evolutionary biology at the University of Massachusetts Amherst. They found that standard engineering springs couldn’t generate the same accelerations as the mantis shrimp’s biological one.
The scientists used a hand crank on their Ninjabot to slowly puts pressure on one end of a long, flat beam spring, flexing it.Sheila Patek, Duke University
Instead they designed a steel robot that amplifies power like a bow and arrow or a pole-vaulter. The robot contains a long beam spring, which is a kind of flat spring. To load it, the scientists used a hand crank that slowly puts pressure on one end of the beam, flexing it. Then a lever releases and the bent metal is suddenly freed. Cox dubbed it Ninjabot after its ninja-like strike.
The resulting ninja-like strike, quite as fast as an actual mantis shrimp, is two orders of magnitude greater than previous underwater models.
With Ninjabot, the scientists can do controlled experiments to study factors that influence how the bubbles form. The robot can be outfitted with a real mantis shrimp appendage for testing, according to Patek.
Roy Caldwell, a professor of integrative biology at the University of California Berkeley, was Patek’s postdoctoral advisor. He’s been studying mantis shrimp since 1965. “It will take a little bit of tweaking to get into the biological realm of capability that she needs, but I think it’s a good start,” he said.
California State University Long Beach biology professor Christopher Lowe has noticed cavitation bubbles form around the hydrophones he uses to record sound underwater while tracking sharks. Although he doesn’t have an engineering background, Lowe thinks the Ninjabot could help us develop materials with new properties, leading to stronger ship propellers and ultrafast underwater vessels.
“It’s just cool that we’re using animals that have solved these problems evolutionarily,” he said.
Patek and Cox described their work in the March 2014 issue of the journal Bioinspiration & Biomimetics.