Penguin Propulsion

The emperor penguin rockets itself through the water with a unique shoulder joint; Jen A. Miller talks to a scientist who is testing a robotic version.

How can you make a machine go faster underwater? When Flavio Noca decided to tackle this question more than 20 years ago, he took a cue from nature—a very cute cue from nature. He based the structure of his underwater rocket on the shoulder joint of the emperor penguin.

Even though these birds waddle on land, emperor penguins turn into powerful rockets underwater, which is why Noca chose the architecture of their shoulders as the inspiration for his device.

He showed off his creation—which he describes not as a penguin device, but rather as a “compact spherical joint capable of transmitting high torques”—in a paper presented at the American Physical Society’s Division of Fluid Dynamics meeting late last year.

He’s worked on the design for more than two decades, drawing first from the 1991 IMAX movie Antarctica, which showed emperor penguins shooting through the water. That same year, the journal Nature published a picture from the movie with the note that emperor penguins can accelerate a standstill to seven miles per second in less a second.

At the time, Noca was a graduate student in the aeronautics department at the California Institute of Technology. He carried a curiosity about how a penguin moves with him to a stint at NASA and now to the University of Applied Sciences Western Switzerland and Swiss Federal Institute of Technology.

“It is important when looking at nature not to mimic it or copy it,” said Noca. “Nature had done some good engineering over millions of years and has found one solution among many, which seems to work for her. We as humans should draw inspiration from nature.”

Emperor penguins create thrust underwater by flapping their wings, much like other birds do in flight. The big difference is that these penguins create thrust while flapping their wings both up and down. Since their wings are permanently extended, and rigid, they have simpler shoulder joints that have what Noca calls a “parallel architecture.” The muscles are linked to the bone through tendons, which are then distributed around the joint. All three act together to rotate the joint.

Compare that to most modern robotic arms, which are built along a serial architecture. Noca compares this to how a human would scratch his or her nose. “If you would like to scratch your nose with your fingers, you will need to bend your elbow and rotate your shoulder. Bending the elbow requires carrying the weight of your forearm as well as the weight of the hand and all of its fingers. At the same time, the shoulder would need to move as well, and will need to carry the weight of the arm, forearm and hand.”

The more links you add to the chain, the less compact the system, and it also loses rigidity and precision. A parallel architecture is much simpler and precise, which allows for a bigger, targeted thrust through the water. Like a rocket. Or an emperor penguin.

So far, Noca’s device is only a prototype and hasn’t been tested on an underwater vehicle yet. However, the shoulder joint can flap freely at a frequency of 2.5 beats per second. He thinks that when it’s perfected, it could enable conventional propellers with the ability to thrust in specific directions and be used on unmanned underwater vehicles that require a higher degree of maneuverability.

“Our immediate goal is not to deliver a final product but to present a first attempt at emulating a compact spherical joint capable of transmitting high torques,” he said, adding that this is a first step in that direction. Or, in this case, a first thrust.

Jen A. Miller is a freelance writer based in the great Garden State. She has written about running for the New York Times, Runner’s World, Running Times, andNew Jersey Monthly. She writes a running column for the Philadelphia Inquirer. She’ll be running her next marathon — slowly — in April 2014.

Her most recent story for The Magazine, available here at Medium, was “Good to the Last Drop,” exploring the potential connection between overconsumption of caffeine and heart-attack deaths at road-run finish lines—and the need for more research on the topic.

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