Kids love penguins. They sing and dance in cartoons, they waddle like Charlie Chaplin on land - but underwater, they are all business, accelerating from 0 to 15 miles per hour in less than a second. 

At the American Physical Society's Division of Fluid Dynamics meeting next week in Pittsburgh, Flavio Noca, who teaches aerodynamics at the University of Applied Sciences Western Switzerland (hepia) and the Swiss Federal Institute of Technology (EPFL), will present a penguin-inspired propulsion system that uses a novel spherical joint mechanism. Based on a penguin's shoulder-and-wing system, the mechanism features a spherical joint that enables three degrees of freedom and a fixed center of rotation.

"Unlike an animal shoulder joint, however, this spherical joint enables unlimited rotational range about the main shaft axis like a propeller," Noca said.

To achieve this they needed to overcome the technical challenges of spherical joints, such as the lack of rigidity and the inability to generate high torques. To understand the challenge involved, just try lifting a 10-pound weight on your hand with your arm extended.

This actuated spherical joint mimics a penguin shoulder while enabling compactness, rigidity and high motion frequencies, as well as unlimited rotation (propeller-like, not shown on the video) about a single shaft. Credit: hepia/B.Sudki-M.Lauria-F.Noca

The researchers maneuvered around these challenges by choosing a parallel robotic architecture for this type of mechanism, because it enables rigidity as well as high actuation frequencies and amplitudes.

"Because the motors are fixed, inertial forces are lower than for a serial robotic mechanism, such as a multi-joint arm," explains Noca. "The resulting spherical parallel mechanism with coaxial shafts was designed and manufactured with these specifications: a fixed center of rotation (spherical joint), a working frequency of ~2.5 Hz under charge, an unlimited rotation about the main axis, and an arbitrary motion within a cone of +/- 60°."

The manner in which penguins swim is still poorly understood, aside from the technological perspective, according to Noca. "By accurately reproducing an actual penguin wing movement, we hope to shed light on the swimming mysteries of these underwater rockets," he said.