Friday, November 15, 2013

Propulsion Systems Drawing Inspiration From Swimming Penguins

November 15, 2013

Image Credit:
April Flowers for – Your Universe Online

“Emperor penguins may be waddling jokes on land, but underwater they can turn into regular rockets… accelerating from 0 to 7 m/s in less than a second.” This caption, published in Nature back in 1991, on a picture taken from the IMAX movie Antarctica was enough to inspire Flavio Noca.
Noca, who at the time was a graduate student in Caltech’s Aeronautics Department, and now teaches aerodynamics at the University of Applied Sciences Western Switzerland (hepia) and the Swiss Federal Institute of Technology (EPFL), examined the possibility of leveraging penguins‘ “rocket” properties to create new propulsion technologies. These technologies have high maneuverability and improved hydrodynamic efficiency.

Noca will present a penguin-inspired propulsion system at the American Physical Society’s (APS) Division of Fluid Dynamics meeting this week. The system uses a novel spherical joint mechanism developed and manufactured by Bassem Sudki, a research assistant within Noca’s aerodynamics group, under the supervision of Professor Michel Lauria, who leads hepia’s Robotics Laboratory.
The mechanism, based on a penguin’s shoulder-and-wing system, 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.

The team needed to overcome the technical challenges of spherical joints, including the lack of rigidity and the inability to generate high torques. An example of this challenge would be lifting a ten-pound weight on your hand with your arm extended.

To get around these problems, the research team chose a parallel robotic architecture for this type of mechanism. The architecture enables rigidity along with 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°.”

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

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


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