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Inspired
by the aerodynamics of flying insects, a project to build a wee
winged robot takes off By Robert Sanders, Media Relations UC Berkeley engineers with the Center for Information Technology Research in the Interest of Society (CITRIS), aiming to build a robotic fly the size of a quarter have attained a major milestone with the creation of a tiny wing that flaps like a real fly wing and generates lift.
The achievement brings them closer to their goal of having, by the end of 2003, a robot weighing a tenth of a gram - less than the weight of a paper clip - that lifts off the ground and hovers. "The complicated thing for us has been to build a wing mechanism which can both flap and rotate simultaneously at 150 times per second, the same speed as a fly's wings beat," said Ronald Fearing, professor of electrical engineering at UC Berkeley and the principal investigator for the project. "What we've shown is that we've got force in at least one direction, which is an important milestone." Fearing's scheme to build a miniature winged robot is one of many innovative projects underway at CITRIS, which is headquartered at UC Berkeley and one of four California Institutes for Science and Innovation. A robotic fly like this, which the team calls a micromechanical flying insect or MFI, could be used in search and rescue or reconnaissance - "keeping people out of harm's way," Fearing said - or even, as he said facetiously, to seek and destroy insect pests in a field of corn. "There's a big gap between the traditionally engineered robot, which is very slow, heavy, dangerous and expensive, and what nature builds, which is lightweight, fast, high-performance and very robust," he said. "It's these capabilities of natural systems that we wanted to capture in a mechanical system." A flying robot also avoids a big problem of miniature legged and wheeled robots. "They get stuck in the shag carpeting," he said. The project, which is funded by the Defense Advanced Research Projects Agency and the Office of Naval Research, is possible because of recent discoveries about the way flies flap their wings and achieve the great maneuverability required for acrobatic feats like landing on the ceiling. Much of this has been discovered by Michael Dickinson, professor of integrative biology at UC Berkeley and a recent MacArthur "genius" award winner. "Dickinson discovered the last of three key ingredients necessary to make a fly fly," Fearing said. These wing motions are delayed stall, which enables beating wings to have a high angle of attack and high lift at the same time; wing rotation at the bottom and top of the stroke, which, like the backspin on a baseball, gives more lift; and wake capture, whereby a wing gets extra lift by swishing back through air it set in motion on the previous stroke. "These are the main aerodynamic secrets for flying insects with beating wings at this size scale," Fearing said. "This aerodynamic breakthrough is going to make the MFI possible."
The goal of Fearing's project, which began in 1998, is to duplicate these wing motions in a fly-sized robot and, with proper computer control, get the device to fly stably under its own control without crashing into a wall In the past three years, he and his team have miniaturized many pieces of the MFI, including the motors. The most recent achievement was a wing-drive thorax composed of thin sheets of stainless steel that, when cut and folded into "beams," turn out to be extremely strong. Two hinged beams are attached as struts to each wing, with a piezoelectric motor driving them. When they move together, the wing flaps; when they move out of sync, the wing rotates. "The wings can't do fancy figure eights or ovals, but they can do simple things, like flap and rotate," Fearing said. The wings, about half an inch long, 1/20 the thickness of a sheet of paper and made of lightweight polyester, look like miniature paddles, and give the fly a wingspan of about one inch. Still to come is a lightweight power source, probably solar panels integrated into the robot's tripod legs, perhaps a gyroscope to tell up from down, and a light sensor. A microprocessor with a small operating system, called TinyOS, has already been developed at UC Berkeley for devices of this size. Eventually the MFI would carry sensors chosen for a specific use. "Because of the revolution in MEMS (microelectromechanical systems), something this small could carry quite a few instruments," Fearing said. "A nose to track pollution plumes, a very low-power communications system, a lightweight imaging device to snap pictures. The electronics and sensing is more advanced now than the robot." All this for a few dollars in materials, Fearing predicts. A commercial version of the MFI could be on the market in 10 years, he said. "We really have a unique team working on this project," Fearing said, "a whole variety of engineers - mechanical, electrical, computer and materials scientists - all taking inspiration from our biology colleagues." |
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