Motor goes all the way around
By Eric Smalley, Technology Research NewsImagine an oversized trackball that moves by itself and you've got the basic idea of a spherical motor that could lead to better robot arms and even cars that slide sideways into tight parking spaces.
Although spherical motors are not new, most have limited ranges of motion. Researchers at Johns Hopkins University have developed a more useful version with an unlimited range of motion.
"We developed the first spherical motor that can turn completely around," said Gregory S. Chirikjian, an associate professor of mechanical engineering at Johns Hopkins University.
The motor looks like a basketball sitting in the open end of a cone. The inside of the ball is lined with common, permanent magnets, and the inside of the cone is lined with electromagnets.
"We sequence the electromagnets turning on and off, and that attracts the permanent magnets inside the ball to cause the ball to turn," said Chirikjian. "In addition, we've developed an encoder, which is a way to determine [the] orientation of the ball."
The current protype has a 12-inch-diameter ball. The design could be scaled down to one inch, said Chirikjian.
One motivation for developing the spherical motor was to build more efficient robot arms, he said. Most robot arms are made of motorized joints that can only move along one axis, requiring as many as six to give the arm full range of motion, Chirikjian said.
"Instead of having many one-degree-of-freedom motors that turn around one fixed axis, you could have relatively few ball-like motors," he said, noting that the human arm has two ball joints, the shoulder and wrist, and one single-axis joint, the elbow.
The spherical motor could have a wide range of applications, said Chirikjian. One possibility is a camera mount. "You could put a camera on the ball and this would be a way to move the camera in any direction," he said.
It could also power a computer mouse that could move itself. "The motor could... push the user over here, over there, to influence the behavior of the user and provide feedback," Chirikjian said.
If they were large enough, the motors could also be used as both wheels and motors for an omnidirectional vehicle, he said.
There are no technical hurdles to implementing the spherical motor, though it will likely be five years before commercial applications are likely, said Chirikjian.
Chirikjian's research colleagues were David Stein and Edward R. Scheinerman. The research was funded by the National Science Foundation.
Timeline: now; 5 years
Funding: Government
TRN Categories: Robotics
Story Type: News
Related Elements: Image 1, Image 2
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January 31, 2001
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