Motor going for a spin

Engineers at Johns Hopkins University have invented a globe-shaped motor that is said to be capable of rotating in any direction. The device, which uses electromagnets controlled by a computer, could give robotic arms greater flexibility and precision.

‘A conventional motor turns on an axis, moving in one direction,’ said Gregory S Chirikjian, an associate professor in the Department of Mechanical Engineering of the Whiting School of Engineering. ‘What we’ve developed is a new type of spherical motor. Basically, there’s a ball inside, and we can rotate it in any direction we want.’

Magnetic forces and computer software make the device work. For their prototype, Chirikjian and doctoral student David Stein mounted 80 permanent magnets inside a hollow sphere, arranging them in a precise pattern.

The magnet-laden sphere was then placed into a tapered base on top of a ‘saddle’ made of 16 circular electromagnets marked with a number. By activating two or more of these electromagnets, the operator causes them to attract certain permanent magnets inside the sphere, pulling the ball into a new position.

The idea of a spherical motor is not new but the Johns Hopkins engineers believe their model is superior to previous efforts because it can achieve a much greater range of motion.

The researchers say that with further refinement the spherical motor could replace the conventional motors that are now used to move robotic arms in three dimensions.

Currently, a robotic arm needs six or more conventional motors to position and orient objects in three dimensions although the spherical motor would behave like a human shoulder joint.

As a result three spherical motors could give a robotic arm a greater range of motion than arms that have six traditional motors said Chirikjian.

The inventors envision other applications for the spherical motor.

‘You could also turn these motors upside down and use each one as a three-dimensional wheel,’ said Chirikjian. ‘It would not only turn around an axis like a conventional wheel, it would have omnidimensional characteristics. For example, if you put a ball in a socket, you can roll it any way you want, unlike a regular wheel, which can only go in one direction without slipping.’