New flat motor drives movers and shakers

Engineers in the US have developed a low-cost, high-torque rotary motor based on ‘smart’ materials that can be configured in a range of formats.

Penn State University engineers have developed a low-cost, high-torque rotary motor based on ‘smart’ materials, which can be configured in a wide range of formats, including one as flat and thin as a CD case.

The inventors say that, in the flat format, the motor could be used to drive changes in the camber of aeroplane wings or fins, essentially shape-shifting the curvature of the wing or fin surface.

In other formats, the motor could work in tightly integrated spaces where other motors can’t fit. For example, the ‘smart’ material motor could serve as the drive element in thinner, lighter, laptop computers or other compact, portable consumer products or in manufacturing equipment that processes items by moving or shaking them.

Dr. Gary Koopmann, distinguished professor of mechanical engineering and director of Penn State’s Center for Acoustics and Vibration (CAV) led the development team. He said the flat motor has a starting torque advantage over conventional electric motors since speed is not required for high torque output.

The prototype flat motor is said to have reached a free speed of 760 revolutions per minute and a maximum torque of 0.4 Nm.

Components for the prototype cost less than $150 off-the-shelf. Koopmann estimates that an optimised version of the flat motor might cost as little as $10 to mass-produce.

The new motor works by translating the bending of a ‘smart’ material into the turning of a shaft. The ‘smart’ material the inventors use is PZT (lead zirconate titanate), an inexpensive, commonly available piezoelectric that elongates when an electric field is applied to it. By bonding PZT to both sides of a tiny, flexible, metallic strip, they create an arm that can bend to the left and right in response to an electric field.

Placing 12 of the arms starfish shape around a central shaft, the inventors stimulate them simultaneously and they all bend in the same direction. A passive clamping system, either a ball and spring arrangement or a commercial one-way roller clutch, acts as a turnstile that only allows the motion to ratchet along in one direction, translating the bending into rotation of the central shaft.

Koopmann said that using passive clamping significantly improves the performance and lowers the cost of the flat motor versus inch-worm type designs, which also use the small oscillatory motions of smart materials but require precision machining.