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Electrostatic motor ‘out-performs standard designs’

15 September, 2014

An American start-up company is developing a novel motor technology that harnesses electrostatic forces instead of electromagnetism. Wisconsin-based C-Motive Technologies predicts that its technology could produce the lightest, most reliable, energy and cost-efficient electric motors, and non-contact power transfer devices, on the market. It adds that its C-Machine motors will produce high torque at a lower cost than any other motor available or under development.

Rather than relying on magnetic fields to create mechanical motion, the technology harnesses the electrostatic (static cling) force of electric fields. C-Motive’s motors use this force to align closely stacked stationary and rotating aluminium plates. 

“We have proven the concept of a new motor that uses electric fields rather than magnetic fields to transform electricity into a rotary force,” explains the company's co-founder, Dan Ludois, who is also an assistant professor of electrical and computer engineering at the University of Wisconsin in Madison. The development could solve a number of practical problems while saving money, he adds.

A C-Machine motor is smaller than a conventional motor, operates without a gearbox, and eliminates the need for copper windings, electrical steel laminations and rare-earth magnets. It is designed to run at 95% efficiency, cutting losses by a factor of three compared to conventional motors. It is also low-maintenance because it is built from low-cost stacked and recyclable aluminium plates that are flexible and adjust themselves automatically, almost eliminating the need for downtime and cutting repair costs.

Electrostatic motors are not new. Benjamin Franklin and others described and built motors based on electrostatic forces in the 18th and 19th centuries, but none achieved practical operation.

Since the widespread adoption of electric motors more than a century ago, magnetism has been the only practical source of rotation. However, Ludois and his colleagues believe that advances in materials, mechanical engineering and manufacturing techniques could now revive the electrostatic motor.

When Ludois was working on his PhD thesis in 2011, he realised that instead of relying on magnetic fields, he could achieve a similar result by manipulating electric fields to create a motor based on electrostatic attraction.

In 2012, Ludois and two other PhD students set up C-Motive to develop and commercialise his ideas. The company’s non-contact capacitive power conversion technology allows power to be transferred wirelessly and could replace high-maintenance slip-rings and brushless exciters while improving control over electric machinery. The technology occupies half the volume of a standard brushless exciter and weighs a tenth as much.

C-Motive says that its innovations allow electrical charges to be stored in high enough densities to produce practical motion on an industrial scale. The secret rests in a patented technology which controls and harnesses these potentially unwieldy forces.

A prototype of C-Motive's electrostatic motor

In the C-Machine, the interleaved stationary and rotating plates are held a hairs-width apart by an air cushion. An electric voltage delivered to the fixed plates creates an electrostatic field that attracts the rotating plates in a way that makes them spin.

“A charge builds up on the surfaces of the plates, and if you can manipulate the charge, you can convert electricity into rotary motion, or transfer electric power from one set of plates to the other,” Ludois explains. The coupling can be used “to power things that move without touching,” he adds.

The technology relies on electronics to control the high-voltage, high-frequency electric fields precisely, and fluid mechanics to keep the surfaces close without touching.

“Nothing is touching, because you are using electric fields to couple the stationary and rotating parts,” Ludois says. “There is no contact, and no maintenance.

“Rather than magnetism,” he continues, “we are using the force that hold your clothes together when you take them out of the drier – electrostatic force. This technique can power anything that needs to move, and that you don’t want to touch while it’s moving.”

The new technique, he suggests, could deliver major advantages in terms of weight, material costs, operating efficiencies and maintenance requirements. It also avoids the need for rare-earth materials and uses aluminium instead of more expensive copper windings.

The technology could also be applied to the design of generators and the first commercial applications could be in wind turbine generators – an application for which C-Motive Technologies has received a Small Business Innovation Research grant from the US National Science Foundation.

The C-Motive technology is said to be ideal for high-torque, low-speed applications such as generators for residential/commercial backup power and for off-grid uses in industries such as construction.

C-Motive, which currently has five employees, is in the final stages of prototyping its electrostatic technology. The company has received backing and funding awards from various sources, including $100,000 in seed funding. Ludois currently devotes his evenings to C-Motive, but still spends his days at the University of Wisconsin.




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