Dyson develops small powerful motor

The composite impeller has been made considerably smaller
Dyson has developed a 'next generation' electrical motor that it says will to power energy efficient technologies of the future. The DDM V2, which is 55.8mm in diameter and weighs 139g, achieves 84% energy efficiency as it spins at more than 100,000rpm.

The motor uses neodymium rare-earth magnets, commonly found in hard drives and electric vehicles. In itself, this is nothing new. What is interesting is that the company is moving away from brushed motor technology for its consumer products.

The technological breakthrough seems to be the high efficiency achieved at high rotational speeds. The desire to have faster motors really stems from the need for more power. And to rotate at these speeds, the motors must have really good bearings and balancing.

Dyson motors engineer Matthew Childe said: "The motor is a single phase brushless DC device which has been designed to have a flat efficiency profile across the speed range of 89krpm to 104krpm. If anything, the efficiency tends to increase from 84% as the motor increases in speed.

"The typical speed at which it will is 95krpm, which gives an efficiency of 84% in normal use."

The DDM V2 has no contact to the rotor, just a strong electromagnetic field generated in the stator. The polarity of this field is switched digitally by a microprocessor, which can make up to 3,300 adjustments each second in response to an input.

Although it is unclear at this time what the exact patents are, the clever and novel bit seems to be the ability to control the magnetic fields at such high rotational speeds. Switching the magnetic field takes energy and normally, at more than 40,000rpm, most of the energy is used to do the switching and in generating heat, rather than being converted into power to the motor.

The motor will drive an impeller made from a carbon fibre reinforced polymer. It is thought that motor speeds are reaching a theoretical limit as the impeller begins to build up shockwaves as it approaches the speed of sound.

"The impeller has been designed to operate subsonic with the tip speed at approximately 200m/s," concludes Childe. "This is far enough away not to affect our impeller efficiency. [Although] increasing the speed does have many benefits, it becomes more challenging as the stress levels go up and the impeller gets closer to becoming transonic."

The technology opens up diverse engineering possibilities for Dyson to power smaller, lighter, greener technologies. V2 is set for mass production and will power 1.2 million Dyson machines in 2009.

J Cunningham

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