Motors: power comes in small packages

Dyson's latest generation of products consist of three new Airblade hand dryer variants, all of which are powered by a new power-dense brushless DC motor.

The Airblade hand dryer emits sheets of high-velocity HEPA filtered and unheated air through tiny apertures, which "scrape" water from hands quickly.

The latest products integrate the technology into a tap, a smaller V-form factor hand dryer for design-conscious premises, and a mk2 standard hand dryer which weighs 1.1 kg less than the original and has a smaller carbon footprint.

The core enabler of these redesigns is the Dyson V4 Digital Motor, whose housing is just 85 mm wide, but is able to accelerate from 0 to 90,000 rpm in less than 0.7 seconds.

PACE talked to Tom Bennett, Dyson Design Engineer, about the development and production process of the motor.

The V4 is the world's smallest and fully integrated 1600 W motor. It is able to quickly accelerate due to the use of digital pulse technology, and at those speeds, generates 30 litres of airflow per second, which is in turn sent through laser-cut slots at 430 miles per hour (192 meters/sec)for fast hand-drying.

Sheer power

While conventional motors use carbon brushes, relying on a closed electrical circuit to a commutator in order to spin, the Dyson Digital Motor uses a strong magnetic field whose polarity is controlled by a microprocessor.

With no contact between the stator and the rotor, and fully digital switching controls, the motor itself does not emit carbon particle emissions from the brushes, and is also mechanically simple. The microprocessor can also optimise polarity switching, allowing the fast acceleration.

According to Dyson engineers, the faster the motor spins, the more energy efficient it becomes, since the power to weight ratio is increased. As a result, the motor can be smaller and lighter, without compromising its output power. 

Smaller is better

While the latest motor has the same power use and overall specifications as the original Dyson digital motor, the team of over 100 engineers focused on condensing the unit into a more compact form in order to fit the new products.

For example, the original motor had the electronics connected to it as a separate module; this is now integrated into a singular unit.

To squeeze an already-optimised design into an even-smaller space means pushing tolerances to their limits, and leveraging the latest production and material technologies to do so. Overall, the motor development effort for the V4 took 10 years, and US$40.9 million.

"[The engineering team] did complex computational fluid dynamics analysis and looked at the precise shapes of the impeller blades, the speed at which it needed to run, the tolerances of every single part inside that," explained Bennett.

The microprocessor optimises polarity switching allowing fast acceleration for the motor.[The microprocessor optimises polarity switching allowing fast acceleration for the motor.]

Hundreds of prototypes were built using Accura BlueStone Stereolithography resin, a 3D printing material which is highly accurate, making it perfect for representing finished parts in prototype within the tight tolerances demanded of the parts.

Dyson engineers also opted for adhesive technology to join the parts of the motor together, thus reducing the space taken up by screws, fixings and bolts. In all, there are over 37 adhesive joints within the motor.

Within the motor sits a compression bonded neodymium magnet, encased in a carbon fibre sleeve. This magnet fits the right tolerances, and also provides the high magnetic strength required by the motor.

The engineers designed the impeller to be made from PEEK, a material made with carbon fibre reinforcement and normally used in aerospace engineering.

The plastic can be moulded into various guises but in each case, it is lightweight yet strong and able to deal with the heat and high speeds generated when the motor spins.

Precision production

Given focus on compactness, the design tolerances and clearances are imperceptibly small: the clearance between the bearing and its housing is just 0.45 microns.

With such small margins of error, a fully automated production process is the only answer. As such, US$30 million, and a large part of the development effort went into the engineering of the production line, based in Singapore.

Unlike previous approaches where Dyson worked in partnership with a local manufacturer, the new facility is owned by the company, and provides double the capacity of their previous arrangement, as well as increased control over the IP. 

"The production line is fully automated. A human is not capable of doing these tasks at this level of accuracy, and it also needs to be a clean room, dust-free. You can only rely on finely-programmed robots to do this task," Bennet told PACE.

With the use of automation, the facility produces 50,000 motors a week.

The fully automated production line is built in a dust-free clean room.[The fully automated production line is built in a dust-free clean room.]

Dyson is continuing to invest over US$15 million a year into motor R&D, and also actively protects its IP – the motor itself is covered by over 100 patents and patents pending, and the company is notoriously mum about new developments. 

A big opportunity for the company is in finding new applications for the V4 motor, which it sees as an enabling technology.

Product development ideas within the organisation are being pushed further thanks to the power and compact form factor of the motor.

With its Singaporean factory continuing to churn out the motors, Dyson's digital motor technology certainly has a lot of potential applications, even within its existing product lines, like vacuum cleaners and fans. It may also be possible for Dyson to leverage this technology to move into new areas, such as power tools.

"The motor is exciting because of all the other opportunities which it presents to us," Bennet said. "We've got bigger plans for it; we don't know what the other products will be yet, but there's lots of exciting things that we know that we can do with this technology."