By Steve Bush 29th June 2009
Dyson has developed gone to 104,000rpm brushless DC technology to combine efficiency and manufacturability in its latest handheld vacuum cleaner.
“Because it is two pole, it is very simple, and when you make it run at high speed, you can make it incredibly small,” Dyson’s Andy Clothier told Electronics Weekly. “It is 84% efficient, which is high at this small size. At this voltage and power level, to get a brushed motor this efficient is very difficult. Our old motor was 40% efficient.”
Overall the motor, dubbed DDM (Dyson digital motor) V2, is 55.8mm in diameter and weighs 139g.
Notoriously tricky to start predictably, the motor uses asymmetric poles. “You have to have enough saliency on the poles to make it start in the right direction,” said Clothier.
With brushless motors, there is a choice: sensored or sensorless – incorporate a magnetic sensor have tell the electronics when to switch coil polarity, or use a more powerful processor and sense rotor position from back-EMF.
“The way we designed it was to integrate the electronics into the motor. It is the least expensive way of doing it,” said Clothier. “The PCB is in exactly the right place to carry a Hall sensor.”
Control comes from a simple 8-bit Microchip microcontroller, not one that has special motor control peripherals, said Clothier: “We used our own motor control technology. To get the absolute best, we make sure the motor produces constant power regardless of speed and the battery voltage.”
The power control is largely open loop – determined from detailed knowledge of the motor and impeller dynamics, combined with motor speed derived from the Hall sensor. Up to 3,300 adjustment per second are made.
The battery is either six or four lithium ion cells depending on the vacuum cleaner model: DC31 (pictured) or DC30 respectively.
Up to 10A at 20V, and up to 13A when the battery voltage drops, is switched into the motor by an H-bridge of mosfets.
To get current to change direction fast enough with such a low supply voltage requires low-inductance windings – in this case twin coils wound in parallel.
The whole motor, and its mechanical and air environment, was modelled extensively.
“That is where most of the work went in: we developed our own simulation tools to model the whole motor including its electronics,” said Clothier. “We also used some commercial finite element software for spot checks and detailed work, but 90% was designed by our own software.”
Modelling, for example, showed the sintered neodymium permanent magnet rotor was small enough not need a carbon fibre sleeve to stop it flying apart at full speed.
“This is the kind of thing that looks simple and needs a lot of work,” Mathew Childe told Electronics Weekly. “We modelled the motor dynamics and made sure it was stable against vibration right up through its acceleration range, checked the acoustic noise and checked the resonances.”
The team also built prototypes that were tested using accelerometers and laser displacement instruments, then fed-back the results. “All the way through, you learn to improve and adapt the modelling process,” said Childe.
High rotational speed put means the impeller can be small, but means it is subjected to high forces. “Most people would use aluminium,” said Childe. “Through simulation we designed out as much stress as possible and so we can make the impeller out of carbon fibre-reinforced polymer.”
A plastic impeller and steel shaft means welding is out of the question. “Everything in the vacuum cleaner is dependent on bonding,” said Childe. “We have had an engineer working for two years on adhesives for the product.”
The motor has been dubbed DDM (Dyson digital motor) V2.
What was effectively DDM V1 was actually dubbed X020 and is the switched reluctance designed used in the company’s Airblade hand dryer.
Tagged with: develop Dyson efficiency manufacturability technology
Keep in mind that Dyson felt the need to trademark “digital motor” with the USPTO so that nobody else can legally use that terminology. When marketing and legal is in charge you tend to end up with made-up terms like this for existing technology. Yes it has some smart sensing and control, but in the end it really is just a brushless DC motor plus some very nicely engineered circuitry to drive it.
If this was really something new I would expect to see a US patent. There seem to be some, but not by Dyson, and those that existed seem to either have been struck or abandoned. Would be interesting to see a patent if someone finds one.
Hi Derek For me, what is remarkable about that motor is that the firm knocked the cost out of the mechanical components – getting that sort of rotational speed from consumer-grade parts, and that almost a decade ago. Dyson research and technology is impressive – although Brexiteer James Dyson was not so impressive, moving his company HQ from the UK Singapore.
I’ve long suspected that Dyson takes the infinite number of monkeys approach to design and here is something to back it up.
Having two windings in parallel does not reduce the inductance, it stays the same. It does reduce the effective resistance but parallel windings on the same core doesn’t alter the inductance. Putting two windings in series does change the inductance upwards.
Maybe ‘skin effect’ gets into the motor winding design at these motor speeds.
Think resonance and the factor of Q.
The sort of thing that FEA can miss?
Hi Henk, let’s hope Dyson did the reliability test – I suspect they did.
Which dyson handheld vacuums have a brushless motor?
Very interesting technology, I like very much these kinds of innovation that goes to the edge. But one warning: usually high speed components like ultracentrifuges have strict limitations on hours of use, on the penalty of risk of explosion. I really hope that Dyson was aware of these risks.
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