How Does the Dyson Motor Work? - Page 1
Forum section: electronics / general

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 22, 2016, 07:57:25 pm
content: He apparently doesn't know either. From a link in the comments that led to one of Dave's early rants he shows the box of an early model dyson cordless vacuum. On the box it clearly says "neodymium magnets" meaning it's a brushless DC motor. But in this motor from the hair dryer there is a magnet, but it's not neodymium because it was weak. I doubt a DC motor would work very well with magnets that weak without something else going on. He says it could be a reluctance motor, but then why have any magnets at all? Are they some sort of "easy-start" thing?

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 08:09:49 pm
content: it's a 2 pole brush-less DC motor.. it has only 2 poles to get the high RPM (the more poles it has the slower it goes at the same switching frequency).

author: Cyberdragon
author_rank: Super Contributor
timestamp: October 22, 2016, 08:21:36 pm
content: Quote from: rob77 on October 22, 2016, 08:09:49 pmAre you saying they are getting 100W of power with a magnet no stronger than a fridge magnet?

author: bktemp
author_rank: Super Contributor
timestamp: October 22, 2016, 08:30:29 pm
content: Quote from: Cyberdragon on October 22, 2016, 08:21:36 pmI don't see why not. That motor does not need to generate a high torque, it is optimized for high RPM.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 08:36:09 pm
content: Quote from: bktemp on October 22, 2016, 08:30:29 pmexactly - the strong magnetic field would be needed for torque not power... i would say the weaker magnetic field is even better to get the very high RPM the impeller needs to move that air volume.

author: johansen
author_rank: Super Contributor
timestamp: October 22, 2016, 08:41:31 pm
content: reluctance motors can have magnets.. we call them hybrid stepper motors.anyhow, the motor control appears to be fairly creative. sensorless, but it is probably measuring the rotor position by measuring its inductance.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 08:54:32 pm
content: Quote from: johansen on October 22, 2016, 08:41:31 pmi would say similar to sensor-less brushless drive - the winding is let to free-wheel for a moment and the generated voltage is measured. with a 3phase drive it's simple because you can have 1 phase floating for measuring the back-emf while the other 2 are energized.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 22, 2016, 09:43:02 pm
content: I'd imagine that at high speeds, a strong permanent magnet might cause eddy current losses.With only 2 connections I'm curious as to how they make sure it starts in the right direction.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 09:53:32 pm
content: Quote from: mikeselectricstuff on October 22, 2016, 09:43:02 pmpersonaly i would give it a nice pulse to make it turn and measure the back-emf till zero cross - if it goes from positive to zero or negative to zero would tell the direction.. counting 2 zero crosses would give the speed - and with a precisely timed pulse you would change it's direction if needed...and then start to comutate to spin it up (pulse, measure back emf till zero cross, comutate , measeure back-emf...etc...)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 22, 2016, 10:08:17 pm
content: Coluld also be that its stationary cogged position is biased towards one pole.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 10:17:48 pm
content: that would make it start always in one direction and eliminate the need for detection of direction and reversal of rotation during the startup - would save few lines of code in the microbut i have no clue how i would achieve that , my imagination has it's limitsi would say the rotor needs to be magnetically symmetric and that would rest always centered - so no clue how i would bias it towards one of the poles.

author: Zero999
author_rank: Super Contributor
timestamp: October 22, 2016, 10:44:29 pm
content: Quote from: mikeselectricstuff on October 22, 2016, 09:43:02 pmShaded pole?I don't see how it could be done any other way.

author: rob77
author_rank: Super Contributor
timestamp: October 22, 2016, 10:55:36 pm
content: Quote from: Hero999 on October 22, 2016, 10:44:29 pmwouldn't that create a significant drag at such a high RPM ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 23, 2016, 04:22:49 am
content: Weak magnetic field because back EMF is proportional to field intensity.If you have a parallel wound DC motor with separate rotor and stator connections, you make it gofasterbyreducing the currentin the stator winding.Likewise, series wound motors have metric shitloads* of torque, because at low RPM, back EMF is low, so the equivalent resistance of the motor is very low, current draw is very high, and stator field is very high. Series-wound motors do not have a constant torque to current ratio, but rather a parabolic curve because the rotor current is multiplied by the field current. (Squaring a negative value also makes a positive number, which is why series motors cannot be ran in reverse: they are also known as 'universal' motors, because they run on AC.)*A technical term.Tim

author: amyk
author_rank: Super Contributor
timestamp: October 23, 2016, 06:04:32 am
content: Quote from: Hero999 on October 22, 2016, 10:44:29 pmShaded or otherwise only very slightly asymmetrical would be enough to ensure the motor spins in the right direction.Too bad he didn't try driving it with a waveform of his own...And that sort of power density isn't so surprising, the RC world has had 100W brushless motors of around that dimension for a long time:http://www.maxxprod.com/pdf/HC2808-xxxx.pdf

author: Refrigerator
author_rank: Super Contributor
timestamp: October 23, 2016, 06:52:31 am
content: Quote from: rob77 on October 22, 2016, 08:09:49 pmBut it's a 4 pole magnet.

author: oldway
author_rank: Super Contributor
timestamp: October 23, 2016, 07:27:29 am
content: http://www.dyson.co.uk/vacuum-cleaners/cordless/dyson-v8/engineering-story.aspxhttp://www.electronicsweekly.com/market-sectors/power/dyson-vacuums-104000rpm-brushless-dc-technology-2009-06/

author: SeanB
author_rank: Super Contributor
timestamp: October 23, 2016, 07:42:34 am
content: Quote from: Refrigerator on October 23, 2016, 06:52:31 am4 poles means 2 N poles and 2S poles, so just 2 actual poles. Then you make the stator slightly offset WRT the coils ( cut 2 of the laminates on the one end to be slightly shorter so a larger air gap there) and, just like a regular shaded pole motor, it will only run in one direction.You get 400Hz aircraft blowers with the same size, and those suckers do move air, though they also scream doing so.

author: rob77
author_rank: Super Contributor
timestamp: October 23, 2016, 08:09:58 am
content: Quote from: SeanB on October 23, 2016, 07:42:34 amthat would make sensethanksi think that's how it's done. a shaded pole would induce a significant drag at that speed. and a software solution in the controller would delay the spin-up.

author: Zero999
author_rank: Super Contributor
timestamp: October 23, 2016, 09:07:46 pm
content: Technically it's not a DC but an AC motor.The person who created the video appears to be pretty clueless. His experiment comparing it to a stepper motor is BS. Of course a stepper motor is optimised for high torque at low speed, so it will generate a relatively high voltage when its shaft is turned slowly. The Dyson hair drier motor is designed for high speed, so it will generate a fairly low voltage, even if turned faster than the stepper motor.

author: rob77
author_rank: Super Contributor
timestamp: October 23, 2016, 09:15:39 pm
content: Quote from: Hero999 on October 23, 2016, 09:07:46 pmyes correct, brush-less DC motors are technically AC motors.. everyone knows that, yet everyone calls them brush-less DC motorsand technically the brush-less DC motors are the closes relatives to stepper motors. and technically stepper motors are also AC motors... aren't they ?the reason for that might be that a brush-less DC motor requires a controller to be operated (which does the switching and also might do sensing of rotor position), therefore the motor and the controller can be considered as a single unit - and that unit is fed by DC.

author: stj
author_rank: Super Contributor
timestamp: October 24, 2016, 06:26:00 am
content: good, now that that is settled.how do they keep the bearings from being destroyed at that speed?

author: Zero999
author_rank: Super Contributor
timestamp: October 24, 2016, 08:07:00 am
content: Quote from: rob77 on October 22, 2016, 09:53:32 pmI don't see how you could sense the direction of a symmetrical single phase motor, without another winding slightly out of phase, a Hall effect or optical sensor. When the motor is unpowered, the pole of the rotor will be aligned with the stator. If a field is applied to the stator to flip the pole, it could go in either direction and the generated back EMF will be identical, thus there is no way to control the direction.If the motor is made to be asymmetrical, then it could be done but then it's easier to just design the motor so it always starts in the same direction, without any complicated software control algorithm.

author: rob77
author_rank: Super Contributor
timestamp: October 24, 2016, 09:55:29 am
content: Quote from: Hero999 on October 24, 2016, 08:07:00 amyes you're right about the back-emf, so it's not doable that way.and i think SeanB provided the most plausible solution for the start in the same direction.

author: johansen
author_rank: Super Contributor
timestamp: October 25, 2016, 08:06:49 am
content: so for what its worth, i've never run across a shaded pole motor with a variable air gap. meaning, the air gap across the section after the shorted turn is the same as the rest of it.and i've never run across a single phase 400hz aircraft blower motor....nor have i ever heard nor read about causing the saturation of half of the pole piece as a way of generating a rotating field.the math behind a shaded pole motor is rather nutty, the same sort of mechanism is going on in a regular induction motor that have a start coil, (high resistance) but they have no start capacitor (btw, adding a capacitor to these motors should increase the starting torque)

author: rob77
author_rank: Super Contributor
timestamp: October 25, 2016, 08:37:44 am
content: Quote from: johansen on October 25, 2016, 08:06:49 amthose two would be mutually exclusive i believe... either shaded pole or asymmetric air-gap. and actually a shaded pole would not make too much sense in a brush-less DC motor.

author: amyk
author_rank: Super Contributor
timestamp: October 25, 2016, 11:02:33 am
content: Quote from: rob77 on October 23, 2016, 09:15:39 pmUnipolar steppers and switched reluctance motors can be driven with DC, there's no reversal of the current through the windings. On the other hand, something like this Dyson motor is clearly being driven with an AC waveform.I found an examination of another Dyson motor, one from their vacuums:https://www.experimental-engineering.co.uk/dyson-dc35-digital-teardown/Inthis imageyou can clearly see what looks like an asymmetrical (and rather large) pole gap.

author: rob77
author_rank: Super Contributor
timestamp: October 25, 2016, 11:31:16 am
content: Quote from: amyk on October 25, 2016, 11:02:33 amno there is no reversal of current in one winding, but the reversal of magnetic field is achieved by a second winding (technically a center taped winding in a unipolar stepper)so i would disagree with that statement... it's like saying a full-bridge driven transformer is fed by AC , but a push-pull driven is fed by DC.. the difference between those transformers is exactly the same as between bipolar and unipolar steppers.Quote from: amyk on October 25, 2016, 11:02:33 amcorrect, it's a brushless DC motor, therefore it's fed by AC.Quote from: amyk on October 25, 2016, 11:02:33 aminterresting teardown, thanks for sharing the link !

author: KalleMp
author_rank: Newbie
timestamp: May 10, 2022, 07:38:06 pm
content: Quote from: amyk on October 25, 2016, 11:02:33 amThere is a Hall sensor for the motor in thepictureat the same site mentioned by amyk.It looks like a Siemens SLIC-HALLTLE 4945Ldevice.The rotor may have an asymmetrical magnetic field (one pole larger than the other perhaps) or the stator pole asymmetry may have something to do with it. However I think it would be a good idea for someone with a good long recording memory scope to examine the waveforms to the H-bridge, and from the stator winding and Hall sensor.While the impeller on these is somewhat directional there are many simple/cheap aquarium water pumps with straight vanes that are self starting in either direction I still believe it would be instructional to find out how Dysonselects or determinesthe designed direction to get the best efficiency.The best would be for a simple circuit that could drive the motor with the H-bridge signals and the Hall Effect feedback without the Dyson legacy battery issues. Having a small circuit that could take any power tool battery pack and run it down to 18V as fast as selected would make the vacuums recyclable and the fans repurposable.

author: KalleMp
author_rank: Newbie
timestamp: May 10, 2022, 08:48:31 pm
content: Found some interestingof a Dyson motor from a Fan I think.