wtf is a digital motor? - Page 1
Forum section: electronics / general

author: Ferroto
author_rank: Frequent Contributor
timestamp: May 01, 2011, 05:20:58 pm
content: 6kcGltYWz3k

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2011, 05:27:11 pm
content: It sounds like a marketing term for a brushless motor.I think it's a good idea: no brushes to wear out, lower power consumption, lighter and will warm up the room much less on a hot day.The video is wrong about Faraday: a brushless motor still works on the principle of electromagnetic induction.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: May 01, 2011, 05:53:59 pm
content: Well In my everyday life I name as digital motor the stepping motors ,found in printers mostly.

author: tecman
author_rank: Frequent Contributor
timestamp: May 01, 2011, 05:58:21 pm
content: Dyson's is not even a stepper, but a PM, electronically commutated motor. Brushless motor to most of the world, and just marketing hype by Dyson. And selling "no carbon emissions" is just such total BS. It is not CO2, but perhaps a few tens of grams in 5 years of carbon dust. That will save the world from global warming.It no wonder that this guy took a thousand prototypes before he had a working model (reference to his TV commercial).paul

author: Ernie Milko
author_rank: Regular Contributor
timestamp: May 01, 2011, 06:09:07 pm
content: And Dyson cleaners are crap!

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2011, 06:13:05 pm
content: Quote from: tecman on May 01, 2011, 05:58:21 pmYes total bollocks, the digital switching has nothing to do with carbon emissions.There's some truth in it being more efficient meaning lower carbon emissions but it won't be zero.Quote from: Ernie Milko on May 01, 2011, 06:09:07 pmEver owned one? It's true some older models suffered from poor build quality but the newer models are very good.

author: Ernie Milko
author_rank: Regular Contributor
timestamp: May 01, 2011, 06:35:19 pm
content: Quote from: Hero999 on May 01, 2011, 06:13:05 pmWell, obviously. I wouldn't have made that statement otherwise.My wife seems to get pulled-in by the sales pitch, which means we have owned several over the last ten years or so.I'm the one who ends up having to dismantle the bloody things when they block.No loss of suction my arse.I took the last one to the tip.I can, however, speak very favourably of Henry and Vax.

author: TheWelly888
author_rank: Frequent Contributor
timestamp: May 01, 2011, 06:40:10 pm
content: Our Dave's already mentioned it in a video bloghttps://www.eevblog.com/forum/index.php?topic=1959.0

author: Zero999
author_rank: Super Contributor
timestamp: May 01, 2011, 07:19:23 pm
content: Quote from: Ernie Milko on May 01, 2011, 06:35:19 pmThe first Dyson we owned is now on the tip because it fell to pieces. We now have a new one (two months old) and are very happy with the build quality and suction. We still have an old Panasonic but the new Dyson is so good it removes more fluff from our new carpet so we tend to use the old Panasonic everyday and the Dyson for more intensive cleaning. The thing I like about it is the way it doesn't emit loads of dust, like all the other bagged vacuumes I've used or those which use a simple filter to remove the dust.

author: Simon
author_rank: Unknown
timestamp: May 01, 2011, 08:05:50 pm
content: that video is voiced over too typical of an advert, total marketing twatery. The motor is not digital but the driving technology may be

author: tekfan
author_rank: Frequent Contributor
timestamp: May 01, 2011, 09:14:25 pm
content: Carbon emissions - yea rightYou probably make more ''carbon emissions'' when you write with a pencil.But what happens when you use an eraser to erase it. Oh no! I'm causing global warming!!!

author: Neilm
author_rank: Super Contributor
timestamp: May 01, 2011, 09:19:06 pm
content: Quote from: Simon on May 01, 2011, 08:05:50 pmMy grandfathers electric drill has a digital control system, it is either stopped or running at full speed. That IS digital.Neil

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 01, 2011, 11:04:51 pm
content: Quote from: tekfan on May 01, 2011, 09:14:25 pmcarbon? dont breath! CO2!

author: Sionyn
author_rank: Frequent Contributor
timestamp: May 02, 2011, 01:13:13 am
content: the digital bit is the mosfetsthat ithardly revolutionaryreminds me of beats audio guff

author: tekfan
author_rank: Frequent Contributor
timestamp: May 02, 2011, 01:24:23 am
content: OK so most of the stuff in the video is possible but how does a headphone jack work if it doesn't contain any metal contacts?

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: May 02, 2011, 03:58:17 am
content: "Digital" means operated by a finger.digitnoun1 any of the numerals from 0 to 9, esp. when forming part of a number.2 a finger (including the thumb) or toe.

author: Simon
author_rank: Unknown
timestamp: May 02, 2011, 07:23:19 am
content: Quote from: Sionyn on May 02, 2011, 01:13:13 ampft what a lot of bollocks ! I like the "audio island" only to see that the output cables obviously have to travel across the whole notebook picking up NOISE. I'm not sure what HP used this for if at all (could be a piss take ?) but if this was advertising material it should be banned

author: Sionyn
author_rank: Frequent Contributor
timestamp: May 02, 2011, 01:42:02 pm
content: agreed simon its all junk

author: kaptain_zero
author_rank: Regular Contributor
timestamp: May 02, 2011, 11:11:56 pm
content: I'd be inclined to suspect it to be a reluctance type motor..... Nova, another company from Dave land, markets the DVR woodturning lathe with the DVR standing for Digital Variable Reluctance. A quick check on Wikipedia pulls up this little blurb:"Electronic driven variable reluctance motor.An electronic driven variable reluctance motor (Figure below) resembles a brushless DC motor without a permanent magnet rotor. This makes the motor simple and inexpensive. However, this is offset by the cost of the electronic control, which is not nearly as simple as that for a brushless DC motor. "I base my suspicions on the appearance of the rotor he's holding in that video....RegardsChristian

author: tecman
author_rank: Frequent Contributor
timestamp: May 03, 2011, 01:22:46 am
content: Video looks like a PM rotor. Simplest and cheap for a small motor such as this.paul

author: scrat
author_rank: Frequent Contributor
timestamp: May 03, 2011, 09:02:41 am
content: Quote from: tecman on May 03, 2011, 01:22:46 amIn the video it seems it's a PM rotor, but herehttp://www.appliancedesign.com/CDA/Archives/3c4028037aa38010VgnVCM100000f932a8c0____they say it's a switched reluctance, and from the drawing you see it's single phase. These motors work similarly to a stepper motor, without magnets on the rotor (so achieving very low cost). There must also be a version with PM (seehttp://www.dyson.com/technology/ddmtabbed.aspthere's the drawing, too), mounted on the handheld version of the cleaner (higher power density is needed there).The photo herehttp://www.telegraph.co.uk/technology/news/5636349/Dyson-unveils-worlds-fastest-motor-in-new-vacuum.htmlshows how tiny these motors are, but nothing so special. In this last page, they also say "We are the only company in the world producing a switched reluctance motor.". That's really annoying!

author: vk6zgo
author_rank: Super Contributor
timestamp: May 03, 2011, 09:53:49 am
content: I have repaired the drive circuits for what could be called a diigital motor".It used DC pulses to produce a rotating magnetic field to operate an induction motor by switching the pulses to successive windings situatedin a circular pattern surrounding the rotor.Initially,the drive circuit set up the rotating field at an arbitrary rate,but when it was running,it received feedback from Hall Effectsensors,indicating the rotor position. This information was then used to stabilise the motor speed.Although this device used Op Amps & a switchmode regulator IC to perform its marvels,it could be done with virtually all of the circuitryin the digital domain.These motors rotated at very high speeds ,& were used to drive "Turbo vacuum pumps" in a Chemistry lab.VK6ZGO

author: Sionyn
author_rank: Frequent Contributor
timestamp: May 03, 2011, 01:33:58 pm
content: here go the carbon emissions thing again

author: Zero999
author_rank: Super Contributor
timestamp: May 03, 2011, 06:17:10 pm
content: http://en.wikipedia.org/wiki/Switched_reluctance_motor

author: vk6zgo
author_rank: Super Contributor
timestamp: May 04, 2011, 03:04:51 am
content: Quote from: Hero999 on May 03, 2011, 06:17:10 pmThe thing described in this link is near as dammit to the device I referred to in my post above.It's a glorified Induction motor,with the rotating field supplied by a dc switching circuit instead of the ac mains.VK6ZGO

author: scrat
author_rank: Frequent Contributor
timestamp: May 04, 2011, 08:34:34 am
content: Quote from: vk6zgo on May 04, 2011, 03:04:51 amSwitched reluctance are synchronous motors, while induction are asyncronous. The latter require rotor currents (induced by the same principle as in a transformer), while the first work because of the inductance difference along the rotor axes, so only require the right current vector in the stator windings (so could be more efficient).

author: vk6zgo
author_rank: Super Contributor
timestamp: May 04, 2011, 09:24:46 am
content: The only way an electric motor can operate,unless it has permanent magnets mounted on its rotor,is from inducedcurrents in the rotor.They may be eddy currents,as in the aluminium disc of a classic Kw/H meter,but they are still induced currents.VK6ZGO

author: scrat
author_rank: Frequent Contributor
timestamp: May 04, 2011, 10:28:19 am
content: No, anysotropy of the rotor is another way it can generate torque without electrically conductive rotor.There are reluctance motors and hybrid (e.g. Interior Permanent Magnet) that work on that principle (different inductance or reluctance on orthogonal directions).There's a component for the torque which is (Ld-Lq)*Id*Iq, where "d" and "q" stand for the direct (aligned to the rotor minimum inductance axis) and quadrature components.The system follows the point of minimum reluctance, which is where the energized coil is aligned with one of the rotor teeth in a switched rel motor.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2011, 04:51:26 pm
content: Quote from: vk6zgo on May 04, 2011, 09:24:46 amNo.If you read the Wikipedia article I linked to, you discover a motor can work without permanent magnets or a wound rotor.If you find that hard to understand make a simple linear motor, wind a coil round a straw with a nail loosely fitted in the middle and you'll discover the nail is pulled into the coil when it's energised.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 05, 2011, 02:40:47 am
content: Quote from: Hero999 on May 04, 2011, 04:51:26 pmOK,do that,then after you have proved a solenoid will draw a nail into it,remove the nail.Is it still magnetic?Where did the magnetic field come from?Would it work with a piece of ferrite material?Note:-I never said you have to have a wound rotor,in fact,the example I gave was of an aluminium discrotating in a magnetic field.They do work,there is one in most meter boxes.OK,I see where you are coming from:-"If the induced magnetic field is from induced currents,why does a permanent magnet attract a non magnetised piece of iron?"Right?So if we can induce a magnetic field in that case without induced currents,why not in a motor?Well,one thing is,that a conductor moving through a magnetic field will have a current induced in it,anyway.The magnetic field is continually changing,so the polarity of the induced magnetic field & hence the alignment of the atomsmaking up the material will change.I suggest that this constitutes a current.OK,I'm not a Physicist,so I'm not able to determine whether magnetic realignments constitute a current,but I will leave you withthese suggestions:-Try making a motor with a ferrite rotor,& an insulator as a shaftTry a motor with the whole rotor assembly made from an insulatorMy guess is neither of them will work.VK6ZGO

author: vk6zgo
author_rank: Super Contributor
timestamp: May 05, 2011, 04:15:56 am
content: Sorry,Hero999,most of my comments in the last posting should more properly be directed at Sprat!You will note,however,that in all of my earlier postings,I referred to an "Induction Motor".I never implied that these type of motors had wound rotors,in fact the majority do not.I incorrectly implied that all electric motors ran due to induced currents---that of course is untrue,as DC /Universal motors& slip-ring AC motors directly energise the armature windings.I still maintain that :-Those motors which do not have a wound,directly energised armature depend upon induced currents in the rotor to function.(Note:- I have avoided the term armature,in favour of rotor in previous posts,leaving armature to refer to the wound device.)Non- magnetic materials will work in an induction motor,non- conductive materials will not.VK6ZGO

author: Rufus
author_rank: Super Contributor
timestamp: May 05, 2011, 10:48:28 am
content: Quote from: vk6zgo on May 05, 2011, 04:15:56 amYou are wrong. Reluctance motors are synchronous. The rotor stays aligned with the rotating magnetic field created by the stator. It doesn't go 'through' any magnetic field to have currents induced.

author: tecman
author_rank: Frequent Contributor
timestamp: May 05, 2011, 12:54:22 pm
content: Quote from: Rufus on May 05, 2011, 10:48:28 amReluctance motors are synchronous, but can "slip" rotation without potentially damaging current, as with a PM motor.paul

author: vk6zgo
author_rank: Super Contributor
timestamp: May 05, 2011, 02:54:13 pm
content: Whatever!VK6ZGO

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: May 05, 2011, 05:22:19 pm
content: Quote from: Sionyn on May 03, 2011, 01:33:58 pmWatching a good engineer diving straight into heavyweight marketing bullshit is upsetting.Pretty much akin to an attractive and smart woman slipping into prostitution.

author: Zero999
author_rank: Super Contributor
timestamp: May 05, 2011, 06:20:07 pm
content: Quote from: vk6zgo on May 05, 2011, 02:40:47 amIt certainly will, the rod inside the solenoid doesn't have to be conductive to be pulled into the coil.Quote from: vk6zgo on May 05, 2011, 04:15:56 amA switched reluctance motor is not an induction motor. The rotor doesn't have to be conductive in order for it to work but it has to be magnetic and by that I mean attracted to a magnet not a permanent magnet. The rotor could be made of non-conductive ferrite and it would still work. If the rotor were to be made from non-magnetic aluminium, it would not work as a switched reluctance motor, the rotor might rotate but it wouldn't be synchronous, it will only turn by induced flux, like an induction motor.A switched reluctance motor is a synchronous machine because the rotor directly tracks the rotating magnetic flux.

author: scrat
author_rank: Frequent Contributor
timestamp: May 05, 2011, 10:14:29 pm
content: @VK6ZGO:I just confirm what Hero is saying.About the "insulator made" rotor, unfortunately it is impossible in thre real world, since almost all ferromagnetic materials are weak conductors.However, rotor (induced) currents are strongly unwanted in synchronous PM, REL or hybrid motors (which do not have slip rings). This is for at least two reasons: "cold" rotor means more efficiency, and control is only based on the rotor PM flux/anysotropy direction vs stator current "direction" (which is mechanically locked to the shaft) giving more accurate torque control (while induction motors' rotor flux is just estimated).Induced currents are usually blocked by using laminated and grain oriented iron materials (http://en.wikipedia.org/wiki/Electrical_steel.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 10, 2011, 03:11:20 am
content: Yes! You were right,& I was wrong!I found a reference which explained it to my satisfaction.The sticking point with me was that I couldn't see how when the current was switched to the stator coils,the change in magnetic field between zero & the full field would not cause induced currents in the rotor.The magic words in the reference were "Laminated rotor",which convinced me that there would be minimalinduced current in the rotor,& hence your explanation was the correct one.Of course,Laminated rotors are used in brush type motors to minimise induced currents in the rotor core ,which areregarded as losses,so I should have remembered that.The motor I repaired the drive board for may have been either a switched reluctance,or an induction motor,asmy main concern was fixing the electronics.VK6ZGO

author: Zero999
author_rank: Super Contributor
timestamp: May 14, 2011, 09:23:35 pm
content: Quote from: vk6zgo on May 10, 2011, 03:11:20 amIt's good you've swallowed your prided any admitted it, other people I know never admit it when they've made a mistake.QuoteCould you please post a link? It may help other people who've also had difficulty understanding it.

author: onemilimeter
author_rank: Frequent Contributor
timestamp: May 14, 2011, 11:48:17 pm
content: I built a switched reluctance drive (the motor and converter) before. It's a synchronous motor. I can confirm that the explanation by Hero999 and scrat are correct.Induction Machine:- Two magnetic fields (one is produced when stator winding is energized, another one is produced when induced current flows in rotor conductors) --> Lorentz Force Law --> torqueSwitched Reluctance Machine:- One magnetic field (produced when stator winding is energized) --> torque production is based on the principle to minimize the reluctance of the magnetic circuit --> reluctance torque- Require rotor with saliency.By the way, Mr Dyson visited our department two days ago! I should have asked him the advertisement about "zero carbon emission"...

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: May 21, 2011, 11:17:09 am
content: The whole vacuum cleaner business is a sham. Using 2kW of power to pick up a few milligrammes of dust and transfer it into a bag is ridiculous.Then Mr Dyson steps out and self-proclaims he is genius because he can get rid of the bag and use brushless motor to power the same old crappy technology.Loads of spin and glitzy looking plastic enveloping the old inefficient century-old technology.

author: Simon
author_rank: Unknown
timestamp: May 21, 2011, 11:34:03 am
content: yea, Mr Dyson is now in my books as a con man. showing off what is current technology as his own personal invention. The guy needs to get with the program

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 21, 2011, 01:05:41 pm
content: thats the problem with people who know shit about ee and try to talk about one. i read his story in reader's digest (friend's, not mine!). he's an artist, like the rest of the artist's who tried to make money.