brushless motors

[robert davies 6Participant @robertdavies6]

Does anyone have details of how to control brushless motors ? or where to access controllers and power supplies. I would like to use one to drive a toolpost miller/drill

[robert davies 6Participant @robertdavies6]

control

[Roger HeadParticipant @rogerhead16992]

You'll find plenty of reasonably priced controllers in the R/C model aircraft field. R/C motors go all the way these days from flea-power into the kW region, all from (relatively) low DC volts.

Roger

[V8EngParticipant @v8eng]

There is already a bit of information which might help on this forum.

http://www.model-engineer.co.uk/forums/postings.asp?th=111634

Edited By V8Eng on 09/12/2015 09:05:12

[mark smith 20Participant @marksmith20]

This guy changed his mini lathe to brushless using RC stuff.

**LINK**

[Michael Cox 1Participant @michaelcox1]

Thanks for that link. Very interesting

Mike

[AjohnwParticipant @ajohnw51620]

From Mark's link it sounds like I should have a play again.

One option for a high current power supply is those used in servers that are plugged in as one unit. Usually described as redundant power supplies as the server has more than one and will switch automatically allowing a replacement to be plugged in. Model aircraft etc people use them to make battery chargers so there is some info about on what pins need shorting out to get them to power up. They crop up very cheaply on ebay at times and can even be new. Stuck with 12v though but some people have disconnected the internal grounding and used 2 in series for things like induction heating.

The motors are rated in power and revs per volt. So say it's a 600 k motor that means 7,200 rpm at 12v. The lower revs per volt ones tend to be aimed at helicopters. 24v will loosely mean 14,400 rpm, more of a problem as I see it. I looked at using timing pulleys to reduce the speed – probably quieter than gears and they can transmit a lot of torque.

I feel that there is a lot of hype kicking about in some areas concerning brushless motors. Comparing apples with apples eg and a conventional universal brushed motor they can be more efficient as would a could a permanent magnet brushed motor – the sewing machine claims for them are correct. Low speed improvement though is more dubious and of course as always actual power drops of with speed reduction as the torque has to remain at similar levels. Belt's, gears etc increase torque when they are used to reduce speed. Brushless motors do have no brushes though which will be a gain at some point if the rest of the motor lasts long enough. There is no reason why the electronics driving a brushless motor should be any more reliable than brushed, same for the motor.

There are industrial sewing machine motors and controllers about. Pricey and they usually spec input power.

There is info about on the web concerning building your own brushless motor. Some of the parts can be bought.

One thing about the model aircraft motors is that it looks like replacing bearings is a manageable job. Replacement shafts are available for them as well.

The web effect as I call it might up the price of redundant power supplies now I have posted that.

Do remember that lots of current will be drawn so cables to the motor need to be short and or rather hefty. The model stuff uses a silicone rubber coated wire as it is likely to get hot at the sizes typically supplied.

John

–

[John Stevenson 1Participant @johnstevenson1]

Posted by John W1 on 12/12/2015 12:10:23:

I feel that there is a lot of hype kicking about in some areas concerning brushless motors. Comparing apples with apples eg and a conventional universal brushed motor they can be more efficient as would a could a permanent magnet brushed motor – the sewing machine claims for them are correct. Low speed improvement though is more dubious and of course as always actual power drops of with speed reduction as the torque has to remain at similar levels. Belt's, gears etc increase torque when they are used to reduce speed. Brushless motors do have no brushes though which will be a gain at some point if the rest of the motor lasts long enough. There is no reason why the electronics driving a brushless motor should be any more reliable than brushed, same for the motor.

John

–

.

Could you elaborate on this statement please John so we know exactly what you are discussing.

I'd hate to reply to something you were only thinking about.

[Neil WyattModerator @neilwyatt]

I think this pages sets out the pros and cons of brushed and brushless motors pretty well:

**LINK**

The real advantages are that brushless can deliver rated torque right from stalled through to rated speed without dropping off at higher speeds like brushed motors, and they are also more tolerant of running at higher than rated power for short periods at low speeds. This is because they are more efficient and so less liable to overheating at low speeds.

Neil

[John Stevenson 1Participant @johnstevenson1]

That is a very good link Neil and explains it very well.

Accurate and informative

[Ketan SwaliParticipant @ketanswali79440]

In the link which Mark posted, 'rocketpatel' and 'Phaeonyx' talk about kick back at low speed, in their low cost rc brushless conversion. Could someone explain what they mean? There is also a comment about back emf earlier in the link topic, which I do understand, and I would have thought that it is a concern, to a certain level, in so far as 'how does this effect household wiring' and in turn how this might effect household building and contents insurance?…I am not scare mongering. It is just an observation which I question. As far as household insurance is concerned, hopefully the machine is in a garden shed, so it does not matter as insurance might not pay out anyway?

Neils link is also interesting, and in particular this point: 'They also require control strategies that can be both complex and expensive. And, they require a controller that can cost almost as much as if not more than the BLDC motor it governs.'

In my opinion, the guy who has changed his lathe using rc stuff might know a lot about rc stuff, and his idea may/might work for hobby conversion, with its issues on torque and kick back? and back EMF, to name a few. I am not knocking that in any way. It does the job for him at perceived low cost, and it is a great boost for his pocket and ego…bravo…rip-off Britain and all that. However, I definitely question his engineering competence in so far as did he have the right machine for his purpose in the first place? and did he know if he was using or abusing his machine?. Yes…I have seen his amazement at the cost of the original components…which are not even for his machine!…and no…this is not the reason for my question…nor is it a sour grapes issue.

However, it is important to note that when a manufacturer of a machine such as SIEG instals brushless motors and controlling systems into their machines, the issues are far more complex, as Neils link suggests. In such installations, the control strategies deal with and provide appropriate and consistent torque throughout the speed range, based on specific requirements and purpose of each machine model in their range. They also have costs of additional components which are required to comply with and go through CE regulatory requirements. These components and costs are not included in U.S. or Canadian machines, which please note.

This is not a PR statement. It is just a clarification which I am bringing to attention in this thread to avoid simplistic comparisons.

In my opinion, it would be more 'correct for the purpose' of conversion to consider a three-phase motor with inverter from one of the reputable advertisers shown on the right here, with CE, and filter, to deal with back EMF, further verified by a qualified electrician as need/required/appropriate. This might be more expensive than rc brushless, but cheaper than 'proper' brushless conversion.

Ketan at ARC.

edited to deal with a buck load of spelling mistakes..sorry

Edited By Ketan Swali on 13/12/2015 16:49:26

[Russell EberhardtParticipant @russelleberhardt48058]

You might like to have a look at this thread on another forum.

Russell.

[MuzzerParticipant @muzzer]

The article on Neil's link has a confusing photo in Fig 3. He said that BLDC motors have permanent magnets on the rotor (correct) – and then posted a picture of a wound rotor from a brushed motor.

Controllers for BLDC motors are more complicated because they require semiconductor switches for each phase (usually 3) to commutate the windings in response to position sensors (usually Hall effect switches), whereas a brushed motor controller typically uses PWM control of the motor (2 terminals).

[Neil WyattModerator @neilwyatt]

I think the real issues with the R/C motor are three-fold:

The power ratings for R/C motors are 'peak' values that bear little resemblance to what the motor can put out under continuous load.

An R/.C motor isn't designed for long periods of continuous use. if you put it's specced 70A into it for an hour, then your model aircraft would need to have three car batteries in it…

As an outrunner motor the cooling is less effective than a motor with external windings

Some nonsense on the conversion page as well, in the discussion he says that the torque is minimal with the motor just turning when the torque/speed graph he links to shows it is at a maximum when stopped.

What is missing from that graph is the rated speed/torque line. This goes horizontally across at constant torque from 0rpm to the rated speed – you can run above the line, but the motor will start to overheat. It would be very interesting to see where that line is for an RC flight motor and compare it with a motor designed for machine tool use. I suspect it is much lower and relies on the short flight times and intermittent power requirements of model aircraft to keep the motor cool.

That said, little outrunner motors are very impressive, although the controllers aren't. I have three R/C brushed motor controllers in the 'dead or dying' box ()one very expensive one and two ebay cheapies). I wouldn't bank on one lasting for day to day lathe use.

Neil

[John HaineParticipant @johnhaine32865]

Of course induction motors are brushless…

I'm rather impressed by the motors that are now fitted to washing machines, small 3-phase induction motors that are run at high maximum frequency so the volume/weight of copper and iron can be reduced, but with wide speed control range. An electronic controller means the the motor can be run up in one direction then decelerated and run in the other direction then reversed again and so on when washing, then spun up to high speed for spinning, you can detect unbalanced loads by monitoring phase currents and so on. Talk about control strategies, these are very sophisticated. And given the production volume of the motors and drive electronics these should be basically cheap compared with "our" induction motors. But finding data on either the motors or drivers seems quite hard though both can be bought from the spares suppliers on eBay – but I did find an NXP (?) application note on control methods.

It would be very interesting to investigate using these for machine tool drives, a better bet I think than the outrunner motors.

Another source of motors is to use car alternators.  These can be driven by similar electronics to brushless DC motors driving the stator (power) windings with 3-phase.  You do need to provide a DC polarisation current for the rotor via the slip rings but this can be quite low, and brushes on slip rings don't wear nearly as badly as on a commutator.  I have seen a chap at a couple of ME exhibitions showing a loco drive using surplus alternators, and there's quite a lot of info on the web too.  Compared to outrunner motors, they have the advantage that the power winding is fixed and well ventilated, and of course alternators in cars have to operate for hours in a hot and nasty environment so they will be pretty robust.

Edited By John Haine on 13/12/2015 17:56:44

[MuzzerParticipant @muzzer]

I've developed alternators for use in hybrid vehicle applications, as an engine starter / generator. It's a compromise because in fact they have very poor efficiency. They aren't optimised for use as a motor in std form, so you need to do some work to make the most of the copper and steel that's in there. However, we were able to start a cold 2.2 litre Transit diesel engine using such a machine. IIRC it managed it somewhere as low as -20C.

I'm not certain but I think you'll find that many (but not all) of the motors in washing machines are switched reluctance machines. That's a whole different field….

[John HaineParticipant @johnhaine32865]

Switched reluctance motors seemed to be popular a decade or two back but a lot of modern machines definitely use induction motors. I remember when I was at Leeds Uni the head of department was one of the main developers of switched reluctance motors for applications such as consumer products and I sort of expected that by now they would be very common, but they seem to have quietly been superceded, presumably because with modern VFDs induction motors are so easy to control and just as easy to make as an SR motor.

[MuzzerParticipant @muzzer]

These boys may have been inspired by your head of department on the basis of their location. They are in the old CEGB buildings in Harrogate and seem to be still going strong. Some of my old colleagues from Farnell ended up there after the Wetherby and Boroughbridge sites were bought and closed.

The power density is lower than a PM machine and it's difficult to minimise the cogging torque enough for many applications. As you say, induction motors seem to have trumped them but there are clearly niche applications where they win out.

[Neil WyattModerator @neilwyatt]

What's the difference between a switched reluctance motor and a BLDC motor (if there is one)?

 

edit – I see it doesn't have permanent magnets but works in essentially the same way

Edited By Neil Wyatt on 14/12/2015 13:18:59

Edited By Neil Wyatt on 14/12/2015 13:21:09

[Beck WickParticipant @beckwick81231]

I am also looking for the suitable BLDC drivers and the suitable supply for it?

Can you please share what are the specifications of your motors?

What power they require?

And what is your application in which you are using them?

[Author]

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