Brushless DC motor for machine tool power

Here is a vid of one putting out more watts than it is rated at so sounds like they are rated about right

**LINK**

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Bob,

Please don't shoot the messenger !!

I simply explained how [to the best of my knowledge] "they" specify these motors.

Of course it's not specified for an industrial spindle ... If it was, it would be too heavy to 'do the day-job'.

MichaelG.

I suppose it is always easier to make tiny things spin around fast compared to a spindle that does actual work.

Also I have been trying to think which lathe it was I heard of that had a worm drive powering the spindle...

Finally found it

http://www.opensourcemachinetools.org/archive-manuals/lathe_design.pdf

Turned out to be a theoretical one :P

This video may be more relevant to potential usage on machine tools.

**LINK**

MichaelG.

i've seen helical gears used in model helicopters Rainbows and I think some more like a multi start worm.

I thought Jason may have found a test that actually measured the output power. I never have but not looked for a long time. Another maker, Scorpion do I think give continuous current ratings.

Price seems to rise at an astronomical rate with shaft diameter. The go cart one may be £200 plus or more. 8 or maybe 10mm shaft. 6mm used to be common and cheap.

Here's a home made one

**LINK**

There is also a 240v one around and details on rewiring a washing machine type for lower voltages. All on YouTube. There were several design sites about and some laminations were available.

There is still some design info around eg

**LINK**

It may help people understand what they are buying.

John

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**LINK**

A car alternator may provide an alternative......

Remove the rotor winding replace with perm magnets,( or feed with a fixed excitation voltage) use the stator energised by the speed controller.....

About 10% more input power than rated?

That is about the right sort of max power for a 5mm shaft. 380-odd watts rather than 1.5kW

Neil

Geee Neil I mentioned 1/2 hp I think earlier - output too not input and at sub 10,000 rpm which I didn't mention. I think you need to consider the various numbers on them. It's also a bit weird that people fly things around using motors like that.

I doubt if many people who bought the motor initially linked to would run it with 6 lipo cells. I wouldn't anyway. If Rainbows wants make use of this style of motor I feel he is looking at the wrong type and wont be running it at max voltage either. There seems to have been a shift from 6mm shafts to 5 but 6 and 8 are still available - generally at a cost though.

Here is one with a 4mm shaft with figures that I might use on it. It can be run at 42 amps.

**LINK**

Thought I had posted a link for Michael that showed a motor that might well be used on the go cart - price over £300 and some makes can be more expensive than that.

John

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The outrunner motors actually do have two bearings, one at each end. You can see in Ajohnw's picture above that the shaft extends out the back of the stator.

There are also brushless inrunner motors used sometimes, although not nearly as common these days.

Mostly in a model aircraft they would be run at 10K or so Rpm, maybe 20K or so at the outside. The propellors are less efficient at higher rpm. I'm not sure how good the bearings would be at really high speeds. It is not unusual for them to need changing.

They do get quite hot, I have had magnets come loose which is because the glue that holds them on is getting too hot. That particular motor was being run at up to about 1200W. (input) The efficiency would not be as high as larger motors, 70% would be more realistic I suspect. Everything is being run at its limits....I have had an ESC catch fire when the prop touched the ground while at full takeoff power. When I say catch fire, I mean there was a fireball, and the ESC was still burning when I got to the plane.

Think of them as being like a hot rod engine.

John

Just as a general aside on this:- I seem to remember seeing an article about making your own Outrunner Motors, using old (small) mains motor parts, this was a few years ago, may have been in ME or MEW but not sure of that.

Having gone through 20 pages of aliexpress brushless motors I found nothing that ticked the criteria of low Kv, ok price, thorough information and >1000w.

Would this motor be better/ useable?

Its the same line of motors as the go cart, lower power though. Way lower Kv for 8400RPM at full voltage. No worm gears involved

I googled it and found a video on youtube of it powering a mill

https://www.youtube.com/watch?v=P57s15SrnCk

It isn't actually cutting for 90% as far as I can tell? Which makes it hard to gauge how well it performs. Atleast it must have cut some stuff out with out imediately melting.

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< sigh >

John,

The motor on the go-cart was specified in the text on the YouTube page ... That's why I provided the link for you; to avoid speculation.

MichaelG.

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Quote:

Published on 17 Apr 2012Model: Turnigy 50CC
Watch my website for details and real tests and video outside 
http://www.masinaelectrica.com/simple-brushless-controller-explained/

Edited By Michael Gilligan on 17/07/2016 05:46:58

Neil the one in the video only has a 3.17mm shaft so that would be nearer to the values you got in your first incorrect calculations but still well within the shafts limits of 1.23Kw when worked out correctly.

John Rudd's suggestion is a good one if you really want a brushless motor. There is a lot of info via Google on converting car alternators into motors using a standard esc and driving the rotor with a low dc current. People like Allegro Microsystems also do control chips for escs if you want to go that far. A car alternator would probably be the right sort of size for a machine tool drive.

Well I think before buying motors I'm gonna get a transformer. 240V 13A becomes 36V 87A.

I am gonna try and power an alternator and see how that goes (though there are still brushes connected to the rotor as far as I can tell?) since they can be £10 and if that fails I can use the ESC and power supply to power a store bought one or a homemade one. Really not sure how to make the stator though.

Sanity-Check, Rainbows ...

The only "affordable" 3kvA transformer that you are likely to find is a 110v site transformer. This could be easily rewired to provide 0-55v instead of 55-0-55 but [continuously rated] they are very big and very heavy.

**LINK**

The other, non-trivial, issue is that you need three phases to drive a typical bldc motor !!

Think about it, before you waste too much effort and money.

MichaelG.

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P.S. ... If you haven't done so yet ... Have a look at the go-kart man's site ... He knows what he's doing.

Edited By Michael Gilligan on 17/07/2016 19:28:50

The ESC generates 3 phase since that is what BLDC motors need anyway. Really, the alternator is just a BLDC on the stator side but has a dc excited rotor instead of a PM one. Yes it has brushes, but these run on slip rings rather than commutator segments, and the current is quite low. There was a gentleman who used to exhibit on one of the club stands at MEXs who demo'd alternators being used as traction motors, with home brew electronics. I pointed him towards the OTS chips from Allegro, not sure if he ever tried them, but people on the web have used them in alternator conversions I think.

In theory you don't need a transformer, you could run the 3 phase windings direct from rectified mains using chopper drives just as standard VFDs do. What is critical is not the voltage across them but the current through them, so you apply the high DC voltage for long enough to get the current you need in a winding through a MOSFET, then turn it off and allow a diode to commutate the current. Standard practice in VFDs and stepper drivers. This is in effect a buck converter, and will act the same as a transformer in giving a step down between the winding current and mains current.

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Quite so, John ... I was simply reminding Rainbows that he needed 3 phases; having seen no mention of him intending to source an ESC.

MichaelG.

"Well I think before buying motors I'm gonna get a transformer. 240V 13A becomes 36V 87A.

I am gonna try and power an alternator and see how that goes (though there are still brushes connected to the rotor as far as I can tell?) since they can be £10 and if that fails I can use the ESC and power supply to power a store bought one or a homemade one."