Brushless DC motor for machine tool power

[John RuddParticipant @johnrudd16576]

Andy,

What about horse power size? Did you go for same as existing, 400 watts?

[AjohnwParticipant @ajohnw51620]

It's a pity you have been put off Rainbows because no one will know what can be done with them unless they try it.

As I mentioned I think 1.5kw is rather ambitious unless you make one yourself. That would need a source of lamination stacks of some what larger diameter than the model motors that are about. I posted a link that shows the shape of these which is needed. Power can be increases by using more than one next to each other. A site linked to off the one Michael posted has some practical aspects on it. There are others.

**LINK**

That site shows a motor made from DC motor lamination stacks and no details. There may be a catch with that method which will spoil the efficiency. The laminations are likely to be thicker than what is ideally needed. That's the laminations that make up the stack of them. This may or may not matter. There is a lot of that in self building. Ideally the stack needs to be epoxy coated to save messing about with kapton tape and having sharp corners etc.

The model motors may be a bit tat but they do have what all brushless motors have in them. They could be modified in all sorts of ways even down to completely dismantling to get the parts or even just rewinding. If some one takes one apart they will see why the shaft and bearings are rather small. I have a couple of 22mm laminations. Sort of size used in ones built from CD motors etc. The hole in the middle of them is 10mm dia.

The ESC's for models are made to be extremely small and light. One way of improving them might be to change the surface mount power devices to leaded types with a heatsink but one of the self builds with some modifications might be a better idea. When these motors stall the current levels are huge so some sort of current monitoring would be a good idea. It could be added to the software used to drive the things.

As you can see it's not a project for a typical defeatist who wants everything laid out in black and white complete with detailed instructions. It's also likely to take some time and be a bit hit and miss.

There seems to be a lot less defeatism about in people who speak English as a 2nd language or not at all. A sign of the times I suspect.

John

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[John RuddParticipant @johnrudd16576]

Rainbows,

Over on RC Groups.com there is a whole section devoted to building brushless motors, various details on lamination sizes and thicknesses, winding patterns LRK method etc. Magnets, clearances etc….All very informative stuff, there may evn be supplier details iirc. Then there's some info in building your own brushless controller in the electronics section….

I dont want to start cluttering up this thread with too much info as its not really model engineering stuff, so best if you have a look there yourself

Edited By JasonB on 18/07/2016 11:52:06

[RainbowsParticipant @rainbows]

The idea does still appeal to me but building a motor is something I would look into after having wired up my inverter and motor. Mixture of low cost, proven equipment and low effort all point to three phase for the short term. (Well usually not low cost but the second hand market is a beautiful thing)

[Andy AshParticipant @andyash24902]

Posted by John Rudd on 18/07/2016 07:24:18:

Andy,

What about horse power size? Did you go for same as existing, 400 watts?

Hi John,

The motor is 1/4 HP which is 180 Watts, considerably less than the rating of the DC motor and PSU I showed.

I just looked up the stall current on the 1/4 HP AC motor. I wanted to compare like with like.

The motor I chose looks like it comes out at 1500 Watts (2HP) in those terms, but there is no way you could use it like that continuously.

A real 1/4 HP (continuous/shaft) is more than enough to drive a small lathe or mill.

[John RuddParticipant @johnrudd16576]

Andy,

Thanks for the info on the motor, it gives me an idea for my own mini mill…

@ Jason,thnx for the hyperlink addition….guess I'm just too damn lazy….

[AjohnwParticipant @ajohnw51620]

This is an interesting paper on brushless motor design

**LINK**

Some pretty thick books mention that even complex modelling has it's limitations and wont be entirely accurate.

John

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