Having used motors of this general type in model aircraft, I would have to say no, they are not suitable for extended periods of use. Typical use would be flights of up to ten minutes or so, not all at full power. They are great little motors for what they are meant for, but not I think very suitable for powering machine tools.

John

Hi Rainbows,

If you start reading from page 8 of this thread, hopefully you may get some of the answers.

Ketan at ARC.

1500W on a 5mm shaft ?

Yer, right.

Not that motor but you MAY have some luck with a much larger motors with much lower revs / volt. It was pretty easy to find these on ebay in the past but not now by the look of it. From memory they were around down to around 500 revs per volt with reasonable power levels. In use these were generally speed reduced with a toothed belt or used to drive rather large props on model aeroplanes.

JS has missed the revs aspect of the motor power. It would be running at 20,000 rpm on 12v and the power is very probably input not output. It's possible to do some simple rough sums as spec's sometime give the winding resistance. That gets lost as heat.

They have been used for directly driving cnc machine spindles in the past but I have no idea how well this worked out. A companies was selling them on their machines.

It's also possible to find info on the web concerning winding and making your own. It's even possible to get high power from smaller laminations by stacking them on the same spindle.

Personally I would bear in mind that cables for 40 amps or so will need to be a bit bigger than the rather short lengths used in models. From memory 1/2 hp out on 12v is probably possible.

Just add that it's probably possible for a model engineer to modify a motor. It wouldn't be difficult to remake the outer casing of an outrunner to use different bearings and maybe cause it to generate some air flow to cool the stator if this sort of thing was found to be needed.

Sorry about the probables. It was cabling that gave me some pause for thought. Ideally the power supply needs to be near the motor.

John

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Edited By Ajohnw on 16/07/2016 11:14:31

Here is an interesting conversion of a mini-lathe touse a brushless dc motor:

Mini Lathe Motor Upgrade

Mike

I've read the ad several times and so far, I can't see the RPM quoted. Working backwards 4000 rpm spindle through a 9:1 worm would require 4000 x 9 = 36,000 rpm at the motor spindle – I can't see that happening, industrial routers running at 24,000 rpm have bearing issues and they are totally enclosed, built in semi-clean room conditions.

Have a look on Arc Euro Trades web site at the high speed spindles to see the difference. I've also looked at Zapp Automation for ideas.

So you're saying he wrong that it's expecting a lot to put 1500 watts (2hp) through a 5mm (0.1" ) shaft?

For small short shafts P=(D^3 x N)/38

(0.1 x 0.1 x0.1 X 20,000) /38 =0.53

In other words is that's the output power, the shaft is overloaded four times.

Even if the motor is only 25% efficient (375w output) it's still right on the limit and while that might work for a prop that's without making any allowance for the shock loads associated with shock loadings.

I think John makes a very good point – 1.5 kilowatts for that motor has as much validity in the real world a 'music power'.

Neil

Edited By Neil Wyatt on 16/07/2016 14:28:59

Short measures again Neil?

There is no side loading on these motors in normal use Neil. Just a prop so the shaft only takes thrust. The set ups have to be well balanced. New shafts and bearings have been available – for smash ups but I doubt if the bearings used last long.

The power figures are also overstated. Some give a most efficient rating which will be rather different to the headline figures. As amps and winding resistance are usually stated it's also possible to work out heat loss to some extent I^2R. Then there are losses in the controller and wiring. It wouldn't surprise me if the headline max amp rating was close to the fuse rating of the copper wire used for the windings or something of the order of a 10 sec rating etc.

This gives some idea how the higher power motors are sometimes used

Wot – no shaft used. Trouble is that it's still rotating on the inner shaft but doesn't bend so easily when they crash. Just add that this sort of set up could be improved by adding a more substantial bearing in a separate housing.

None of this really matters for their intended use as generally all that matters is the thrust the inevitable prop on the end gives in use. Different sizes and kv ratings are intended for use with prop's of a given diameter and pitch plus a reasonable flight time. There is bound to be info on this subject about on the net.

Worms and wheels aren't very efficient at transferring torque especially with high reduction ratios. Gears as per electric drills and angle grinders etc are better but noisier.

Personally I think Rainbows is expecting too much of them and looking at the wrong kv ratings even though these appear to offer more torque. The higher reving ones wont be easy to gear down to what are usually regarded as useful spindle speeds. For directly driving a tiny carbide milling cutter at high speed they might work out.

John

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Edited By Ajohnw on 16/07/2016 16:33:49

.

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.

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

**LINK**

MichaelG.