BLDC motor questions

DC motor questionsAll,
I am making, or at least attempting to make, an electric high speed
spindle that fits in a confined space. I do not want to use air as the
motive force. So I have been experimenting with BLDC motors made for
model airplanes and the like. I would like to cool the stator, I think
I may need to in fact if I want the motor to run continuously. Liquid
cooling would be best. To do this most efficiently the stator should
be submerged in the cooling liquid. There is not enough space between
the windings for even very small diameter tubes carrying fluid to fit
through. So if the stator gets submerged the liquid must be
constrained to the stator only. I thought about making plastic end
caps for the stator and sealing the perimeter of the stator with a
sheet of plastic or maybe plastic and some sort of metal sheet. The
motor is built with the outer rotating, inside out compared to most
motors we see, but common in floppy drives. There is about .008" air
gap between the outer diameter of the stator and the magnets. I'm
afraid that if I use brass sheet, for example, to wrap around the
stator it will short out the laminations and increase eddy current
losses in the motor. If the brass sheet could be insulated from the
laminations would eddy currents in the brass sheet start to heat it
significantly? This is a 1000 watt motor and the stator is about 1.18
diameter x 1.18 long (30mm x 30mm). If the stator can be wrapped with
something to seal it what kind of fluids would not tend to soften
varnish on the windings? Anybody here know?
Thanks,
Eric

 

[Tim Wescott]

On Mon, 03 Nov 2014 10:37:37 -0800, etpm wrote:

DC motor questionsAll,
I am making, or at least attempting to make, an electric high speed
spindle that fits in a confined space. I do not want to use air as the
motive force. So I have been experimenting with BLDC motors made for
model airplanes and the like. I would like to cool the stator, I think I
may need to in fact if I want the motor to run continuously. Liquid
cooling would be best. To do this most efficiently the stator should be
submerged in the cooling liquid. There is not enough space between the
windings for even very small diameter tubes carrying fluid to fit
through. So if the stator gets submerged the liquid must be constrained
to the stator only. I thought about making plastic end caps for the
stator and sealing the perimeter of the stator with a sheet of plastic
or maybe plastic and some sort of metal sheet. The motor is built with
the outer rotating, inside out compared to most motors we see, but
common in floppy drives. There is about .008" air gap between the outer
diameter of the stator and the magnets. I'm afraid that if I use brass
sheet, for example, to wrap around the stator it will short out the
laminations and increase eddy current losses in the motor. If the brass
sheet could be insulated from the laminations would eddy currents in the
brass sheet start to heat it significantly? This is a 1000 watt motor
and the stator is about 1.18 diameter x 1.18 long (30mm x 30mm). If the
stator can be wrapped with something to seal it what kind of fluids
would not tend to soften varnish on the windings? Anybody here know?
Thanks,
Eric

It sure sounds to me like you're approaching the point where air will be
less work!

What power will you be using to drive the motor? If you're driving a
1000W motor with 1000W or less, then I would expect that air cooling would
be sufficient -- just make sure that it mostly goes over the stator. You
can get centrifugal fans for those things, which should do the job well
(the OS motors come with them built in).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[default]

On Mon, 03 Nov 2014 10:37:37 -0800, etpm@whidbey.com wrote:

DC motor questionsAll,
I am making, or at least attempting to make, an electric high speed
spindle that fits in a confined space. I do not want to use air as the
motive force. So I have been experimenting with BLDC motors made for
model airplanes and the like. I would like to cool the stator, I think
I may need to in fact if I want the motor to run continuously. Liquid
cooling would be best. To do this most efficiently the stator should
be submerged in the cooling liquid. There is not enough space between
the windings for even very small diameter tubes carrying fluid to fit
through. So if the stator gets submerged the liquid must be
constrained to the stator only. I thought about making plastic end
caps for the stator and sealing the perimeter of the stator with a
sheet of plastic or maybe plastic and some sort of metal sheet. The
motor is built with the outer rotating, inside out compared to most
motors we see, but common in floppy drives. There is about .008" air
gap between the outer diameter of the stator and the magnets. I'm
afraid that if I use brass sheet, for example, to wrap around the
stator it will short out the laminations and increase eddy current
losses in the motor. If the brass sheet could be insulated from the
laminations would eddy currents in the brass sheet start to heat it
significantly? This is a 1000 watt motor and the stator is about 1.18
diameter x 1.18 long (30mm x 30mm). If the stator can be wrapped with
something to seal it what kind of fluids would not tend to soften
varnish on the windings? Anybody here know?
Thanks,
Eric

Hoping the 1000 watts is a typo... Your major cooling would be
radiated heat and light...

 

[Maynard A. Philbrook Jr.]

In article <xnr3xiluz6.fsf@delorie.com>, dj@delorie.com says...

Phil Allison <pallison49@gmail.com> writes:
A 1000W motor smaller than a golf ball ?

No, a 1000W motor with a stator smaller than a golf ball. Most RC
motors are outriggers, with the stator in the center and the rotor on
the outside. The total motor size is bigger than just the stator, and
the power/size ratios they're getting are pretty ridiculous.

The problem is, those motors are designed for high speed air cooling.
Using them for anything else poses serious cooling problems.

1.666 HP ?

Jamie

 

On Wed, 5 Nov 2014 17:22:23 -0500, "Maynard A. Philbrook Jr."
<jamie_ka1lpa@charter.net> wrote:

In article <xnr3xiluz6.fsf@delorie.com>, dj@delorie.com says...

Phil Allison <pallison49@gmail.com> writes:
A 1000W motor smaller than a golf ball ?

No, a 1000W motor with a stator smaller than a golf ball. Most RC
motors are outriggers, with the stator in the center and the rotor on
the outside. The total motor size is bigger than just the stator, and
the power/size ratios they're getting are pretty ridiculous.

The problem is, those motors are designed for high speed air cooling.
Using them for anything else poses serious cooling problems.

1.666 HP ?

Jamie

I did a rudimentary test to measure the torque and rpm at the same
time.Using a friction disc on the end of an 6 inch pound max torque
wrench and slowing the rpm to about 30,000 rpm with the motor drawing
about 40 amps at 12 volts I got about 1.2 inch pounds. That's a little
over .5 hp. The motor got quite hot since it was not rushing through
the air. The motor is rated at 70 amps as I recall. And 14.8 volts.
The test was rudimentary, but it showed that the little motor may be
able to consume 1000 watts for short periods without melting. The
planes that use these motors don't fly very long at full power. I
won't be able to get 1 hp out of it constantly, I think. But pretty
close.
Eric