Forums

BLDC motor questions

Started by Unknown November 3, 2014
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
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
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
Oh -- any brass on the outside of the stator will, I think, divert a hefty proportion, if not the majority of, the energy that would otherwise go to spinning the motor. As a means of melting brass and making a mess, it's probably excellent. As a means of cooling a motor -- probably less so. As for the varnishes, I dunno. Worse, it'll depend on the motor -- there's different enamels available for different applications. I'd suggest that you cut and try starting with whatever coolent most appeals to you, and go from there. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
et...@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
** This poster must be mentally defective. A 1000W motor smaller than a golf ball ? Liquid cooling with no liquid flow ? In what universe .... .... Phil
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.
On Tue, 04 Nov 2014 12:46:21 -0500, DJ Delorie <dj@delorie.com> wrote:

> >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.
Which is why I want liquid cooling. I can buy water cooled outrunners but they don't spin fast enough. . Eric
DJ Delorie wrote:

> 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.
** Makes no difference to my point - a golf ball is 43mm dia.
> Most RC motors are outriggers ...
** Ain't that some kind of a canoe ?
> with the stator in the center and the rotor on > the outside.
** Known as "outrunners". The high powered types all have internal rotors and one can cool the case with a water jacket.
> The total motor size is bigger than just the stator, and > the power/size ratios they're getting are pretty ridiculous.
** The published numbers might be, the realty ain't.
> The problem is, those motors are designed for high speed air cooling. > Using them for anything else poses serious cooling problems.
** No worries if you submerge the lot in liquid Nitrogen. ... Phil
On Tue, 04 Nov 2014 14:51:36 -0800, etpm wrote:

> On Tue, 04 Nov 2014 12:46:21 -0500, DJ Delorie <dj@delorie.com> wrote: > > >>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. > Which is why I want liquid cooling. I can buy water cooled outrunners > but they don't spin fast enough. . > Eric
I think you'll save money overall by going with bigger motors, and blowing lots of air through them. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
On Tue, 04 Nov 2014 17:55:54 -0600, Tim Wescott
<seemywebsite@myfooter.really> wrote:

>On Tue, 04 Nov 2014 14:51:36 -0800, etpm wrote: > >> On Tue, 04 Nov 2014 12:46:21 -0500, DJ Delorie <dj@delorie.com> wrote: >> >> >>>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. >> Which is why I want liquid cooling. I can buy water cooled outrunners >> but they don't spin fast enough. . >> Eric > >I think you'll save money overall by going with bigger motors, and blowing >lots of air through them.
Greetings Tim, I know I could save money by using a larger purpose bought spindle. At least I think I could. But I have not been able to find one small enough. I want to put a 32000 RPM spindle in my CAT 40 machine by using a CAT 40 tool holder modified to accept my spindle. So I need a lot of power in a small space. Speeders cost in the neighboorhood of $1500.00 for a used one. And many of them won't go fast enough anyway. I now have three engraving jobs coming up that would benefit greatly from the increased feed allowed by a faster spindle. Ideally the spindle will connect automatically to power and coolant when the tool change occurs. So this why I have chosen this route. Eric
On Tue, 04 Nov 2014 16:24:42 -0800, etpm wrote:

> On Tue, 04 Nov 2014 17:55:54 -0600, Tim Wescott > <seemywebsite@myfooter.really> wrote: > >>On Tue, 04 Nov 2014 14:51:36 -0800, etpm wrote: >> >>> On Tue, 04 Nov 2014 12:46:21 -0500, DJ Delorie <dj@delorie.com> wrote: >>> >>> >>>>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. >>> Which is why I want liquid cooling. I can buy water cooled outrunners >>> but they don't spin fast enough. . >>> Eric >> >>I think you'll save money overall by going with bigger motors, and >>blowing lots of air through them. > Greetings Tim, > I know I could save money by using a larger purpose bought spindle. At > least I think I could. But I have not been able to find one small > enough. I want to put a 32000 RPM spindle in my CAT 40 machine by using > a CAT 40 tool holder modified to accept my spindle. So I need a lot of > power in a small space. Speeders cost in the neighboorhood of $1500.00 > for a used one. And many of them won't go fast enough anyway. > I now have three engraving jobs coming up that would benefit greatly > from the increased feed allowed by a faster spindle. Ideally the spindle > will connect automatically to power and coolant when the tool change > occurs. So this why I have chosen this route. > Eric
I'm not arguing against the model airplane BLDC motors -- just the use of liquid cooling. You know they work if sufficient air is rammed through them -- so ram sufficient air through them, and be happy! -- Tim Wescott Wescott Design Services http://www.wescottdesign.com