Anyone here know BLDC motors well? Hobby ones particularly?

I want to use a hobby BLDC motor to power a compact high speed
spindle to be used for engraving and the like. Mainly because they are
so compact for the power and speed. I cannot find, for a price I can
justify, a 24,000 to 40,000 RPM spindle that will fit in the space I
want to put it.
Looking at some hobby BLDC motors and then buying some to
experiment with leads me to think that one of these motors may work.
I have looked online for answers about these motors and maybe I'm
just dense (good possibility) but I haven't been able to find exact
answers. Maybe someone here can help.
Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?
The ESCs (Electronic Speed Controller) are voltage and current
rated. Could the output an ESC rated for a lower voltage and current
be used to drive control power transistors in order to get around the
lower voltage and/or current rating if a sensored motor is being used?
I don't need to use a hobby ESC but they are plentiful and cheap.
And all assembled. Which is most important. But I would be fine using
some other BLDC motor driver in order to get the desired RPM that I
want.
I can do all the precision machining necessary to make the spindle
that will hold the carbide cutting tools and to interface the motor
with the spindle. I do not yet know enough about balancing in order to
dynamically balance a motor which causes too much vibration from an
out of balance condition but I think I can learn enough to do it. I am
good with mechanical systems and have a pretty good intuitive feel for
them. It's the electronics I'm no so good at.
Thanks,
Eric

 

[Jasen Betts]

On 2018-05-07, etpm@whidbey.com <etpm@whidbey.com> wrote:

Looking at some hobby BLDC motors and then buying some to
experiment with leads me to think that one of these motors may work.
I have looked online for answers about these motors and maybe I'm
just dense (good possibility) but I haven't been able to find exact
answers. Maybe someone here can help.
Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?

Yeah, RPM is limited by the back-emf. That is the motor acts like a
generator when running and the driver for the motor needs to make a
voltage that exceeds the voltage that the motor is generating. The
faster the motor is spinning the more voltage is needed.

The ESCs (Electronic Speed Controller) are voltage and current
rated. Could the output an ESC rated for a lower voltage and current
be used to drive control power transistors in order to get around the
lower voltage and/or current rating if a sensored motor is being used?

That depends on how the ESC interacts with the motor to monitor the
rotation of the motor.

I don't need to use a hobby ESC but they are plentiful and cheap.
And all assembled. Which is most important. But I would be fine using
some other BLDC motor driver in order to get the desired RPM that I
want.

Probably yes.

--
ŘŞ

 

[Ecnerwal]

In article <tl5veddea9rr8d4hlp236f3l0g0hf4vk52@4ax.com>,
etpm@whidbey.com wrote:

Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?

Remember that at some point (likely to be "experimentally determined",
whether or not you intend to) the rotor may mechanically fail when
overspeeded. This tends to lead to an abrupt stoppage and the need to
sweep the remains into the trash.

--
Cats, coffee, chocolate...vices to live by
Please don't feed the trolls. Killfile and ignore them so they will go away.

 

[Phil Hobbs]

On 05/06/18 20:36, etpm@whidbey.com wrote:

I want to use a hobby BLDC motor to power a compact high speed
spindle to be used for engraving and the like. Mainly because they are
so compact for the power and speed. I cannot find, for a price I can
justify, a 24,000 to 40,000 RPM spindle that will fit in the space I
want to put it.
Looking at some hobby BLDC motors and then buying some to
experiment with leads me to think that one of these motors may work.
I have looked online for answers about these motors and maybe I'm
just dense (good possibility) but I haven't been able to find exact
answers. Maybe someone here can help.
Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?
The ESCs (Electronic Speed Controller) are voltage and current
rated. Could the output an ESC rated for a lower voltage and current
be used to drive control power transistors in order to get around the
lower voltage and/or current rating if a sensored motor is being used?
I don't need to use a hobby ESC but they are plentiful and cheap.
And all assembled. Which is most important. But I would be fine using
some other BLDC motor driver in order to get the desired RPM that I
want.
I can do all the precision machining necessary to make the spindle
that will hold the carbide cutting tools and to interface the motor
with the spindle. I do not yet know enough about balancing in order to
dynamically balance a motor which causes too much vibration from an
out of balance condition but I think I can learn enough to do it. I am
good with mechanical systems and have a pretty good intuitive feel for
them. It's the electronics I'm no so good at.
Thanks,
Eric

You have to watch out for shaft whirl, which happens when the rotation
rate is close to the first bending resonance of the armature. It'll
destroy itself if run near that speed for anything but the briefest of
moments.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Mon, 7 May 2018 15:23:25 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 05/06/18 20:36, etpm@whidbey.com wrote:
I want to use a hobby BLDC motor to power a compact high speed
spindle to be used for engraving and the like. Mainly because they are
so compact for the power and speed. I cannot find, for a price I can
justify, a 24,000 to 40,000 RPM spindle that will fit in the space I
want to put it.
Looking at some hobby BLDC motors and then buying some to
experiment with leads me to think that one of these motors may work.
I have looked online for answers about these motors and maybe I'm
just dense (good possibility) but I haven't been able to find exact
answers. Maybe someone here can help.
Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?
The ESCs (Electronic Speed Controller) are voltage and current
rated. Could the output an ESC rated for a lower voltage and current
be used to drive control power transistors in order to get around the
lower voltage and/or current rating if a sensored motor is being used?
I don't need to use a hobby ESC but they are plentiful and cheap.
And all assembled. Which is most important. But I would be fine using
some other BLDC motor driver in order to get the desired RPM that I
want.
I can do all the precision machining necessary to make the spindle
that will hold the carbide cutting tools and to interface the motor
with the spindle. I do not yet know enough about balancing in order to
dynamically balance a motor which causes too much vibration from an
out of balance condition but I think I can learn enough to do it. I am
good with mechanical systems and have a pretty good intuitive feel for
them. It's the electronics I'm no so good at.
Thanks,
Eric


You have to watch out for shaft whirl, which happens when the rotation
rate is close to the first bending resonance of the armature. It'll
destroy itself if run near that speed for anything but the briefest of
moments.

Cheers

Phil Hobbs

Yeah, I learned about that years ago when designing and building a
stepper motor driven positioning table. I had to watch out for whip in
the leadscrew when I changed the drive to a much faster servo motor.
Eric

 

[whit3rd]

On Sunday, May 6, 2018 at 5:30:44 PM UTC-7, et...@whidbey.com wrote:

I want to use a hobby BLDC motor to power a compact high speed
spindle...24,000 to 40,000 RPM spindle that will fit in the space I
want to put it.

At 40,000 rpm, an electric motor has high frequency AC on its soft iron
parts, and a permanent magnet rotor is hard (because magnets aren't
easily machinable) to balance.

Have you considered air-powered options? At 25,000 rpm, a
dental handpiece is considered 'low-speed'. I'd consider
the low-cost option of using those...