Permeability in a DC Motor

Two motors were evaluated to find the ratio of the speed of the rotor over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of times faster than the electrons move in the drive current. For example, the Mabuchi RE 280RA motor has a current running electrons at a speed of 5*10^-6 meters per second and its rotor is moving at 8 meters per second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at which an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor speed and electron speed estimated at 2.7*10^-5 meters per second. Plus or minus a big amount.

This implies that maybe the permeability of free space (mu zero) is involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times faster than the electron in the coil, during conditions where there is no mechanical load on the motor. That is the maximum speed for a motor but going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second in Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square meter, using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil does not set the maximum RPM speed. The number of turns can increase the torque but not the no-load speed. The no-load speed of the motor is set by the speed of the electrons in the coil. The flux density (B) does not change the speed limit of a rotor, all flux has the same velocity amplification (H) relative to electron motion. That mechanical amplification has a factor of 1/mu.

Please check your motors for the ratio of rotor speed over electron speed, no load. Is it 796,000?

 

On Wednesday, June 1, 2016 at 5:41:39 AM UTC-10, Tim Wescott wrote:

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the rotor
failing (or at least deforming) from centripetal acceleration. On some
motors there's probably a secondary limit on the armature overheating
because you're exceeding the design limit on eddy current or (possibly, I
don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light oil
(20W is probably perfect, but "sewing machine oil" would work), then
attach it to a variable power supply that'll go up to twice the motor's
rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the motor's rated
voltage and observe the speed -- you'll see that it goes right up. Keep
this up until the motor breaks. Then disassemble, and figure out which
bit broke.

A friend of mine had a job testing brushless motors to destruction. The
project goal was to get the most powerful motor in the smallest space.
The limit was keeping the magnets on the rotor. They regularly exceeded
30,000 RPM.

Hi Tim W.,

I understand that the maximum RPM is limited by a destructive event, but my point is not about that limit. I am proposing a new law of motor generators. To test it, use a low current so the motor is not destroyed. Calculate the average velocity of electrons in the armature current:

ve = I / NQA

ve = electron speed, I = current, N =electron density in copper 8*10^28/meter^3, Q is electron charge, A is area of wire

Calulate speed of a proton (vp) in an Iron magnet, relative to the orthogonal copper coil:

vp = 2 pi R omega

R is rotor radius, omega is angular velocity, radians per second

Law proposed

vp/ve < 797,000

where 797,000 meters = 1 / permeability of free space

Law proposed: The speed of a motor is less than 797,000 times the speed of an electron in the driving current.

That is in an ideal case where the RPMs are low enough that the motor is not damaged. The permeability of free space is Henrys per meter. Magnetic field H is amps per meter. Magnetic flux density B is Webers per square meter. using these standard terms, the Law will show that the magnetic field is a velocity:

H = meters per second = B/permeability

H = second^-1 / Henry*meter^-1

Weber = Coulomb per second = Ampere

therefore ... law under construction...

 

[Tim Wescott]

On Tue, 31 May 2016 15:32:40 -0700, omnilobe wrote:

Two motors were evaluated to find the ratio of the speed of the rotor
over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of times
faster than the electrons move in the drive current. For example, the
Mabuchi RE 280RA motor has a current running electrons at a speed of
5*10^-6 meters per second and its rotor is moving at 8 meters per
second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at which
an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor speed
and electron speed estimated at 2.7*10^-5 meters per second. Plus or
minus a big amount.

This implies that maybe the permeability of free space (mu zero) is
involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times faster
than the electron in the coil, during conditions where there is no
mechanical load on the motor. That is the maximum speed for a motor but
going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second in
Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square meter,
using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil does not
set the maximum RPM speed. The number of turns can increase the torque
but not the no-load speed. The no-load speed of the motor is set by the
speed of the electrons in the coil. The flux density (B) does not change
the speed limit of a rotor, all flux has the same velocity amplification
(H) relative to electron motion. That mechanical amplification has a
factor of 1/mu.

Please check your motors for the ratio of rotor speed over electron
speed, no load. Is it 796,000?

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the rotor
failing (or at least deforming) from centripetal acceleration. On some
motors there's probably a secondary limit on the armature overheating
because you're exceeding the design limit on eddy current or (possibly, I
don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light oil
(20W is probably perfect, but "sewing machine oil" would work), then
attach it to a variable power supply that'll go up to twice the motor's
rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the motor's rated
voltage and observe the speed -- you'll see that it goes right up. Keep
this up until the motor breaks. Then disassemble, and figure out which
bit broke.

A friend of mine had a job testing brushless motors to destruction. The
project goal was to get the most powerful motor in the smallest space.
The limit was keeping the magnets on the rotor. They regularly exceeded
30,000 RPM.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

 

On Wednesday, June 1, 2016 at 9:43:24 AM UTC-10, Tim Wescott wrote:>

Oh, I'm sorry -- I thought you were seriously interested in something real..

My bad.

Real motors is what I am discussing. The motors that are not damaged can be tested to prove my new Law of motor-generators. For example, for a motor with a maximum allowed RPM of 9200, run it at less than 9200 RPM so it is not damaged. Force a small current so it runs at 8000 RPM.

Calculate the velocity of the motor divided by the velocity of the electron current. The ratio of those two speeds is always below the inverse permeability. This is handled with mathematics that employ primitive units of measure: meters and seconds

B = second^-1 = magnetic flux density

H = meters per second = Magnetic field intensity

mu zero = 1 Henry per 797,000 meters

B = (mu zero) H

B/ mu zero = velocity

where B is one line of flux for one electron and one proton in a pair.

 

On Wednesday, June 1, 2016 at 8:41:39 AM UTC-7, Tim Wescott wrote:

On Tue, 31 May 2016 15:32:40 -0700, omnilobe wrote:

Two motors were evaluated to find the ratio of the speed of the rotor
over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of times
faster than the electrons move in the drive current. For example, the
Mabuchi RE 280RA motor has a current running electrons at a speed of
5*10^-6 meters per second and its rotor is moving at 8 meters per
second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at which
an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor speed
and electron speed estimated at 2.7*10^-5 meters per second. Plus or
minus a big amount.

This implies that maybe the permeability of free space (mu zero) is
involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times faster
than the electron in the coil, during conditions where there is no
mechanical load on the motor. That is the maximum speed for a motor but
going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second in
Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square meter,
using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil does not
set the maximum RPM speed. The number of turns can increase the torque
but not the no-load speed. The no-load speed of the motor is set by the
speed of the electrons in the coil. The flux density (B) does not change
the speed limit of a rotor, all flux has the same velocity amplification
(H) relative to electron motion. That mechanical amplification has a
factor of 1/mu.

Please check your motors for the ratio of rotor speed over electron
speed, no load. Is it 796,000?

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the rotor
failing (or at least deforming) from centripetal acceleration. On some
motors there's probably a secondary limit on the armature overheating
because you're exceeding the design limit on eddy current or (possibly, I
don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light oil
(20W is probably perfect, but "sewing machine oil" would work), then
attach it to a variable power supply that'll go up to twice the motor's
rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the motor's rated
voltage and observe the speed -- you'll see that it goes right up. Keep
this up until the motor breaks. Then disassemble, and figure out which
bit broke.

A friend of mine had a job testing brushless motors to destruction. The
project goal was to get the most powerful motor in the smallest space.
The limit was keeping the magnets on the rotor. They regularly exceeded
30,000 RPM.

In that case, an outer-rotor brushless motor should last longer, since centripetal forces simply press the magnets harder into the rotor..?

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

Michael

 

[Tim Wescott]

On Wed, 01 Jun 2016 11:09:23 -0700, omnilobe wrote:

On Wednesday, June 1, 2016 at 5:41:39 AM UTC-10, Tim Wescott wrote:

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the
rotor failing (or at least deforming) from centripetal acceleration.
On some motors there's probably a secondary limit on the armature
overheating because you're exceeding the design limit on eddy current
or (possibly, I don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light
oil (20W is probably perfect, but "sewing machine oil" would work),
then attach it to a variable power supply that'll go up to twice the
motor's rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the
motor's rated voltage and observe the speed -- you'll see that it goes
right up. Keep this up until the motor breaks. Then disassemble, and
figure out which bit broke.

A friend of mine had a job testing brushless motors to destruction.
The project goal was to get the most powerful motor in the smallest
space. The limit was keeping the magnets on the rotor. They regularly
exceeded 30,000 RPM.

Hi Tim W.,

I understand that the maximum RPM is limited by a destructive event, but
my point is not about that limit. I am proposing a new law of motor
generators. To test it, use a low current so the motor is not destroyed.
Calculate the average velocity of electrons in the armature current:

ve = I / NQA

ve = electron speed, I = current, N =electron density in copper
8*10^28/meter^3, Q is electron charge, A is area of wire

Calulate speed of a proton (vp) in an Iron magnet, relative to the
orthogonal copper coil:

vp = 2 pi R omega

R is rotor radius, omega is angular velocity, radians per second

Law proposed

vp/ve < 797,000

where 797,000 meters = 1 / permeability of free space

Law proposed: The speed of a motor is less than 797,000 times the speed
of an electron in the driving current.

That is in an ideal case where the RPMs are low enough that the motor is
not damaged. The permeability of free space is Henrys per meter.
Magnetic field H is amps per meter. Magnetic flux density B is Webers
per square meter. using these standard terms, the Law will show that the
magnetic field is a velocity:

H = meters per second = B/permeability

H = second^-1 / Henry*meter^-1

Weber = Coulomb per second = Ampere

therefore ... law under construction...

Oh, I'm sorry -- I thought you were seriously interested in something
real.

My bad.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

 

On Wednesday, June 1, 2016 at 1:28:46 PM UTC-10, Tim Wescott wrote:

In that case, an outer-rotor brushless motor should last longer, since
centripetal forces simply press the magnets harder into the rotor..?

I don't know if they tried that -- it was long before outrunners were
commonly used. They did have rotors with titanium bands shrunk on over
the magnets -- which would fail, leaving magnet-sized inverse dimples in
the ring.

It didn't have squat to do with the ratio between electron velocity in
the wires and the rotor velocity; I know that.

Hi Tim, I have been reading up on motors and the websites do not discuss these electrical engineering standard variables:

H Magnetic Field Intensity

B Magnetic Flux Density

mu permeability

Magnetic motor websites have equations about voltage, current, torque, and rpm, but few even hint that a Magnetic Field Intensity is involved in a motor equation. mu is not in their equations. I am trying to put the H, B, and mu in the motor equations.

1/mu zero = 797,000 meters

That inverse permeability is profound and mysterious.

 

On Wednesday, June 1, 2016 at 4:28:46 PM UTC-7, Tim Wescott wrote:

On Wed, 01 Jun 2016 14:36:24 -0700, mrdarrett wrote:

On Wednesday, June 1, 2016 at 8:41:39 AM UTC-7, Tim Wescott wrote:
On Tue, 31 May 2016 15:32:40 -0700, omnilobe wrote:

Two motors were evaluated to find the ratio of the speed of the rotor
over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of
times faster than the electrons move in the drive current. For
example, the Mabuchi RE 280RA motor has a current running electrons
at a speed of 5*10^-6 meters per second and its rotor is moving at 8
meters per second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at
which an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor
speed and electron speed estimated at 2.7*10^-5 meters per second.
Plus or minus a big amount.

This implies that maybe the permeability of free space (mu zero) is
involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times
faster than the electron in the coil, during conditions where there
is no mechanical load on the motor. That is the maximum speed for a
motor but going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second in
Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square
meter, using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil does
not set the maximum RPM speed. The number of turns can increase the
torque but not the no-load speed. The no-load speed of the motor is
set by the speed of the electrons in the coil. The flux density (B)
does not change the speed limit of a rotor, all flux has the same
velocity amplification (H) relative to electron motion. That
mechanical amplification has a factor of 1/mu.

Please check your motors for the ratio of rotor speed over electron
speed, no load. Is it 796,000?

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the
rotor failing (or at least deforming) from centripetal acceleration.
On some motors there's probably a secondary limit on the armature
overheating because you're exceeding the design limit on eddy current
or (possibly, I don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light
oil (20W is probably perfect, but "sewing machine oil" would work),
then attach it to a variable power supply that'll go up to twice the
motor's rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the
motor's rated voltage and observe the speed -- you'll see that it goes
right up. Keep this up until the motor breaks. Then disassemble, and
figure out which bit broke.

A friend of mine had a job testing brushless motors to destruction.
The project goal was to get the most powerful motor in the smallest
space. The limit was keeping the magnets on the rotor. They regularly
exceeded 30,000 RPM.


In that case, an outer-rotor brushless motor should last longer, since
centripetal forces simply press the magnets harder into the rotor..?

I don't know if they tried that -- it was long before outrunners were
commonly used. They did have rotors with titanium bands shrunk on over
the magnets -- which would fail, leaving magnet-sized inverse dimples in
the ring.

Stronger than a band of titanium! Maybe they could have marketing put a positive spin on that... (hey, was that a pun?)

It didn't have squat to do with the ratio between electron velocity in
the wires and the rotor velocity; I know that.

On one hand, I hear electrons in atomic orbitals move at a significant fraction of the speed of light; on the other, I hear that due to electrons frequently bumping into each other, I can run faster than the electrons move through a wire. Which is it?

--

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

I'm looking for work -- see my website!

Have you tried Freelancer.com?

Cheers,

Michael

 

[Tim Wescott]

On Wed, 01 Jun 2016 14:36:24 -0700, mrdarrett wrote:

On Wednesday, June 1, 2016 at 8:41:39 AM UTC-7, Tim Wescott wrote:
On Tue, 31 May 2016 15:32:40 -0700, omnilobe wrote:

Two motors were evaluated to find the ratio of the speed of the rotor
over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of
times faster than the electrons move in the drive current. For
example, the Mabuchi RE 280RA motor has a current running electrons
at a speed of 5*10^-6 meters per second and its rotor is moving at 8
meters per second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at
which an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor
speed and electron speed estimated at 2.7*10^-5 meters per second.
Plus or minus a big amount.

This implies that maybe the permeability of free space (mu zero) is
involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times
faster than the electron in the coil, during conditions where there
is no mechanical load on the motor. That is the maximum speed for a
motor but going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second in
Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square
meter, using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil does
not set the maximum RPM speed. The number of turns can increase the
torque but not the no-load speed. The no-load speed of the motor is
set by the speed of the electrons in the coil. The flux density (B)
does not change the speed limit of a rotor, all flux has the same
velocity amplification (H) relative to electron motion. That
mechanical amplification has a factor of 1/mu.

Please check your motors for the ratio of rotor speed over electron
speed, no load. Is it 796,000?

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the
rotor failing (or at least deforming) from centripetal acceleration.
On some motors there's probably a secondary limit on the armature
overheating because you're exceeding the design limit on eddy current
or (possibly, I don't design motors) B-field strength in the iron.

As a test, take your cheap Mabuchi motor, oil the bearings with light
oil (20W is probably perfect, but "sewing machine oil" would work),
then attach it to a variable power supply that'll go up to twice the
motor's rated voltage. Ramp the voltage up to 2x (or 3x or 4x) the
motor's rated voltage and observe the speed -- you'll see that it goes
right up. Keep this up until the motor breaks. Then disassemble, and
figure out which bit broke.

A friend of mine had a job testing brushless motors to destruction.
The project goal was to get the most powerful motor in the smallest
space. The limit was keeping the magnets on the rotor. They regularly
exceeded 30,000 RPM.


In that case, an outer-rotor brushless motor should last longer, since
centripetal forces simply press the magnets harder into the rotor..?

I don't know if they tried that -- it was long before outrunners were
commonly used. They did have rotors with titanium bands shrunk on over
the magnets -- which would fail, leaving magnet-sized inverse dimples in
the ring.

It didn't have squat to do with the ratio between electron velocity in
the wires and the rotor velocity; I know that.

--

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

I'm looking for work -- see my website!

 

On Wed, 1 Jun 2016 13:16:38 -0700 (PDT), omnilobe@gmail.com wrote:

On Wednesday, June 1, 2016 at 9:43:24 AM UTC-10, Tim Wescott wrote:

Oh, I'm sorry -- I thought you were seriously interested in something real.

My bad.

Real motors is what I am discussing. The motors that are not damaged can be tested to prove my new Law of motor-generators. For example, for a motor with a maximum allowed RPM of 9200, run it at less than 9200 RPM so it is not damaged. Force a small current so it runs at 8000 RPM.

Calculate the velocity of the motor divided by the velocity of the electron current. The ratio of those two speeds is always below the inverse permeability. This is handled with mathematics that employ primitive units of measure: meters and seconds

B = second^-1 = magnetic flux density

H = meters per second = Magnetic field intensity

mu zero = 1 Henry per 797,000 meters

B = (mu zero) H

B/ mu zero = velocity

where B is one line of flux for one electron and one proton in a pair.

For real DC permanent magnet motors the only thing that limits rpm is
the load on the motor. If there was no load, and the motor materials
were of infinite strength, the motor would rotate at just below the
speed of light. No matter how fast the electrons were moving in the
motor windings.
Eric

 

[Bob Engelhardt]

On 6/1/2016 4:16 PM, omnilobe@gmail.com wrote:
> Calculate the velocity of the motor divided by the velocity of the electron current. The ratio of those two speeds is always below the inverse permeability. ...

And how is that useful?

 

[Tim Wescott]

On Wed, 01 Jun 2016 19:10:57 -0700, mrdarrett wrote:

On Wednesday, June 1, 2016 at 4:28:46 PM UTC-7, Tim Wescott wrote:
On Wed, 01 Jun 2016 14:36:24 -0700, mrdarrett wrote:

On Wednesday, June 1, 2016 at 8:41:39 AM UTC-7, Tim Wescott wrote:
On Tue, 31 May 2016 15:32:40 -0700, omnilobe wrote:

Two motors were evaluated to find the ratio of the speed of the
rotor over the speed of the electron in the coil.

ratio = speed(rotor) / speed(electron)

ratio = 8 meters per second / 10 microns per second

Some calculations show that DC electric motors rotate thousands of
times faster than the electrons move in the drive current. For
example, the Mabuchi RE 280RA motor has a current running
electrons at a speed of 5*10^-6 meters per second and its rotor is
moving at 8 meters per second. Plus or minus a big number.

The mechanical motor runs a million times faster than the speed at
which an electron is flowing in its coil.

A second motor was examined: Maxon Motor: 8 meter per second rotor
speed and electron speed estimated at 2.7*10^-5 meters per second.
Plus or minus a big amount.

This implies that maybe the permeability of free space (mu zero)
is involved to set that ratio of speeds:

1/(mu) = 796,000 meters per Henry

Then a rotor velocity limit can be expected to be 796,000 times
faster than the electron in the coil, during conditions where
there is no mechanical load on the motor. That is the maximum
speed for a motor but going faster makes it into a generator.

H = B/mu

H is magnetic field (units: Amps per meter, or meters per second
in Continuum Science)

B is magnetic flux density (units: second^-1 or Weber per square
meter, using Coulomb=area theory)

Henry is Webers per Ampere (units = 1)

1/mu = 796,000 meters

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Conclusion: It seems that the number of turns in a motor coil
does not set the maximum RPM speed. The number of turns can
increase the torque but not the no-load speed. The no-load speed
of the motor is set by the speed of the electrons in the coil. The
flux density (B) does not change the speed limit of a rotor, all
flux has the same velocity amplification (H) relative to electron
motion. That mechanical amplification has a factor of 1/mu.

Please check your motors for the ratio of rotor speed over
electron speed, no load. Is it 796,000?

Limits on DC motor rotor speed comes from bearings burning up, brush
float (on a brushed motor) or, once you've solved that problem, the
rotor failing (or at least deforming) from centripetal acceleration.
On some motors there's probably a secondary limit on the armature
overheating because you're exceeding the design limit on eddy
current or (possibly, I don't design motors) B-field strength in the
iron.

As a test, take your cheap Mabuchi motor, oil the bearings with
light oil (20W is probably perfect, but "sewing machine oil" would
work), then attach it to a variable power supply that'll go up to
twice the motor's rated voltage. Ramp the voltage up to 2x (or 3x
or 4x) the motor's rated voltage and observe the speed -- you'll see
that it goes right up. Keep this up until the motor breaks. Then
disassemble, and figure out which bit broke.

A friend of mine had a job testing brushless motors to destruction.
The project goal was to get the most powerful motor in the smallest
space. The limit was keeping the magnets on the rotor. They
regularly exceeded 30,000 RPM.


In that case, an outer-rotor brushless motor should last longer,
since centripetal forces simply press the magnets harder into the
rotor..?

I don't know if they tried that -- it was long before outrunners were
commonly used. They did have rotors with titanium bands shrunk on over
the magnets -- which would fail, leaving magnet-sized inverse dimples
in the ring.


Stronger than a band of titanium! Maybe they could have marketing put a
positive spin on that... (hey, was that a pun?)


It didn't have squat to do with the ratio between electron velocity in
the wires and the rotor velocity; I know that.

On one hand, I hear electrons in atomic orbitals move at a significant
fraction of the speed of light; on the other, I hear that due to
electrons frequently bumping into each other, I can run faster than the
electrons move through a wire. Which is it?

Individual electrons in a wire move pretty quick. But the average speed
of any one electron in a wire is dog slow. However, that average is
superimposed on a whole lot of shakin'.

Electrons in orbitals move pretty quick, too, but you don't have to make
relativistic corrections until you get to the really heavy atoms, like
gold (which is a different color than the initial computations indicated,
because some of the inner orbitals are smaller than predicted without
using relativistic corrections -- once you correct for those electrons'
mass being bigger, then things work).

That's all I know about this -- I'm just barfing out things I've read; I
couldn't do the math to save my life.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

 

[Tim Wescott]

On Wed, 01 Jun 2016 16:59:59 -0700, etpm wrote:

On Wed, 1 Jun 2016 13:16:38 -0700 (PDT), omnilobe@gmail.com wrote:

On Wednesday, June 1, 2016 at 9:43:24 AM UTC-10, Tim Wescott wrote:

Oh, I'm sorry -- I thought you were seriously interested in something
real.

My bad.

Real motors is what I am discussing. The motors that are not damaged can
be tested to prove my new Law of motor-generators. For example, for a
motor with a maximum allowed RPM of 9200, run it at less than 9200 RPM
so it is not damaged. Force a small current so it runs at 8000 RPM.

Calculate the velocity of the motor divided by the velocity of the
electron current. The ratio of those two speeds is always below the
inverse permeability. This is handled with mathematics that employ
primitive units of measure: meters and seconds

B = second^-1 = magnetic flux density

H = meters per second = Magnetic field intensity

mu zero = 1 Henry per 797,000 meters

B = (mu zero) H

B/ mu zero = velocity

where B is one line of flux for one electron and one proton in a pair.
For real DC permanent magnet motors the only thing that limits rpm is
the load on the motor. If there was no load, and the motor materials
were of infinite strength, the motor would rotate at just below the
speed of light. No matter how fast the electrons were moving in the
motor windings.
Eric

You're thinking of a shunt-wound motor, not a permanent-magnet motor. A
friction-free DC motor (or one with superconducting coils) turns at a
constant speed proportional to voltage.

And I suspect that in a shunt-wound motor the rotor inductance would
limit things, even in the absence of any loss mechanism.

--
Tim Wescott
Control systems, embedded software and circuit design
I'm looking for work! See my website if you're interested
http://www.wescottdesign.com

 

Average velocity of free electron = v

v = I / NQA

I is current, N is density of electrons in Copper, 8*10^28/meter^3, Q is electron charge, A is area of wire

for copper wire 1mm square, 0.01 amp

v = 0.01 / (8*10^28 1.6*10^-19 10^-6)

v = 10^(-2-29+19+6)

v = 0.000001 meter per second

Non relativistic speed, but magnetic enough to turn a motor at 796 cm per second

 

On Wednesday, June 1, 2016 at 9:01:13 PM UTC-7, Tim Wescott wrote:

....

I don't know if they tried that -- it was long before outrunners were
commonly used. They did have rotors with titanium bands shrunk on over
the magnets -- which would fail, leaving magnet-sized inverse dimples
in the ring.


Stronger than a band of titanium! Maybe they could have marketing put a
positive spin on that... (hey, was that a pun?)


It didn't have squat to do with the ratio between electron velocity in
the wires and the rotor velocity; I know that.

On one hand, I hear electrons in atomic orbitals move at a significant
fraction of the speed of light; on the other, I hear that due to
electrons frequently bumping into each other, I can run faster than the
electrons move through a wire. Which is it?

Individual electrons in a wire move pretty quick. But the average speed
of any one electron in a wire is dog slow. However, that average is
superimposed on a whole lot of shakin'.

Electrons in orbitals move pretty quick, too, but you don't have to make
relativistic corrections until you get to the really heavy atoms, like
gold (which is a different color than the initial computations indicated,
because some of the inner orbitals are smaller than predicted without
using relativistic corrections -- once you correct for those electrons'
mass being bigger, then things work).

Yup, gold, and lead, which is almost as heavy as gold, and a lot cheaper, too

I'm pretty sure the "1s" orbital is the one that gets super tiny in lead and gold, and the electrons in there are going so fast you need relativistic corrections, but I'm trying to find the article I found years ago and I'm not finding it :/

.... but I found this
http://www.uwgb.edu/dutchs/petrology/WhatAtomsLookLike.HTM

That's all I know about this -- I'm just barfing out things I've read; I
couldn't do the math to save my life.

I'm reminded of a TV show I saw as a kid - they were making fun of Soviet news broadcasts, where a reporter was reading the news with a pistol aimed at his head, just to the side (but within view of the camera). My Fluid Mechanics class sure felt like that. "Learn this or die."

Michael

 

On Wed, 01 Jun 2016 22:56:47 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:

On Wed, 01 Jun 2016 16:59:59 -0700, etpm wrote:

On Wed, 1 Jun 2016 13:16:38 -0700 (PDT), omnilobe@gmail.com wrote:

On Wednesday, June 1, 2016 at 9:43:24 AM UTC-10, Tim Wescott wrote:

Oh, I'm sorry -- I thought you were seriously interested in something
real.

My bad.

Real motors is what I am discussing. The motors that are not damaged can
be tested to prove my new Law of motor-generators. For example, for a
motor with a maximum allowed RPM of 9200, run it at less than 9200 RPM
so it is not damaged. Force a small current so it runs at 8000 RPM.

Calculate the velocity of the motor divided by the velocity of the
electron current. The ratio of those two speeds is always below the
inverse permeability. This is handled with mathematics that employ
primitive units of measure: meters and seconds

B = second^-1 = magnetic flux density

H = meters per second = Magnetic field intensity

mu zero = 1 Henry per 797,000 meters

B = (mu zero) H

B/ mu zero = velocity

where B is one line of flux for one electron and one proton in a pair.
For real DC permanent magnet motors the only thing that limits rpm is
the load on the motor. If there was no load, and the motor materials
were of infinite strength, the motor would rotate at just below the
speed of light. No matter how fast the electrons were moving in the
motor windings.
Eric

You're thinking of a shunt-wound motor, not a permanent-magnet motor. A
friction-free DC motor (or one with superconducting coils) turns at a
constant speed proportional to voltage.

And I suspect that in a shunt-wound motor the rotor inductance would
limit things, even in the absence of any loss mechanism.

Whoops! I better go back and read that book again.
Eric