Left Hand Rule Applied to a Winding

[jake jot]

V=IR so 9.8 V = 1 A x 24 Ω means something is not right.
It should need 24 V to drive 1 A through 24 Ω resistance, even when it's not moving. When it moves, it should require even more voltage.

As someone else said, it's hard to guess which bit is wrong when you're not there to see exactly what's going on. My guess would be to distrust the resistance reading. Have you checked the meter shows zero when you short the test leads together?
Otherwise, the 1 A has to be too high.

I borrowed a meter but it's an ac clump meter with current in AC. But it has ohm meter and I measured the same 24 ohms. Using my multimeter. I tried to measure the current again. I noticed it is always negative (-) even if i changed the terminals. Also the amperage was not steady. So I guess it just can't read the ampere of it properly because the waveform is not really pure dc but something like the following? But I wonder why it always displays negative no matter how i changed the leads. When I changed the current to AC. It displays even higher reading (double).

What is the shape of the current for the above? Is it sinusoidal, like the above, or just plain flat line dc?

 

[Merlin3189]

It should be something like your graph, a full wave rectified sinewave. I'd reckon a bit peakier, with the sine shape being distorted by non-uniform field and the nodes being distorted by a dead spot as the brushes are either in a gap or are shorting both sectors.

" It's the only hand crank available for about 7 billion humans. "
I'm sure I could build one myself. Maybe a bit more refined than the bits of wire I put together for your first experiment - though that did work. I think Meccano might be suitable.

I'm not quite sure what I'd be trying to find out though? These sort of motors are pretty well understood, so you can work out what should happen a lot easier than you can measure it. And lazy people like me can get all the info we want off the internet.

If you really want to measure things, this is not an easy project. A simple bit of equipment like this demo device is probably intended to show qualitative effects. Friction, resistance and efficiency are not the key factors in its design.

 

[jake jot]

It should be something like your graph, a full wave rectified sinewave. I'd reckon a bit peakier, with the sine shape being distorted by non-uniform field and the nodes being distorted by a dead spot as the brushes are either in a gap or are shorting both sectors.

" It's the only hand crank available for about 7 billion humans. "
I'm sure I could build one myself. Maybe a bit more refined than the bits of wire I put together for your first experiment - though that did work. I think Meccano might be suitable.

I'm not quite sure what I'd be trying to find out though? These sort of motors are pretty well understood, so you can work out what should happen a lot easier than you can measure it. And lazy people like me can get all the info we want off the internet.

If you really want to measure things, this is not an easy project. A simple bit of equipment like this demo device is probably intended to show qualitative effects. Friction, resistance and efficiency are not the key factors in its design.

Ok. I just want to understand the basic concepts and I think it's all enough for me.

One last question I need to know to conclude the thread is the following.

In pole attraction motor like brushless motors or the amazon motor where the solenoid with iron core creates north-south poles. So the purpose of commutator is to make sure it is north or south at one side so the rotor continues to rotate. I understand this concept well. And the purpose of the current is to produce the poles electromagnetically and make it switch or maintain north, south via commutator. I need to know the following thought experiment to make sure I understand the basic concept.

Supposed you had a pole attraction motor where the rotor has one end a monopole that switches north and south, and the other end also a monopole that switches north and south opposite to the other. Will the motor runs continuously without any current? So it will keep rotating because of Newton's 1`st law which states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it?

Kindly answer the above and not say it is bad example. Because this whole thread is to understand the above thought experiment. Thank you.

 

[Merlin3189]

Supposed you had a pole attraction motor where the rotor has one end a monopole that switches north and south, and the other end also a monopole that switches north and south opposite to the other. Will the motor runs continuously without any current? So it will keep rotating because of Newton's 1`st law which states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it?

? Well, AFAIK monopoles don't exist, but if you had monopoles at each end which were always opposite polarity, that would be a dipole, which does exist !
Putting such niceties aside, you seem to be describing our little commutated DC motor, except that you want the rotor magnet to reverse without any input. I don't think that will happen. Either you need current to make it a magnet at all, of whichever polarity, or the remnance which keeps ferromagnetic materials magnetised after you remove the current, leaves it permanently magnetised in that polarity. Then you need a current to reverse the polarity. So no free lunch as far as I can see.
Newton's third law is irrelevant because there are forces acting on the rotor. If it has magnetic poles, they are attracted or repelled by the stator poles and that's forces. If you get rid of all the magnets, then you just end up with a flywheel. Well designed with low friction, that could continue spinning for some time, but would gradually slow down. It's a basic law of nature for macroscopic objects. If you want to see perpetual motion, maybe you need to look at the subatomic level (so don't ask me!) Some particles seem to have permanent spin, though whether these Physicist types mean that in the same sense as I do when talking about motors, I doubt.

 

[jake jot]

? Well, AFAIK monopoles don't exist, but if you had monopoles at each end which were always opposite polarity, that would be a dipole, which does exist !
Putting such niceties aside, you seem to be describing our little commutated DC motor, except that you want the rotor magnet to reverse without any input. I don't think that will happen. Either you need current to make it a magnet at all, of whichever polarity, or the remnance which keeps ferromagnetic materials magnetised after you remove the current, leaves it permanently magnetised in that polarity. Then you need a current to reverse the polarity. So no free lunch as far as I can see.
Newton's third law is irrelevant because there are forces acting on the rotor. If it has magnetic poles, they are attracted or repelled by the stator poles and that's forces. If you get rid of all the magnets, then you just end up with a flywheel. Well designed with low friction, that could continue spinning for some time, but would gradually slow down. It's a basic law of nature for macroscopic objects. If you want to see perpetual motion, maybe you need to look at the subatomic level (so don't ask me!) Some particles seem to have permanent spin, though whether these Physicist types mean that in the same sense as I do when talking about motors, I doubt.

Before I put these in box and stored in the attic. I need to make a little project. I want to make the solenoid so thin it will be purely pole attraction. Remember earlier we were not sure whether it is:

"Force Exerted on a Current-Carrying Conductor in a Magnetic Field" or

"Force Exerted by Like or Opposing Poles of Magnets"

maxwell_demons gave us the distinctions. Although the amazon generator is of the former mechanism.

Do you know commercially available solenoids so thin I can just add it above instead of building one?

 

[jake jot]

? Well, AFAIK monopoles don't exist, but if you had monopoles at each end which were always opposite polarity, that would be a dipole, which does exist !
Putting such niceties aside, you seem to be describing our little commutated DC motor, except that you want the rotor magnet to reverse without any input. I don't think that will happen. Either you need current to make it a magnet at all, of whichever polarity, or the remnance which keeps ferromagnetic materials magnetised after you remove the current, leaves it permanently magnetised in that polarity. Then you need a current to reverse the polarity. So no free lunch as far as I can see.
Newton's third law is irrelevant because there are forces acting on the rotor. If it has magnetic poles, they are attracted or repelled by the stator poles and that's forces. If you get rid of all the magnets, then you just end up with a flywheel. Well designed with low friction, that could continue spinning for some time, but would gradually slow down. It's a basic law of nature for macroscopic objects. If you want to see perpetual motion, maybe you need to look at the subatomic level (so don't ask me!) Some particles seem to have permanent spin, though whether these Physicist types mean that in the same sense as I do when talking about motors, I doubt.

I was looking for a thin solenoid in the net to power the motor (see last message) to prove pole attraction is the mechanism and found most have iron cores. It seems this is required to increase the magnetic flux. I wonder if my motor would even run if there is no iron core. I read about about solenoid and rules of windings. What size of wire is the most useful in your experience so I can maybe buy a small roll of it.

But what perplexed me so much was when I came across the so called Permanent Magnet DC motor. I watched most youtube videos about it and read many articles. But there is none that explains it clearly as the ordinary iron core dc motors.

What are coreless DC motors? (motioncontroltips.com)

Do you know a site that explains it. After 3 hours of googling and reading dozens of articles and videos. There is none that explains it clearly and I can't seem to fathom it. How does it work compared to the typical iron core motors?

 

[jake jot]

I was looking for a thin solenoid in the net to power the motor (see last message) to prove pole attraction is the mechanism and found most have iron cores. It seems this is required to increase the magnetic flux. I wonder if my motor would even run if there is no iron core. I read about about solenoid and rules of windings. What size of wire is the most useful in your experience so I can maybe buy a small roll of it.

But what perplexed me so much was when I came across the so called Permanent Magnet DC motor. I watched most youtube videos about it and read many articles. But there is none that explains it clearly as the ordinary iron core dc motors.

What are coreless DC motors? (motioncontroltips.com)

View attachment 274888

Do you know a site that explains it. After 3 hours of googling and reading dozens of articles and videos. There is none that explains it clearly and I can't seem to fathom it. How does it work compared to the typical iron core motors?

My dilemma started when I planned to get Neodymium core, but I read these are permanent magnets. We know that in the motor iron core beneath the winding, the direction of flux changes at every commutator contact changes. So how can a permanent magnet worked there I wondered. Then I read this site.

Permanent magnet Vs. iron cored DC motors (eurekamagazine.co.uk)

This paragraph confused me:

"Like the iron core magnet the conductors themselves produce a magnetic field which is not always contributing to the field of the permanent magnet and superimpose themselves on the existing magnetic field. This weakens the field of the permanent magnet and is avoided by increasing the air gap between the magnets and the coil. Increasing the air gap however means the flux density is reduced which in turn effects the amount of torque the motor can produce."

Then I read and watched videos about Permanent magnet dc motors. Now I think what confused me was the article above was mixing the concepts. It mentioned Permanent magnet but it is not the same as the Permanent Magnet DC motor. This line can clarify it.

What is a conventional DC motor? Isn't our amazon motor a conventional DC motor? I thought conventional DC motor used magnets. So they don't? And therefore my amazon motor belonged to the category of Permanent Magnet DC Motor?

If so, then what I wanted to understand was the so called coreless DC motor after all, which the first article above mentioned was the same as permanent dc motor. Hence the confusions.

In this site How to Select a DC Motor: Coreless and Iron Core Brushed DC Motors | PTE (powertransmission.com)

The permanent magnet within the rotor doesn't move along with it, correct? Because unless it is brushless dc motor, I can't fathom how you can replace the iron core with permanent north and south magnet and still work with commutator (note the above still has commutator, you don't need commutator and brushes in brushless dc motor but it needs complex circuity to synchronize the current in the stator).

So in the following description quote earlier and quoting again for emphasis, the permanent magnet inside the rotor doesn't move with the rotor, right? If it still moves, then I still don't get it how it works. What is this describing then?

"Like the iron core magnet the conductors themselves produce a magnetic field which is not always contributing to the field of the permanent magnet and superimpose themselves on the existing magnetic field. This weakens the field of the permanent magnet and is avoided by increasing the air gap between the magnets and the coil. Increasing the air gap however means the flux density is reduced which in turn effects the amount of torque the motor can produce."

Merlin3189 and other experts in motors, what you think? Thank you.

 

[Merlin3189]

This is an interesting sort of motor. I only came across it quite recently, when looking for a low inertia motor.
It is very definitely a "wire in magnetic field" because there is no rotating iron/magnet.
The field is generated by the fixed core magnet, which is inside the rotor, but doesn't rotate with it. (You could have the magnet outside, but then it would be bigger and Neodymium is expensive.)
The rotor is made up of lots of coils, as you can see from the multi-sector commutator. The exact way of winding these, I'm still looking for, but it looks as if each coil is twisted and overlaps the adjacent coils. This presumably helps make the construction rigid, but I think also smooths the torque.
Because there is just the coils with no iron, the mass and moment of inertia of the rotor is much lower than in a traditional motor. So the motor accelerates and decelerates much quicker.

They also mention here (something I'd not thought of) that it is more efficient, because you are not continually reversing the field inside iron (or other ferromagnet.) The magnet and iron/ferrite shell are all static and have a more or less static field.
In an iron cored rotor the polarity of the magnetisation is reversed every half cycle by the commutation. When you do this, there is hysteresis and energy is lost on each cycle. You can read up on this, if you don't know about it.

The magnet and shell are joined at the far end. The coil pushes into the gap from the near end. (sorry I've missed out the axle hole in the centre of the magnet.) The coil is like a cylinder open at the far end, with the commutator at the near end. The coil is encapsulated in resin for rigidity.
The windings run on a helical path for half a turn along the sides of the coil, then double back for the second half. The next turn is slightly offset (by the width of the wire). The diagram says it is a Felix Faulhaber design, so you can look it up, if you've a better brain for 3D contortions than mine. I gather it gives a more even torque than (relatively) simple paraxial coils.

 

[jake jot]

This is an interesting sort of motor. I only came across it quite recently, when looking for a low inertia motor.
It is very definitely a "wire in magnetic field" because there is no rotating iron/magnet.
The field is generated by the fixed core magnet, which is inside the rotor, but doesn't rotate with it. (You could have the magnet outside, but then it would be bigger and Neodymium is expensive.)
The rotor is made up of lots of coils, as you can see from the multi-sector commutator. The exact way of winding these, I'm still looking for, but it looks as if each coil is twisted and overlaps the adjacent coils. This presumably helps make the construction rigid, but I think also smooths the torque.
Because there is just the coils with no iron, the mass and moment of inertia of the rotor is much lower than in a traditional motor. So the motor accelerates and decelerates much quicker.

They also mention here (something I'd not thought of) that it is more efficient, because you are not continually reversing the field inside iron (or other ferromagnet.) The magnet and iron/ferrite shell are all static and have a more or less static field.
In an iron cored rotor the polarity of the magnetisation is reversed every half cycle by the commutation. When you do this, there is hysteresis and energy is lost on each cycle. You can read up on this, if you don't know about it.

View attachment 274927The magnet and shell are joined at the far end. The coil pushes into the gap from the near end. (sorry I've missed out the axle hole in the centre of the magnet.) The coil is like a cylinder open at the far end, with the commutator at the near end. The coil is encapsulated in resin for rigidity.
The windings run on a helical path for half a turn along the sides of the coil, then double back for the second half. The next turn is slightly offset (by the width of the wire). The diagram says it is a Felix Faulhaber design, so you can look it up, if you've a better brain for 3D contortions than mine. I gather it gives a more even torque than (relatively) simple paraxial coils.

About "In an iron cored rotor the polarity of the magnetisation is reversed every half cycle by the commutation". I'm familiar with the whole concept and the purpose of the commutator and recently the iron core and magnetization. I have spent a whole week working with the commutators in my amazon motor and generators. That's the whole purpose of them, to have hands on experience.

In the coreless dc motor. If the magnet inside it is fixed, then it all makes sense. I just can't fathom a permanent magnet in rotor that moves unless it's a brushless dc motor with current synchronization circuitry.

So the permanent magnet inside the rotor acts just like stator with the winding rotating outside with respect to it. This is the punchline of it right?

What is the size of the winding that is the most useful? so I can buy it now and try different winding length in my amazon motor and generator to see how they would behave.

The last time I tried to wind coils was 30 years ago.

At that time, i was finding out the claim about the so called scalar wave, which is allegedly produced when one cancels magnetic field. So I wired the above in photo according to the instructions.

What I found out was simply when one separated the 2 wires (they power a lamp with AC source). There were less cancellation of the magnetic field and this disturbed the body sentient bioetheric field. It's the AC 60 Hertz frequency not friendly. When the wire was put together, the magnetic field was less so less disturbance. This is all there is to it. So much for scalar waves.

 

[Tom.G]

This is an interesting sort of motor. I only came across it quite recently, when looking for a low inertia motor.
It is very definitely a "wire in magnetic field" because there is no rotating iron/magnet.

Another advantage of those "Ironless Rotor" motors is they don't cog when run at slow speeds.

They also do not have a "detent action" when powered down and manually rotated. This was crucial in one project that had a "lighthouse" style rotating LASER beam. There were occassions where the motor would have to be stopped and the beam aimed manually at a specific spot. That was not possible with a motor core that had Iron in it.

Cheers,
Tom

 

[jake jot]

Another advantage of those "Ironless Rotor" motors is they don't cog when run at slow speeds.

They also do not have a "detent action" when powered down and manually rotated. This was crucial in one project that had a "lighthouse" style rotating LASER beam. There were occassions where the motor would have to be stopped and the beam aimed manually at a specific spot. That was not possible with a motor core that had Iron in it.

Cheers,
Tom

Without iron core, the magnetic field induced in the rotor is weaker. I will try to wind my motor without iron core in the rotor. I don't know if it will run or need much higher current.

Now in the coreless dc motor. Wont the rotor induced magnetic field be poorer without any core. Then how does it differ to conventional dc motor without any iron cores as far as the rotor in concerned?

 

[Tom.G]

Wont the rotor induced magnetic field be poorer without any core.

Yes it will. You will need more turns and/or more current for the same torque due to the weaker magnetic field.

Cheers,
Tom

 

[jake jot]

View attachment 274847

Before I put these in box and stored in the attic. I need to make a little project. I want to make the solenoid so thin it will be purely pole attraction. Remember earlier we were not sure whether it is:

"Force Exerted on a Current-Carrying Conductor in a Magnetic Field" or

"Force Exerted by Like or Opposing Poles of Magnets"

maxwell_demons gave us the distinctions. Although the amazon generator is of the former mechanism.

Do you know commercially available solenoids so thin I can just add it above instead of building one?

I finally did my second amazon motor modification to test pole attraction by making the rotor winding thinner than the original.

I used nail and steel screw as core (because I couldn't find 2 nails). Need these to wrap the AWG #28 windings (4 times) around the shalf center. This is video of it running.


I initially used 2 AA batteries, it didn't run unlike the original amazon rotor. I then tried to use 4 batteries, It still won't run. I need 6 batteries to make it run.

Does the above prove the principle of "Force Exerted by Like or Opposing Poles of Magnets". Or do you still think there is possibility of "Force Exerted on a Current-Carrying Conductor in a Magnetic Field"?

Say, when doing winding, what happens if say one side of rotor has more winding (say double)? because I couldn't make them totally equal in length. It's tiring to rewind so I'd not make any more project, hence just need to know what would theoretically happens, like how it would behave if the north is more powerful than the south (is this possible)?.

Thanks guys!

 

[jake jot]

Yes. The iron shell guides the flux from the magnet at the top and produces a horizontal field around the rotor.
Your first diagrams used two magnets one on each side of the rotor. The field can be strengthened by joining the outside faces with iron, completing the manetic "circuit".
Early motors sometimes used horseshoe magnets to have the same effect.
This idea is very economical because you need only one simple magnet, then the cheap shaped piece of iron brings the field to where you want it.

Yes. The iron shell guides the flux from the magnet at the top and produces a horizontal field around the rotor.
Your first diagrams used two magnets one on each side of the rotor. The field can be strengthened by joining the outside faces with iron, completing the manetic "circuit".
Early motors sometimes used horseshoe magnets to have the same effect.
This idea is very economical because you need only one simple magnet, then the cheap shaped piece of iron brings the field to where you want it.

I was trying to commute at different locations in the last project above (see last message). It can rotate when commuted at horizontal. When trying to commute vertically. It won't and I noticed the configuration of the amazon motor was not the typical ones shown at youtube. You mentioned above about "The iron shell guides the flux from the magnet at the top and produces a horizontal field around the rotor."

But how come when I used a magnet of same polarity that repelled the top magnet, it didn't do likewise in the lower metal connected to it? Then I tried this experiment:



Without the metal, I held the the magnets at the top and it rotated.

Do you have illustrations how the iron shell guides the flux from the magnet? Why doesn't it have any polarity as putting magnetic north at the metal won't repel it?

Now pertaining to your illustration at msg #45

I know commuting at vertical won't rotate the rotor. But when you have north and south pole magnets put at top without any metal to extend the fluxes (this won't create any north or south in the metal itself). The analysis is different than your illusration but still understandable. One can just imagine you lower bottom left side as the top.

What motor used the same magnets at top like the amazon motor? It proves the principle of "Force Exerted by Like or Opposing Poles of Magnets". Or do you still think there is possibility of "Force Exerted on a Current-Carrying Conductor in a Magnetic Field"?