End turns bad?

End connection also called end turn ...yeah well is that a definition or stating a naming mistake. Of course in this case of a 2 pole rotor there is not much flux in play and the length is large ...but I bet there is some flux of that North Pole flux jumping to that South Pole through the "end turns". But speaking engineeringly if it contains the word "turn" then it's a winding and not a "connection". Did I just create a new word?

engineeringly: speaking or thinking like an engineer or in an engineering way.

liveforphysics said:

The end turns do obviously make magnetic fields proportional to current, but the axis they produce the field makes thrust axis direction forces on the rotor vs torque forces, and when it's symmetrical end turns on both sides of the tooth the thrust axis forces balance out.

You can do an easy experiment to find out by wrapping say 5turns around a given motor tooth as tightly as possible, applying say 10amps through that winding and measuring the torque needed to cog the motor over.

Next, wind a tooth with the same 5 turns, but have the end turns hanging way out of the slot however far you want, so the end turns are feet away from the motor if you want.

It will make the exact same cog-over torque at the same 10amps, it just means that to drive the same 10amps it requires higher voltage due to higher winding resistance from being a longer path.

Click to expand...

Thanks for the explaination about relationship with torque.
I won't test it myself because i trust in your words

What about voltage induction? Will it also balance out like the forces?

This is what Dr Hanselman has to say about end turns, which is more or less what Major stated at the outset:

"According to the BLv and BLi laws, the distribution of the coil end turns does not influence back EMF or
torque; rather, it is the slot placement of coils that influences back EMF and torque.
The end turns exist solely to transport current from one slot to the next."

Page 130
Brushless Permanent Magnet Motor Design
Second Edition
Dr. Duane Hanselman

Dr Hanselman is an internationaly acknowledge expert in motor design.

The James Mevey M.Sc thesis has been quoted many times on ES says this about the flux created by end turns:

Magnetizing flux is that which crosses the airgap and links both the rotor and stator steel
(shaded regions). The leakage flux shown is produced by stator current but it does not link
the rotor. In addition additional leakage flux is associated with end turns and harmonic slot
leakage, but there is no disadvantage to grouping them together. The leakage flux cannot
contribute to torque production but it does contribute to the electrical inductance of the winding.

SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS PERMANENT MAGNET SYNCHRONOUS MOTORS

JAMES ROBERT MEVEY, MSc Thesis

Member Miles posted a copy here:

https://endless-sphere.com/forums/viewtopic.php?p=302385#p302385

Mevey also has a very good description of the Lorentz Law and how it applies to motor modeling, a good read for sure.

liveforphysics said:

The end turns do obviously make magnetic fields proportional to current, but the axis they produce the field makes thrust axis direction forces on the rotor vs torque forces, and when it's symmetrical end turns on both sides of the tooth the thrust axis forces balance out.

Click to expand...

Thanks for posting this, it confirms what I thought, but feared it was too simple an explanation and so I must be missing something. I imagined a cylindrical winding core producing a 360° ring of field lines spraying from the pole, with only those aligned to the approaching magnet resulting in torque. By extension a square pole would produce a nice "sheet" of useful field lines on the edge aligned to the magnet.

So someone needs to make a tapered slot with narrow core thickness (bigger core slots) at the ends to minimize the end turn length. Problem solved! I will still question what they say as that end turn creates magnetic field and it does get into the core. We now also need to make a very thin core length motor with mostly all end turns and see if it runs!

Punx0r said:

liveforphysics said:

The end turns do obviously make magnetic fields proportional to current, but the axis they produce the field makes thrust axis direction forces on the rotor vs torque forces, and when it's symmetrical end turns on both sides of the tooth the thrust axis forces balance out.

Click to expand...

Thanks for posting this, it confirms what I thought, but feared it was too simple an explanation and so I must be missing something. I imagined a cylindrical winding core producing a 360° ring of field lines spraying from the pole, with only those aligned to the approaching magnet resulting in torque. By extension a square pole would produce a nice "sheet" of useful field lines on the edge aligned to the magnet.

Click to expand...

You do both realise that in a BLDC, ALL Lorentz forces, however big or small they are, contribute exactly nothing to the torque of the motor?

Why? Because the coils are attached to the stator, as in static, as in can not apply/supply any torque to the rotor.

kiwifiat said:

...

Mevey also has a very good description of the Lorentz Law and how it applies to motor modeling, a good read for sure.

Click to expand...

Does it say how Lorentz forces acting on the coils in the stator of a BLDC motor, could impart any torque at all to the rotor?

Cos that's a magic trick I'd like to see.

(It seems clear that every one tries to apply the principles and formula from that wire loop (brushed) text book motor -- where the coil is the rotor and the magnets are stationary -- to brushless motors where the coils are fixed and the magnets rotate -- even the guys writing books! But it simply does not work! )

Buk___ said:

Does it say how Lorentz forces acting on the coils in the stator of a BLDC motor, could impart any torque at all to the rotor?

Click to expand...

Newton's Third Law?

Buk___ said:

(It seems clear that every one tries to apply the principles and formula from that wire loop (brushed) text book motor -- where the coil is the rotor and the magnets are stationary -- to brushless motors where the coils are fixed and the magnets rotate -- even the guys writing books! But it simply does not work! )

Click to expand...

You're arguing that a brushed and BLDC motor operate on fundamentally different principles? Ditto for inrunner and outrunner BLDCs? Even though the construction of all of them: a winding around iron teeth in conjunction with permanent magnets is the same?

Ok I will concede that any wire perpendicular to the core and in line with magnetic fields produces no torque.
I happen to know a little bit about cores and windings.

major said:

Definition of end-turns and active (effective) conductor length.

MotorCoilEndTurns.png

MotorCoilEndTurns2.png

Click to expand...

If our motors were like that textbook simple wire loop example, those definitions are clear, but nobody manufactures or uses motors like that.

But the motors we use look more like this (except there are many more smaller loops each side, and they are turned through 90 degrees)

Now the definition of which bits of wire outside the plane of the magnets constitutes "end turns" is less simple.

In the version I've shown above, the ends of the smaller loops should be considered end turns, as in a purely Lorentz force motor like that, they contribute little or nothing to torque.

But then, the simple text book motor produces little or no torque anyway; even if you add many (large) loops of wire:

The popup shows the results of running an integration to calculate the total Lorentz force acting on all 18 loops of conductor, with 25Aamps running through each, and reads: "Torque about (0,0): -0.24299 N*m"

And that is with the loops oriented at it most favorable position.

Now let's go back to my modified simple loop diagram. (Again, the smaller loops are orient wrong in the diagram, but it serves the purpose.)


I'm sure I don't need to produce a simulation to show that the Lorentz forces generated by 2 of the 3 conductors on one side of the motor, exactly cancel each other. And no matter how many smaller loops (turns around stator teeth), you added, you would never increase the torque due to Lorentz forces, because each loop would self cancel.

There is simply no point in adding coils to a pure Lorentz force motor design.

And yet, every BLDC motor produced today has many coils containing many turns; and motors of a similar scale to that I simulated above are producing hundreds of Newton.meters of torque, not the derisory 1/4 Nm the pure Lorentz force motor above produces.

(And that's using 250,000 mm^3 of N52 neodymium magnets; which is probably more than one of Luke/John's HubMonster motors contain.)

The motors we use outside of text books do not create their torque using Lorentz force; and those textbook diagrams and calculations are not applicable.

The motors we use have much more complex topology, and far more complex and contained magnetic circuits. Something like this (simulated on a similar 100mm diameter scale to the wire loop motor simulation above):

Punx0r said:

Buk___ said:

(It seems clear that every one tries to apply the principles and formula from that wire loop (brushed) text book motor -- where the coil is the rotor and the magnets are stationary -- to brushless motors where the coils are fixed and the magnets rotate -- even the guys writing books! But it simply does not work! )

Click to expand...

You're arguing that a brushed and BLDC motor operate on fundamentally different principles? Ditto for inrunner and outrunner BLDCs? Even though the construction of all of them: a winding around iron teeth in conjunction with permanent magnets is the same?

Click to expand...

I do wish you would stop trying to put words in my mouth.

I you wish to infer that a statement you are making, is the logical equivalent of a statement I've have made, then please develop that inference with an argument to demonstrate their equivalence.

In this case, I am saying that textbook diagrams do not describe real life motors; and the simplified math&physics used to describe those science fair project motors, is too simple to describe real ones.

I think some confusion about the orientation of the coils in the diagram may be the problem here ... I do not believe that they are perpendicular to the magnets but just look that way. If they were perpendicular then yes the torque would cancel assuming constant flux density through the coils between North and South Pole magnets.

Magnetic flux, like electrical current, will follow the path of "least resistance", in this case the lowest reluctance to magnetic flux. Thus, once the iron is introduced, it will determine the field shape, and the shape of the iron will dominate, and the coils themselves will cease to have significant effect on the magnetic flux as well as the magnetic forces. The coils serve merely to generate the flux while the iron conducts and shapes it.

Alan B said:

Magnetic flux, like electrical current, will follow the path of "least resistance", in this case the lowest reluctance to magnetic flux. Thus, once the iron is introduced, it will determine the field shape, and the shape of the iron will dominate, and the coils themselves will cease to have significant effect on the magnetic flux as well as the magnetic forces. The coils serve merely to generate the flux while the iron conducts and shapes it.

Click to expand...

Indeed. With the magnet's field being "wave-guided" through the head and stem of the tooth iron, rather than surrounding the coils, and the coils being so far away, the Lorentz forces on the coils are miniscule.

I'd add that when the coils are activated, the soft iron tooth becomes, for all intents and purposes, a bar magnet, with its magnetic polarity defined by the electrical polarity in the coil surrounding it.

And just as a bar magnet does not use or need Lorentz force to cause the needle of a compass to deflect, thus creating a torque via pure magnetic attraction and repulsion, so neither does a BLDC require Lorentz force to cause the magnets to rotate to align with favorably polarised stator teeth (or escape unfavorably polarised ones).

major said:

Buk___ said:

Does it say how Lorentz forces acting on the coils in the stator of a BLDC motor, could impart any torque at all to the rotor?

Click to expand...

Newton's Third Law?

Click to expand...

Magnetic field from the magnet interacts with the electrical field in the conductor: action.

The conductor experiences a mechanical force: reaction.

For that mechanical force to impart force onto the remote,isolated magnet, via the only medium that connects them -- the magnetic field -- would be a reaction to a reaction?; and would require the mechanical force on the conductor be converted to magnetism, flow back against the flow of magnetism, and then be converted back to a mechanical force.

I'm having trouble applying newton to that?

However...I know that a boat moving down a canal imparts energy to the banks with its bow wave. And some percentage of that bow wave is reflected back against the flow of the wave as pressure wave. Similarly, you get back pressure waves in air. But that's in a physical medium.

You get "reflections" in conductors -- they use them to determine how far from the exchange or house a telephone wire has been cut.

I'm not aware of any back pressure equivalent in magnetism.

Yeah there is force exerted on the windings which is one of the reasons that they get wapped tightly and varnished. If they are even slightly loose they actually make noise from the phase changes and some from the PMW if driven that way which is why sine wave driven motors are a little more quiet. I work with low inductance low turn winding motors that get driven with variable voltage DC. The 6 FET bridge is between the three phase windings and a bank of caps which supply the adjustable voltage.
The discription of how the coils couple to the core and interact with the magnetic poles and Permanent Magnets just posted here I completely agree with. Well said I might add also.

Buk___ said:

major said:

Buk___ said:

Does it say how Lorentz forces acting on the coils in the stator of a BLDC motor, could impart any torque at all to the rotor?

Click to expand...

Newton's Third Law?

Click to expand...

...
I'm having trouble applying newton to that?
...

Click to expand...

Lenz Law?

major said:

Buk___ said:

major said:

Buk___ said:

Does it say how Lorentz forces acting on the coils in the stator of a BLDC motor, could impart any torque at all to the rotor?

Click to expand...

Newton's Third Law?

Click to expand...

...
I'm having trouble applying newton to that?
...

Click to expand...

Lenz Law?

Click to expand...

Chicken and egg I think. The magnet has to move first, so if it was responsible, there's be no torque from stationary.

For Lenz Law, the magnet moves first, the current induced creates a field that opposes the magnets movement. And it seems to be a pretty weak affect.

And all the diagrams show the magnet moving toward and/ or through the coil; not rotating passed orthogonal to the coil's axis.

Seems like we're getting off track here.

Current in the wire around the iron tooth generates flux in the iron.

Flux in the gap generates force.

Force perpendicular to the pole tip's radius generate torque. The controller's job is to sequence the currents to maximize the torque inducing forces.

No motion is required for torque generation.

Motion generates back EMF.

The bad "end turns" are the part of the coil not generating flux in the tooth.

Any part of the wire contributing flux in the tooth is good.

Any part of the wire generating flux elsewhere is waste and the cost is i squared r.

Alan B said:

Seems like we're getting off track here.

Current in the wire around the iron tooth generates flux in the iron.

Flux in the gap generates force.

Force perpendicular to the pole tip's radius generate torque. The controller's job is to sequence the currents to maximize the torque inducing forces.

No motion is required for torque generation.

Motion generates back EMF.

The bad "end turns" are the part of the coil not generating flux in the tooth.

Any part of the wire contributing flux in the tooth is good.

Any part of the wire generating flux elsewhere is waste and the cost is i squared r.

Click to expand...

So called "leakage flux" around the end turns, is only the return path of the flux those end turns are inducing into the tooth (from the side), that is contributing to the torque the tooth is generating at its tip.



The end turns are generating flux in the tooth, and their return paths through air aren't even contributing to iron losses.

Buk___ said:

major said:

Buk___ said:

major said:

Newton's Third Law?

Click to expand...

...
I'm having trouble applying newton to that?
...

Click to expand...

Lenz Law?

Click to expand...

Chicken and egg I think. The magnet has to move first, so if it was responsible, there's be no torque from stationary.

For Lenz Law, the magnet moves first, the current induced creates a field that opposes the magnets movement. And it seems to be a pretty weak affect.
...

Click to expand...

No. Example. Motor at stall produces torque when current is present in armature. Initially current increased from zero. Change of current along with inductance of coil will represent work which is energy stored in magnetic field (which is a force field). Lenz says opposing force exist which is displayed as torque. No motion of magnet or coil. And can be very strong. Often is the maximum torque for a motor.

major

major said:

No motion of magnet or coil. And can be very strong. Often is the maximum torque for a motor.

Click to expand...

Sorry, but that contradicts everything I've read.

Eg.

First caption:

1. No change in inducing flux. 2. No induced current. 3. No induced flux.

Click to expand...

You appear to be saying that the (non-induced) phase current flowing in the windings, can oppose the motion of the magnets which aren't moving, and cause them to move.

I don't know what that is, but it isn't Lenz Law.

Buk___ said:

I do wish you would stop trying to put words in my mouth.

I you wish to infer that a statement you are making, is the logical equivalent of a statement I've have made, then please develop that inference with an argument to demonstrate their equivalence.

In this case, I am saying that textbook diagrams do not describe real life motors; and the simplified math&physics used to describe those science fair project motors, is too simple to describe real ones.

Click to expand...

I'm not. I'll quote it again and highlight the salient part:

(It seems clear that every one tries to apply the principles and formula from that wire loop (brushed) text book motor -- where the coil is the rotor and the magnets are stationary -- to brushless motors where the coils are fixed and the magnets rotate -- even the guys writing books! But it simply does not work! )

Click to expand...

You are stating it matters a jot whether it's the magnets or the coils that rotate.

And of course the simple motors in textbooks diagrams work on the same principles as real-world motors. The utility of a textbook is the distil the physical principles into their simplest practical manifestation to aid understanding.



I'm not sure why you're so ready to dismiss those who write the text books as not knowing what they're talking about. It seems if you find someone's explanation confusing it must be wrong and you seem to get confused often:

Here you didn't know what would occur if you put two motors of different Kv on a bicycle: https://endless-sphere.com/forums/viewtopic.php?f=30&t=92280&hilit=torque

Here you didn't know why you couldn't just feed a motor higher and higher voltage to get unlimited top speed: https://endless-sphere.com/forums/viewtopic.php?f=30&t=92280&hilit=torque

Here you couldn't understand how an ebike could ever accelerate because power = torque x speed and a motor at rest has no velocity: https://endless-sphere.com/forums/viewtopic.php?f=30&t=16376&hilit=torque&start=50

And here you suggested putting li-ion batteries and super-capacitors in series not realising current is the same through all parts of a series circuit and thinking the capacitance of the caps in series wouldn't reduce in the normal manner: https://endless-sphere.com/forums/viewtopic.php?f=14&t=93115&start=25

Considering the above, you'll understand if I believe the motor designers and textbook authors over your personal musings!

Punx0r said:

...

Click to expand...

You're right. I don't claim to know it all; and I have no problem asking -- nor being seen to ask -- about those things that don't quite make sense to me.

I also do not take things as read without questioning stuff, until my own understanding gells with received wisdom, or surpasses it.

I certainly don't hang on the coat tails of others -- John was right, Miles was right, Major was right -- especially when in two out of 3 of those cases, they weren't.

Nor do I follow people around from thread to thread, posting non-contributory "how dumb are you that you had to ask that question"; and when challenged, construct a character assassination piece in a fit of pique.

Punx0r said:

Considering the above, you'll understand if I believe the motor designers and textbook authors over your personal musings!

Click to expand...

That's fine!

I didn't ask anyone to "believe me". I stated the conclusion that I'd reached, and why.

Since then Miles and AlanB have chosen, presumably freely, to offer counter reasoning, and I've attempted to provide clear, logical, documented responses to their lines of reasoning. Their contributions have forced me to examine my reasoning in minute detail; and maybe my responses have caused them to question some of their own assumptions. Or not.

On the other hand , your posts in this thread -- as with many others -- are entirely non-contributory. They appear to consist entire of "I believe X, because he's got lots of posts" and "Who are you to contradict him".

If this place is closed to inquiring minds, then I guess your role as the "Status Quo Gatekeeper" has some validity; but if there are people here who don't mind those of us new to the field fumbling their way to understanding, by reading the literature, working through the math and sometimes questioning what is written, then it would serve us both if you ceased wearing your chips in public and allowed others to decide for themselves whether my questions are worthy of response and debate.