what is cogging torque?

[Hummina Shadeeba]

For a cleaner back emf ?
For a easier rolling system ?
For less wear on the bearings ?

For an easier rolling system. For less current needed to produce the same unpowered “coast”as a non-cogging motor. And also I believe the cogging torque is present at all speeds so less power needed to overcome that resistance at all speeds


What I’m hoping someone can show:
Is cogging a loss of momentum for starters?(seems obvious in that it does)
Is cogging due to iron losses and most likely hysteresis?


I believe a skewered stator produces less torque ripple AND less cogging torque. A cogging motor takes more current to coast unpowered than a lower cogging motor.

if u are still unsure of the questions read them again and if u have no evidence maybe someone who knows can tell


An easy answer would be hysteresis but I haven’t seen that in my little searching. Not that that means it’s the case. That’s why I’m asking.

“ Cogging torque produces zero net-work”
https://upcommons.upc.edu/bitstream/handle/2117/99998/MASTER%20THESIS.pdf?sequence=1&isAllowed=y
Maybe that means the loss of momentum must be attributed to iron losses.

it makes sense that a slotless motor would have greater hysteresis as it has more iron that is being exposed to the switching field and therefore should have MORE cogging...if cogging were a result of hysteresis

 

[Ianhill]

The loss of momentum would be down to the load connected if your referring to the back emf.

Dead short the windings and the motor will lock up fast more electrical resistance and less torque can be scavenged till there infinite resistance as such open phase so differing batterys will regen harder than others as its IR dependant and the skewered motor will give a less erratic signal good for power generation.

I may of misunderstood your question and taken your curiosity of sudo science and seen your looking for something that doesn't exist.

I urge you to reconsider magnet motors as fiction all motors to date play a game of push and pull by flipping the magnetic state any way of flipping a magnet will take energy and the torque load will be places on the pivot point of each magnet itself giving a full throttle situation that would just see it snap to bits outside of the controller field strength and timing it all in a way it gathers speed and not stall and lock up.

Vesc will show how picky motors and timings are mess that field up and swap the pwm frequency and the motor will grrrr like an angry woman in a long que.

 

[Hummina Shadeeba]

The loss of momentum would be down to the load connected if your referring to the back emf.

im not
Dead short the windings and the motor will lock up fast more electrical resistance and less torque can be scavenged till there infinite resistance as such open phase so differing batterys will regen harder than others as its IR dependant and the skewered motor will give a less erratic signal good for power generation.

not what I’m talking about
I may of misunderstood your question and taken your curiosity of sudo science and seen your looking for something that doesn't exist.

may be. That’s what I’m trying to find out

I urge you to reconsider magnet motors as fiction all motors to date play a game of push and pull by flipping the magnetic state any way of flipping a magnet will take energy and the torque load will be places on the pivot point of each magnet itself giving a full throttle situation that would just see it snap to bits outside of the controller field strength and timing it all in a way it gathers speed and not stall and lock up.not what I’m talking about

Vesc will show how picky motors and timings are mess that field up and swap the pwm frequency and the motor will grrrr like an angry woman in a long que.

not what I’m talking about


Please read my specific question and answer them if u can.

 

[thepronghorn]

For an easier rolling system. For less current needed to produce the same unpowered “coast”. And I believe the cogging torque is present at all speeds so less power needed to overcome that cogging period.

Theyre just questions. If u don’t have evidence that’s fine and don’t bother writing then.

Again:
Is cogging a loss of momentum for starters?(seems obvious in that it does)
Is cogging due to iron losses and most likely hysteresis?


I believe a skewered stator produces less torque ripple AND less cogging torque. A cogging motor takes more current to coast unpowered than a lower cogging motor.

if u are still unsure of the questions read them again and if u have no evidence maybe someone who knows can tell


An easy answer would be hysteresis but I haven’t seen that in my little searching. Not that that means it’s the case. That’s why I’m asking.

“ Cogging torque produces zero net-work”
https://upcommons.upc.edu/bitstream/handle/2117/99998/MASTER%20THESIS.pdf?sequence=1&isAllowed=y
Maybe that means the loss of momentum must be attributed to iron losses.

No cogging is not a loss of momentum or energy. As we've said again and again, the force as a magnet approaches a stator tooth and as it leaves the tooth is equal and opposite. That is the definition of cogging.

No cogging is not an iron loss nor a hysteresis loss. It is not a loss. It is a net zero torque ripple. It gives and takes equally as the motor rotates through a full revolution. The paper you linked says exactly this on page 16 in section 2.6 "Cogging Torque".

For an easier rolling system, you need to reduce the parasitic drag of the motor. That means reducing hysteresis losses, eddy current losses (in both the stator and rotor), bearing lossses, etc. There is no loss from cogging.

 

[Hummina Shadeeba]

For an easier rolling system. For less current needed to produce the same unpowered “coast”. And I believe the cogging torque is present at all speeds so less power needed to overcome that cogging period.

Theyre just questions. If u don’t have evidence that’s fine and don’t bother writing then.

Again:
Is cogging a loss of momentum for starters?(seems obvious in that it does)
Is cogging due to iron losses and most likely hysteresis?


I believe a skewered stator produces less torque ripple AND less cogging torque. A cogging motor takes more current to coast unpowered than a lower cogging motor.

if u are still unsure of the questions read them again and if u have no evidence maybe someone who knows can tell


An easy answer would be hysteresis but I haven’t seen that in my little searching. Not that that means it’s the case. That’s why I’m asking.

“ Cogging torque produces zero net-work”
https://upcommons.upc.edu/bitstream/handle/2117/99998/MASTER%20THESIS.pdf?sequence=1&isAllowed=y
Maybe that means the loss of momentum must be attributed to iron losses.

No cogging is not a loss of momentum or energy. As we've said again and again, the force as a magnet approaches a stator tooth and as it leaves the tooth is equal and opposite. That is the definition of cogging.

No cogging is not an iron loss nor a hysteresis loss. It is not a loss. It is a net zero torque ripple. It gives and takes equally as the motor rotates through a full revolution. The paper you linked says exactly this on page 16 in section 2.6 "Cogging Torque".

For an easier rolling system, you need to reduce the parasitic drag of the motor. That means reducing hysteresis losses, eddy current losses (in both the stator and rotor), bearing lossses, etc. There is no loss from cogging.

Why would a slotless motor, which has more iron subjected to a switching field, and you’d assume therefore more hysteresis, have less or no cogging?

I’m not looking for someone to say this is how it is and except it. I’m looking for evidence as there’s evidence I’ve seen and, just as I wrote above, that conflicts with what I should be assuming.

 

[Ianhill]

Detent torque thank me later.

Didn't mention slotless either just straight slot vs skewed we debated.

 

[Hummina Shadeeba]

Detent torque thank me later.

Didn't mention slotless either just straight slot vs skewed we debated.

Detent torque is the same thing as cogging torque. u get no thanks for that.


I’m mentioning slotless now. Answer any question you want.

Please explain how with a slotless motor, which has more iron in contact with the switching field of the rotor than a toothed stator, and therefore I assume would have greater hysteresis, yet can have no cogging.


Again I’m not looking for someone to tell me how it is in a condescending manner without presenting evidence. I learn through this process of weeding through what seems conflicting understanding on my part.

 

[thepronghorn]

For an easier rolling system. For less current needed to produce the same unpowered “coast”. And I believe the cogging torque is present at all speeds so less power needed to overcome that cogging period.

Theyre just questions. If u don’t have evidence that’s fine and don’t bother writing then.

Again:
Is cogging a loss of momentum for starters?(seems obvious in that it does)
Is cogging due to iron losses and most likely hysteresis?


I believe a skewered stator produces less torque ripple AND less cogging torque. A cogging motor takes more current to coast unpowered than a lower cogging motor.

if u are still unsure of the questions read them again and if u have no evidence maybe someone who knows can tell


An easy answer would be hysteresis but I haven’t seen that in my little searching. Not that that means it’s the case. That’s why I’m asking.

“ Cogging torque produces zero net-work”
https://upcommons.upc.edu/bitstream/handle/2117/99998/MASTER%20THESIS.pdf?sequence=1&isAllowed=y
Maybe that means the loss of momentum must be attributed to iron losses.

No cogging is not a loss of momentum or energy. As we've said again and again, the force as a magnet approaches a stator tooth and as it leaves the tooth is equal and opposite. That is the definition of cogging.

No cogging is not an iron loss nor a hysteresis loss. It is not a loss. It is a net zero torque ripple. It gives and takes equally as the motor rotates through a full revolution. The paper you linked says exactly this on page 16 in section 2.6 "Cogging Torque".

For an easier rolling system, you need to reduce the parasitic drag of the motor. That means reducing hysteresis losses, eddy current losses (in both the stator and rotor), bearing lossses, etc. There is no loss from cogging.

Why would a slotless motor, which has more iron subjected to a switching field, and you’d assume therefore more hysteresis, have less or no cogging?

I’m not looking for someone to say this is how it is and except it. I’m looking for evidence as there’s evidence I’ve seen and, just as I wrote above, that conflicts with what I should be assuming.

By slotless motor, do you mean closed slots? Look on page 19 of that paper. It says "closed slots like in Figure 16 (c) can be a great solution since there is a better flux path through the stator teeth" which means there is less variability in the reluctance of the stator which means the amplitude of the torque ripple from cogging is smaller. The closed slots do short some of the rotor flux away from the stator teeth, so there is a loss of torque.

I'm not sure that you can assume that your "slotless motor" will have greater hysteresis losses. Anyway, hysteresis losses aren't the same as cogging torque, so stop worrying about that relationship.

 

[Hummina Shadeeba]

For an easier rolling system. For less current needed to produce the same unpowered “coast”. And I believe the cogging torque is present at all speeds so less power needed to overcome that cogging period.

Theyre just questions. If u don’t have evidence that’s fine and don’t bother writing then.

Again:
Is cogging a loss of momentum for starters?(seems obvious in that it does)
Is cogging due to iron losses and most likely hysteresis?


I believe a skewered stator produces less torque ripple AND less cogging torque. A cogging motor takes more current to coast unpowered than a lower cogging motor.

if u are still unsure of the questions read them again and if u have no evidence maybe someone who knows can tell


An easy answer would be hysteresis but I haven’t seen that in my little searching. Not that that means it’s the case. That’s why I’m asking.

“ Cogging torque produces zero net-work”
https://upcommons.upc.edu/bitstream/handle/2117/99998/MASTER%20THESIS.pdf?sequence=1&isAllowed=y
Maybe that means the loss of momentum must be attributed to iron losses.

No cogging is not a loss of momentum or energy. As we've said again and again, the force as a magnet approaches a stator tooth and as it leaves the tooth is equal and opposite. That is the definition of cogging.

No cogging is not an iron loss nor a hysteresis loss. It is not a loss. It is a net zero torque ripple. It gives and takes equally as the motor rotates through a full revolution. The paper you linked says exactly this on page 16 in section 2.6 "Cogging Torque".

For an easier rolling system, you need to reduce the parasitic drag of the motor. That means reducing hysteresis losses, eddy current losses (in both the stator and rotor), bearing lossses, etc. There is no loss from cogging.

Why would a slotless motor, which has more iron subjected to a switching field, and you’d assume therefore more hysteresis, have less or no cogging?

I’m not looking for someone to say this is how it is and except it. I’m looking for evidence as there’s evidence I’ve seen and, just as I wrote above, that conflicts with what I should be assuming.

By slotless motor, do you mean closed slots? Look on page 19 of that paper. It says "closed slots like in Figure 16 (c) can be a great solution since there is a better flux path through the stator teeth" which means there is less variability in the reluctance of the stator which means the amplitude of the torque ripple from cogging is smaller. The closed slots do short some of the rotor flux away from the stator teeth, so there is a loss of torque.

I'm not sure that you can assume that your "slotless motor" will have greater hysteresis losses. Anyway, hysteresis losses aren't the same as cogging torque, so stop worrying about that relationship.

Yes I mean closed slots.
“ It says "closed slots like in Figure 16 (c) can be a great solution since there is a better flux path through the stator teeth" which means there is less variability in the reluctance of the stator which means the amplitude of the torque ripple from cogging is smaller.”

Ok. allow me to put in my criticism based on my understanding and maybe you can set me straight.

https://en.m.wikipedia.org/wiki/Magnetic_reluctance:

“The definition of magnetic reluctance is analogous to Ohm's law in this respect. However, magnetic flux passing through a reluctance does not give rise to dissipation of heat as it does for current through a resistance. Thus, the analogy cannot be used for modelling energy flow in systems where energy crosses between the magnetic and electrical domains. An alternative analogy to the reluctance model which does correctly represent energy flows is the gyrator–capacitor model.”



The gyrator-capacitor model tells of the possibility of losses in transmission. those loses are what or how does that work, or maybe since it wouldn’t be energy flow across domains. I think ur saying there’s a loss in the motor as it coasts that’s not an iron loss but a loss in maybe the magnetic field. If u can explain how my hub motor has a bad coast please do.
Thanks for your input and getting to something I can work with and I’m sure I’m frustrating. I’m frustrated. But maybe I have it wrong to begin with that there is no loss in momentum..my quickly slowing slotted motor vs the non-slotted tells me there is.

 

[Ianhill]

Detent torque thank me later.

Didn't mention slotless either just straight slot vs skewed we debated.

Detent torque is the same thing as cogging torque. u get no thanks for that.


I’m mentioning slotless now. Answer any question you want.

Please explain how with a slotless motor, which has more iron in contact with the switching field of the rotor than a toothed stator, and therefore I assume would have greater hysteresis, yet can have no cogging.


Again I’m not looking for someone to tell me how it is in a condescending manner without presenting evidence. I learn through this process of weeding through what seems conflicting understanding on my part.

You change the question to suit yourself slotless blaa blaa blaa didnt even say that you said skewed slots its there for everyone to read.

I give you a topic to research the correct terminology of cogging torque but your a pleb and throw toys out so jog on fella you will make shit all important with your method of learning you acting like a child and want sir motor god to come along and blow smoke up your arse think again anyone that has a phd in this shit will shoot you down with ease if i can with a crappy nvq education.

Your copy and pasting shit from wiki with fuk all idea what your taking about trying to look clever ffs i just gutted you out twice.

 

[Hummina Shadeeba]

Skewered or slotted whatever you want to talk about abs I brought up both. You’re free to bring up any design if you think it better explains. I’m not trying to trick anyone or impress but trying to figure what’s what and I don’t have the education..that’s what I’m here for.

Indent torque isn’t the “correct terminology”. It’s one of many terms. when I say that I’m trying to get on the same page. I’m not attacking you or insulting you.

Yes I’m waiting for a PhD to come shoot me down or clue me in, whatever you want to call it. I don’t think I’m looking very clever. Magnetic reluctance and how it’s modeled is foreign to me and not pretending to know. I don’t think posting a quote from wiki conveys you’re trying to be clever, more so trying to get on the same page.


When u say you’ve gutted me twice..does that mean you’ve brought evidence that answers two questions? What?

 

[mxlemming]

Hummina, Ian is ripping you off. You can get free energy from a nice coggy stator, you just have to only take the electrical energy when it's pulling, and when it's pushing you just need to apply reactive energy only.

Sometimes it helps to use a magnetic monopole which you can create by pointing all the South poles inwards and taping them together.

 

[Hummina Shadeeba]

You can get free energy

Forget the term free energy if that’s too hard to swallow and don’t think I used that term. I think fair to say that the force of permanent magnets ADD to the force of the motor due to their orientation with no cost. So there’s potential for forces, such as gravitational or magnetic fields, to do work if they’re oriented correctly. An example being the satellite’s path being greatly..enhanced..due to its interaction with gravitational fields. I can imagine something similar with magnetic fields being possible. How about if you added a rope from one planet to another and at one end was connected a motor/generator? There you’re getting electricity from gravitational fields for “free”. Do you think that would work? Why? You would be subtly altering the paths of orbiting planets but that need not even be a loss and in that altering you could be sending planets into new orbits with potentially new gravitational fields

 

[mxlemming]

If you managed to arrange a rope pulling a linear generator between a planet and a slingshoting satellite I guess yes, you would be able to extract energy from the planets momentum.

Regarding the magnets, the cogging pulls the rotor 50% of the time increasing its kinetic energy and the other 50% it pushes it back, decreasing it's kinetic energy.

The high current to overcome cogging only happens at start up, when you overcome the first cog step. After that, subsequent cogging steps cancel each other out. They are heard as a wining sound as the motor spins but the loss to them use very small - sound doesn't carry much energy. Cogging is an elastic phenomena, like a spring.

There's a loss to Eddie currents due to the change in magnetic field through the iron as Ian says, this is a result of Faraday's induction, or can be seen from Maxwell's equations where a changing magnetic field induces an electric field (and therefore a current where there's a conductive medium). Eddie currents are not an elastic phenomena, they are like a damper.

This happens regardless of the cogging, they are separate phenomena but the loss of energy to Eddie currents and heat damps the cogging from vibrating forever.

If you still don't understand cogging, read this over and over again until you do.

I'm not a PhD like you requested, but I do have a master's degree in engineering from Cambridge university, studied electrical machines, wrote FOC from scratch for lolz and did my master's thesis in simulating diffuse electromagnetic fields so... I think I've got a vague idea what I'm talking about.

Ian may not have this, I don't know or care, but he's been basically right with all his explanations so far...

 

[Hummina Shadeeba]

If cogging is being produced by eddies they would be astronomical in resistance at higher speeds with eddies being exponentially produced, no? Hysteresis? Maybe and the resistance seems more linearly produced but I don’t know. I’m not taking someone’s word for it as you’re telling me it’s eddies which doesn’t sound like a good explanation for the above reason.

You say cogging only needs to be overcome at start up and once going the push and pull cancel each other out. This isn’t my experience with hub motors and there’s a continuous resistance at all speeds. A slotless motor doesn’t have ANY resistance yet has MORE iron being subjected to the switching field which I’d think would produce greater hysteresis or eddies. Magnetic reluctance being greater WITH slots seems a good lead and maybe would explain how that’s possible. Haven’t heard a satisfying answer yet.

If you still don't understand cogging, read this over and over again until you do..

That it’s eddies? I don’t think so.


Hoping for someone capable of explaining without the know-it-all attitude yet leaving no evidence. Don’t say it..post it.

 

[Chalo]

Magnetic braking isn't the same as cogging, but it occurs everywhere cogging does.

 

[mxlemming]

I literally wrote the exact opposite. It's not Eddies.

I. wrote. The. exact. opposite.

This happens regardless of the cogging, they are separate phenomena but the loss of energy to Eddie currents and heat damps the cogging from vibrating forever.

This isn't something you need evidence for. It's blindingly obvious from basic physics, the equations for electromagnetic induction (Maxwell's ones) and the equations for magnetic reluctance force.

But since you can't even read, I guess you're a lost cause.

 

[Hummina Shadeeba]

Magnetic braking isn't the same as cogging, but it occurs everywhere cogging does.

Or u could have magnetic braking without cogging. Generally I think magnetic brakes are done with eddies although hysteresis is out there. But still the slotless motor not cogging..how is that possible? Maybe hysteresis isn’t as simple as a ferromagnetic material passing a magnet as I generally understand it and someone said reluctance.

 

[Hummina Shadeeba]

There's a loss to Eddie currents due to the change in magnetic field through the iron as Ian says, this is a result of Faraday's induction, or can be seen from Maxwell's equations where a changing magnetic field induces an electric field (and therefore a current where there's a conductive medium). Eddie currents are not an elastic phenomena, they are like a damper.

Doesn’t sound like the opposite to me. So what is causing the loss in momentum other than eddies? You didn’t even mention hysteresis and your last paragraph is confusing but gives no answer.

“ This happens regardless of the cogging, they are separate phenomena but the loss of energy to Eddie currents and heat damps the cogging from vibrating forever.”
So what are you saying IS the loss of momentum going towards?

 

[mxlemming]

Evidence.

I have a motor, a small rc one.

It takes 3.5A to make it start.

Once started, a phase current of 0.1A will keep it spinning.

 

[Hummina Shadeeba]

Evidence.

I have a motor, a small rc one.

It takes 3.5A to make it start.

Once started, a phase current of 0.1A will keep it spinning.

There’s mass that needs to be put in motion.


But don’t get upset folks if I’m critical of your input. I contrast it with my own experience and spout how I see it.


But how much current does it take to spin a slotless motor of otherwise the same design? It too will need more current to start but will it take more current to continuously run at the same unloaded speed? Would it have less hysteresis or eddies?

 

[mxlemming]

There's a loss to Eddie currents due to the change in magnetic field through the iron as Ian says, this is a result of Faraday's induction, or can be seen from Maxwell's equations where a changing magnetic field induces an electric field (and therefore a current where there's a conductive medium). Eddie currents are not an elastic phenomena, they are like a damper.

Doesn’t sound like the opposite to me. So what is causing the loss in momentum other than eddies? You didn’t even mention hysteresis and your last paragraph is confusing but gives no answer.

“ This happens regardless of the cogging, they are separate phenomena but the loss of energy to Eddie currents and heat damps the cogging from vibrating forever.”
So what are you saying IS the loss of momentum going towards?

The loss of momentum of your bike and hub motor is going towards changing the rotational speed of the earth.

The loss of rotational energy is going to Eddie currents, friction in the seals, regen into the battery, and maybe your phase wires are partially shorted if it's really bad.

Are you trolling?

 

[mxlemming]

Evidence.

I have a motor, a small rc one.

It takes 3.5A to make it start.

Once started, a phase current of 0.1A will keep it spinning.

There’s mass that needs to be put in motion.


But don’t get upset folks if I’m critical of your input. I contrast it with my own experience and spout how I see it.


But how much current does it take to spin a slotless motor of otherwise the same design? It too will need more current to start but will it take more current to continuously run at the same unloaded speed? Would it have less hysteresis or eddies?

Ok, let me rephrase...

It takes 3.5A to overcome the cogging.

The mass could be accelerated by 0.11A.

 

[Hummina Shadeeba]

Evidence.

I have a motor, a small rc one.

It takes 3.5A to make it start.

Once started, a phase current of 0.1A will keep it spinning.

There’s mass that needs to be put in motion.


But don’t get upset folks if I’m critical of your input. I contrast it with my own experience and spout how I see it.


But how much current does it take to spin a slotless motor of otherwise the same design? It too will need more current to start but will it take more current to continuously run at the same unloaded speed? Would it have less hysteresis or eddies?

Ok, let me rephrase...

It takes 3.5A to overcome the cogging.

The mass could be accelerated by 0.11A.

So the slotless motor of otherwise the same design you believe would take only .11A to go from stopped and would only take the same .11A to run at the same speed as the slotted motor?
Maybe when the motor is powered that’s how it would go I don’t know but if you were to run the two motors only externally, so essentially coasting, the slotless or skewered motor will take less power to spin the same speed right?

I’m just asking questions and haven’t insulted anyone. I see people upset that I’m not taking their answers at their word. Consider it an intellectual exercise and take on the challenge without taking it personally. I’ve been insulted and condescend towards repeatedly but it’s fine and I see how that could happen. Just play along. I’m not believing eddies are the cause. Maybe hysteresis. But that’s not even what you’ve been telling me. If you really want to shut me up bring something solid and satisfying. This is the motor discussion section in an educational chat room so it’s not a stretch my asking

channel your annoyance into the greatest google search ever!! or maybe liveforphysics or someone can shut me up. i think i remember him saying it was hysteresis long ago but would like to know ...you know... why the slotless motor spins freely despite greater iron passing the magnets? (for starters or maybe that will explain all). the best lead seems to be magnetic reluctance. but i dont know what im really talking about. you said it and i liked it.

 

[mxlemming]

I've got an idea...

Why don't you go and pedal really really hard for 20 minutes, and see what gets hot? If it is the iron, it's Eddie currents. If it's the suspension forks and tires it is the cogging transmitting vibrations into the frame. If nothing gets hot, pedal harder.

The equivalent slotless motor will experience the same change in magnetic field, so will experience the same magnetic hysteresis otherwise it's not really equivalent...