what is cogging torque?

[Hummina Shadeeba]

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.

i thought you said strongly it wasnt eddies and i had misunderstood you. if the iron is getting hot i believe it could be either eddies or hysteresis no?
will a slotless hub motor being pedaled produce the same heat as the cogging slotted at the same speed and duration? maybe the grin simulator potentially can show that

 

[Ianhill]

A stopped motor has no induced currents in its core try put a led across a phase bet you get nothing happen.

Soon as it turns the emf builds up and the phase resistance increases with rpm, the emf grows in turn so the faster a motor turns the less current it can absorb by design but from a stall situation where torque is calculated normally its about phase resistance thats why torque drops off on graphs we see after efficency range the emf has grown so great its fighting the incoming current.

I suggest you research how an inductor apposes change in current flemings left hand rule and maxwells equations i had to do them all and so should you by the looks.

As the motors INDUCTANCE grows with RPM from a larger emf being generated from more electrical charge being created from breaking field lines we end up in a situation of self sustainability the motor can't damage itself at that range with out being overloaded with torque to slow down to a point of less emf and inductance more current can flow and the heat gathers fast

Im done know ive talked enough motors to make me want to apply for my phd i might aswell clearly gone further than my nvq class took me.

 

[Hummina Shadeeba]

A stopped motor has no induced currents in its core try put a led across a phase bet you get nothing happen.

Soon as it turns the emf builds up and the phase resistance increases with rpm, the emf grows in turn so the faster a motor turns the less current it can absorb by design but from a stall situation where torque is calculated normally its about phase resistance thats why torque drops off on graphs we see after efficency range the emf has grown so great its fighting the incoming current.

I suggest you research how an inductor apposes change in current flemings left hand rule and maxwells equations i had to do them all and so should you by the looks.

As the motors INDUCTANCE grows with RPM from a larger emf being generated from more electrical charge being created from breaking field lines we end up in a situation of self sustainability the motor can't damage itself at that range with out being overloaded with torque to slow down to a point of less emf and inductance more current can flow and the heat gathers fast

Im done know ive talked enough motors to make me want to apply for my phd i might aswell clearly gone further than my nvq class took me.

im talking about an unpowered pedaled motor as the last poster told. can you answer one of the questions directly?

what youre talking about is not what the topic is and remember you told me cogging was related to the bare iron teeth and the magnets, not the windings. (I’ve never heard of phase resistance increasing with rpm where you get that? )


there would be inductance in the pedaled unpowered motor and a back voltage created determined by the rpm, sure,... how would that relate to cogging i dont know. do you? go the step further and explain it then, or roll away in a huff if you need to.

 

[mxlemming]

It could be hysteresis if you have especially poor steel, good motor and transformer steels are designed to have very low hysteresis.

My statement still stands. Cogging and Eddie currents are different. One is elastic, one is not. The energy is lost to Eddies (and hysteresis, though I suspect this is small https://en.m.wikipedia.org/wiki/Electrical_steel says 2-10W/kg at 60hz1.5T). The difference between the affected steel mass in slotted and slotless motors is going to be of the order of fractions of a kilo so not really noticeable.

There will be some degree of loss to vibration caused by the cogging. I suspect this is small otherwise it would be remarkably unpleasant to ride.

Thinking about hysteresis, which is the iron becoming permanently magnetised, this means the iron now stores some magnetic energy. It's released as the dipoles flip, but where did that energy go? Heat. From throwing electrons about in the metal as the pole flips. Sounds like a small Eddie current.

 

[Ianhill]

The steel is not in a complete electrical circuit only a magnetic one

Take the copper from the steel and spin just the iron in a hub motor for example and it will act like a induction hob building up heat the laminated sections will slow the build up compared to a solid piece of metal but it will get hot over time and enough rpm will see enough field lines broken to get it real warm like melting hot soecially around its teeth area first but thats if the magnets where not also heat sensitive and they gathered eddys themself.

Look at an induction hob it basicly spins a strong magnetic field around in a circle below the pan a solid piece of magnetic material induces a current that builds great enough to heat the pan and its food contents.

The heating of the metal from currents stays in the metal its transformed into heat whats in the copper as emf can be reclaimed as regen but heating is lost same as me now theres not much left to answer.

Elasticated cogging is just beyond earthling knowledge.

 

[Hummina Shadeeba]

will an unpowered slotless hub motor being pedaled produce the same heat as an otherwise same motor but slotted? (same speed and duration)

 

[Hummina Shadeeba]

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?

 

[Ianhill]

will an unpowered slotless hub motor being pedaled produce the same heat as an otherwise same motor but slotted? (same speed and duration)

Yes same heat as its the same magnetic field just the cogging torque, detent torque,open circuit torque will have a linear appearance compared to an erratic of a straight slot motor and the emf appeaewnce will reflect this

https://www.motioncontroltips.com/whats-the-difference-between-cogging-torque-and-torque-ripple/

Cogging torque/detent torque/open circuit torque.

 

[thepronghorn]

will an unpowered slotless hub motor being pedaled produce the same heat as otherwise the same motor but slotted? (same speed and duration)

Roughly yes. A closed slot stator has a different magnetic path compared to the open slot motor, so the eddy current losses may be a little different, but for the same size and similar tooth design, they should be close.

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?

No it should be similar. It sounds like you have these motors. Perhaps you have some data you could share?

 

[Ianhill]

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?

Wrong the torque you apply will be linear for the skewed motor just like the emf we get back for a given steady rpm,
To spin a skewed motor will feel steady not lumpy like a common straight slot motor but a constant torque both equal the same over the 360 degree turn.

Skewed are used in power generation mainly to simplify the rectifying circuits no need for massive capacitive buffers to fill in the low spots.

 

[Ianhill]

Hang on we changed from slotted to skewed to slotless to suit your hypothesis.



Slotless will have less heating as the lams are further away from the magnetic field so induce less current

 

[Ianhill]

 

[Hummina Shadeeba]

I don’t believe cogging is due to eddies or hysteresis. The root of my problem was thinking cogging is not net-zero and is a loss. The motors I’d seen that coasted similar to a regular wheel I thought due to their not cogging but they must either have been slotless motors having very low flux density or more likely externally powered to overcome the humps of the cogging. All pm motors will have a resistance due to the iron losses and unavoidable and not related to the cogging.
I’ve been under this misunderstanding for many years.
Id incorrectly understood that just as the magnets were a boon in the motor due to their orientation, the slowing of the motor while coasting was due to their bad orientation. Not the case and rotor and its orientation with the stator is going to be without any advantage or disadvantage.


But even now knowing this I still believe in the potential for a magnet motor and the ability to harness magnetic fields through their orientation just as I believe you could with gravitational fields and planets tied together as I described. So..if anyone wants to try to convince me one way or the other on that I’m game but otherwise my cogging question is solved.

 

[Ianhill]

I believe i can fly.
I believe i can touch the sky.
I think about it every every nite and day.
I spread my magnets and fly away.
Ohhhhh i can fly so very high magnets can't pass me by wooooowowowowo i can fly. Ahahahaha

 

[Hummina Shadeeba]

I dont mean to sound like a nob and can be snappy on times and apologise

I’ll take your apology in advance again. If you are interested in explaining why you think not possible that’s preferred.

I think just as a rope could be attached to two orbiting planets some way of harnessing the force of a magnetic field would be possible

https://www.powerelectronics.com/technologies/alternative-energy/article/21864056/is-a-permanent-magnet-motor-feasible


But my original question is solved and maybe best to cut the thread there.

 

[Ianhill]

No no la la land boy nothing solved here read the comments in the link you supplied.

To date there is no useful working example so stop making things up you want to prove it link us some working examples please.

 

[Ianhill]

You need a good thunderfooting

 

[Hummina Shadeeba]

No no la la land boy nothing solved here read the comments in the link you supplied.

To date there is no useful working example so stop making things up you want to prove it link us some working examples please.

I’m not here to prove anything just bounce ideas.

I did read the comments and they don’t say the science discovery isn’t real just the implementation. But I just threw that up and didn’t look into it.
Just because it’s not here doesn’t mean it’s impossible. I’m not making anything up. But take it easy and try to have a day without spreading your hostility.

Another:
https://spacenews.com/experiment-designed-harness-magnetic-field-propulsion/
Not spectacular in its low power but still it’s an example of utilizing what’s out there.

 

[Ianhill]

Practical implementations fail because there is no substantial energy in magnets that could be employed for propulsion or to compensate for energy losses. The force between permanent magnets is conservative as the magnetic field follows a potential, so that there is no work done over a closed cycle.

Basiclly we got to turn the magnets to do any work the effort of turning the magnet and its attached mass through its drive then falls directly onto your magnet flipping device and the magnets themselfs basiclly acting as a clutch.

Bigger picture is missed by many not easy to follow at this level incuding myself, hostility is due to your behaviour nothing else.

 

[Ianhill]