Science, Physics, Math, & Myth

[Triketech]

My Father-in-Law used to tell me:

• “There are two types of people in this world: Those that can count…”
  (with anticipation of a conclusion that never arrived)

The answer is "Those who count".

Not in the mathematical sense.

Way back in the 60's slot car racers used to wind their own motors. Made for some really fast teeny-tiny hot rods. It would be something if some of the hot-rodders of today were more inclined to that sort of thing.

 

[teslanv]

It would be something if some of the hot-rodders of today were more inclined to that sort of thing.

Don't think we aren't.

 

[Rix]

It would be something if some of the hot-rodders of today were more inclined to that sort of thing.

Don't think we aren't.

Apparently he hasn't seen Luke's custom wound H35xx with 40kw flowing through it make it catch fire.

 

[Arlo1]

Yup I have wound a few as well its an insane amount of work to try to do better then the little Chinese lady who does it in the first place.
Your best bet is to experiment with solid slots or hair pin turns with a tig welder.

 

[johnrobholmes]

It is pretty hard to beat the chinese old lady's who wind all day for a living. I've had them show me up before, able to fit more copper than I thought possible. That will teach me to send joke purchase orders with "Impossible" wire fill again. The trick is to make sure everything is spec'd properly. If you ask (and have the proper volume of order), most factories will use 200C rated insulation, super high slot fill, high temp epoxy, and NEH magnets.

 

[johnrobholmes]

My Father-in-Law used to tell me:

• “There are two types of people in this world: Those that can count…”
  (with anticipation of a conclusion that never arrived)

The answer is "Those who count".

Not in the mathematical sense.

Way back in the 60's slot car racers used to wind their own motors. Made for some really fast teeny-tiny hot rods. It would be something if some of the hot-rodders of today were more inclined to that sort of thing.

Hot rodders of today's slot car racing still exist, but a few people are much better at building motors from years of experience. For some, it is worthwhile to wind and build themself. For the other folks that are trying to squeeze out that last 3% of gain, it is a lot cheaper to spend hundreds on a custom made motor instead of spending many tens of hours building a motor that isn't as good as the professional builder.


Like it has been stated, in hubmotors it is pretty hard to beat what most factories can do. It's also a LOT more difficult to understand winding a hub motor VS pattern winding a little 3 slot toy car motor.

 

[markz]

I've learned something, I hope it sticks in my brain.
https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907&start=375#p986251

I thought the 8x8 was longer strands with smaller cross sectional area = smaller guage, hence higher resistance then its counter-part with the same fill, 16x4.
The 16x4 would be shorter wire but thicker wire making it less resistance?

Its all making sense to me as I play with the motor simulator. The high torque at zero to low rpm is what threw me off, and still does, I wanted to sell my 4T and buy a 7T, but when I am riding I am not starting on a hill at a dead stop, I usually run up to the hill at 20-30kph, and thats right where the higher turn motors torque is cliffed downward. So I will keep my 4T, a comment from another seasoned member in another thread threw me off, stating something like if you want a hill climber you wouldnt get a high kv low turn motor, but looking at the motor simulator, its exactly what you want. I like John in CR's analogy of buying a vehicle, why buy a slow one that is only really good up to its peak power in my case 30kph. Thats whats its only good for, beyond that it dives and the lower T motor wins time and time again. Id rather go up a 15% hill faster then 30kph.

One part I do not understand is, the reading of Motor Amps, seems to always be 30A higher in a 4T compared to 6T Mxus 3000w. But battery volts and amps are always the same. The "Over Heats In" column is quite concerning. The 4T overheats quicker then the 6T, but thats corrected by smaller diameter tire if I am not mistaken.

 

[Hummina Shadeeba]

I've learned something, I hope it sticks in my brain.
https://endless-sphere.com/forums/viewtopic.php?f=2&t=64907&start=375#p986251

I thought the 8x8 was longer strands with smaller cross sectional area = smaller guage, hence higher resistance then its counter-part with the same fill, 16x4.
The 16x4 would be shorter wire but thicker wire making it less resistance?

Its all making sense to me as I play with the motor simulator. The high torque at zero to low rpm is what threw me off, and still does, I wanted to sell my 4T and buy a 7T, but when I am riding I am not starting on a hill at a dead stop, I usually run up to the hill at 20-30kph, and thats right where the higher turn motors torque is cliffed downward. So I will keep my 4T, a comment from another seasoned member in another thread threw me off, stating something like if you want a hill climber you wouldnt get a high kv low turn motor I thought high kv would be low turn, but looking at the motor simulator, its exactly what you want. I like John in CR's analogy of buying a vehicle, why buy a slow one that is only really good up to its peak power in my case 30kph. Thats whats its only good for, beyond that it dives and the lower T motor wins time and time again. Id rather go up a 15% hill faster then 30kph.

One part I do not understand is, the reading of Motor Amps, seems to always be 30A higher in a 4T compared to 6T Mxus 3000w. But battery volts and amps are always the same. The "Over Heats In" column is quite concerning. The 4T overheats quicker then the 6T, but thats corrected by smaller diameter tire if I am not mistaken.

over heats sounds bad. I think the low turn( equals high kv) motor has to put out more amps to get the torque you're wanting and that's creating too much heat. sounds like the low kv motor may still be a good thing. do you mean bigger circumference or diameter, because a narrow tire wont do anything

 

[John in CR]

It doesn't matter how you try to reword the myth. With the same total copper around the teeth it doesn't matter how many turns to get there, for the same torque at any given rpm the differently wound motors will make the same amount of heat. Manipulations of simulators that produce different results are apples and oranges comparisons resulting from inputs that make a proper comparison of different windings of the same motor impossible.

If you want better more efficient (less heat producing) hill climbing then use a smaller diameter wheel, because that's the only thing that will make a meaningful difference.

 

[Hummina Shadeeba]

It doesn't matter how you try to reword the myth. With the same total copper around the teeth it doesn't matter how many turns to get there, for the same torque at any given rpm the differently wound motors will make the same amount of heat. Manipulations of simulators that produce different results are apples and oranges comparisons resulting from inputs that make a proper comparison of different windings of the same motor impossible.

If you want better more efficient (less heat producing) hill climbing then use a smaller diameter wheel, because that's the only thing that will make a meaningful difference.

please excuse my forgetfulness.. I think I'm remembering that while the motor with the greater amount of turns will produce more torque per amp, it's greater electrical resistance due to thinner longer wires will amount to the same amount of heat. I think

so even given an extreme such as a 1 turn motor will produce the same heat as a 10 turn motor to make equivalent torque?

 

[markz]

I dont know if it produces more torque per amp. I do remember discussion about that.
Someone more knowledgable then me will have to reply about that.
But for me, that contradicts the 4T and 6T produces same, just have to readjust certain parameters.

I dont know about 8x8 or 16x4, I just thought I remember reading that somewhere.

----------

sounds like the low kv motor may still be a good thing. do you mean bigger circumference or diameter, because a narrow tire wont do anything

No the low kv/high Turn is not a good thing. I meant a lower diameter wheel, going from 26" to 19" is better for the motor in higher efficiency. Narrower tire is preference on riding terrain.
----------

It doesn't matter how you try to reword the myth. With the same total copper around the teeth it doesn't matter how many turns to get there, for the same torque at any given rpm the differently wound motors will make the same amount of heat. Manipulations of simulators that produce different results are apples and oranges comparisons resulting from inputs that make a proper comparison of different windings of the same motor impossible.

If you want better more efficient (less heat producing) hill climbing then use a smaller diameter wheel, because that's the only thing that will make a meaningful difference.

Re: Science, Physics, Math, & Myth

I am still misunderstanding things here. I thought the 16x4 mxus had the most copper fill or 2nd most copper fill. Which was good.
But for same copper, same torque, same heat. Which might mean then to me that the 6T might have same copper fill, but this comment says otherwise

The 6T should have a bit over 4 times the resistance, because it's double the length and 10 strands vs 21 strands.

part of this
https://endless-sphere.com/forums/viewtopic.php?f=2&t=63142&p=1079946&hilit=copper+fill#p1079946
So a 6T at anything over 60A phase will overheat. https://endless-sphere.com/forums/viewtopic.php?f=2&t=63142&p=1079946&hilit=copper+fill#p1079994
The 4T is rated at something like 200A phase amps. But I think its been said that the phases should be 160-180A with some sort of ratio.

Anyway I shouldnt comment on something thats not crystal clear to me. I dont want to propogate no myths.

 

[John in CR]

Yes Mark, more turns means more torque per amp, but it's thinner copper on each turn and more turns means that thinner copper is longer, so resistance is higher resulting in more heat per amp. That also means it has lower current handling. It is all proportional such that if you treat voltage and current as variable, that different windings of the same model motor are actually the same motor. They're capable of the same power, same torque, same speed, and for the same performance they just require different voltages and current for the same power in and power out.

Regarding copper fill, the manufacturers can't always fit exactly the same total copper around each tooth for all the different windings, but the version with the most will have the lowest resistance per unit of torque, making it the most efficient of the bunch. The variance is usually small, and there are other things with far greater influence on overall real world efficiency.

 

[Hummina Shadeeba]

John does varying the voltage and current become impractical and that's why they do different kv? If you rewound a bike hub motor to 3000kv you'd need it to run on something like an 1/8 a volt. I thought I read somewhere for optimum performance a motor should generally be run at 80 percent of it's max rpm based on the kv x volts. Does that sound right?

 

[Chalo]

Yes, there are practical limits to using fast wind motors at low voltage. High current requires more expensive controllers, bigger cables, bigger connectors. If you need 1HP max, 48V x 20A is way more feasible than 12V x 80A, or 5V x 200A.

 

[sn0wchyld]

John does varying the voltage and current become impractical and that's why they do different kv? If you rewound a bike hub motor to 3000kv you'd need it to run on something like an 1/8 a volt. I thought I read somewhere for optimum performance a motor should generally be run at 80 percent of it's max rpm based on the kv x volts. Does that sound right?

For the most part, yes. Hub motors for instance need to get their phase wires out through near the axle. As such there's a limited ammount of space, so running a 12V 300kv motor at 200A isn't really 'possible' as it woudl require very fat phase wires, creating a pretty hard upper limit to to max motor kv. There's also the point that high KV motors have lower resistance and inductance than an otherwise equal low kv motor, and are thus 'harder' for a controller to run (ie more likely to blow it up).

There's also the point that the best 'bang for buck' point of mosfets is currently at around 80-90V. Running 80-ish volts nets you the best power density out of your controller, so many are built to run somewhere around that target voltage. So that creates a lower limit to motor kv's, if a very soft one since higher voltage controllers are easily made, just not as power dense (and tend to be more $$ too).

so it comes down to a somewhat complex balance of what size wheel (for hub motors), what voltage battery, what current controller (and battery) you're running as to what 'kv' will be best for a given application. Regardless though, the power/efficiency of the motor will not change with differing kv.

 

[Hummina Shadeeba]

saying a motor will have the same max power output regardless of winding seems vague. If you want a motor to have high torque for a short period of time wouldn't the motor wound to have a low kv be better suited? It would produce greater inductance and therefore more torque, and as long as it wasn't run till it burned up it would draw less amps to get there right?

 

[John in CR]

saying a motor will have the same max power output regardless of winding seems vague. If you want a motor to have high torque for a short period of time wouldn't the motor wound to have a low kv be better suited?

No. They're the same motor. What part of same heat for the same torque isn't sinking in?

From a real world standpoint the opposite turns out to be true, and people have heat problems and burn up slow wind hubmotors with far greater regularity. I'm not aware of anyone burning up a fast wind motor, yet at 10rpm/volt and below, the examples of dead motors on the forum would fill trucks. That's because most treat current like a d#%k measuring contest, and controllers that can handle high enough current to burn up the skinny little wiring of slow wind hubbies are readily available. People even burn them up accidentally simply due to a lack of understanding of their real current limits.

Ignore sn0wychyld's mention of wheel size above, because wheel size has absolutely nothing to do with winding....same torque for the same heat covers that arm of the Myth.

You or someone else asked before why different windings are made:
1. The Myth remains broadspread, and the resellers who definitely don't know any better like the marketing aspect of "torque model" and "speed model".
2. Even the technical people at the factory may not know any better. Look at KF who started this thread with such certainty that he was right.

I've dealt with multiple factories who do "get it". They make exactly one winding version of each size of motor, and steadfastly dismiss requests for different turn counts. None are slow winds, since all had a Kv of 14rpm/volt or higher, and all their motors have had higher more consistent build quality than the generic parts motors all too common on the forum...no gaps in the magnets, spinning parts of the motors don't cut wire harnesses, no broken strands in the phase windings, no substandard halls, and axles are of adequate size.

 

[Hummina Shadeeba]

saying a motor will have the same max power output regardless of winding seems vague. If you want a motor to have high torque for a short period of time wouldn't the motor wound to have a low kv be better suited?

No. They're the same motor. What part of same heat for the same torque isn't sinking in?

From a real world standpoint the opposite turns out to be true, and people have heat problems and burn up slow wind hubmotors with far greater regularity. I'm not aware of anyone burning up a fast wind motor, yet at 10rpm/volt and below, the examples of dead motors on the forum would fill trucks. That's because most treat current like a d#%k measuring contest, and controllers that can handle high enough current to burn up the skinny little wiring of slow wind hubbies are readily available. People even burn them up accidentally simply due to a lack of understanding of their real current limits.

Ignore sn0wychyld's mention of wheel size above, because wheel size has absolutely nothing to do with winding....same torque for the same heat covers that arm of the Myth.

You or someone else asked before why different windings are made:
1. The Myth remains broadspread, and the resellers who definitely don't know any better like the marketing aspect of "torque model" and "speed model".
2. Even the technical people at the factory may not know any better. Look at KF who started this thread with such certainty that he was right.

I've dealt with multiple factories who do "get it". They make exactly one winding version of each size of motor, and steadfastly dismiss requests for different turn counts. None are slow winds, since all had a Kv of 14rpm/volt or higher, and all their motors have had higher more consistent build quality than the generic parts motors all too common on the forum...no gaps in the magnets, spinning parts of the motors don't cut wire harnesses, no broken strands in the phase windings, no substandard halls, and axles are of adequate size.

No gaps in the magnets? but I read complete magnet fill is a waste of money and inefficient as it makes "noise" and the ideal magnet width is dependent on the stator teeth shape.

so a motor with one turn on a stator tooth can be just as efficient at getting torque for a short or long period if given the right mix of volts. Since volts are generally preferred to amps for getting wattage due to their lack of heat, ideally we'd be running with higher turn motors and thicker wires just in the motor.

 

[John in CR]

I was talking about non-equally spaced gaps in the magnets. I've yet to see a good hubbie with spaces between magnets. Whether it's a wasted amount of magnet I have no idea, but I have little doubt that perfect spacing would be difficult. I run the the highest efficiency best quality hubmotors available, and the curved magnets used have no gaps, and they run nearly silent even with common controllers.

Like anything there are practical limitations. I have a very big 1.5 turn motor that makes controllers tremble when you turn up the current, so 2 turns is a somewhat safer limit, but that's with the common high pole count and slot designs that I've gotten away from due to rpm limitations. The idea of voltage being more variable than current I must take exception with. I can economically get most any reasonable current, but I need a controller solution for 148V nominal or higher that doesn't cost more than the motors being driven. These aren't for in-wheel use obviously.

Trying to defend the cheapest made motors with the skinniest wires is a losing cause with me, because it has proven to be the wrong way to go simply based on the failure rates seen on the forum. That doesn't mean you can't get good use out of one. Just learn it's realistic current limitations. eg Measure the phase to phase resistance and be sure to cap copper losses based on phase current well below 500-750W if you ride in tough conditions or big loads unless you make cooling mods.

 

[sn0wchyld]

saying a motor will have the same max power output regardless of winding seems vague. If you want a motor to have high torque for a short period of time wouldn't the motor wound to have a low kv be better suited?

No. They're the same motor. What part of same heat for the same torque isn't sinking in?

From a real world standpoint the opposite turns out to be true, and people have heat problems and burn up slow wind hubmotors with far greater regularity. I'm not aware of anyone burning up a fast wind motor, yet at 10rpm/volt and below, the examples of dead motors on the forum would fill trucks. That's because most treat current like a d#%k measuring contest, and controllers that can handle high enough current to burn up the skinny little wiring of slow wind hubbies are readily available. People even burn them up accidentally simply due to a lack of understanding of their real current limits.

Ignore sn0wychyld's mention of wheel size above, because wheel size has absolutely nothing to do with winding....same torque for the same heat covers that arm of the Myth.

You or someone else asked before why different windings are made:
1. The Myth remains broadspread, and the resellers who definitely don't know any better like the marketing aspect of "torque model" and "speed model".
2. Even the technical people at the factory may not know any better. Look at KF who started this thread with such certainty that he was right.

I've dealt with multiple factories who do "get it". They make exactly one winding version of each size of motor, and steadfastly dismiss requests for different turn counts. None are slow winds, since all had a Kv of 14rpm/volt or higher, and all their motors have had higher more consistent build quality than the generic parts motors all too common on the forum...no gaps in the magnets, spinning parts of the motors don't cut wire harnesses, no broken strands in the phase windings, no substandard halls, and axles are of adequate size.

yea i should have made the point better that wheel size wasn't refering to torque per heat unit, but to your desired speed vs battery voltage etc.

 

[madin88]

John,
what you say is correct in THEORY, but look how it is in practice:

- lower turn count motors often end up with lower copper fill beacause it's harder for the workers to fit the strands
- even if copper fill is the same, the lower turn count motor produces a bit more heat because it has percental more copper losses between winding-interconnections inside the motor -> that even would be THEORY!!
- phase wires, controller wires, battery wires all needs to be upgraded when using high kV motors because manufacturers usually only use one sort of wire for all type of windings
- High kV motors have lower inductance what means the controller will be stressed a lot more at high phase amps / during acceleration -> more controller losses

What i would like to point out is that it is not practial anymore if one needs to upgrade things for similar performace.

there must be a reason why KTM uses 300V for the freeride-E. or look at RC model builder they also tend to use higher volts (up to 14s) and lowering current for higher overall efficiency.

 

[Hummina Shadeeba]

what happens when you have too high a kv for your voltage? Something like a 3000kv hub motor for a bike for example and a 22 volt esc. I'm guessing it uses a lot more amps and drains your battery faster.

 

[markz]

I believe someone had the MXUS 3T and had problems originally get it going with a lower FET controller. I cant remember what happened, perhaps it was stuttering.
I believe, if I remember correctly as soon as they went to 18+ FET they could get it going after some programming of the controller.

Thats an example of your high turn, low fet controller "problem", but as an extreme like you mention, I just dont think it would work at all, why? I got no clue.
My assumptions aka guess would be induction, just cuz I read it somewhere :wink: :lol:

 

[John in CR]

John,
what you say is correct in THEORY, but look how it is in practice:

- lower turn count motors often end up with lower copper fill beacause it's harder for the workers to fit the strands
- even if copper fill is the same, the lower turn count motor produces a bit more heat because it has percental more copper losses between winding-interconnections inside the motor -> that even would be THEORY!!
- phase wires, controller wires, battery wires all needs to be upgraded when using high kV motors because manufacturers usually only use one sort of wire for all type of windings
- High kV motors have lower inductance what means the controller will be stressed a lot more at high phase amps / during acceleration -> more controller losses

What i would like to point out is that it is not practial anymore if one needs to upgrade things for similar performace.

there must be a reason why KTM uses 300V for the freeride-E. or look at RC model builder they also tend to use higher volts (up to 14s) and lowering current for higher overall efficiency.

I don't recall ever recommending the use of cheap generic parts motors manufactured as substandard out of the box. I haven't recommended using undersized controllers either. In practice I use the highest performance and efficiency hubmotors available, and they're all faster wind motors. Let me know when you have a slow wind hubbie that you think comes remotely close in performance and we'll do a comparison. I prove the theory correct every time I ride using motors that require no modifications unless you push to extreme performance where cooling mods become necessary.

 

[cal3thousand]

Yes Mark, more turns means more torque per amp, but it's thinner copper on each turn and more turns means that thinner copper is longer, so resistance is higher resulting in more heat per amp. That also means it has lower current handling. It is all proportional such that if you treat voltage and current as variable, that different windings of the same model motor are actually the same motor. They're capable of the same power, same torque, same speed, and for the same performance they just require different voltages and current for the same power in and power out.

Regarding copper fill, the manufacturers can't always fit exactly the same total copper around each tooth for all the different windings, but the version with the most will have the lowest resistance per unit of torque, making it the most efficient of the bunch. The variance is usually small, and there are other things with far greater influence on overall real world efficiency.

John has explained this now forwards, backwards, sideways and then some. I've shed the myth towards the front of this thread and have read most of it to this point.

I will say that this particular wording is one of the most concise available on this site, hitting torque/amps, copper length vs thickness, voltage v current, efficiency, and copper fill.

Read this one over and over if you are missing the concept.