MXUS 3000 Hub Motor - V1 V2 V3

teslanv said:

John,
It sounds like you think a 3T (or whatever the "fastest" wind available is) is the preferred choice in every circumstance? Do I understand that correctly?
I understand that a 3T wind is better able to handle more phase amps than a slower wind, and that the amount of phase current a motor can handle before reaching saturation is directly related to the aggregate cross-dimensional area of the strands of copper making the circuit around each stator tooth.
Are there no circumstances where say you are limited to a larger tire diameter by design, that you would choose a "slower" wind motor for that specific application, provided it had the same total copper fill?

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I want maximum power, which means maximum rpm (all winds can make the same torque and power is torque X rpm), and I prefer to stay below 100V. 2 turns are much harder on controllers as you go to high current due to the inductance being too low, otherwise that would be my choice. Gearing is wheel size and large wheels are geared too high (again regardless of the winding turns). That's why we see no electric motorcycles with large wheels running hubmotors, yet scooters can have sufficient power to drive a motorcycle. If the myth was true, they would simply put more turns on the teeth and make electric motos with hubmotors, but the physics don't work.

You light guys may be able to get away with the larger wheels, but it's a severe handicap, and so with the smaller wheel the fat guy in Costa Rica on the bike with a smaller wheel on a hubbie has more performance. I do have a set of 21" moto wheels (26-26.5" OD) ready to go on a build for road and trail use using a hubmotor, but that hubmotor won't be in the wheel so I can gear it properly. I'll gear it to the equivalent of about a 12" OD wheel and run high enough voltage to get the speed I want. Even below 100V I should be able to gear it for 80kph top end, and the gearing will be low enough handle off road without the complication of a 2nd set of sprockets to move the chain over to lower gearing for off-road. If it falls short I have high voltage controllers available, and I'll increase voltage 40-50%, decrease current 10-20% (for the sake of the controllers) and decrease the gearing by 25-30%. The end result will be even lower stress, more power, higher top speed, and more torque at the wheel. It's a 3kw rated motor like the Mxus, but not as rpm limited due to better steel and less than half the magnet poles, so the Mxus3000 could be run in a similar manner, but not similar extremes. You guys don't have the same load mine has to push, so your results could be quite similar though the big diameter motor will be harder for you to fit.

Regarding saturation, the beginnings of saturation are where increasing current results in progressively lower additional torque up to full saturation, which is the point where the electromagnets of the stator cannot be make more flux. The number of turns determines the current to get there, but that stuff all varies in direct inverse proportion with the current the copper can handle and make the same heat, which is why motors with the same copper fill are identical motors and winding doesn't change the wheel size they can swing. The only thing running higher turn count accomplishes is being able to use smaller wires, and that's a silly benefit to give up power in exchange. It gives up power because we are voltage limited, and you can't make up the difference with current.

All evidence contrary to these statements is anecdotal and not supported by the physics. Just because some guys are pushing low enough loads to get away with gearing too steep (large wheels) doesn't change the fact that they will absolutely get better performance by reducing the wheel size. They're commonly so steeply geared with the big wheel, that decreasing wheel size doesn't even change top speed, but the increased torque at the wheel is always noticed. Our hubmotor systems are very forgiving so these things can easily go unnoticed, but when you push the envelope that quickly rear their ugly head. That's why so many slow wind motors have been burned up by forum members pushing far lighter loads than mine push, and by mine I mean before HubMonster when the motors I ran (and are still running on ebikes) were identical in terms of the stator as Xlyte H40's. I'm not aware of a single speed wind motor getting burned up.

Way to go KF, you're mixing fact with fiction and forwarding myths.

Kingfish said:

Defining Speed – using mathematics

If we know the Power (P) and the Tire Size (given C, r, or d), theoretically we can calculate Speed (Linear Velocity, mph, kph).

• Mechanical Power (P) (kW) = (τ (Nm) * 2π * rpm)/60000
  ω = 2π * Revolutions per second (rps)
  τ = Force (F) * 2r
  Electrical Power (P) = Current (I) * Voltage (V)
  The motor constant (K) is determined by Torque (τ) divided by Angular velocity (ω).
  K = τ/ω
  Kv = RPM (rads/s)/Volt (V)
  Kt = Torque (t)/Amps (I)

Therefore Kv is relative to Tire Size. If we keep Power the same, Kv and Kt will change proportionally to the Tire Size.

In the ideal world, Kv and Kt are at inverse of each other: High Kv motors will have low Kt, and vice versa.

The highest efficiency the motor will display is during no-load at the highest possible battery voltage and current provided by the system, regardless of tire size – so long as it doesn’t overheat. It goes downhill from there.

• High Kv motors benefit from smaller tire sizes to improve their Kt.
• Conversely, high Kt motors will benefit from larger tire sizes to boost Kv.

Therefore, if desiring speed, higher-wind motors work best with larger tire sizes, and lower-wind motors work best with smaller tire sizes… Unless you have 2WD, where you can definitely use lower-wind motors on larger tires and still have an excellent torque experience at higher speed.

I just love it when it snows and I have winter tires front and back!
Good hunting, KF

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Math and physics are fiction? That's news to me.

I propose a dyno test of two systems:

Systems to have the same battery, controller model and motor format with the same copper fill.

System A Will have a High-Speed Motor with a small diameter wheel

System B will have a High-Torque motor with a large diameter wheel.

Test "Speed" will be the same on both systems, which means the smaller wheel will have to turn a faster RPM than the larger wheel.

Both systems will run the same total power, but the higher speed motor will require proportionally lower voltage and higher current than the High Torque motor.

If John's Hypothesis is correct, then the Fast-turn motor & smaller diameter wheel should produce less waste heat than the High-torque large diameter wheel.

If KF's Physics and Math are correct, then both systems should perform identically.

Then perhaps we can dispel these "myths"

Umm, I think there is some confusion here… I never said low-winds on small wheels will perform identical to high-winds on large wheels. What I said was -> You can take a high-wind motor and place it on a larger diameter tire to increase Kv and decrease Kt, and vice versa on lower-wind motors. A consumer could do that, it's worth exploring, but they will not perform the same, and here is why:

Winds – More or Less

Based upon my previous post wherein I’ve defined some of the math…

• Torque (τ) = Force (F) * 2 * Radius (r)
  F = Current (I) * Length of Conductor (L) * Magnetic Flux Density (B)

Basic physics says “longer conductors will provide more force”

However there’s a pesky little problem called Resistance that works against blanket employment of longer conductors (I think we all get that without going through the Proof). :wink:

• If Power (P) is the same: More winds produce higher Torque and lower Angular Velocity.
• More winds = longer conductors = higher resistance, therefore Voltage and Current must change.
  Electrical Power (P) = Current (I) * Voltage (V)
  Resistance (R) = Voltage (V) / Current (I); Voltage (V) = Current (I) * Resistance (R)
• Conservation of Energy requires that more Winds necessitate higher Voltage and Lower Current.

Higher Winds also produce larger eddy currents which in turn add to motor heating. That math is complex and based upon motor physicality of which I’m not privy to. However FEMM does a pretty good job of simulating the losses if the model is correct.

In general, high-wind motors are better suited for applications that require robustness, such as hill climbing, and they are less desirable for speed. There is a really good thread around here that discusses the effects of fill-factor. Ideally, we want the highest fill possible for most bang per Erg; on the 9C – that was determined to be the 2808. Ah, found it; here’s the thread. But don’t get caught up in the argument that “I must have the most efficient wind”. There’s more to it: The consumer should focus on which wind works best for their need, e.g. higher velocity, economy, or hill climbing.

Conclusion: Math and reality easily display that all winds do not perform the same; they can’t – not even theoretically.

John in CR: You know... I think we sometimes say the same thing but in different ways due to writing style, therefore it can be difficult to ascertain a “kindred opinion”. That said, I cannot answer the question of “myth” because I don’t know what myth you are talking about. I’m here for the facts man. Can we talk about that in a friendly manner?

More coffee, KF

KF,

Your math is flawed. I think maybe the different way I just explained it in a pm may help.

The same speed pushing the same load up the same hill requires a fixed amount of power. With speed the same the same size wheel, then rpm is the same. That means torque is the same. With rpm the same, iron losses, and parasitic losses like bearings and stuff are all the same. Efficiency is power in minus losses, so the only thing left is copper losses, and those are the same too, because that's simply resistance. The higher current to make the same torque with the fast wind motor passes through shorter thicker copper as discussed before, and the proportions are the same, assuming equal copper fill, that copper losses are identical.

That means all efficiency differences, if any, occur in the wiring and controller, not in the motor. Any advantages of a slow wind motor are there. Since our throttles vary quite effectively the voltage "seen" by the motor, it makes low speed work just fine even with a high speed wind motor. That means given our practical limitation of pack voltage due to a lack of controllers, only the high speed motor is capable of high speed, so they're the only ones that come close to having your cake and eating it too. When set up for a higher top speed though you give up efficiency during acceleration, because you've spread the efficiency curve, and that goes for slow wind and fast wind motors equally. By acceleration I mean increasing speed, not accelerating against gravity, which if ground speed is fixed, then the power and rpm are fixed too, which I consider steady state operation.

An important factor in overall efficiency is whether the controller is running 100% duty cycle or not. If you run a motor at full throttle AND the load is not so high that the controller goes into current limiting, the duty cycle will be essentially 100% (other than commutation).

As soon as the load increases enough that the controller starts throttling, you get large additional losses in both the motor and controller as it goes into PWM. Both will heat up significantly more.

The trick is to get the motor kV/tire size dialed in so you can operate in this range most of the time.
Starting out or going up a very steep hill, PWM is going to kick in and efficiency is going to drop. Going to the extreme, if you hit saturation, the motor efficiency drops dramatically. Effective gear ratio should be designed to avoid getting even close to saturation.

motor comparison without controller (step-down conversion) losses:



it shows the same as the datasheet from Astro, Joby motors and others (the 2808 9C has a bit more copper fill therefore more efficiency). but because it is WITHOUT controller and wire losses, things will look a bit different in REAL WORLD.
thats why many who want to push their drive system to the limits prefer lower kV motors and higher voltage. as an example the KTM Freeride E-motocross has 300V and only 2600Wh battery. thats extreme. Also RC model builder went up to 14s LiPo instead of using faster-wound motors. sure also weight plays a role there and larger wires / connectors are heavier.

John, i share the opinion with you that for high continuous power a high kV motor in a small wheel is best (primarily due to the 100V limitaton of most controllers), but i personally never would go below 22" OD wheels because riding comfort is more important for me than a cooler motor. Its about to find the balance for oneself..

Madin88,

Anyone pushing their system to its limits is doomed to component failure issues. Durability is one of the big benefits of electric, so why give that up? Pushing the limits is really only applicable to racing. My suggestions for enhancing performance are about moving the limits, and awesome performance is easy without introducing stress into the system. These Mxus3000's are great for reasonably high power at low cost, assuming Mxus doesn't pull a Crystalyte move and install 2 cent halls, cheap epoxy for the magnets, crap axles, etc.

The whole small wheel thing is bullocks. Admittedly it's harder to achieve a well proportioned look, but ride comfort??? That's the beauty of single track, it's easy to go around holes. If you're riding where they are unavoidable, then the far bigger compromise is the unsprung weight. Those who insist on large wheels need to understand that it is a performance compromise regardless of how the motor is wound, and increasing the number of turns doesn't help one iota. A slower wind is not a change in gearing, and that is exactly the opposite of what you and everyone else who helps perpetuate the myth leads people to believe. DD hubmotors are geared too steeply for running more than rated power in large wheels, and large loads during strong acceleration, climbing hills, or even the wind at high speed leads to motor stress when pushed. The only ways to fix that are to set up for slower speeds and lower power, or decrease the wheel size. Better cooling helps get rid of the additional heat, but not the cause. Lower gearing helps to make less heat, enough less that you can increase power and every category of performance and still have a cooler motor, so whatever imaginary compromise (have you ever even run a 20" wheel other than your suspensionless BMX when you were a kid?) is more than offset by the gains. I don't hear Zappy complain and I think it's an 18" that he runs on his vented MagPie that he uses offroad showing up his friends who are on motorcycles.

WRT overall efficiency, simply use larger wire and a more capable controller, which can be incredibly cheap these days if you stay below 100V, and I personally don't count 24s of lipo in that. Yes the controllers are larger, but so is the battery needed for running higher power. With the higher speed that the vast majority are counting on with higher power, if efficiency is a primary concern, then the focus needs to be where the big gains exist. That's in aerodynamics, not a few % at most in the wiring and controller or 1% or so more in the controller for increased switching losses. Don't forget the performance and efficiency gains of a smaller wheel, which even going down just to a 22" are significant.

Take a slow speed wind motor in a big wheel and try to get 60mph out of it. Then put 80-100lbs in a backpack and take it on even just moderate hills. That's what my ebikes have been doing since 2009, except much more than just moderate hills, without a single motor failure other than some hall wires on a sealed motor whose insulation melted enough to cause intermittent shorts and was still able to ride home. If what I've been saying in this thread wasn't factual then my ebikes must run on magic, but they don't My newest ebikes have a bit of magic running ridiculous power, but HubMonster relies purely on physics magic and higher quality more expensive materials combined with unique design to achieve the high efficiency that makes the magic possible. 8)

John in CR said:

The whole small wheel thing is bullocks. Admittedly it's harder to achieve a well proportioned look, but ride comfort??? That's the beauty of single track, it's easy to go around holes. If you're riding where they are unavoidable, then the far bigger compromise is the unsprung weight. Those who insist on large wheels need to understand that it is a performance compromise regardless of how the motor is wound, and increasing the number of turns doesn't help one iota. A slower wind is not a change in gearing, and that is exactly the opposite of what you and everyone else who helps perpetuate the myth leads people to believe.

Click to expand...

How else should i say instead of ride comfort?
With small wheels you notice every little bumb while the larger one will just runs over them. The unsprung mass also has less bad effect if the wheel is larger.
I have compared it so i know what im talking about simply saying "than go around the holes / surface irregularities" is a good advice, but not everyone has smooth surface roads at his place and not to mention how a small wheel will perform in woodland or trails..

As for the different turn counts i think most of us here got it (same nominal RPM, same nominal torque, same efficiency) and i did not say something different.

I ride on the street in So.Cal. so a franken bike or a clown bike is out of question, I go with the homeless model. And will go with that again. So 26in. Bike rim just trying to make it work. With these large spoke holes.

999zip999 said:

I ride on the street in So.Cal. so a franken bike or a clown bike is out of question, I go with the homeless model. And will go with that again. So 26in. Bike rim just trying to make it work. With these large spoke holes.

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So a Hanebrink would be unacceptable I guess. Keep running large wheels, as long as you understand it is a significant performance compromise that results in lower efficiency and less acceleration regardless of how the motor is wound.

madin88 said:

John in CR said:

The whole small wheel thing is bullocks. Admittedly it's harder to achieve a well proportioned look, but ride comfort??? That's the beauty of single track, it's easy to go around holes. If you're riding where they are unavoidable, then the far bigger compromise is the unsprung weight. Those who insist on large wheels need to understand that it is a performance compromise regardless of how the motor is wound, and increasing the number of turns doesn't help one iota. A slower wind is not a change in gearing, and that is exactly the opposite of what you and everyone else who helps perpetuate the myth leads people to believe.

Click to expand...

How else should i say instead of ride comfort?
With small wheels you notice every little bumb while the larger one will just runs over them. The unsprung mass also has less bad effect if the wheel is larger.
I have compared it so i know what im talking about simply saying "than go around the holes / surface irregularities" is a good advice, but not everyone has smooth surface roads at his place and not to mention how a small wheel will perform in woodland or trails..

As for the different turn counts i think most of us here got it (same nominal RPM, same nominal torque, same efficiency) and i did not say something different.

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You must be running with no rear suspension. My daily rider has a 5" wide scooter scooter tire 19.25" in diameter and it rides smooth like a big ole land barge Cadillac.

999zip999 said:

So 26in. Bike rim just trying to make it work. With these large spoke holes.

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You can get 3mm or #4 screw washer at almost any hardware store. That should work with any spoke from 12-14G. I thought about not using washers with my 12G spokes but decided It might need them for the large 4mm holes. The spoke heads are only 5mm.

On comfort,

full suspension, fat soft creepy crawlers, soft cushioned seat

seriously I couldn't imagine how much softer my ride needs to be.

If you need to ride up stairs sure I understand but I don't think I can ever go back to 26".

Sure it doesn't look like what people are used to but no ebike does unless it's got not much motor, controller or battery to hide.

The front 26" makes sure I don't eat dirt.



The radial lace is tough enough to take the amount of air I am comfortable for the rest of the bike to endure
[youtube]u9qPGbjosaY[/youtube]

The mountain climbing up hill onroad never sees over heating. The faster I go the less I keep away from hundred.
[youtube]QzkNZVdH-4M[/youtube]

At slow off road speeds it heats up but I see 30% improvement. I used to have to stop almost every hill, now every few hills or one big mountain.
[youtube]WGpVrSVEgMM[/youtube]

Hope this is not to much of a digression but the last page of posts is actually more interesting to me than the motor in the title which I wouldn't mind buying.

In case anyone was wondering, like I was, whether a higher pole count would providing lower "gearing", the answer is, apparently "no". More poles = less iron & copper, bringing us back to John's point about copper fill being the dominating factor.

I think various winding options are only offered so people/manufacturers can select a desired top speed for a certain voltage battery with little regard for maximum power handling. Off-the-shelf or OEM ebike batteries tend to be 24, 36 or 48V and speed between 15-30mph for the bikes they are fitted to. Changing the motor wind seems like an easy way to reconcile the two.

So yes, small wheel, low turn-count, high voltage = win. Unless you need to ride off road, where small wheels suck. Then you're just stuck between a rock and a hard place and have to put up with a poorly geared direct-drive hubmotor. Larger diameter motors are what's needed.

Would you guys recommended a 24/26 rim for 4T motor?

Thanks!

John in CR said:

You must be running with no rear suspension. My daily rider has a 5" wide scooter scooter tire 19.25" in diameter and it rides smooth like a big ole land barge Cadillac.

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i have rear suspension on my bike :wink: went from 16" x 2,5" to 17" x 2,75" wheels (22,4" OD) and now it definitely rides more comfortable. lowering tire pressure also helps a LOT with heavy hubs, but i want to keep rolling resistance low. mostly i ride with 2bar / 30psi (front and rear). what pressure do you have in your tires?

BoomerChomsi said:

Would you guys recommended a 24/26 rim for 4T motor?
Thanks!

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The smallest tire you can live with the better regardless of what motor or what number of turns on the motor.

I'm sure Madin88's 22" OD wheels work great for him, and only if you live out at the limits in terms of power and load (hills or weight) for your motor does the absolute minimum become more important. In his case, that's about a 15% increase in torque, and from the motor's perspective it sees a 15% lower load.

John in CR said:

KF,

Your math is flawed. I think maybe the different way I just explained it in a pm may help.

Click to expand...

Sorry – I was busy Sunday and I’m just now seeing this.

“The same speed pushing the same load up the same hill requires a fixed amount of power. “

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Presume same manufacturer & motor series. All motors = All winds? Therefore with the same load, all motors going the same speed use the same power or a “fixed” amount? What do you mean by “fixed”; can you clarify please?

With same speed, same wheel, rpm is equal... Torque is equal.

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Agreed! This is given by the equation Mechanical Power (P) = Torque (τ) * Angular Velocity (ω)
It’s a good formula all by itself for getting started on the path of sizing the wheel to meet the application. The first thing we notice is that τ directly varies with ω, allowing us to adjust the wheel size to best match the optimum motor output. (I hope there’s no argument here).

~KF

Thank you John for sharing your knolege I have learnt more about motors here with all of you uarguing than in the whole spanish forum :|

You have explained how you could measure the saturation of A in a motor. Could you do something similar with V? Does A saturation have any relation to V saturation?

chucho said:

Thank you John for sharing your knolege I have learnt more about motors here with all of you uarguing than in the whole spanish forum :|

You have explained how you could measure the saturation of A in a motor. Could you do something similar with V? Does A saturation have any relation to V saturation?

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Thanks chucho,

If I get just a few guys seeing the truth instead of propagating the myth, it's worth the trouble.

I'm pretty sure that saturation has nothing to do with voltage. AFAIK measuring where saturation starts requires using a dyno to measure torque, and you'd also have to measure phase current. In practical use we need to stay well away from saturation, because copper losses from resistance get out of hand before that. With a stock sealed motor it's even more important, since heat escapes the motor so slowly. Copper losses (heat) = current squared X resistance. With the strand size, number of strands on each turn, and the turn count, we can reasonably estimate the resistance for these 45mm 51 tooth stators (17 teeth per phase). Don't forget to double it, since the current goes into one phase and back to the controller through another. Keep in mind that the motor sees only phase current, so early in acceleration the heat in the windings can more than double when all too common high phase current/battery current limit ratios are used.

Heat is an unforgiving enemy, and as push toward high performance, you have to chip away at it in any way you can, because heat increasing with the square of current makes you quickly realize why people burn up slow wind motors when half the Kv means 4X the resistance.

I chosen a 5t because, I like my 9c 2810@ 72v 2300watts. it tops out at 30mph. I think the 5t will work fine as I'm on the street and can't be going 50mph. And have many hills I find high speed motors bog down and get hot.

The 'Myth Vs. Math' argument is annoying, but healthy for constructive discussion and discovery I suppose

Volting up and gearing down has been a reliable recipe for almost every eBike builder trying to reliably squeeze higher acceleration and speeds from their machines for several years. Motor wind count, wheel diameter and voltage/current settings are the only ways to modify the 'gearing' of a hub motor depending on whatever the performance goals may be. Thermal management typically becomes the next challenge, and there are many approaches documented by ESers that have effectively addressed that issue.

Empirical evidence wins - every time.

Looking forward to seeing your MXUS 3kW builds/modifications folks!

John in CR said:

chucho said:

Thank you John for sharing your knolege I have learnt more about motors here with all of you uarguing than in the whole spanish forum :|

You have explained how you could measure the saturation of A in a motor. Could you do something similar with V? Does A saturation have any relation to V saturation?

Click to expand...

Thanks chucho,

If I get just a few guys seeing the truth instead of propagating the myth, it's worth the trouble.

I'm pretty sure that saturation has nothing to do with voltage. AFAIK measuring where saturation starts requires using a dyno to measure torque, and you'd also have to measure phase current. In practical use we need to stay well away from saturation, because copper losses from resistance get out of hand before that. With a stock sealed motor it's even more important, since heat escapes the motor so slowly. Copper losses (heat) = current squared X resistance. With the strand size, number of strands on each turn, and the turn count, we can reasonably estimate the resistance for these 45mm 51 tooth stators (17 teeth per phase). Don't forget to double it, since the current goes into one phase and back to the controller through another. Keep in mind that the motor sees only phase current, so early in acceleration the heat in the windings can more than double when all too common high phase current/battery current limit ratios are used.

Heat is an unforgiving enemy, and as push toward high performance, you have to chip away at it in any way you can, because heat increasing with the square of current makes you quickly realize why people burn up slow wind motors when half the Kv means 4X the resistance.

Click to expand...

Thank you again!!
I suspect there was no real voltage saturation but had to ask before i asked my real doubt
Following the "rule" of "increase voltage 40-50% and decrease current 10-20%". That seems to match my small experience till now. What would you say it will be the limit? By limit i mean where there is not enough A to work with such amount of V (if this can realy happen...). And if this could happen in real life or theorical what would we observe?

Talking about heat... I intuit by this posts and others i have read from you long time ago that you have refined your air circulation in motors (i really dont know why people after all this time still make simple holes without judgment insted of trying to make air go in and out ) I am designing one with less "holes" than i usualy see and blades (6-8). Theoretically it should work very good... in the practise i think it cant be worst than simple holes :lol: If in the future you want to share some info on air circulation think of me cause i would love to hear about it.

Thank you for teaching us a bit more each day :wink:

Here is the basics of inductors explained with math that isn't too complex.http://info.ee.surrey.ac.uk/Workshop/advice/coils/Faraday/

The short of it is an iron for inductor like a permenant magnet hub motor will have a maximum amount of flux that the core can produce before it is saturated. If a 4 turn motor takes 40a at 100v to reach 100kmh, then a 2 turn motor on that same core should be able to reach 100km/hr at 80a 50v because it produces the same amount of flux. These motors will produce the same torque at these levels because the flux is the same. The advantage of lower turn count motors comes into play most often when you make a gearing change.

Put the 2 turn motor in a 13" wheel and the 4 turn in a 26" wheel and the 13" in an ideal config ignoring losses will produce 2x the power at 100v than the 4 turn motor at 100v. This is because the 2 turn motor has about 2x the KV of the 4 turn motor and therefore 2x the rpm.

Ignoring wheel diameter now, we'll say the 4 turn motor spins at 500rpm at 100v. The 2 turn motor at 100v spins at 1000rpm. If it's possible to take advantage of the higher rpm, one can make more power.

Hp=rpm x torque / 5252.

The 2 turn motor produces half the torque as the 4 turn at the same volts and amperage. To get it equal to the 4 turn motor you must double the current.

This is all a balancing game when deciding what motor to choose. The above examples also assume the iron core inductor is not saturated with flux. Core and motor come into play here but that's a more complex issue.

I believe I have the above correct, but it is subject to change if a correction is required.