What is the point of a 3T, 4T, 5T winding if torque per amp is the same?

[anddan]

The low speed torque is a function of the motor controller amperage, with the same current but less turns you will have lower torque. To get the same current though you will need a higher voltage for the higher turn motor, since it has more resistance, so the increased torque isn't for free. If you consider top speed only for the same voltage and current, the higher turn motor will indeed go faster, but it will also heat up faster, so its also not for free. You can get the lower turn motor to go just as fast by increasing the phase current.

A.

 

[john61ct]

You can get the lower turn motor to go just as fast by increasing the phase current.

False.

Only higher voltage gets you faster top speed.

Until Field Weakening comes into the picture, which usually (always?) requires a true FOC controller.

That feature really is the way to both get higher torque at lower speeds (lower phase voltages, higher phase amps)

as well as a higher top speed once high torque is no longer needed

 

[MadRhino]

All this is only significant with smaller motors. A 50mm stator is more than is needed for an ebike. It can go faster than you can build safe with bicycle components, and can produce more acceleration than required to ride ahead of everyone in the city. Nobody will build an ebike for long distance on highways, you need a motorcycle for that, and motorcycles are sh*t with hub motors. It is natural that some always want more speed, more power, but there is one point where you need more bike. We build ebikes the best we can with bicycle components, on the best bicycle frames, making them as light as we can and that cost more than a motorcycle. There is no valuable reason to want more of an ebike. This is the line where motorcycles begin, where you’d have to give up the essential meaning of ebikes and start building on heavy frames with heavy components, heavy wheels, and loose the handling for the little extra performance that will make you lame by motorcycle standards, and a sh*t ride by ebike standards.

 

[dogman dan]

Well stated. When I started wanting real speed, I got a fast gas scooter. Then upgraded last spring to a huge BMW.

Its fun though, to watch these ES discussions get to the point where they are debating how many angels can fit on the head of a pin.

But for sure, if he's going with a motor with big fat wide magnets, its hard to overheat it without crashing first, wheelieing off it, or just riding it without using full throttle, ever. Killing motors that big is quite hard, generally taking something like 500 pounds or more of weight load. Something like a pedicab.

But a racetrack can be incredibly harsh on a motor. Quickest I ever killed a smaller motor was on a kart track. It had about 20 turns in a mile, and 50 mph straights. So it was full throttle, full brakes, every few seconds. A bigger GP type track would not be so hard on it.

Is that what he's doing? Building a race bicycle for a grand prix type road course?

 

[anddan]

If you take the same motor and wind it with twice the number of turns of copper, then k will double, so the motor will require twice the voltage to reach the same speed, but it will only need 1/2 the current to output a particular torque. Notice that the power input (V*I) for a given torque and speed is the same in both cases. The power lost in the copper is the same too, since twice the number of turns means twice the length at half the wire area, so 4 times the resistance. Power loss goes as I2R, so halving the current is exactly canceled by a 4-fold increase in R. The important point here is that rewiring the motor for a different K value does _not_ change the motors fundamental performance in any way, provided that the same total amount of copper is used.


but yes for any given motor, the top speed will increase with increasing voltage

You can get the lower turn motor to go just as fast by increasing the phase current.

False.

Only higher voltage gets you faster top speed.

Until Field Weakening comes into the picture, which usually (always?) requires a true FOC controller.

That feature really is the way to both get higher torque at lower speeds (lower phase voltages, higher phase amps)

as well as a higher top speed once high torque is no longer needed

 

[sean1072]

im just using the 5T version with an unlocked svmc72150 (200A DC, 450A phase) on a nominal 85.8V battery (93.6V max), i can get up to 100+ kmh with my 26 fat wheels (31inch with the tire). im getting about 32KGM of momentum, 300nm of torque and 18750w peak (theoretically), im doing power wheelies at speeds above 40kmh

 

[_GonZo_]

I think what Justin was trying to get all understand is; that different KV (Different winding turns) of the same motor model are going to develop almost the same power, and torque. The basic difference is speed.
So don't choose strange components for your build, if you want to go 45Km/h get a motor able to go up to that, do not get a motor able to go up to 100Km/h and then limit it.
Or other wise if you want to go 100Km/h get a motor for that, do not get a motor that is too low KV and then rise up to 300V+ or run always at field weakening ...

But obviously there is differences on how different winding motors deliver their power, so in some applications it can be interesting to get out of the norm... See picture for reference.

Actually I did some tests long time ago about having a motor that could change its windings in the fly for in-wheel motors that will benefit most from it. And it is promising but quite difficult to create as it means that it is necessary to run 6 power cables out of the motor. And actual designs of in-wheel motors makes that extremely difficult.
Anyway I happily discovered that this "2 motors" or "2 gears" in one is used in solar cars racing where they try to get the most of every component.
Maybe in the future we will be able to get this kind of motors and controllers that can handle them.