For me, the main reason ive ordered a set of reacher 7490s isnt that theyre more efficient in output power to input power, its that i can push more current into them without them catching on fire. The flipsky 6384’s im using right now are struggling a bit thermals wise, and im hesitant to push them above 100A phase as a result. If anyone has any bench tests they can show me how to run in vesc tool, ill gladly do so for you guys to get a good baseline comparison between 6384 and 7490 motors.
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This is an awesome question @glyphiks and to me, based on what little I know, the answer is “we still lack the needed standards” to answer definitively. AFAIK “bigger” when we say “bigger motor” might mean different things to different folks, depending on their interpretation of “bigger.”
Can size is the most visually apparent difference… but do all motors with the same can size have the same amount of copper wound in them? Do they have the same volume and quality of magnet, adhesive, etc?
Like others, My experience has been that larger motors can handle more energy without overheating, but do they need to be larger to accomplish that? I honestly don’t know. I agree with everyone that more metal generally equals more thermal dissipation, but does the material type impact that?
For years people have been hung up on the can length, can width, and KV as the key defining factors that motivate motor selection. There’s got to be more to it than that!
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The larger motor can have lower winding resistance for the same kv. Consequently at low speeds when you’re hitting the motor current limit it will draw less battery current for the same torque. At higher speeds when you’re hitting the battery current limit, it will have higher motor current and therefore higher torque for the same battery current.
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PS If smaller motors were more efficient then Tesla automobiles would use ESK8 sized motors for automotive use.
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I might sound like a total offensive douchebag now, but theres ALOT of power electronics literature on motors, from beginners to advanced.
Stop the guesswork if you’re uncertain/dont agree with f.e @Fatglottis which pretty much summed a whole chapter up in a very simple manner.
If you really want to get better understanding, get a library card 
(insert kind and fatherly tone)
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coolest card in town!
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If anyone is interested in learning more about motors, this guy’s youtube channel is a goldmine.
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Some very interesting conclusions in this video. He seems to be valuing some specs which never really get mentioned in esk8, i.e. weight, and surface area.
I guess it makes sense that weight would be a decent shorthand for overall power output, assuming that you’re comparing motors with similar construction. Maybe we should be comparing stator weight only.
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Generally the diameters ability to grow on our motors isn’t super vast. Hub motors is a good example, from a performance perspective hubmotors start to make alot more sense once they grow to bike size appilcations.
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I think the OP is a bit misleading. the answer is technically “yes” but bigger motors don’t provide more power. bigger motors enable more power to be applied to them.
other motor specs like winding thickness change how that power is translated onto rotational energy
If you have 2 motors of the same kv, and one of them is bigger and has lower resistance, and you set a battery current limit but no motor current limit, then during full throttle acceleration the bigger motor will accelerate faster, because it will receive more motor current for the same battery current on account of the lower resistance. both have the same torque per motor amp, but the bigger motor gets more motor amps for the same number of battery amps.
another way to think of it is for the same number of motor amps and torque, the bigger motor generates less heat because its electrical resistance is lower. consequently because the bigger motor produces less heat for the same motor current and torque, the bigger motor draws less battery amps for the same torque at the same speed, because it takes less battery amps to produce less heat, which increases range.
suppose you rode both motors at the same constant speed with the same torque and motor amps, then the bigger motor gets more range because it produced less heat for the same performance and it was drawing less battery amps.
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Do we know how much this is offset by the weight increasing drag?
This post gives some idea:
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This is right. The torque constant for a motor is directly proportional to the motor Kv.
In the real world, if you are running a 6355 and a 6396 motor at the same amps and Kv, they will perform nearly identical.
We use bigger motors because they are ok with higher continuous current.
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The bigger motor will have better range if you’re running the same motor current or the bigger motor will have more torque if you’re running the same battery current, because when the resistance changes (switching between bigger or smaller same kv motor), the ratio between motor amps and battery amps at a particular speed changes. When the resistance decreases, supplying the same number of motor amps requires fewer battery amps.
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A motor 3x the size could end up with less power output fighting the increased iron losses.
The grin motor simulator is a great tool.
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Not always, bigger motors almost always have more core losses, quite a bit more sometimes, so your range will decrease because it will be running at lower efficiency
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Switching from single to dual drive has similar consequences for efficiency as switching from single to a 2x size motor.
Hello
Bigger motor have real more Torqe.
and have no Limit you see 135KV 60Volt you have easy 115 amps.
Withe 20S you have easy 70Volt and 130-150Amps…
a0958ed67ac9bca3e37fc925fcd3783c.xls (41 KB)
