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Originally Posted by sleebus.jones
I've got some thoughts on this, that aren't really backed up by any sort of real-world use, but as Scotty says, "ya canna change tha laws of phyziks!"
1. Higher voltage is good. In the real world, as electric motor horsepower goes up, so does the voltage. Why? That's so the amp draw of the motor doesn't become unmanagable, which would require huge wire gauges. The higher the voltage you run, the less current you need to do the same amount of work. This means less strain on your battery and ESC system. For instance:
2S liPo driving a 1000w motor:
watts/volts = amps
1000/7.4= 135 amps
3S LiPo driving a 1000w motor:
1000/11.1 = 90 amps
The benefits there are obvious. Same amount of work being done, but with 33% less amp draw. The more amps you draw, the more you are fighting the internal resistance of the wires/battery/motor/esc and your system is running less efficiently. Let the voltage do the work, rather than the amperage.
2. Lower speed motors don't have to fight as much frictional resistance. It's not hard to see that a motor spinning at 65,000 rpm is fighting much more frictional resistance than one at 40,000 rpm. Gearing up then puts that high speed load on the driveline, rather than the motor.
3. Here's one that'll probably start everyone arguing: the torque of a brushless motor is determined by its power delivery system, not the motor itself! For instance, if you take the Fiegao line of the same size motors, all can produce the exact same torque, regardless if it's a 6XL or a 10XL. If you do see torque differences, it's because your battery system isn't up to snuff with the current demands of the motor, not because of the motor. This becomes more and more apparent the smaller number motor you pick, because the amp draw goes up as the number goes down. Yes, this goes completely contrary to brushed motor thinking, but then, these aren't brushed motors, are they? :027:
Discuss! :)
Sleebus
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That argument makes sense. I agree with your statement about frictional resistance somewhat (I'm sure there IS parasitic loss, but it can't be THAT much). I agree with the power calculations. I also agree about your point about very high currents being unmanageable.
However, physcial load has to be taken into consideration. A heavy physical load, whether from a heavy vehicle or very tall gearing, effectively is trying to stall the motor, or at least slowing it down. The motor's coil resistance is a VERY small part of the current limiting factor. Most of the motor's resistance comes from inductive reactance from the back EMF of the coils and moving magnets.