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Old 03-25-2013, 06:06 PM   #21 (permalink)
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The normal set of motors dont allow me to run anywhere near the 80 to 90 percent throttle range that is ideal for most speed controllers.
So use Kontroik, Jeti or YGE speed controls, they have no problems running at 50-60% PWM duty cycle with only a small drop in efficiency (which is almost always more than offset by the reduction in drag from the lower HS.
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Old 03-27-2013, 10:47 PM   #22 (permalink)
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This article was a great read! =) (should be a sticky somewhere)

Maybe if I didn't disagree with just about everything in the OP If you are going to get up on a soapbox and preach you better be correct.
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Old 03-27-2013, 11:24 PM   #23 (permalink)
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You are free to think what you like about how energy is conserved, but the cool thing about science is that it does not care about your opinion.
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Old 03-27-2013, 11:27 PM   #24 (permalink)
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You are free to think what you like about how energy is conserved, but the cool thing about science is that it does not care about your opinion.

Correct, just the facts. I am just not a fan of the further spreading of bad information in this hobby.
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Old 03-27-2013, 11:29 PM   #25 (permalink)
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Do you have something to add to this conversation or not?
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Old 03-27-2013, 11:30 PM   #26 (permalink)
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Sure. I would implore anyone interested in the topic to do alittle bit of research, there are many great resources out there that explain basic motor theory properly.
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Old 03-27-2013, 11:33 PM   #27 (permalink)
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So, no?
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Old 03-28-2013, 12:01 AM   #28 (permalink)
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Contrary to the way an IC engine is rated, the power of an electric motor is an indirect way of describing its efficiency. These ratings represent the motors ability to handle a certain amount of power without overheating, they do not mean, necessarily, the motor produces this amount of power.
Not really, it is a way of saying it can handle X amount of heat. But a motor with a lower efficiency but excellent cooling can produce substantially more output power than a high efficiency motor with poor cooling. The rating is a thermal limit.

If a motor is correctly rated for say 2000W, that means it will not overheat when drawing that much input, likely the output is somewhere around 1700W so the motor will need to dissipate 300W of heat. A more efficient motor with the same rating may give you 1800W output.

But getting 2000W from a motor with 90% efficiency (2222W input) and getting the same 2000W from a motor with 80% efficiency (2500W input) can both be achieved but the less efficient motor will need additional cooling.

Given the specs manufacturers publish though, little can be learned, since there is no standards for how the measurements are made. The numbers are pretty much meaningless (see the 800MX catching fire after ~25s at its rated CONTINUOUS max current).
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Old 03-28-2013, 12:15 AM   #29 (permalink)
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Agreed. That is why I say 'indirect' description of efficiency, maybe I should have been more clear about that. The power ratings describe the motors ability to disipate a certain amount of energy before reaching a critical temperature. The heat produced is a direct function of the motor's efficiency, and the cooling describes its ability to dissipate it. A motor with better cooling can sustain being less efficient, although that does not help us from a performance stand point as much as making it produce less heat in the first place!

We are just talking semantics, I know and I don't meant to split hairs, but contrary to your statement, it is not a thermal limit, it is a power limit that equates to a particular amount of heat generation limit.

My intention with this thread was to illistrate that IC engine power and what we call "power ratings" for electric motors are two very different things. With that in mind, the key number we should all be concerned with is efficiency.

I agree that the numbers handed out on power should be taken with a grain of salt. Too bad we don't have a means to easily determine motor output and therefore efficiency at home easily.

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Last edited by Jon h2; 03-28-2013 at 08:26 AM..
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