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Old 12-10-2007, 09:22 PM   #16
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Peak power will not vary, but it's possible to dramatically increase the operating speed of the motor - and thus the "area under the curve" - of a motor by employing field-weakening techniques. With a BLDC motor, field weakening involves using large amount of phase advance; i.e. more timing. Within the world of high-performance AC motors, this is a well-known technique. If you don't believe me, enter "bldc field weakening" into Google. Make sure to set aside an hour or two for some heavy reading.
Regardless of where you are on the curve, when the timing is optimal, your power output is limited by the strength of the electromagnetic field against the natural magnetic field (neodymium magnets in this case).

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This is not a true statement.
Oh that sentence clears everything right up. Thanks! You simply cannot make a 21.5 generate the same power as a 3.5 at the same voltage/amps. The difference is the electromagnetic field strength.
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Old 12-11-2007, 05:22 AM   #17
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Regardless of where you are on the curve, when the timing is optimal, your power output is limited by the strength of the electromagnetic field against the natural magnetic field (neodymium magnets in this case).
When you're operating under the base speed of the motor, what you say is correct. Keep in mind, though, that "optimal" timing changes with the delivered torque of the motor, and therefore should be changed dynamically in proportion to winding current.

Also please understand that large amounts of timing can allow the motor to run above the base speed, and that allows it to make some power (albeit not nearly as much as the peak power) where there was none before. Thus, messing around with timing until I'm blue in the face can indeed help! As I suggested above, spend some time doing some online searches on the topic, as the principle of field weakening in BLDC motors is rather attractive in many applications that don't employ multi-ratio transmissions.

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Oh that sentence clears everything right up. Thanks! You simply cannot make a 21.5 generate the same power as a 3.5 at the same voltage/amps. The difference is the electromagnetic field strength.
At the same input voltage and current, both will make the same nominal power - they'll do it at different speeds, though, and the gearing must be changed to accommodate this (also note that I say "nominal power" - in reality, the winding resistance of the higher-turn motor will increase the copper losses, and the higher speed of the lower-turn motor will increase the iron losses). If my supply and ESC don't limit the current, the lower turn count motor will make more power - doing so, however, requires more current at the same voltage. That's just simple physics.

Last edited by Eric Bryant; 12-11-2007 at 11:13 AM.
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