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equations for brushless motors?

Old 12-07-2010, 07:16 AM
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hasek1616
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Default equations for brushless motors?

i'm doing a project in my engineering class involving brushless motors and i need to know how to calculate the efficiency of a motor, the rpm's of a motor, the kv of a motor, and how much work a it does, thanks for the help
Old 12-07-2010, 07:30 AM
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Argess
 
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Default RE: equations for brushless motors?

Basically, brushless follows the same theorey as brushed with the exception of efficiency. I think efficiency depends on too many things to calculate, such as I^2 R losses, commutator timing in brushed, or ESC timing in brushed, etc.

The KV rating is the max rpm @ 1 volt. So for a 5700 KV rating, applying 10 volts would yied a max rpm of 57,000 rpm. Not to be confused with KiloVolts.

Basically, the pic below shows what to expect, and the two pics below that have some theory which was done for some comparison work concerning identical motors except for the KV rating, number of turns, etc:





Old 12-07-2010, 12:33 PM
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hasek1616
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Default RE: equations for brushless motors?

thank you, thats exactly what i needed
Old 12-07-2010, 02:06 PM
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Default RE: equations for brushless motors?

Good....now please note.......when I did this, a long, long time had expired since I played around with this stuff. Best go over it to make sure I didn't make a mistake.
Old 12-07-2010, 03:16 PM
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Default RE: equations for brushless motors?

Looks good.

It may be worthwhile to note (even though it should be obvious) that the difference between low and high kv motors is only valid for motors of the same construction; it's not a universal comparison.

It can also be shown that higher Kv motors put out more power than low kv motors. If you gear a low kv and a higher kv motor to the same wheelspeed, the higher kv motor will have more torque at the wheel. Once again though, this is only valid for the same motor construction.

ORIGINAL: Argess

Good....now please note.......when I did this, a long, long time had expired since I played around with this stuff. Best go over it to make sure I didn't make a mistake.

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