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Originally Posted by BrianG
I still don't think the feedback pulses are perfect sine waves. You are applying a high current square wave signal to a coil. When the field collapses, it will generate a back-EMF spike. However, since this is happening kinda fast, the spikes aren't as bad as they normally would be. It probably looks more like a semi-sinusoidal pulse with a little decay before the next pulse from the ESC comes in.
Now, if we were talking about variable frequency sine-wave drives, then yes, the feedback would be a perfect sine wave. Man, I wish I still had access to a o-scope to check this!
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Yes we are giving the coils square wave drive pulses, and the BEMF would also be a primarily square wave. But, the BEMF pulse is influenced by the present magnetic field to the effect of a sinusoidal wave being factored in as the rotor passes each coil. The same is true for wye winds or delta winds. So if you filter out the inverse of the drive pulse, timing included, you'll be left with a sinewave.
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