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Old Jan 29, 2004, 04:47 AM
KreAture is offline
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Impossible? Hah!
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Oslo Fornebu, Norway
Joined Jun 2003
3,074 Posts
Calculating the phase offset won't be much of a pain. You can calculate it based on time between the last commutation and the time you detect the emf transition. If the time between commutation and detection is half the time between the two last commutations, and it stays that way for some time, then it is in phase. If not, then finding out how much it is out of phase is simple math. A small phase increase since last time would indicate both that the motor is speeding up and that the phase distortion is increasing a tiny bit. (If I don't have this backwards.)

Also, I don't understand what the drive voltage has to do with anything. Only thing that happens as you increase voltage and drive rpm increase, is that back EMF increase too. The offset of the EMF wave will ofcource be shifted along with the center point of the drive vcoltage, but the amp/comparator is supposed to be balanced on the drive voltage and should handle this.
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