[Al_The_Man]

Wether BLDC or AC sinusoidal there has to be some feedback at least for commutation, both require the amplifier drive unit to know the position of the armature. BLDC use hall effect or equiv. and can be located on the encoder disc if one is present, AC sinusoidal often have a resolver, this gives 2 phases back to the controller which produces the third artificially, some AC have an encoder disk, which is required for initial position on power on, after that it keeps track of rotor angle. But this only provides the commutation angle for the motor, after this the motor should be under true torque command from the position (motion) controller which feeds the correct digital or analogue signal into the amplifier with feedback from an encoder or other feedback device.
What motors are they?
Al