A apparatus is provided for estimating the position of a rotor of a commutated brushless motor operating without a shaft position sensor. The apparatus includes a tank circuit that incorporates a phase winding of the motor. A low-power signal of a frequency F.sub.1 is injected into the tank circuit. The frequency F.sub.1 is much greater than the switching frequency F.sub.s of the phase winding. Because the effective inductance (L) of the phase winding incorporated into the tank circuit changes in a cyclic manner in response to changes in the mechanical angle .THETA. of the rotor, the characteristic resonant frequency F.sub.0 of the tank circuit varies between maximum and minimum values. The effect of the variation of the resonant frequency F.sub.0 on the output characteristics of the tank circuit are used by a detection circuit to resolve the mechanical angle .THETA. of the rotor and, thereby, control the timing of the phase firing sequence. The two illustrated embodiments detect changes to the amplitude and phase, respectively, of the signal from the tank circuit in response to the changing inductance of the phase winding incorporated into the tank circuit.