Abstract: Methods and apparatus are disclosed for calibrating a field-commutated motor (10) when under load, wherein initializing the motor (10) refers to relating data representative of the angle of the rotor in an uncalibrated coordinate system to a coordinate system having a known relationship to the excitation coils (17), typically mounted with the stator (16). The angular data can then be used for exciting the excitation coils (17) in the proper sequence and with the proper timing to obtain the desired speed, torque, direction or rotation, etc. of the motor (10). Test voltages having a known orientation are applied to one of the stator and the rotor, (whichever mounts the excitation coils (17)), and the angle of the rotor produced by the application of each of the test voltages noted. An equation is disclosed for determining an error angle between the uncalibrated and the known coordinate system as a function of the angles of the rotor produced by application of the test voltages.