Great job three d printing the alternator. How ever when you were talking about how the internal parts work the explanation you gave about the voltage regulator was not correct. The voltage regulator controls the current going into the rotor windings. More or less current in the rotor winding equals more or less magnetic field that is generated by the rotor winding. Stronger or not as strong magnetic field reacts with the stator winding more or less thereby generating the output of the alternator. Stronger magnetic field in the rotor equals more out put in the stator. Weaker magnetic field in the rotor equals less out put in the stator. That out put is then rectified by the diodes to create DC current and sent to the battery. This intent of this comment is to help not criticize your work