Synchronous Motor

ToneWheel Hammonds use a *synchronous motor* to turn the ToneGenerator. A synchronous motor is a electric motor whose rotational SynchronousSpeed is locked to the AC line frequency. A motor consists of the *armature* built into the frame of the motor and the rotor* which turns inside the *armature.

The *armature* consists of copper windings that convert the incoming alternating current into a pulsating magnetic field. Organs used on 60Hz power systems use a six winding or "six-pole" armature. On a 50Hz power system, the *armature* has four-poles. A two-pole *rotor* turns inside the armature. The rotational speed of a synchronous motor is equal to (120 x Power Frequency) / No. of Poles in the Armature. So the *rotor* inside the six-pole *armature* turns at (120 x 60) / 6 = 1200 RPM. On a 50Hz organ, the *rotor* turns at (120 x 50) / 4 = 1500 RPM.

Before organs, Hammond made HammondClocks --- the first clocks to use the AC line frequency for a time reference.

Synchronous motors are not self starting: the HammondClocks have a knob in the back that one has to spin to start the clock. The Hammond organ patent application showed a hand crank on the side of the organ to start the motor! Wisely, Hammond added a separate inductive StartMotor which is used to get the ToneGenerator up to speed. See HowToStartAHammond.