Basic Armature Design

An armature (pictured on right) has a continuous series of windings from each bar on the commutator, which loop around the iron stack teeth and connect to the next bar on the commutator. The winding continues to loop all the way around the armature in the same manner. Loops are either single or parallel conductors (wires), and can circle any number of times around the stack teeth (called turns in a coil). The wire can vary in gauge as is required for the design of the motor. Each wire is insulated with an enamel coating, isolating it from every other wire in the loop, and only terminates at a commutator bar. The turns in every coil wrap around the iron stack to create an electro-magnet. When energized, an electro-magnetic field is generated in the motor armature. This EM field inter-acts with the magnetic fields of the permanent magnets in the motor (in the case of a permanent magnet motor) or with the electro-magnetic field created by the stator (in the case of a universal motor). These magnetic forces work to attract each other, inducing a torque on the armature shaft, causing it to turn.
If a motor is driven too hard for its environment and temperatures are allowed to rise beyond the thermal limits of the insulation, it is possible for the insulation on the wires to break down and short together, or short to the armature stack. If windings are shorted together, the electro-magnetic fields cannot be created for that coil, causing the motor to run erratically or fail all together.