Basic Motor Principles

Motors convert electrical energy into mechanical energy or motion. There are three principles related to electric motors:

  • electric currents produce electric fields,
  • the direction of the current determines the polarity of the magnetic field that is produced, and
  • like magnetic poles repel while unlike poles attract.

Likewise, an electric motor consists of three main parts – the “armature,” which moves, the “stator,” which is stationary, and the “commutator,” which reverses the polarity. In case you didn’t know, the “stator” of a motor is the set of components that make up the non-moving part of the motor, i.e., the part that doesn’t turn. The stators of electric motors have an iron core with one or more coils. When they are supplied with electricity they act like an electromagnet. The stators of many small motors use a permanent magnet instead of an electromagnet. The motors on this website show both either permanent magnets or a coil windings.

The “armature” consists of of a rotating shaft with a coil of wire wrapped around it. The coil becomes an electromagnet when current moves through the wire. The armature is positioned within the stator. The commutator is made up of components called commutator segments. It is responsible for delivering the current from the power source to the armature.

The electric current causes the armature and stator to become temporary magnets, each with a north pole and south pole. As you already know, like poles repel and unlike poles attract, the south pole of the armature is attracted to the north pole of the stator, making the armature revolve half a turn. As the commutator segments have also revolved, the segment that touched the positive brush has now turned and made contact with the negative brush. This reverses the polarity of the armature, which then gives another half turn. Therefore, while the current is turned on, it is the forces of attraction and repulsion that keep the armature turning because the polarity is continually being reversed.

Here is another description if the first description was a little confusing. The stator has two stationary magnets; these magnets are either permanent magnets or windings that make an electromagnet. One permanent magnet can be considered a north pole and the second magnet can be considered a south pole. As current passes through the armature, it creates a magnetic field. When the armature’s north pole is near the north pole of the stationary magnet, the armature is repelled and makes a half turn, approaching the south of the other permanent magnet to which it is attracted.

Just as the armature reaches the south pole, the current to the armature is reversed (by the “commutator”). This reversal (which acts almost like a switch) causes the armature’s north pole to become a south pole. Once again, two like poles are next to each other and the armature is repelled, making another half turn rotation. This process continues as long as current is present in the armature.

This description comes from several books on motor experiments; one of the books was called Electrical Connections and another one came from Super-charged Science Projects among others.


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