How an electric motor rotates?
Here, in this short animation video, we will learn the basic structure and function of a simple electric motor. Once you understand a simple motor, your idea of ​​those complex motors will be made.
In a simple motor, the two poles of a horse-shoe magnet are placed very close to each other.
The lines of magnetic field are always oriented from the North Pole to the South Pole. These green particles are pointing to the lines of magnetic field.
Each motor has a loop-shaped, twisted, insulated wire. It's called armature. Armature, typically may consists of multifold loops of wire. But, for the sake of simplicity, we have discussed a single wire armature here. The armature is held in such a way, that its two functional arms, the red coloured arm and the blue coloured arm, always remain perpendicular to the magnetic field.
Two semicircular metal sheets are attached to each ends of the armature wire. These semicircular pieces are called commutators.
The armature is held tight by means of an insulated cylinder-shaped bar and two ball bearings, in such a way that the armature can rotate very easily.
Two gas-carbon brushes are placed next to the commutator. Brushes are placed in such a way that when one brush touches a commutator, the other brush will touch the another commutator.
We need a battery. One end of the battery is to be connected to a switch, through a wire. Then, using another wire, the switch, and, a carbon brush, is joined.
Another wire is taken, to connect the other end of the battery to other carbon brush.
A switching starts a steady current. This flow of current starts from positive end of the battery to switch. Switch to carbon brush. Carbon brush to commutator. Commutator to armature. Armature to another commutator. Another commutator to another carbon brush. And at last to the negative end of the battery.
Now let us see the functions of the commutators.
When the rotating armature lays between angles of 280 degree, that is, minus 80 degree and plus 80 degree, the positive end of the battery comes in contact with the red commutator. And the blue commutator is stuck to the negative end of the battery. In this situation, through the red arm near the south pole, an electric current will flow inwards. And, in the blue arm near the North Pole, electric current will flow outwards.
If the armature rotates further, at angles between, 80 degree and 100 degree, the commutators will lose connection with the brushes. And there will be no electric current to flow.
Then, from 100 to 260 degree angle, again the connection will be established. However, the direction through the armature will be changed. Because of this, in the blue arm near the South Pole, current will flow inwards, just as it was in the red arm before. And, in the red arm near the North Pole, the electric current will flow outwards. In the previous instance, when the blue arm stayed there, a similar inward current was observed.
There after, the armature is rotated a bit to lay between 260 and 280 degree with respect to the horizontal line. And in this case, line is disconnected again. So, the current stops flowing.
But, shifting towards 280 degree, that is, minus 80 degrees and upto plus 80 degree, will create a situation like the first one. And the electrical current will flow.
So, we observed that, rotation of commutators bring changes in current flow in the armature. It starts, stops and changes direction of the current, periodically.
Also, note that, whichever arm comes closer to south pole, its current will be inwards. And, the arm near the north pole, will flow current outwards. These are the functions of the commutators.
Parts of motor are roughly classified into two types. The rotor, and the stator. The rotor is the parts of the entire motor that can rotate. For example, armature, commutator, cylindrical bar, etc are rotors. And the parts that remain fixed, are called stators. Stators are, magnets, ball bearings, carbon brushes, wires, et cetera.
When an electric current flows through a magnetic field. That magnetic field exerts a force on the current carrying wire. The direction of the force can be determined by using Fleming's left-hand's rule.
If we arrange our left thumb, index finger, and middle finger, perpendicular to each other. And if the index is pointing towards the magnetic field. And the middle finger is in the direction of current. Then, the force will be in the direction of the thumb.
And this force will push the electric wire to this direction.
How does Fleming's left-hand rule drive electric motors?
If the motor is switched on, the electrical current will start.
Applying Fleming's left-hand rule to the arm near the South Pole, we will see that an upward force is acting on the arm.
Again, by applying Fleming's left hand rule to the arm that is near the North pole, it will be seen that a downward force is acting on the arm.