It is composed by 3 pieces instead of two, and the gaps are in circular pastern with 120 o angle. Of course, the 3 coils require now a different construction of the commutator. Finally, if the motor had 2 coils and it was stopped in this position where the commutator is short-circuited, it would be impossible to start it again. And because the coils have 120 o angle between them, the torque provided by the motor is much more smooth and never falls to 0. Also, while in operation, always two or three coils will be active and interact with the permanent magnets. These 3 coils will solve the following 3 problems: First of all, there is no more this position that the commutators are short-circuited, and the motor will provide all the time torque, without the problems from over-current. Instead of 2, there are actually 3 coils that takes part. Nevertheless, the theory of operation is absolutely the same as above. This is a schematic drawing of the coil arrangement of a real motor. Now, its worth to see this video that explains exactly how the DC motor is made: Later on, i will explain how this is avoided. This of course does not happen in real life. During this time, the motor produces no power at all, and also the short-circuit can cause several damages due to over current. Notice also, that there is one moment that the commutator is short-circuited. This is the basic operation of the DC motor. Notice how each part of the commutator changes polarity as it rotates. The left one shows the brushes and the commutator from above, while the right one shows how the electric and magnetic polarity is changed. The following two animations indicates this procedure. The current direction is changed and - due to the rule of the right-hand screw - the poles of the electromagnets will also change. This change of the electric poles, has an affect on the magnetic poles as well. This causes the poles of the power supply provided to the coils to change. But while the shaft of the motor rotates, the commutator rotates as well. Giving thus power to both half-rings, is like giving power to the coils. Each semi-ring has one pole of each coil. The commutator is fixed on the shaft of the motor. The following drawing explains how these parts are: The commutator is a metallic ring, also conductive and able to stand friction, that is divided in two parts. The brushes are pushed (by the spring action of the metallic part) against the commutator. On the other side, they have the pin that the power supply is applied to the motor. On one side, they have a piece of conductive material, usually made of carbon to stand against friction. So, how this is done? The brushes are two metallic pieces that act like springs. The brushes are the way that the motor provides the coils with power, and the geometrical characteristics and position of the brushes (and the commutator of course) will be responsible for changing the magnetic field of the two electromagnets according to the position of the rotor. This kind of DC motor is called "Brushed DC motor". The commutator and the brushes of a DC motor In all other occasions, the magnets are either PULLED from the opposite pole or PUSHED from the same pole and therefore the mechanical power is generated. This is the time that the basic DC motor provides no torque at all. If you watch this animation, you will see that there is one moment that both electromagnets are turned off. I have with RED color the North pole and with BLUE the South pole.
Motr mustafa full#
The following animation indicates how the two electromagnets changes magnetic polarity during a full rotation: Look at the following drawing of the basic DC motor: Thus, when one electromagnet is North, the other is South and vice versa. Moreover, the windings of the two magnets are winded in reversed direction.
Thus, each electromagnet will change its magnetic polarity.
For now, you only need to know that during a full cycle of the rotor, the current that runs through each winding change direction once. The coils are powered from the commutator and the brushes. The basic DC motor has actually two windings and two permanent magnets.
This is called "the right-hand screw rule". If you had the coil inside your hand and your fingers (except the thumb) was showing the direction of the current, then the thumb shows the direction of the magnetic lines as well as the orientation of the North pole. Close your fist and hold your thumb upwards, like thumbs-up. Using your right hand, you can find out the direction of the magnetic lines as well as the North pole orientation.