The working principle of dc motor is based on the interaction between the magnetic field of rotating armature and that of fixed stator. When the North Pole of the armature is attracted to the South Pole of the stator (and vice versa), a force is created on the armature, causing it to rotate. Commutator is the process of switching the magnetic field in the armature winding to produce a constant torque in one direction, while the commutator is the device connected to the armature to achieve this switching of current.
The lever arm of the torque generated on the armature varies with the coil Angle (cos). Thus, no torque is generated when the coil is perpendicular (perpendicular) to the stator's magnetic field. This is why dc motors have multiple coils. Thus, even if a coil is perpendicular to the magnetic field, the armature mechanism will continue to bear the force.
The basic purpose of reversing is to ensure that the torque acting on the armature is always in the same direction. The voltage generated in the armature is essentially ac, and the commutator converts it to direct current. In short, the commutator turns on and off the coil to control which direction the electromagnetic field points. The current should always be "lost" on one side of the coil and "flowing" on the other. This ensures that torque is always generated in the same direction. Otherwise, the coil will rotate 180 degrees in one direction and then switch directions.
The commutator itself is an open ring, usually made of copper, each part of which is connected to both ends of the armature coil. If the armature has multiple coils, the commutator will similarly have multiple segments - one on each end of each coil. The spring brush is located on each side of the commutator and in contact with the commutator as the commutator rotates, providing a voltage to the commutator plate and the corresponding armature coil.
When the brush passes through a gap in the commutator, the supplied charge switches the commutator plate, thus switching the polarity of the armature coil. This switch of polarity in the coil keeps the armature rotating in one direction. The voltage amplitude between the brushes fluctuates between zero and maximum, but remains the same polarity all the time.
As mentioned earlier, the commutator is constructed in segments that are insulated from each other. When a brush is passed from one piece to another, there is a moment when the brush touches both pieces simultaneously. This is called the neutral surface, where the induced voltage is zero. Otherwise, the brush will short-circuit both ends of the coil and cause a spark due to high voltage.
The term "brush" was coined in the early days of dc motors made of copper wire. These devices require frequent replacement and damage the commutator ring. Modern DC motors usually use "brushes" made of carbon, which wear out more slowly and do less damage to the commutator.
It is important to note that the above discussion relates to traditional brushless DC motors, which mechanically reverse direction. A brushless DC motor also requires reversing, but for brushless designs the reversing is done electronically via an encoder or hall effect sensor, which monitors the position of the rotor to determine when and how the coil is energized.