How a DC Motor works

Next lesson we will cover how to build a DC motor.

Learn.

Below is a diagram of the components of a DC motor.

Electric DC Motors - Direct Current Motor Basics,Types and Application
Source: El Pro Cus

Components of a DC Motor belong either to the rotar, which are the rotating components in a DC motor, or the stator, which are the stationary components of a DC motor. Additionally, there are the components which connect the stator and rotor together – these are the contacts.

Rotor:

Armature

  • The armature is typical soft laminated sheets of iron, to reduce magnetic flux leakage by reducing the size of the eddy currents, the copper coil’s are wound around these creating the electromagnet which interacts with the magnets in the stator to create torque.
DC Shunt Motors: Where Are They Used?
Diagram of armature from Motion Control Chips

Axle

  • The axis which the rotar components are fixed to which passes through the center creating an axis of rotation for the motor and allows the torque to be out putted for use.

Rotor coils

  • These are the current carrying conductors which are wrapped around the armature. These coils act as miniature electromagnets which flip polarity when the direction of current is turned up. The number of n in a motor is referring to the number of these. Having multiple makes the torque output more constant and increases the torque output and efficiency as they keep the angle at a maximum. We will cover this formula later, emf = nBA cos (theta)

Stator:

A pair of curved permanent magnets

  • Two permanent magnets on opposite sides of the motor so the North of one is facing the South of the other. The magnetic field lines cut the rotor. To maximize efficiency, these sometimes wrap around the armature creating a uniform radial magnetic field, therefore, the plane of the coil is continually perpendicular to the field maximizing emf. This repels and attracts the rotor, since the magnets are fixed the rotor will move relative to the magnetic coils.

Stator coils (pair of electromagnet coils)  [ This is an alternative to permanent magnets]

  • These can provide greater magnetic field strength then same size permanent magnet. Same idea as permanent magnets, however, a electromagnet is used instead of a permanent magnet hence it can be switched off.

Contacts:

Brushes

  • The brushes link the electrical current from the stator to the rotor, by not being fixed to the rotor, the wires are not tangled whilst the motor is rotating. Typically mounted on opposite sides of the commutator, the spring loaded brushes make close contact without creating to much friction. Therefore, the commutator has an external power supply.

Split ring commutator

  • The split ring commutator reverses the current every half rotation of a coil, hence the motor can rotate a full 360 degrees. If there are multiple armatures there will need to be multiple commutators. They reverse the current by being connected on opposite sides.

Some of the limitations of a brushed DC motor include

DC motors, however, do have their limitations. These include the brushes wearing out due to the high friction which requires the motor to be less efficient and higher maintenance. Addotionally, the commutator also wears out as well as sparks which has the potential to cause fires. AC motors overcome these limitations, we will cover these in a later lesson.

Master.

Question 1. [3 marks]

Explain what will happen if a student forgets to include a split ring commutator in a DC motor.

Question 2. [6 marks]

Evaluate the effectiveness of the DC motor design.

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