1、What is DC Motor?

A DC motor is any type of rotating motor that converts direct current energy into mechanical energy. The most common type relies on the force generated by a magnetic field. Almost all types of DC motors have some internal mechanism, either electromechanical or electronic, to periodically change the direction of the current in parts of the motor. Many applications that require control of speed or torque use DC motors because the control system of DC motors is easier to implement than AC motors

2、Different Parts of DC motor

Rotor （Rotating part：armature winding）

The rotor of a DC motor is a cylinder composed of mutually insulated magnetic sheets. The rotor is perpendicular to the axis of the cylinder and is a rotating part that rotates on its axis and is separated from the field coil by an air gap.

Stator （Static part：Permanent magnet）

The stator of a DC motor is a non-moving part on which a magnetic field is wound to produce a magnetic field. This electromagnet has a cylindrical cavity between its two poles.

Commutator

The commutator of a DC motor is a cylindrical structure consisting of copper segments stacked on top of each other but insulated from each other with mica. The main function of the commutator is to supply current to the armature winding.

Brushes

The brushes of a DC motor are made of graphite and carbon structures. These brushes conduct the current from the external circuit to the rotating commutator.

3、HOW A DC MOTOR WORKS

When a DC supply is connected the armature winding, an electric current sets up in the armature conductors which experience a force due to the magnetic field. One side of armature conductor under North-pole carries current in one direction whereas the other side under South-pole carries current in the opposite direction and hence force on each side will act opposite to each other. Therefore, if one side of the armature moves in upward direction, the other side will move in the downward direction which results in a driving torque rotating the armature in clockwise direction. When the conductor moves from one side of a brush to the other, the current in that conductor is reversed. At the same time, it comes under the influence of the next pole which is of opposite polarity. Consequently, the direction of the force on the conductor remains unchanged. It should be noted that the commutator reverses the current in each conductor as it passes from one pole to another which helps to develop a continuous and unidirectional torque in order to keep rotating the rotor. Otherwise, the direction of the force would have reversed every time when the conductor comes under the influence of opposite magnetic pole.

When the armature of a DC motor rotates, the conductors also cut the magnetic flux lines and hence an emf induces in the armature winding according to the Faraday’s law of electromagnetic induction. The direction of this induced emf is such that it opposes the armature current and hence called back-emf.

4、Two types of DC motors (DC motors)

• （BLDC）Brushless Direct Motors

• Brushed Direct Current (DC) Motors

Comparison of Brushed DC motor and brushless DC （BLDC） motor

1、What is Core-less Motor (Hollow-Shaft) Motor ?

无芯直流电动机，是直流电动机的一种特殊形式。这些电机用于需要小型电机和快速加速的地方。与普通直流电机相比, 这种类型的电机有一个没有任何铁芯的转子，因此被称为无芯。

下图是空心杯直流有刷电机示意图：

Instead of the heavy iron core, in a core-less DC electric motor you’ll find:

• Housing which guides the magnetic field and acts as a magnetic return path.

• A hollow cylinder, also called a basket, with copper coils wound in a self-supporting honeycomb or skewed pattern.

• The permanent magnet fits inside the basket and therefore sits inside the rotor. An air gap separates the magnet and the housing. The magnet produces the magnetic field.

• Brushes and commutators are usually made of precious metals.

• Bearings that support the rotor so it can rotate around the magnet.

2、Advantages and Disadvantages of a Coreless Motor

Advantage：

• The high efficiency is paired with a compact design that is lighter compared to many other motors on the market. Core-less motors typically have less current loss, making them more efficient overall than the types with iron cores.

• Low draw current: It does not draw as much current as some other motors, so when powered by a battery, the battery will last longer.

• Because the Core-less motor has a lighter rotor, it does not cause as much inertia as other motors, so acceleration and deceleration can be handled quickly.

• No cogging，core-less motors do not create a misalignment of the rotor and stator magnetic circuit. This means that the motor can run very smoothly.

• Safe and durable, since there is no iron core, there is less chance of arcing and sparking between the brushes and commutator as often happens in cored motors, there will not be much electromagnetic interference (EMI), and the hollow cup motor will have a longer service life.

• Easy to control, users can easily control the motor and manage its speed.

• Low noise level and quiet operation.
  

Disadvantage：

In a core-less electric motor there’s no heat sink for the winding, so to cool the machine down, your DC motor’s housing must have good thermal conductivity. This is especially important if your motor will often speed up and slow down in rapid succession.

In the case of overheating, the motor will break down because the windings’ bonding adhesive will lose its efficacy. Thus, core-less DC motors won’t be able to handle an overloaded system as well as a cored motor.

3、The Many Applications of Core-less Motors

• The healthcare industry

• Robotics

• Automation & Actuators

• Laboratories

• Office equipment