I. What are the different types of brushed DC motors?
1. Disc-wound DC motor: This structure uses rare earth materials bonded to the cylinder body, so that the enameled wire is wound into a disc winding and placed inside the cylinder body to form a rotor. The phase of the DC motor is adjusted by the commutator, which is fixed to the rear cover. The carbon brushes rub against the rotating commutation surface to adjust the voltage phase.
The carbon brushes of this type of DC motor are constantly wearing down, and their lifespan generally does not exceed 2,000 hours. However, the motor speed is relatively high, so if a speed reduction device is needed, a two-stage gear reduction must be used. In this case, the noise will be relatively loud, and the efficiency loss will also be significant, generally only 68-72%. Low efficiency will lead to increased power consumption.
2. Printed winding DC motor: It uses printed copper foil as windings, which reduces the weight of the DC motor. This type of DC motor has a lifespan of about 3,000 hours, low noise, and an efficiency of 72-76%.
3. Press-wound DC motor: This type of motor is commonly used in electric bicycles. It is made by pressing pre-wound copper wire into a winding, and the efficiency can reach 74~78%.
4. Hub-type geared DC motor: The armature of this type of DC motor is disc-shaped, and the disc-shaped armature is a high-speed rotor. The torque of the DC motor is transmitted to the gear through the shaft. The gear reduces speed and drives the hub housing to rotate. Because the disc-shaped armature of this type of DC motor is very thin, it is very small in size and light in weight. However, it is relatively noisy.
5. Miniature permanent magnet DC motor: This type of DC motor can be said to be the flagship product of Tianfu Micro Motor, and it is also the most common type of DC motor. It uses permanent magnets to generate a magnetic field. Of course, the magnetism of permanent magnets will decay over time. Generally, adding windings to permanent magnets can prevent the loss of magnetism. The stator magnetic field is constant. Miniature permanent magnet DC motors respond very quickly to voltage changes.
6. Shunt-wound DC motor: The excitation coil and armature of a micro DC motor are connected in parallel, and the current in the excitation coil and the current in the armature are independent. Therefore, this type of DC motor has excellent speed control capability and will not experience magnetic loss.
7. Series-wound brushed DC motor: This type of motor cannot control speed, but it has very high torque, making it an ideal choice for high-torque applications.
8. Compound-wound DC motor: This type of DC motor is quite powerful. It is a combination of shunt-wound and series-wound DC motors, capable of generating both series-wound and shunt-wound magnetic fields. It combines the performance of both types of DC motors and features high torque and speed control.
II. Structural Components of a Brushed DC Motor
Most brushed DC motors consist of three main sub-assemblies: the stator, brush holder end caps, and the rotor. The stator comprises a central and cylindrical bipolar permanent magnet, an iron core supporting the bearings, and a steel tube with a closed magnetic circuit. High-quality rare-earth magnets ensure excellent performance within a small package. Sintered bearings and ball bearings are available depending on the load and requirements of the mechanical equipment application.
The brush holder end caps are made of plastic. Depending on the intended use of the motor, the brushes can be of two different types: carbon or multi-wire. Carbon brushes use copper-graphite or silver-graphite and are ideal for incremental motion applications requiring high continuous torque and peak torque. Multi-wire brushes use precious metals, ensuring low start-up voltage and higher efficiency, making them a perfect match for portable battery-powered applications. Motor engineers can design end caps to reduce electromagnetic noise and meet EMC requirements.
The rotor is the core of a brushed DC motor. The coils are wound directly and continuously onto a cylindrical support, which is then removed, eliminating excessive air gaps and inactive coil ends that contribute nothing to torque generation. The self-supporting coils require no iron structure, resulting in low rotational inertia and no cogging effect (the rotor will stop at any position). Unlike other conventional DC coil technologies, the absence of iron eliminates hysteresis, eddy current losses, and magnetic saturation. The motor exhibits perfectly linear speed-torque characteristics, with operating speed dependent solely on the supply voltage and load torque.
