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Coreless motor and permanent magnet

Everyone may have heard of coreless motors. What is a coreless motor? What is the difference between coreless motor and ordinary motors? What kinds of permanent magnets are used in coreless motors? Today yueci will take everyone to learn about the coreless motor and its permanent magnet.

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With the continuous development of science and technology, motor technology is constantly innovating. Especially now that the industrial field continuously puts forward higher expectations and requirements for the servo characteristics of the motor, the hollow-cup motor has also emerged. Coreless motors are DC permanent magnet servo and control motors, and they can also be classified as micro motors. The hollow-cup motor breaks through the rotor structure of the traditional motor in structure, and uses an iron-core rotor, also called a hollow-cup rotor. This novel rotor structure completely eliminates the power loss caused by the formation of eddy currents in the iron core.
At the same time, its weight and moment of inertia are greatly reduced, thereby reducing the mechanical energy loss of the rotor itself. Due to the structural change of the rotor, the operating characteristics of the motor have been greatly improved. It not only has outstanding energy-saving characteristics, but more importantly, it has the control and drag characteristics that cannot be achieved by iron core motors. The hollow cup motor has outstanding energy saving characteristics, sensitive and convenient control characteristics and stable operation characteristics, and its technological advancement is very obvious. As a high-efficiency energy conversion device, it represents the development direction of electric motors in many fields.

The structure and principle of coreless motor

The following figure shows the structure diagram of a general coreless motor. The coreless motor is a DC permanent magnet motor. The main difference from ordinary brushed and brushless DC motors is that it uses a coreless rotor, also called a hollow cup rotor.
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The rotor is directly wound by wires, and there is no other structure to support these windings. The winding itself is made into a cup shape, which constitutes the structure of the rotor (as shown below). Due to the structural change of the rotor, the operating characteristics of the motor have been greatly improved. It not only has outstanding energy-saving characteristics, but more importantly, it has the control and drag characteristics that cannot be achieved by iron core motors.

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Coreless motors are divided into two types: brushed and brushless. Brushless coreless motors have no iron core in the rotor, and brushless coreless motors have no iron core in the stator. Common coreless motors in the market have diameters Φ4, Φ6, Φ7, Φ8, Φ10, Φ12, Φ15, etc.

The main characteristics of coreless motors

Coreless motors mainly have the following characteristics:

  • 1. Energy-saving features: the energy conversion efficiency is very high, the maximum efficiency is generally above 70%, and some products can reach above 90% (the iron core motor is generally 70%).
  • 2. Control characteristics: starting and braking are fast, the response is extremely fast, the mechanical time constant is less than 28 milliseconds, and some products can reach within 10 milliseconds (the iron core motor is generally more than 100 milliseconds); under high-speed operation in the recommended operating area , You can easily adjust the speed sensitively.
  • 3. Drag characteristics: the stability of operation is very reliable, and the fluctuation of the speed is very small. As a miniature motor, the fluctuation of the speed can be easily controlled within 2%.

In addition, the energy density of the coreless motor is greatly improved, and its weight and volume are reduced by 1/3-1/2 compared with the iron core motor of the same power.

The advantages and applications of coreless motors

Coreless motor has a series of advantages such as high power density, high efficiency, no torque lag, no cogging effect, low starting torque, no radial force between the rotor and stator, smooth speed curve, low noise and good heat dissipation effect. .
Because the hollow cup motor overcomes the insurmountable technical obstacles of the iron core motor, and its outstanding features are concentrated on the main performance of the motor, it has a broad application field. Especially with the rapid development of industrial technology, higher expectations and requirements are continuously put forward for the servo characteristics of the motor, so that the hollow cup motor has an irreplaceable position in many applications.
The application of hollow-cup motors has developed rapidly after entering the large industrial and civilian fields from the military and high-tech fields for more than a decade, especially in industrially developed countries, where most industries and many products have been involved.

  • 1. A servo system that needs quick response. Such as the rapid adjustment of the flying direction of the missile, the follow-up control of the high-magnification optical drive, the fast automatic focusing, the highly sensitive recording and testing equipment, the industrial robot, the bionic prosthesis, etc. The hollow cup motor can well meet its technical requirements.
  • 2. Products that require stable and long-lasting drive components. Such as all kinds of portable instruments, personal equipment, instruments and equipment for field operations, electric vehicles, etc., the same set of power supplies, the power supply time can be more than doubled.
  • 3. Various aircrafts, including aviation, aerospace, model airplanes, etc. Utilizing the advantages of hollow-cup motors of light weight, small size and low energy consumption, the weight of the aircraft can be reduced to the greatest extent.
  • 4. Various civil electrical appliances and industrial products. The hollow cup motor is used as the actuator, which can improve the product quality and superior performance.
  • 5. Using its advantages of high energy conversion efficiency, it can also be used as a generator; using its linear running characteristics, it can also be used as a tachogenerator; with a reducer, it can also be used as a torque motor.
  • With the progress of industrial technology, the strict technical conditions of various electromechanical equipment put forward higher and higher technical requirements for servo motors. At the same time, the application range of coreless motors has completely broken away from the limitations of high-end products, and is rapidly expanding in general The range of applications on low-end products such as civilian use to widely improve product quality. According to relevant statistics, hollow-cup motors have been maturely applied to more than 100 civilian products in industrially developed countries.

Coreless motor magnet

Sintered NdFeB permanent magnets are generally used in coreless motors. They have the characteristics of high remanence, high coercivity, and high energy product. They are the most suitable permanent magnet materials on the market that meet the requirements of coreless motors. Under the same size of motor and winding data, the strength of the magnetic steel directly affects the speed of the motor. Common neodymium iron boron magnets suitable for coreless motors are ring-shaped, with performance such as N40, N45, etc., and the temperature resistance is about 100°C.
Source: China Permanent Magnet Manufacturer –



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