There are also brushed and brushless versions of the coreless motor. There is no essential difference between the hollow cup motor and the traditional brushed DC motor and brushless DC motor in terms of functions, but it can be understood as an upgraded version. The reason is that the hollow cup motor has stronger performance under the same volume. In other words, the hollow cup motor can be made smaller. At the same time, the hollow cup motor will be better in sensitivity and efficiency. This is why the main application scenarios of hollow cup motors are in aircraft model, military industry and medical treatment.
1. Principle of hollow cup motor
The hollow cup motor breaks through the rotor structure of the traditional motor in structure, and adopts an ironless rotor, also called a hollow cup rotor.
This rotor structure completely eliminates the power loss caused by the eddy current formed by the iron core, and at the same time its weight and moment of inertia are greatly reduced, thereby reducing the mechanical energy loss of the rotor itself. Therefore, the hollow cup motor belongs to the DC, permanent magnet, servo micro-motor.
2. Advantages and disadvantages of hollow cup motors
Advantages of hollow cup motor:
1. High power density
Power density is the ratio of output power to weight or volume. The copper coil type motor is small in size and good in performance. Compared with the traditional coil, the induction coil of the copper plate coil method is lighter.
There is no need for winding and slotted silicon steel sheets, which eliminates the eddy current and hysteresis losses generated by them; the eddy current loss of the copper coil method is small and easy to control, which improves the efficiency of the motor and ensures higher output torque and output power.
2. High efficiency
The high efficiency of the motor lies in: the copper coil method has no eddy current and hysteresis losses caused by winding and slotted silicon steel sheets; in addition, the resistance is small, which reduces the copper loss ( I^2*R ).
3. No torque lag
The copper plate coil method has no slotted silicon steel sheet, no hysteresis loss, and no cogging effect, which reduces the speed and torque fluctuations.
4. No cogging
The copper plate coil method has no slotted silicon steel sheet, which eliminates the cogging effect of the interaction between the slot and the magnet. The coil is a structure without an iron core, and all the steel parts either rotate together (for example, a brushless motor), or all stand still. (eg brushed motors), cogging and torque hysteresis are noticeably absent.
5. Low starting torque
No hysteresis loss, no cogging, low starting torque. At start-up, usually the bearing load is the only obstacle. In this way, the starting wind speed of the wind turbine can be very low.
6. There is no radial force between the rotor and the stator
Since there is no static silicon steel sheet, there is no radial magnetic force between the rotor and the stator. This is especially important in critical applications. Because the radial force between the rotor and the stator will cause the rotor to become unstable. Reducing radial forces will improve rotor stability.
7. Smooth speed curve and low noise
There are no grooved silicon steel sheets, reducing torque and voltage harmonics. At the same time, since there is no AC field in the motor, there is no AC noise. Only noise from bearings and airflow and vibration from non-sinusoidal currents.
8. High-speed brushless coil
In high-speed operation, it is necessary to have a small inductance value. A small inductance value results in a low start-up voltage. By increasing the number of poles and reducing the thickness of the case, the smaller inductance value helps reduce the weight of the motor. At the same time, the power density is increased.
9. Quick response brushed coil
The brushed motor of the copper plate coil type has a low induction value, and the current responds quickly to the fluctuation of the voltage. The moment of inertia of the rotor is small, and the response speed of torque and current is equivalent. Therefore, the rotor acceleration is twice that of a conventional motor.
10. High peak torque
The ratio of peak torque to continuous torque is large because the torque constant is constant when the current rises to the peak value. The linear relationship between current and torque allows the motor to generate large peak torques. In traditional motors, when the motor reaches saturation, no matter how much current is added, the torque of the motor will not increase.
Disadvantages of hollow cup motor:
When the DC motor is in a static state, if one phase of the winding is cut off or one phase of the power supply is cut off and the power is turned on, the two magnetic fields generated by the windings are equal in size and opposite in direction. They cancel each other out, and the zero starting torque motor cannot start, which is the disadvantage of the hollow cup geared motor.
The disadvantage of the hollow cup gear motor is that it is a very dangerous fault. First, we need to check whether the DC motor is faulty, check whether there is a circuit breaker in the power circuit, whether there is a fuse, and then check whether there is a current interruption in each phase of the three-phase winding.
