March 14, 2025

DC motors come in various designs and configurations, each tailored to specific applications requiring different levels of speed control, torque, and efficiency. Among these, a unique type of DC motor features a rotor shaped like a hollow cylinder or cup—this is known as the Coreless DC Motor or Ironless DC Motor. Coreless DC motors are widely used in precision applications such as robotics, aerospace, medical devices, and high-performance industrial equipment due to their lightweight structure, fast response, and high efficiency. This article explores the working principle, advantages, disadvantages, and applications of coreless DC motors while comparing them to conventional brushed and brushless DC motors. Understanding Coreless DC Motors A coreless DC motor (also called an ironless DC motor) is a type of brushed or brushless motor that has a rotor made from a hollow cylindrical or cup-shaped winding. Unlike conventional DC motors that have an iron-cored rotor, coreless motors eliminate the iron core and instead use a self-supporting coil structure. Key Features of Coreless DC Motors: The rotor is hollow and cylindrical, with windings forming a self-supporting structure. The rotor spins around a stationary central magnet. The lack of an iron core reduces inertia, making it extremely responsive to voltage changes. Eliminating the iron core reduces eddy current losses, leading to higher efficiency. Working Principle of Coreless DC Motors The coreless DC motor operates on the same principle as traditional brushed or brushless DC motors, relying on electromagnetic force to generate rotational motion. Working Mechanism: Stator Configuration: The stator consists of permanent magnets arranged in a circular pattern. It provides the magnetic field required for motor operation. Rotor Design: The rotor is hollow or cup-shaped, consisting of a coil winding suspended around the stator. When electric current flows through the coil, it generates a magnetic field. Electromagnetic Interaction: The interaction between the magnetic field of the stator and the current in the rotor windings generates torque. The absence of an iron core prevents cogging and allows for smooth and precise motion. Coreless DC Motor Structure: Below is a simple schematic representation of a coreless DC motor compared to a conventional DC motor. Feature Coreless DC Motor Conventional DC Motor Rotor Design Hollow cylinder/cup Solid iron core Efficiency High Moderate Speed Response Fast Slower Cogging Effect Minimal Present Inertia Low High Heat Dissipation Better Moderate Comparison Between Coreless DC Motors and Traditional DC Motors Coreless motors are often compared with traditional brushed and brushless DC motors. Below is a detailed comparison: Characteristic Coreless DC Motor Brushed DC Motor Brushless DC Motor (BLDC) Rotor Shape Hollow Cylinder/Cup Iron-core cylindrical Permanent magnets Efficiency High (low eddy current loss) Moderate High Response Time Very fast Slow Fast Starting Torque High Moderate High Cogging Effect Very low Present Low Heat Dissipation Efficient Moderate High Maintenance Low Requires brush replacement Very low Noise & Vibration Low High Low Applications Robotics, medical devices Power tools, toys Drones, EVs, precision drives Advantages of Coreless DC Motors Higher Efficiency Eddy current-induced iron losses are absent with coreless motors. Eliminating the iron core reduces energy waste, improving overall motor efficiency. Rapid Response & High Acceleration Due to their low inertia, coreless motors accelerate and decelerate much faster than conventional motors. This makes them ideal for precision control applications. No Cogging Effect Conventional DC motors experience cogging, which is a jerky motion due to magnetic interaction with the iron core. Coreless motors provide smooth motion, crucial for high-precision tasks. Compact & Lightweight The hollow cylindrical rotor reduces overall weight. These motors are ideal for portable or weight-sensitive applications like drones and medical equipment. Reduced Heat Generation Since there is no iron core, heat dissipation is more effective. The motor can run cooler, improving longevity. Disadvantages of Coreless DC Motors While coreless DC motors offer numerous benefits, they also have some limitations: Higher Manufacturing Costs The complex winding structure increases production costs. The cost of materials (especially high-performance magnets) is higher. Lower Torque Density Coreless motors lack an iron core, which means they cannot produce as much torque per unit size. They are not ideal for heavy-load applications. Delicate Rotor Structure The hollow cylindrical winding is fragile compared to iron-core designs. These motors require careful handling to avoid damage. Limited Power Output Due to their compact size and lightweight nature, coreless motors have a lower power output compared to conventional brushed or brushless motors of the same size. Applications of Coreless DC Motors Coreless DC motors are used in applications requiring precision, low inertia, and high-speed response. Industry Application Medical Devices Surgical tools, infusion pumps, prosthetics Aerospace Satellites, UAV actuators, precision motion control Robotics Servo actuators, robotic arms, exoskeletons Industrial Automation High-speed actuators, scanning heads Consumer Electronics Drones, gimbals, high-performance audio devices Conclusion Coreless DC motors, with their hollow cylindrical or cup-shaped rotors, offer a unique set of advantages, including high efficiency, rapid acceleration, smooth motion, and minimal cogging effects. They are perfect for precision applications in the industries of robotics, aerospace, and medicine because of these qualities. However, they also come with higher costs, lower torque density, and delicate construction, making them unsuitable for high-load applications. When selecting a motor, it is essential to consider factors like efficiency, torque, speed, and cost to determine whether a coreless DC motor is the right choice for your application.

Brushless and brushed DC motors essentially perform the same function of converting electric current into rotational motion. However, there are still several differences between the two types of motors. Working principles will be explained before we talk about their differences. Working principle of a brushed DC motor When the motor works, the coil and commutator rotate, the magnet and carbon brush do not rotate, and the alternate change of coil current direction is achieved by the commutator and brush that rotate with the motor. Brushed motors are divided into high speed brushed motors and low speed brushed motors in the electric vehicle industry. A brushed DC motor consists of two main parts: stator and rotor. The stator has magnetic poles (winding type or permanent magnet type) and the rotor has winding, and when energized, the rotor also forms a magnetic field (magnetic poles), and there is an angle between the magnetic poles of the stator and rotor. By changing the position of the brushes, the direction of the stator-rotor pole angle can be changed, thus changing the direction of rotation of the motor. Working principle of a brushless DC Motor An electric brushless BLDC motor takes electronic commutation, where the coil does not move and the magnetic poles rotate. It uses a set of electronic devices to sense the position of the magnetic poles of the permanent magnets through Hall elements. Electronic circuits are used to switch the direction of the current in the coils at the right time to ensure that the correct direction of magnetic force is generated to drive the motor. These circuits are the motor controllers. The controller of a brushless motor can also realize some functions that cannot be realized by a brushed motor, such as adjusting the power switching angle, braking the motor, reversing the motor, locking the motor, and stopping supplying power to the motor by using the brake signal. A brushless DC motor consists of a motor body and driver, which is a typical mechatronic product. Since the brushless DC motor operates in a self-controlled manner, it does not add another starting winding to the rotor like a synchronous motor that starts under heavy load under frequency regulation. Differences between brushed DC motors and brushless DC motors 1. Mode of speed regulation The speed regulation process of brushed DC motors is to adjust the motor power supply voltage level. The adjusted voltage and current are converted through the rectifier and brushes to change the strength of the magnetic field generated by the electrodes, thus changing the speed. This process is called variable voltage speed regulation. The speed control process of a brushless DC motor is to keep the voltage of the motor power supply unchanged, change the control signal of the ESC, and then change the switching rate of high power MOS tube through microprocessor to realize the change of speed. This process is called variable frequency speed regulation. 2. Simple structure and long development history of the brushed DC motor A brushed DC motor is a traditional product with more stable performance, and a brushless DC motor is an upgraded product with better life performance than ba rushed motor. However, the brushless motor has a complicated control circuit, so it has a more strict aging screening requirement for components. Soon after the brushless motor was born, people invented the brushed DC motor. The brushed DC motor has been widely used once it was launched on the market due to its features: simple mechanism; easy to produce, process, maintain, and control; fast response; large starting torque; rated torque is available from zero speed to rated speed. 3. Fast response and large starting torque of the brushed DC motor The brushed DC motor has fast starting response, high starting torque, and smooth variable speed, so vibration can hardly be felt when the speed changes from zero to maximum, and a larger load can be driven when starting. The electric brushless BLDAC motor has large starting resistance (inductive resistance), so the power factor is small, the starting torque is relatively small, there is a humming sound accompanied by strong vibration when starting, and the starting drive load is smaller. 4. The brushed DC motor runs smoothly and has perfect starting and braking effect The speed of the brushed DC motor is regulated by voltage regulation, so it starts and brakes smoothly, and runs smoothly at a constant speed. The brushless DC motor is usually digital frequency conversion control that converts AC into DC, then DC into AC again, and controls speed through frequency change, so the brushless motor cannot run smoothly and vibrates strongly. 5. High precision control of brushed DC motors Brushed DC motors are usually used together with gearboxes and decoders to make the motors have more output power and higher control accuracy, thus allowing the moving parts to stop almost anywhere. All precision machine tools use DC motors to control accuracy. Brushless motors are not smooth in starting and braking, so the moving parts will stop at different positions every time, and must be stopped at the desired position by means of positioning pins or limiters. 6. Brushed DC motors have low cost and are easy to maintain Its simple structure, low production cost, many manufacturers, and mature technologies enable the brushed DC motor to have more widespread applications, such as factories, processing machine tools, and precision instruments, etc. In case of motor failure, you should only replace the carbon brush. Brushless DC motor has immature technology and expensive price, so it has limited applications, such as inverter air conditioners, refrigerators, and other constant speed equipment. 7. The brushless DC motor has low interference According to the brushless motor factory, the most immediate change of a brushless DC motor is the absence of electric sparks generated by the brushed motor operation, which greatly reduces the interference of electric sparks to remote control radio equipment. 8. Low noise and smooth running Without brushes, brushless motors run smoothly with much less friction

The permanent magnet synchronous motor, referred to as PMSM, is actually an AC motor. Its stator runs with a three-phase difference alternating current, while its rotor is a permanent magnet. Do you know its advantages? Most of you may know that it can help save much electricity, and it’s true. But do you know other advantages? If not, Jiangsu Leili Motor Co., Ltd., a well-known micro-motor supplier with the ability of R&D and manufacture, will explain four major advantages of permanent magnet synchronous motor. 1. High efficiency High quality synchronous motor factory finds that the high efficiency does not only mean that the efficiency of permanent magnet synchronous motor at the rated power is higher than that of ordinary three-phase asynchronous frequency-controlled motor, but also refers to that the excitation field of permanent magnet synchronous motor is provided by permanent magnets in the whole speed range. And the rotor requires no excitation current, which increases the motor efficiency. It can save electricity at any speed point compared with an asynchronous frequency-controlled motor, especially at low speed. 2. Low starting current and high starting torque Due to the characteristics of the inverter, the asynchronous variable speed motor has low main magnetic field, low power factor, heavy starting current and small starting torque when starting at low frequency, while Jiangsu Leili permanent magnet synchronous variable speed motor that is made by a well-known China synchronous motor supplier, has constant main magnetic field, active stator current, low starting current and high starting torque. 3. Excellent energy consumption indicators The energy consumption indicators of the motor are the product of motor efficiency and power factor. When an asynchronous variable speed motor works under load, its efficiency, power factor, and energy consumption indicators decrease. However, the efficiency and power factor of Jiangsu Leili permanent magnet synchronous motor approximate a horizontal curve, and its energy consumption indicators are under full load even when the motor is only loaded, which further improves the electricity efficiency and power quality factor. 4. Small size and light weight High-performance permanent magnet materials are used to provide a magnetic field, which greatly enhances the air gap magnetic field and reduces the size and weight of a permanent magnet motor compared with an induction motor. Based on the above advantages, permanent magnet synchronous motor is the best choice for inverter drive motor because it’s more efficient and energy-saving than ordinary three-phase asynchronous inverter motor!

Control Modes of A Servo Motor A motion controller usually uses two types of commands to control servo motors: digital pulse and analogue signal. 1. Digital pulse In this method, which is similar to the control mode of the stepper motor, the motion controller sends “pulse/direction” or “CW/CCW” type pulse command signal to the servo motor driver, which works in the position control mode and completes the position closed loop. This control model is adopted by most Japanese and domestic servo motor products. Pros: easy to debug the servo motor system; not easy to produce interference. Cons: low servo system response. 2. Analog signal In this control mode, the motion control system sends +/-10V analog voltage commands to the servo driver, and receives position feedback signals from position detection elements such as motor encoders or linear encoders. Most of the servo products in Europe and America adopt this mode of operation. Pros: fast servo response. Cons: more sensitive to field interference; slightly complicated debugging. Since you have known the above two control modes of the servo motor, Leili Motor will next describe six steps to debug the servo motor by analog signal. 6 Debugging Steps 1. Parameter initialization Initialize the parameters before wiring. On the controller: Choose the control mode, reset the PID parameter, set off the enable signal when the controller is energized as default, store this condition and ensure that when the controller is energized the next time, this condition is as default. On the servo motor: Set the control mode, set to enable controlling from outside, gear ratio output by encoder signal, set the proportional relation between control signal and motor speed. Generally, it is suggested that the maximum design speed in servo operating should correspond to 9V control voltage. 2. Wire connection Shut down the controller and connect the signal wire between the controller and servo motor. The following wires must be connected: the analogue output wire of the controller, enabling signal wire, and encoder signal wire output by the servo motor. After the wire connection is rechecked and there is nothing wrong, energize the servo motor and the controller (including PC). And then the servo motor should have no motion and can rotate easily by external force. If not, check the setting of enabling signal and wire connection. External force should be used to rotate the servo motor to check if the controller can detect the motor position change. If not, check wire connection and setting of encoder signal. 3. Direction testing For one closed loop control system, if the direction of feedback signal is incorrect, the consequences must be disastrous. Turn on the enable signal of the servo motor attachments via the controller, and the servo motor should rotate at a lower speed, which is called “zero drift”, whose command or parameter will be displayed on the controller. The command or parameter can help you to confirm whether the speed and direction of the servo motor can be controlled by the command or parameter. 4. Zero drift inhabitation During the closed loop control, the existence of zero drift will have certain influence on the control effect and you’d better restrain it. Adjust carefully using the parameters of zero drift inhabitation on the controller or the servo motor to make the motor speed close to zero. 5. Closed-loop control building Turn on the servo enable signal again by the controller and input a smaller ratio gain on the controller. Turn on the enable signal of the controller and servo motor. 6. Closed loop parameter adjustment Adjust the control parameters finely to ensure that the servo motor moves in accordance with the command from the controller.