In the development of modern technology, the coreless motor has become an innovative technology in the field of micro motors due to its unique design. Traditional motors rely on iron cores for magnetic conduction, while the coreless motor, through its coreless design, significantly improves energy conservation, response speed, and control precision. Whether in micro robots or aerospace, the coreless motor, with its small size and powerful performance, has redefined the boundaries of precision drive technology.
Definition and Structure
Definition
The Coreless Motor, whose full name is DC Permanent Magnet Servo Coreless Motor, is a type of DC motor with a coreless rotor. Its coil is in the shape of a cup, hence the name.
Structure
Brushed Coreless Motor: The rotor is composed of a coreless cup winding (without an iron core), and the permanent magnets are located on the stator side. Mechanical commutation is achieved through brushes and a commutator.
Brushless Coreless Motor: The stator is a coreless cup winding (without an iron core), and the permanent magnets are located on the rotor side. Contactless commutation is achieved through an electronic controller.
Explanation
Traditional iron-core motors require silicon steel sheets for magnetic conduction in the stator/rotor, while coreless motors use epoxy resin or special plastics to support the windings, completely eliminating iron loss.
Material Supplement
The windings use high-purity oxygen-free copper wires or aluminum wires (in lightweight scenarios). The proportion of copper wires exceeds 90% to reduce resistance loss.
Working Principle
The working principle of a coreless motor is based on the interaction between electromagnetic induction and permanent magnets. When an electric current passes through the windings of the motor, it interacts with the permanent magnets, thus driving the motor to rotate. Since the coreless rotor made of enameled wires lacks the support of an iron core, in order to ensure its sufficient strength for self-supporting function and to ensure that the magnetic field can be evenly distributed inside the rotor, special methods need to be adopted for the winding and arrangement of the windings.
Supplementary Commutation Mechanism
Brushed Type: The brushes and the commutator periodically switch the current direction of the windings to generate continuous torque.
Brushless Type: Hall sensors or back electromotive force detect the position of the rotor, and the controller switches the current direction in real time.
Effect
Due to the absence of iron-core hysteresis loss, the torque output has a highly linear relationship with the current, which is beneficial for precise control.
Advantages and Characteristics
Efficiency Data Calibration
The typical efficiency range is 75% to 90% (the efficiency of iron-core motors is usually 30% to 60%). The peak efficiency is related to the power, and the efficiency at the microwatt level may be lower than 70%.
Core Advantages
Low Inertia: The moment of inertia is only 1/10 to 1/5 of that of an iron-core motor, achieving millisecond-level start and stop response (mechanical time constant < 10ms).
Zero Cogging Effect: The absence of an iron core avoids periodic changes in magnetic resistance, and the torque ripple is < 1%. It is suitable for ultra-smooth movement.
Newly Added Disadvantage Explanation
The torque density is relatively low (about 50% of that of an iron-core motor), and it is not suitable for high-load scenarios.
The manufacturing cost is high (the windings require precise winding equipment, and the scrap rate is relatively high).
Expansion of Application Areas
Due to its unique advantages, the coreless motor has been widely used in multiple fields, including high-tech industries such as military and medical fields, as well as in various types of aircraft. With the growth of industrial demand, the coreless motor also plays an irreplaceable role in industrial robots, bionic prosthetics, recording and detection equipment, and other aspects. In addition, it is also widely used in consumer electronic products such as the autofocus systems of single-lens reflex cameras and portable instruments.
Strengthening of Precautions
Refinement of Thermal Management
For continuous operation, forced heat dissipation is required (such as using micro fans/thermal conductive silicone). The instantaneous power needs to be limited within the thermal saturation threshold (usually < 30 seconds of full-load operation).
Newly Added Design Constraints
Avoid axial impact (the mechanical strength of the coreless cup structure is relatively low).
A low-inductance drive circuit needs to be matched (the inductance of the windings is only at the μH level, and traditional PWM is likely to cause excessive current ripple).
Technological Frontiers
Innovation Directions
Integrated windings through 3D printing, superconducting coreless motors (in the laboratory stage).
Industry Standards
IEC 60034-30 standardizes the efficiency classification of micro coreless motors.
The technology of coreless motors is constantly being upgraded, representing the trend of the industry towards miniaturization and intelligence. Although there are still challenges at present, such as torque density and manufacturing cost, with the application of 3D printing windings, superconducting materials, and intelligent drive algorithms, coreless motors show greater potential. It has application prospects in micro implanted medical devices, the drive of soft robots, and the ultra-lightweight actuators of space probes. In the future, this technology may become the key power source in various fields, promoting the development of precision drive technology and facilitating humanity’s journey to explore both the microscopic and macroscopic worlds.