1. Core Principle: Breaking Away from the Traditional "Iron-Core" Motor Structure
The coreless motor (also known as a hollow cup motor) is often regarded as the "crown jewel" of the micro motor field. Its name originates from its cup-shaped rotor structure, which is completely ironless. If rotary actuators are compared to the "joints" of a robot, then coreless actuators are closer to the "nerve endings" and "finger muscles" of humanoid robots, serving as key drive units for achieving high-precision operations.
At its core, the driving force comes from the coreless motor itself. By eliminating the conventional silicon steel lamination core, the rotor is formed by a self-supporting cup-shaped winding, while the stator adopts high-performance permanent magnets. When energized, the current flowing through the winding interacts with the magnetic field and generates Ampere force, directly driving the rotor to rotate. Through reduction mechanisms or transmission components, this motion is converted into displacement, speed, or torque output, enabling precise control.
From an energy conversion perspective, this structure relies on electromagnetic induction and Lorentz force principles to achieve efficient conversion from electrical energy to mechanical energy. With the complete removal of the iron core, cogging torque and hysteresis losses found in traditional motors are entirely eliminated, resulting in exceptionally smooth operation.
In addition, coreless motors feature extremely low rotational inertia. Their mechanical time constant is typically less than 10 ms, which provides outstanding dynamic response performance, making them particularly suitable for high-speed start-stop and precision control scenarios.
2. Structural Design: The Engineering Art of Miniaturization and High Integration
The structure of a coreless motor essentially represents a reconstruction of traditional motor topology, consisting of three main components:
Rotor (cup-shaped winding): Formed by cross-winding high-performance enameled wire into a self-supporting hollow structure
Stator (permanent magnet): Typically located at the center, providing a stable magnetic field
Magnetic yoke (outer housing): Forms a complete magnetic circuit and enhances flux density
In high-end applications such as humanoid robots, coreless motors are rarely used alone. Instead, they are integrated into high-performance actuator modules, typically structured as:
Coreless motor + micro planetary gearbox + lead screw mechanism + encoder
This integrated configuration enables high-precision conversion from rotary motion to linear motion and is widely used in dexterous hands and micro-actuator systems.
From an engineering decomposition perspective, key components include:
Output shaft: delivers the final mechanical output
Front and rear bearings: ensure stability and precision at high speeds
Coreless winding rotor: the primary driving unit determining dynamic performance
Built-in permanent magnets: provide a high energy-density magnetic field
Magnetic housing: optimizes magnetic circuit closure efficiency
Commutation system (brushed structure): switches current direction
End caps: integrate connections and provide structural protection
3. Material System: High Performance Comes with High Cost
The performance of coreless motors is highly dependent on their material system, which generally leans toward high-end selections.
The magnetic circuit typically uses neodymium iron boron (NdFeB) permanent magnets with high remanence and coercivity to ensure strong and stable magnetic field output. The windings use high-purity enameled copper wire, and some high-end products even employ silver-plated copper wire to reduce resistive losses and improve conductivity.
In brushed structures, brush materials are often made from gold, silver, or platinum alloys to achieve low contact resistance and long service life. The magnetic housing uses high-permeability soft magnetic materials to ensure efficient magnetic flux closure.
Structurally, housings are commonly made of aluminum or magnesium alloys to achieve lightweight design while maintaining good heat dissipation. Bearings typically use high-precision bearing steel or ceramic materials to enhance wear resistance and operational stability. The insulation system relies on high-temperature polyimide materials to ensure long-term reliability.
4. Manufacturing Process: Winding Technology as the Core Barrier
The manufacturing difficulty of coreless motors is significantly higher than that of conventional motors, with winding technology being the most critical technical barrier.
Current mainstream processes include skew winding and straight winding methods, with skew winding offering superior consistency and performance. Since the winding is entirely self-supporting, even minor deviations can directly impact motor performance.
Key process controls include:
Dynamic balancing: highly sensitive at high speeds (up to tens of thousands of rpm)
Forming and resin impregnation: ensure structural stability of the winding during high-speed operation
Precision joining: laser welding is used to connect windings with commutators or terminals
Overall, the manufacturing of coreless motors is essentially a combination of micron-level precision manufacturing and advanced process control capabilities.
5. Key Challenges: Thermal Management and Consistency Bottlenecks
Despite their superior performance, coreless motors still face significant engineering challenges.
The first is heat dissipation. Due to the ironless and hollow rotor structure, thermal capacity is limited. Under high current density conditions, heat accumulation can occur, affecting insulation life or even leading to failure.
The second is manufacturing consistency. The cup-shaped winding has extremely thin walls, making it challenging to maintain cylindrical accuracy, concentricity, and dynamic balance during automated production.
Additionally, as products continue to move toward extreme miniaturization, integrating encoders and drive electronics within limited space places higher demands on microelectronic packaging and system integration capabilities.
6. Market Landscape: European Leadership with Rapid Domestic Catch-Up
Globally, the coreless motor market has long been dominated by European manufacturers:
Maxon (Switzerland): a benchmark in high-end applications, widely used in aerospace and scientific research
Faulhaber (Germany): pioneer of skew winding technology
Portescap (Europe/US): highly competitive in medical equipment applications
In recent years, driven by the rapid growth of humanoid robotics and precision automation, Chinese manufacturers have risen quickly. Companies such as MOONS', Dingzhi Technology, and Topband have developed strong advantages in shipment scale and cost control.
7. Development Trends: Brushless, Integrated, and Intelligent Evolution
Future development of coreless motors will focus on the following directions:
First, extreme miniaturization. With the growth of surgical robots and minimally invasive devices, demand for drive systems with diameters of 6 mm or even smaller continues to rise.
Second, brushless design and integration. Brushless configurations improve lifespan, while integrating encoders and drivers into the motor forms "servo coreless modules," significantly enhancing system integration.
Third, cost optimization and domestic substitution. As winding equipment and processes mature, coreless motors are expected to gradually replace traditional iron-core micro motors.
Fourth, intelligence and networking. Support for industrial communication protocols such as EtherCAT and Profinet will enable remote control and system-level coordination.
Fifth, material and structural innovation. Technologies such as carbon fiber composite rotors and high-temperature permanent magnets will further improve power density and environmental adaptability.
Sixth, industry-specific customization. For high-end fields such as medical devices, semiconductors, and humanoid robotics, dedicated structural designs and control algorithm optimization will become key differentiators.
