01 What is a Frameless Torque Motor?
A frameless torque motor is a highly efficient and energy-saving type of electric motor. Its most distinctive feature is the removal of components found in traditional motors, such as the shaft, bearings, housing, and end caps, retaining only the two core components: the rotor and the stator.
This structural design allows the motor to be seamlessly integrated into the machine structure, utilizing the machine's own bearings to support the rotor, significantly enhancing system integration and compactness.
Frameless torque motors are measured by their output torque, unlike the output power rating commonly used for servo motors. This enables them to deliver high torque at low speeds, perfectly adapting to the motion requirements of robotic joints.
02 Unveiling the Working Principle
The working principle of a frameless torque motor is based on the law of electromagnetic induction. When the motor's driver applies power, three-phase electricity excites a rotating electromagnetic field in the stator windings. This electromagnetic field interacts with the permanent magnets in the rotor, generating torque that causes the rotor to rotate.
The entire process is controlled by the driver, which shapes the electromagnetic field via the U/V/W three-phase power. The rotor with permanent magnets rotates under the influence of this field. Frameless torque motors can use Hall elements for feedback signals or utilize signals from an added encoder.
The driver compares the feedback value with the target value to adjust the rotation angle of the rotor, achieving precise servo control.
03 Differences from Traditional Motors
Compared to traditional framed motors, frameless torque motors offer multiple advantages: They improve machine performance, enabling direct coupling (no backlash) and higher system bandwidth; the structure is more compact, resulting in a smaller machine footprint and higher torque per unit volume.
They also possess high stiffness and can serve as a direct drive power source, driving the load directly without the need for belts and pulleys, lead screws, or gearboxes; operation is quiet, as direct integration into the machine's structure alters the transmission method, leading to significant noise reduction.
Furthermore, they reduce maintenance needs due to fewer mechanical parts and no components prone to wear or requiring regular upkeep.
04 The Core Power of Humanoid Robots
In the era of rapid development in artificial intelligence and robotics technology, humanoid robots are deeply penetrating numerous fields such as industry, services, and healthcare 4. Frameless torque motors have become the mainstream driving components in the joints of humanoid robots.
Tesla's Optimus utilizes frameless torque motors as the power source in all 28 of its joints. These joints include 14 rotary joints and 14 linear joints, with each actuator containing a frameless torque motor.
The rotary joints consist of a frameless torque motor, harmonic reducer, torque sensor, position sensor, encoder, etc., distributed across the shoulders (6), wrists (2), hips (4), and torso (2).
The linear joints consist of a frameless torque motor, planetary roller screw, torque sensor, position sensor, etc., distributed across the elbows (2), wrists (4), hips (2), knees (2), and ankles (4).
05 Three Key Roles
Frameless torque motors play three key roles in the flexibility of humanoid robot joints:
Providing High Torque Output: During task execution, robot joints often need to output high torque at low speeds to overcome lever effects and load inertia. Frameless torque motors can generate high torque output even at relatively low speeds.
Enabling Precise Control: They are tightly integrated with components like high-precision encoders and torque sensors to form a high-performance integrated drive unit. The controller can read joint position information from the encoder feedback in real-time and, combined with torque data from the torque sensor, fine-tune the motor's torque and speed.
Improving Joint Response Speed: With extremely low rotor inertia, the motor can respond to control commands at millisecond speeds. Even if the external environment changes or actions are suddenly altered, the robot joints can quickly adjust their posture, ensuring the robot's stability and safety.
06 Broad Application Fields
The application fields of frameless torque motors are very extensive. They are primarily used in robot joints and arms to provide high torque and high-precision control.
In medical equipment, frameless torque motors are matched with surgical robots, medical imaging systems, etc., to achieve highly precise and smooth motion control. They can be used in medical fields such as medical imaging and surgical robots, performing operations with high precision in areas far smaller than what the human hand can handle.
In the field of high-end CNC machine tools, frameless torque motors can be used in high-precision five-axis machines to improve accuracy and repeatability in processes like forming, grinding, and drilling.
Furthermore, they are also used in applications within the aerospace field, such as radars, inertial navigation systems, and turntables.
07 Vast Market Prospects
The market prospects for frameless torque motors are very broad. The global frameless torque motor market size was 4.5 billion CNY in 2022 and is expected to reach 22.4 billion CNY by 2030, with the humanoid robot market segment accounting for 16.3 billion CNY.
According to Valuates Reports data, the global frameless torque motor market size was USD 670 million in 2022 and is expected to grow to USD 1.17 billion by 2029, representing a compound annual growth rate (CAGR) of 8%. It is anticipated that with the rapid growth of collaborative robots and intelligent demand, the frameless torque motor market will maintain high-speed development.
08 Technical Challenges and Future Trends
Although frameless torque motors show great potential in the field of humanoid robots, there are still some challenges in their technology and production.
From a technical perspective, further increasing the torque density of frameless torque motors while reducing their temperature rise and narrowing the gap between rated speed and maximum speed places high demands on electromagnetic design.
Cost-wise, as a critical component of humanoid robots, the cost remains high due to the currently low domestic production rate of its core components within China.
Future development trends include: the continuous improvement of performance indicators for frameless torque motors to meet the higher requirements for joint flexibility and power in humanoid robots.
Simultaneously, optimizing production processes and reducing production costs will become important goals for future development.
As humanoid robots move from "lab demonstrations" to "initial commercialization in specific scenarios," frameless torque motors, as their core power source, are entering a golden period of development.
2025 is seen as a critical year for the mass production of humanoid robots. Frameless torque motors account for 16% of the value of a humanoid robot. Current prices range from a few hundred CNY to over a thousand CNY, depending on power and size.
In the future, with scale expansion and process innovation, their prices are expected to decrease significantly, further promoting the adoption of humanoid robots.
This compact yet powerful technology, the frameless torque motor, is becoming the unsung hero behind the flexible joints of humanoid robots, quietly supporting the rapid development of the robotics industry.
