How to select robot drive components? Understand one article!
Starting from 2024, multiple robotics companies around the world will launch new hardware products for humanoid robots. The application of AI big models and reinforcement learning technology will help humanoid robots solve the problem of motion algorithms and stability issues. With the addition of autonomous AI capabilities, there is a chance to truly achieve "embodied intelligence".

So for humanoid robots that have not yet achieved "embodied intelligence" at this stage, the components that drive the robot's movement are the most crucial. Below, we will briefly analyze the mainstream robot drive components on the market and understand the differences in the selection of different components.

According to the current existing products, the actuators that drive the movement of robots can be mainly divided into hydraulic and electric motors based on the different sources of power. In the early stages of robot research, there were also some pneumatic driven robots, which were widely used in industrial automation. However, for humanoid robots, it was difficult to achieve precise control and low driving efficiency, so they were gradually phased out.

And motors can achieve precise position, speed, and torque control, which is crucial for mimicking complex human joint movements and maintaining dynamic balance. At the same time, the energy conversion efficiency of the motor is extremely high, and the power density of some motors themselves is also relatively high, which can be easily applied in the smaller structural space of humanoid robots. In terms of cost, the cost of mass production of motors is lower compared to other driving methods. Overall, motors are more in line with the comprehensive needs of humanoid robots for dynamic performance, maintainability, and commercial feasibility, making them the mainstream driving core of current humanoid robots.
However, direct drive motors are also difficult to meet the torque requirements of various joints in robots. Therefore, in practical robot applications, in addition to motors, driving actuators also require components such as reducers, screws, encoders, and force sensors.

At present, the commonly used motors on humanoid robots can be divided into several types: torque motors, hollow cup motors, frameless torque motors, and permanent magnet synchronous motors.
 

Torque motor: It adopts an axial arrangement of stator and rotor in the structure, with a large volume but compact axial dimensions; Equipped with low-speed and high torque output capability, it can be directly driven, suitable for fast start stop and precise control. Due to the characteristics of direct drive, torque motors are suitable for use on the hip joints of humanoid robots.

Frameless torque motor: Compared to torque motors, frameless torque motors simplify the housing structure by only providing a stator and rotor, and the motor needs to be embedded in the mechanical structure of the robot. Generally, it needs to be combined with harmonic reducers and encoders to form a compact joint module. The advantage of this type of motor lies in its high torque density, heat dissipation that can be optimized together with the structure of the robot, high upper limit of heat dissipation efficiency, high space utilization, while maintaining high precision. In humanoid robots, frameless torque motors are applied in dexterous hands, knee joints, and other parts.

Hollow cup motor: The rotor adopts a hollow cup winding, with a coreless design and extremely light weight; The moment of inertia is only 1/10 of that of traditional motors, and the response speed is extremely fast; No iron loss, energy conversion efficiency can reach over 90%. In summary, it has the advantages of ultra lightweight, fast response, low noise, no cogging effect, and high efficiency. However, its disadvantages include low output torque, easy burnout due to overload, and high cost. Therefore, hollow cup motors are suitable for some low torque scenarios, such as medical micro surgical instruments, insect bionic robots, etc. In humanoid robots, hollow cup motors are also widely used in dexterous hands.

Permanent magnet synchronous motor: This is a widely used type of motor, which is used in new energy vehicles and two wheeled electric vehicles. The main structure consists of a rotor embedded with permanent magnets and a stator with three-phase windings, requiring complex algorithms for directional control of the magnetic field. But the advantages are obvious, with high torque density, high precision, and efficiency greater than 95%. In the field of robotics, permanent magnet synchronous motors are used in the driving parts of industrial robot arms and wheel foot robots.