What is a DD Motor? How to Select a DD Motor?

DD motor, full name Direct Drive motor, is a motor that directly drives the load without using reduction devices such as gears, belts or ball screws. Its working principle is based on high torque output, allowing it to be directly connected to the moving equipment, thereby eliminating the need for intermediate connection parts such as fasteners, gearboxes and belts. This design not only simplifies the system structure, but also improves the operating accuracy of the system. DD motor usually adopts DC motor technology, and its structure is specially designed to generate large torque and low speed in limited space and voltage. To achieve this, DD motors usually adopt a flat structure and have a large number of pole pairs to reduce torque and speed fluctuation. In addition, DD motors use absolute encoders, which can determine the current position without returning to origin, providing high-precision positioning capability.

How does a direct drive motor work？

The control principle of DD motor involves current control, magnetic field control, feedback system and control algorithm. Current control is the key to achieving precise torque control, while magnetic field control is used to adjust the rotation direction and speed of the motor. The feedback system provides real-time position and speed information through encoders or sensors, helping to correct errors and ensure precise position control. Control algorithms such as PID and model predictive control (MPC) are used to adjust current and magnetic field according to feedback signals and motion commands, thereby achieving high-performance motion control.

What are the types of direct drive motors？

Classified by motion type

According to motion type, it can be divided into rotary direct drive motor and linear direct drive motor.

Classified by rotor structure

According to rotor structure, it can be divided into outer rotor and inner rotor.

What are the characteristics of outer rotor DD motors

Structural feature: rotor outside, stator inside, larger output radius

Advantages: large inertia, high torque density

Application: large load inertia, medium speed, medium acceleration applications

Typical products: TDB-170, TDB-263, TDB-112 series (all TDB series are outer rotor design)

What are the characteristics of inner rotor DD motors？

Structural feature: rotor inside, stator outside

Advantages: small inertia, fast response speed

Application: small load inertia, high speed, high acceleration applications

Note: under the condition that torque and speed are satisfied, selection between inner and outer rotor

How are DD motors classified by encoder type

DD motor can choose incremental encoder or absolute encoder. Incremental encoder has lower cost and is compatible with most servo drives. Absolute encoder features no position loss after power-off and higher safety, improving automation system efficiency.

How are DD motors classified by Hall sensor？

HONPINE DD motor can be selected with or without Hall sensor.

With Hall sensor: easier startup, compatible with more drives, easier debugging

Without Hall sensor: simpler structure, dedicated drive solution, faster response

What are the advantages of direct drive motors

High precision: DD motor repeat positioning accuracy can reach ±0.5 arcseconds, i.e. ±0.00796 degrees, making it very useful in high-precision applications.

High efficiency: direct drive design reduces energy conversion loss and improves system efficiency.

Low maintenance: due to the absence of complex transmission mechanisms, maintenance requirements are greatly reduced.

Low noise and low vibration: without traditional transmission parts, operation is smoother, and noise and vibration are effectively controlled.

Fast response: no intermediate transmission parts, resulting in faster response speed.

Flexible application: can be used for various complex motion control requirements, such as equal division or even unequal division.

What are the disadvantages of direct drive motors？

First, direct drive linear motors have high power consumption, especially under high load and high acceleration motion, which places heavy burden on the power supply system.

Second, vibration is high. The dynamic stiffness of linear motors is very low and cannot provide damping, which may cause resonance of other machine parts during high-speed operation.

Third, heat generation is large. The moving part of the linear motor installed at the bottom of the worktable is a high heat source, and the installation position is not conducive to natural heat dissipation, which brings great challenges to temperature control.

Fourth, there is no self-locking. To ensure operational safety, motion axes driven by linear motors, especially vertical axes, must be equipped with additional locking mechanisms, increasing system complexity.

How to learn more about DD motors？

About DD motor, if you have any questions, please contact us to obtain full DD motor technical materials.