Selecting a direct drive motor for a precision rotary system requires more than matching motor torque to the equipment weight. Engineers need to evaluate gravity torque, inertial torque, wind torque, friction, rotational inertia, speed, acceleration, duty cycle, and positioning requirements. In this guide, Theodore Li, Technical Director at HONPINE, explains a practical approach to direct drive motor sizing and torque calculation using an azimuth and elevation turntable as an engineering example. The article covers continuous and peak torque calculation, motor selection criteria, and the application of frameless direct drive motors in integrated rotary systems.

Direct drive motors can generally be divided into two types: frameless direct drive motors and housed direct drive motors. A frameless direct drive motor mainly consists of a stator and rotor. Users need to integrate components such as the rotor mounting shaft, encoder, and bearings, making system integration more complex but allowing a highly compact equipment structure and greater design flexibility.A housed direct drive motor integrates the stator, rotor, bearings, encoder, and motor housing into one unit. It is easier to install, align, and operate, making it suitable for applications requiring convenient integration. Compared with conventional motor-and-gearbox systems, direct drive motors simplify the mechanical structure by driving the load directly. They can improve positioning accuracy, dynamic response, and motion smoothness while reducing mechanical transmission components, production cycle time, and maintenance requirements.