26 n MOTORS May 2026 www.drivesncontrols.com attractive price point and energy-efficient operation. Various technical factors help to determine your choice of motor. It must have the required torque and power to handle the load. It must be suitable for the inertia (load dynamics), so that the required acceleration and deceleration are achieved efficiently and safely. In high dynamic applications, this can require the use of low-inertia rotors. For applications with variable loads, a BLDC or a synchronous servomotor should be suitable. BLDC motors offer good speed control and can handle changes in load without any significant drop in performance, making them a good choice for applications such as power tools, drones and compact robots. Synchronous servomotors are an excellent choice for variable loads due to their high torque capabilities and precise control. They are well-suited to applications in robotics and handling, printing, and CNC applications around interpolated motion. Matching the motor and its drive electronics to a site’s electrical infrastructure is another technical consideration. For example, harmonic currents – commonly caused by non-linear loads – can adversely affect the operation of electrical equipment. For DC power, a brushless motor is the best option because it has no harmonic effect. For AC power, a synchronous motor would be the best choice. Synchronous motors maintain a constant speed regardless of the load, which means they do not contribute to harmonic distortion in the power supply. Using a VSD (variable-speed drive) with a synchronous motor can help to mitigate harmonics. Physical space constraints also influence motor selection. Depending on the application requirements, there are three main choices. Brushless DC motors are compact and capable of high speeds. They can be battery-powered (from 12/24/48V DC supplies) and have low maintenance requirements. Servo and stepper drives offer better performance and are typically smaller than VSDs, saving panel space. They also need less cooling, which further reduces space and costs. Stepper motors are available in smaller sizes for applications requiring lower power, while synchronous servomotors offer higher power densities. Commercial considerations include the initial unit cost compared to the lifetime cost of the motor. Closed-loop motors, such as synchronous servomotors with integrated encoders, can be more expensive than AC induction motors due to their precision components and the need for additional control electronics. However, they offer higher efficiencies, precision and performance, which may be desirable for the application. These characteristics can also lead to cost savings over time through reduced energy consumption and maintenance costs. So, while the initial cost of a closed-loop motor may be higher, it may offer other important benefits that will deliver a lower TCO. For example, Festo has a new generation of stepper motors with encoders that offer a low-cost entry point to closedloop control, especially where dynamic speed and variable torque are not needed. The need for maintenance is a further commercial consideration. Reducing wiring complexity makes it easier to trace faults. Decentralised drives that can be mounted onto a motor, or nearby, is one way of achieving this. Rather than needing multiple cables running back to a central control cabinet, decentralisation uses a daisy-chain configuration, with a single cable running from one motor to another, providing both power and communications with the controller. Festo offers decentralised drives that also allow I/O modules to be connected in the same daisy-chain, allowing sensors to be added without adding to the wiring requirements. This decentralised approach keeps machine design simple, even in complex automation systems, cutting machine wiring times, and saving the space and cost of cable containment. Selection aids Online tools are available to help engineers and machine-builders by making product selection quicker and more accurate. For example, Festo has a free-to-access electric motion-sizing tool that helps to choose the correct motor/drive combination, with or without a mechanical axis, using either the manufacturer’s or third-party guides. It is suitable for rotary or linear applications, where motors and mechanics must be sized together. Users simply enter some key parameters, and the software identifies possible standard or extra-low-voltage options within seconds, prioritised by cost. It also displays the servodrive and motor workloads, allowing users to make an informed choice. Detailed results can be downloaded and the proposed motors can be connected to ProfiNet, EtherCat, Modbus TCP or EtherNet IP networks without further work. Tool of this type can therefore reduce design and build times dramatically. Choosing the best motor technology is not a process to be rushed or left to familiar convention. Given the complexity of balancing technical specifications with commercial realities such as TCO and energy efficiency, the use of simulation and selection tools is recommended. By adopting a mechanical fact-based, systematic approach, engineers and machine-builders can ensure they install the most suitable, efficient and costeffective motor technology, futureproofing their applications and delivering significant improvements in productivity and sustainability. n This drive system consisting of a Festo CMMT-AS servodrive and EMMT-AS AC synchronous servomotor is designed for demanding, dynamic industrial applications. It uses a space-saving single-cable system to carry power and data. It offers high path accuracies and low cogging torque, making it suitable for applications such as robots, CNC machinery, conveyor systems and packaging equipment.
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