Servo vs. Stepper vs. Brushless DC Motors
About DC Electric Motors
DC electric motors convert direct current electricity into mechanical power by generating magnetic fields that spin rotor positioning attached to a motor’s output shaft. There are several common types of electric motors, including servo, stepper, and brushless DC motors. We’ll compare mechanical and electrical differences of each, then explain the key factors to consider when selecting the appropriate motor solution for your customer purposes.
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Servo Motors
A servo motor has a similar mechanical build and flat-torque curve of a brushless DC motor with the characteristics and ability to control position, speed, and acceleration at fine-angular points. The servo’s ability to operate requires a position feedback sensor which interfaces with a servo driver module, commanded by a programmable logic controller (PLC). When installed, servo motors are “application specific” as they require manual tuning relative to the application’s inertial load, gain evaluation of the system’s command output vs. input, and homing corresponding to the motion profile’s “start” position.
Stepper Motors
A stepper motor (also commonly recognized as a step or stepping motor) has a set mechanical tooth design on both the stator and rotor components to move the front shaft’s rotational position to specific angles relative to an identified home position. Current excites the stator’s phases by a separate driver that sends revolution-specific voltage pulses using an open-loop system, demarcated by equal step divisions around the shaft. While a stepper can reliably position the rotor in equal step distance between mechanical teeth angles, closed-loop feedback remains an available option for applications that require precise angular positioning measurements. Stepper motors can also operate in continuous duty when the appropriate voltage, current, inertial load and torque are below the motor’s pullout curve. The advantages of utilizing a stepper over other motor types are high response acceleration between angular positions, continuous high torque at low speeds, the ability to add a low-cost encoder for closed-loop feedback, and the elimination of servo tuning/gain output analysis.
Brushless DC Motors
Conventional DC motors require electrical contact points, or carbon brushes, between a stationary electrical feed and the rotary shaft. The current is sent to a commutator designed to maintain the motor’s rotational energy. The disadvantage of a brushed motor is significantly lower duty cycles (less operation time between profile cycles in a single day), and brushes that wear with continued use. A brushless DC motor (BLDC) transmits direct current to the rotor electronically by intricately timed electromagnetic pulses in place of brushes. BLDC motor technology allows for continuous duty below the rated torque across a specified speed range.
Servo vs. Stepper vs. Brushless DC Motors
Deciding between a BLDC vs servo vs stepper motor is simple when you consider the simultaneous need for accurate motor positioning, design simplicity, and component longevity. The latter point is crucial when comparing a stepper to a servo motor because a functioning servo requires additional parameters than simply sending pulse signals. Servo motors cannot function independently of a complex encoder to calibrate the motor’s feedback sensor and controller. If a component fails or an inertial load is changed, the motor can risk equipment damage and costly delays.
By contrast, a stepper motor utilizes the mechanical structure of the internal components’ tooth design to execute open-loop positioning capability. With its integrated step divisions, stepper motors can position the rotary shaft with precision while also offering the ability to attach an encoder for closed-loop feedback. All that’s required is to select a stepper motor with specifications that match the intended application.
If wear is a primary consideration for variable speed applications and your motion profile requires a consistent rated torque across a speed range, a BLDC motor is an optimal choice. Eliminating the need for brushes significantly increases product lifespan, decreases the cost of maintenance, and overall is a more powerful motor capable of continuous-duty operation.
Electric Motors by Elinco International JPC
DC electric motors are present across all automation-related industries that require unmanned motion profiles. The decision to select a suitable product is as important as a motor’s quality for achieving efficiency, reliability, and effectiveness. If you have further questions about the advantages of selecting a stepper motor vs. servo motor, or how to select the right BLDC motor for you, contact us and speak with one of Elinco International’s highly knowledgeable service technicians.