The Different Types of Electric Motors

No matter what you’re working on, you need a motor to get things moving. Electric motors take the raw power of an electrical current and convert that electrical energy into mechanical energy. Electricity, magnetism, and force come together to power electric motors across a wide swath of applications. Tools, appliances, robotics, and CNC technology all rely on different types of electric motors in order to operate. Electric motors come in several varieties with differences in electric current, performance level, construction, and efficiency, all of which make different motors better suited to different jobs. We’ll take a look at some of them here.

AC/DC

Electricity travels in one of two currents: alternating current (AC) or direct current (DC). In a direct current, the current flows in only one direction at a constant rate, while an alternating current reverses back and forth in what you would graph as a sine wave. The most common source of alternating current is from plugging a plug into a wall socket, whereas DC power is better associated with batteries.

Motors that run on DC make efficient use of their energy and can manage high levels of rotational force, or torque. When you need high torque that stays high, a direct-current motor is the way to go. Elevators, cranes, and conveyor belts are just three of the situations where DC motors come into play.

Stepper Motors

One of the most common and versatile varieties of DC motor is the stepper motor, named for its incremental revolutions. Stepper motors have a permanent magnet in one of two places: the rotor or the stator. The location of the electromagnet determines the peak performance of the stepper—magnetized stators offer higher speeds than magnetized rotors. In some cases, a stepper uses a hybrid model where two rotors with opposite polarity turn within a magnetized stator. 3-D printers and CNC mills for hobbyists make use of stepper motors, which are affordable and less likely to break down than other more complex DC motors. The downside to stepper motors is that when they lose magnetization or wear down, they’ll usually require outright replacement.

Servo Motors

The servo motor is a more advanced form of DC motor. Like the stepper motor, the servo motor operates in a series of discrete increments, or steps, but a servo motor is able to attain a considerably higher RPM than a simple stepper. Servo motors attach to a transmission, or gearbox, which allows them to increase their torque while increasing their speed far beyond what a stepper motor could handle, along with a controller that sends more intricate signals to the motor. 3-D printers, CNC mills, and other commercial and industrial applications will use servo motors rather than stepper motors, where higher speed and precision are necessary. However, with higher speeds, gearboxes, and controllers all involved in the operation of a servo motor, they are more prone to breakdown than stepper motors from the addition of so many more moving parts.

Brushed vs. Brushless Motors

AC and DC motors alike can vary in whether they incorporate brushing. A brush, in this context, is an additional component that conducts electrical current between the rotor and stator of the motor. These brushes are typically made of carbon and a motor will generally include several brushes. The brushes’ points of contact touch a slip ring, which transfers power from the stationary object to the rotating object. While brushes are effective in conducting current, the friction of constant rotation can wear down the brushes. With this in mind comes the brushless motor, which substitutes a permanent electromagnet for the carbon brush and vastly reduces damage from friction. Brushless DC motors, which are very close to stepper motors, are smaller than their brushed counterparts, as well as longer lasting. Brushless AC motors use permanent electromagnets to generate magnetic fields in their stators, which turn both the stator and rotor. The advent of the AC brushless motor was an important development in the field of motion control, where their powerful current and high durability make them an attractive choice.

Linear Motors

Not all motors are concerned with rotation. By “unrolling” the stator and rotor, a linear motor substitutes torque, or rotational force, for linear force. To move something along only one axis, a linear motor can be highly effective. Like stepper motors, linear motors experience little wear as they work, but unlike the rotary-based stepper motor, linear motors can achieve high speeds and high accuracy while avoiding this wear. Looms use linear motors to slide the shuttle along, and you’ll even find linear motors powering the sliding doors in commercial buildings. The railgun, a cannon which substitutes an explosive propellant for electromagnetic energy, is effectively a weaponized instance of a linear motor.

Direct Drive

Cutting out the middleman is always advantageous. One drawback of servo motors is that they require transmissions, or gearboxes, to improve torque. A direct drive motor streamlines the process by connecting the load directly to the motor. Like servo motors, direct drive motors are most often brushless and rely on permanent electromagnets. Direct drive motors, however, still require dedicated and precise control mechanisms. You can find direct drive motors running at high and low speeds alike in a number of industrial and consumer applications, from record players to CNC machinery.

Get Your Motor Running With Moley

Across the different types of electric motors, you should be able to find the type and model that’s right for you. Moley Magnetics offers AC and DC motors from such esteemed brands as Hyundai, Worldwide, Baldor, and Leeson. Furthermore, they also service and repair those motors, protecting and protracting your valuable investments. When a factory-standard motor model isn’t quite what you need for your job, Moley Magnetics offers custom electric motors that are purpose-built just for you and your specific application. If ever those custom motors should need a second look, Moley provides on-site electric motor repair services as well, providing the service after the sale that distinguishes the best motor providers. Shop our selection of motors or inquire about customization and get the gears turning on your next project.