In the world of motors, there are four main types: AC motor, DC motor, servo motors, and stepper motors. Each has unique characteristics and has different applications, advantages and limitations.

From general use in home appliances and industrial machinery to precise control of robots and CNC machine tools, let me explore what these four motors have to offer.

What is AC motor?

An AC motor is a kind of electric motor that uses an electromagnetic induction phenomenon. An alternating current drives this electric motor.

It is a type of electric current that periodically reverses direction and changes its magnitude continuously with time.

This current contrasts to direct current, or ‘DC,’ which flows only in one direction. An AC motor can offer a comparably efficient method of producing mechanical energy from a simple electrical input signal.

An AC motor commonly consists of two essential parts: a stator and a rotor. The stator stays outside, which is the stationary part of the motor. It has coils and is supplied with alternating current to produce a rotating magnetic field.

The rotor stays inside, which is the rotating part of the motor. It produces a second rotating magnetic field by being attached to the output shaft. Permanent magnets, reluctance saliency, or electrical winding may produce the rotor magnetic field.

1. How Does an AC Motor Work?

To understand how an AC motor exactly works, we need to know it’s essential characteristic. An AC motor is distinct from many other motor types, especially DC motors. But the fundamental reason for that is the fact that it runs explicitly on alternating current.

An Alternating current or charge is one whose flow direction around a circuit is reversed at regular intervals. It also means that the voltage on an AC circuit changes periodically, whereas a DC circuit remains relatively constant.

Now, the AC motor relies on a device called an alternator to produce this alternating charge direction. It is a specialized type of electrical generator. When electricity is passed through a spinning shaft, the rotor, an electromagnetic field, or EMF is usually created in that generator.

Meanwhile, the stator turns around itself or within a set of static wire coils. When the rotor turns in relation to the stator, the resulting EMF switches direction or polarity at set points relative to the stator.

It happens because it is created by a charged rotor turning on a fixed axis. As a result of switching polarity, the periodic reversal of the current direction in an AC motor happens at regular and predictable intervals.

All of this can be compared with a piston or paddle, which moves water around a ducting system. When the piston moves water in and out at a consistent speed, it pushes the water back and forth in turn through the conduit.

2. Advantages of AC Motors

As pioneer in the manufacturing of motors, DHmotor understand the several benefits that our AC motors can bring to industries across the globe. Take a look at a few of them

Durable

AC electric motors are extremely durable because unlike most DC motors, they do not have brushes. Brushes can become worn down easily and creates the need for more regular maintenance.

As AC motors do not have this problem, this means they usually have a long lifespan and are favored by those looking for an extremely long-wearing solution.

Low Power Required For Start-Up

With low power required for start-up, this means AC motors can distribute their power more evenly and can maintain a consistent level of power throughout their operation.

It also decreases the chance of burn out, which can occur when a motor becomes overworked at start-up.

Controlled Acceleration

Controlled acceleration within AC motors means they allow for steady and controlled movement, which is key for many demanding applications across the globe.

It also reduces wear and tear as speeds are not increasing and decreasing abruptly, therefore placing less pressure on the motor.

Controlled acceleration is particularly important for an application such as caravan movers, where speed must remain stable and constant to ensure it performs as it should.

3. Disadvantages of AC Motor

• The disadvantages of ac motor include the following.
• The starting torque of this motor is very less
• At low speeds, it won’t operate
• Poor positioning control
• Limited speed through the frequency supply

4. Application of AC motor

• Home Appliances
• Computers
• Fans and air conditioners
• Hydraulic and irrigation pumps
• Transportation equipment

These motors are used in power tools, clocks, disk drives, fans, blowers, pumps, compressors, compressor drives, conveyor system, audio turntables, home appliances, washing machines & industrial areas.

What is DC motor?

“DC Motor is an electrical device that converts electrical energy into mechanical energy”. Going by the dc motor full form, the device uses Direct Current (DC) for its operation.

A rotary component called an armature coil rests inside the motor’s casing surrounded by strong permanent magnets.

When a current is applied to the armature through a rotary electric switch called a commutator, the magnetic field created by the armature interacts with the magnetic field of the stationary magnet to apply a torque on the armature, causing it to rotate.

We introduce DC motors in more detail in this article a comprehensive guide to DC motors, you can click on it to learn more.

1. How does a DC motor works?

The rotor is normally located on the inside of the motor, while the stator is located on the outside. The rotor contains coil windings that are powered by the DC current and the stator contains either permanent magnets or electromagnetic windings.

When the motor is powered by DC current, a magnetic field is created within the stator, attracting and repelling the magnets on the rotor. This causes the rotor to start rotating. To keep the rotor rotating, the motor has a commutator.

When the rotor aligns with the magnetic field, it would stop spinning, but in this case the commutator would reverse the current through the stator and this way reverse the magnetic field. This way the rotor can keep spinning. Below is a diagram showing schematic display of how the dc motor works.

2. Advantages of DC Motor

• They are suitable for low-speed torque
• They have adjustable speed
• They offer a wide range of speed control both below and above the rated speed
• They have a very high and strong starting torque
• They are used in appliances such as electric trains and cranes having overwhelming burdens in the beginning conditions
• They are more affordable
• Their maintenance is easy and takes little to no time

3. Disadvantages of DC motor

• DC motors have a high initial cost.
• Maintenance cost is high and increased operation due to the presence of brushes and commutator.
• Due to sparking at brush DC motors cannot operate in explosive and hazardous conditions.
• As the speed increases, the shaft gets vibrated and the armature gets damaged.
• Converters are required to supply power to the motor.

4. Applications of DC motor

DC (Series) motors are used where high starting torque is required and variation of speed is possible. Series motors are used in traction systems, cranes, air compressors, vacuum compressors, sewing machines, etc.

DC (Shunt) motors are a special type of motor used where constant speed is required. These motors are used in blowers, weaving machines, spinning machines, lifts, etc.

Clcik to leaen: Comprehensive guides to choosing a DC motor

What is servo motor?

Servo motor is a type of motor that can rotate with great precision. Normally this type of motor consists of a control circuit that provides feedback on the current position of the motor shaft, this feedback allows the servo motors to rotate with great precision.

If you want to rotate an object at some specific angles or distance, then you use a servo motor. It is just made up of a simple motor which runs through a servo mechanism. If motor is powered by a DC power supply then it is called DC servo motor, and if it is AC-powered motor then it is called AC servo motor.

1. Advantages of Servo Motor

Higher Output Power: A servo motor produces a high output power. If you are into intense mathematical problems, you can calculate the output independently, but you can also let a servo drive do the job for you.

Accelerated Torque: Looking at the differences between a servo and a stepping motor, you will find that a servo motor can speed up loads due to its high torque ratio. It gets the increased torque from using gearboxes along with the engines to provide a reliable speed.

Short Period Management: An excellent detail about a servo motor is that it uses as much power as necessary, meaning it won’t exert any extra energy, allowing for efficient power and torque usage for shorter periods.

2. Disadvantages of Servo Motor

• Intricate Controller
• Controlling the motor can be challenging. You must establish the proportional integral derivative (PID) parameters while adjusting them, which can be a complicated task for many to handle.
• Potential Damage from Overload
• A motor may be more susceptible to damage due to overload because peak torque is limited to only one percent duty cycle.

Higher Cost

Lastly, it’s likely that installing a servo motor system will cost than a stepper motor. If the task requires minimal speed and accuracy, a stepper motor might be your best bet. However, for the more intense assignments, a servo is worth the extra price.

3. Applications of Servo Motors

Servo motors have a wide range of applications in various fields and industries. Some of the common applications are:

Robotics: Servo motors are used to provide precise motion and force for robotic arms, legs, joints, grippers, etc. They enable robots to perform tasks such as picking, placing, welding, assembling, etc.

CNC machinery: Servo motors are used to drive the axes of CNC machines such as lathes, mills, routers, etc. They enable CNC machines to perform accurate and complex machining operations such as cutting, drilling, engraving, etc.

Automated manufacturing: Servo motors are used to control the movement and position of various components and devices in automated manufacturing systems, such as conveyors, feeders, loaders, unloaders, etc. They enable automated manufacturing systems to achieve high productivity and quality.

Medical equipment: Servo motors are used to operate various medical devices and instruments such as surgical robots, scanners, pumps, ventilators, etc. They enable medical equipment to perform precise and safe operations and treatments.

What is Stepper Motor?   

Stepper motors are a type of electric motor that moves in precise, small increments or steps rather than continuously. In another definition, stepper motor is a brushless, synchronous electric motor that converts digital pulses into mechanical shaft rotation.

They are commonly used in industrial applications that require precise motion control, such as robotics, 3D printing, CNC machines, and automated production lines.

1. Advantages of Stepper Motor  

Flexibility: Stepper motors offer flexibility in application for a wide range of applications because the design of the stepper motor provides a constant holding torque without the need for the motor to be powered.

Greater Torque: The torque of a stepper motor of that of the same size of a servo motor, at lower speeds is greater than that of a servo motor.

Cheaper than Servo Motors: The Stepper Motor is often used in an Open Loop System that does not require positional or torque feedback making the Stepper Motor simpler and less costly to control. The Stepper Motor is in itself the position transducer.

Excellent Low Speed Torque: Stepper Motors offer excellent low speed torque, which means, the motor will drive many loads without having to utilize any additional gearing or gearbox mechanisms.

2. Disadvantages of Stepper Motor

Limited Speed Range: One of the most significant disadvantages of stepping motors is their limited speed range. They excel at low-speed applications but struggle to maintain high speeds efficiently.

As the speed increases, the torque output diminishes rapidly, leading to a phenomenon known as “cogging.” This limitation restricts their use in applications requiring high-speed continuous rotation.

Lack of Smooth Motion: Stepping motors produce motion in discrete steps, which can result in a noticeable “stepping” effect in certain applications, especially when moving at slow speeds.

This characteristic can lead to vibrations and noise, making them unsuitable for applications that demand smooth and quiet motion, like high-end camera gimbals.

Resonance Issues: Stepping motors are susceptible to resonance, a phenomenon where mechanical vibrations can cause a loss of accuracy and even lead to missed steps.Controlling resonance can be challenging and often requires additional damping mechanisms or sophisticated control algorithms.

3. Applications of Stepper Motor   

Stepper motors are widely used in various industries and applications that require precise motion control.

Robotics: Stepper motors are used in various robotic applications, including robotic arms, grippers, and mobile robots. The precise motion control provided by stepper motors is essential for these applications.

CNC Machines: Stepper motors are commonly used in computer numerical control (CNC) machines for precise control of the cutting tool. The stepper motor provides accurate positioning, which is critical for high-quality machining.

3D Printing: Stepper motors are widely used in 3D printers for accurate control of the print head and the movement of the printing bed.

Textile Industry: Stepper motors are used in textile machines for precise control of the fabric feed and the movement of the weaving head

What are the differences between these four types of motors

1. Stability

If stability is a requirement, you will want to gravitate towards stepper motors. Servo motors tend to pulsate even at a standstill, so if you have a situation where the motor needs to hold a load still, or another application where lack of stability could interfere with the process, you should generally use a stepper motor.

2. Torque

DC motors, known for their ability to generate high torque, are valuable in applications where speed control is essential.This type of electric motor, often compared to its counterpart, the AC Motor, can provide a more constant and stable torque across various speed ranges.

Generally, DC motors deliver faster response to load changes compared to AC motors.AC motors, on the other hand, excel in scenarios requiring variable torque and high speed.

However, it’s important to note that AC motors typically experience slip and induction current loss, leading to efficiency issues.

In contrast, DC motors, a key category in the AC Motor and DC Motor spectrum, are considered to be approximately 30 percent more efficient due to their use of permanent magnets.

In the comparison between stepper and servo motors, it’s often found that you can achieve roughly the same torque from a stepper motor as from a servo motor.

Servos generally offer higher performance, with a more flexible speed curve and a time-dependent peak torque rating. Yet, an optimized stepper motor can usually perform the same job more affordably in many AC Motor and DC Motor applications.

Conclusion

It is instructive to learn about the four types of motors in this review. If you are still wondering and puzzled at which motor is best among all, the fact is each one is best based on its unique application and functional role and reading this post will help you choose correctly.

Related Reading: Brushless vs.brushed DC motors