Servo Motor Vs DC Motor: What are the Main Differences?

You might not always give it much thought, but many items in your daily life require different kinds of motors to function. Everything from the smoothie maker that makes your breakfast to the DVD player that entertains your kids has a motor of some kind.

It’s worth noting that not all motors are the same and feature a host of different variables that make each type better suited to different applications. What is the difference between a servo motor and a DC motor? Read on as we delve into the basic features of each type as well as the pro and cons of each one. Servo motor vs DC motor – which is better?

What is Servo Motor?

Essentially, servo motors consist of DC motors capable of providing extremely precise motion control. If you’re looking for infinite resolution of the output angle, then you’re definitely looking for a servo motor.

The average servo motor is made up of four components namely:

• DC motor
• Gearing set
• Control circuit
• Usually a Potentiometer in the form of a position sensor

For the most part, the servo motor uses a three-wire system, namely power, ground, and control. The servo controller regulates the current drawn to drive the motor. Servo motors don’t spin continuously like standard DC motors unless they’re specifically modified to accommodate continuous rotation motors.

How Does a Servo Motor Work?

A servo motor features a positional control sensor, also referred to as a feedback encoder, on the last gear. The closed-loop control compares the position of the rotor to its desired position and produces an error signal. Based on this error signal, the motor generates the necessary control signal to move the rotor to the required position. Essentially, to control a servo motor PWM, a signal is used.

Additionally, the duration of the positive pulse decides the position and not the speed of the servo shaft. Depending on the type of servo motor, the servo control pulse is usually repeated every 20 milliseconds. A shorter pulse will rotate the shaft anti-clockwise. A neutral pulse value, on the other hand, will keep the shaft in a center position.

What is Servo Motor Used for?

Since servo motors don’t rotate freely & continuously as most DC motors do, they’re ideal for use in more specified applications. Additionally, servo motors can only run at their peak torque for a short time. They are ideally used as positioning motors rather than for continuous rotation or spinning.

With a more complex setup with PWM tuning, some of the more common servo motors uses include the following:

• Robotic arms, robot legs and many other robotic applications
• Foot & rudder control systems
• Radio-controlled cars
• DVD & Blu-ray disc players
• Cameras
• Telescopes
• Antennas

Pros and Cons of Servo Motor

When considering your servo motors, it’s important to be aware of the pros and cons of this option. They may be the deciding factor in your choice.

Pros 

• Closed-loop control
• Very reliable
• Features high acceleration
• Superior efficiency
• Provides high output power that is relative to its size
• Operates quietly at desired speeds with a high torque value  

Cons 

• Require tuning to stabilize the feedback loop
• Peak torque is limited to a 1% duty cycle
• The motor can become unpredictable when another component breaks
• The controller is complex and requires electronic feedback & encoder support

What is DC Motor?

In short, DC motors run direct currents to generate mechanical rotation. DC motors are made up of a two-wire system, power, and ground and feature a continuous rotation motor. As the power supply is applied, DC motors start rotating until the power is detached. Many DC motors also run at considerably high revolutions per minute or high RPM.

The speed of DC motors is controlled using Pulse Width Modulation (PWM) as it’s commonly called. This allows you to easily turn the power on and off on your applications.

Types of DC Motors

There are a variety of different DC motors currently on the market. The two most common types are brush and brushless. Let’s look a what makes them different.

Brushed DC Motor

AssunMotor’s Coreless Brushed DC Motor Diagram.

The brushed DC motor can be traced back to the mid-1830s. Whether you spend the day in an office, your home, or a busy workshop, you’re surrounded by applications using this type of motor.

This type of motor is called brushed because the current that makes the motor work is provided by two stationary metallic brushes that react with different segments on the ring. The rotation of the motor is created by the brushes continuously contacting the next segment.

What is Brushed DC Motors Used for?

As technology has advanced, brushless DC motors have replaced brushed DC motors in many applications. However, brushed motors are still the superior options for many industrial, commercial, and household applications that require constant and high torque.

Brushed DC motors are ideal for applications that require simple control schemes and low cost. Some of the more popular uses for brushed DC motors include:

• Handheld fans
• Mobile phone vibrators
• Car windows
• Small power tools such as cordless drills
• Small kitchen appliances such as smoothie makers and coffee machines

Brushless DC Motor

When it comes to simplicity, brushless DC motors are mechanically less complex than their brushed counterparts. Unlike brushed motors, the brushless DC motor features only one moving part namely the rotor.

Quite simply, the rotor eliminates the different complications often found in the other components of a brushed DC motor. The rotor features a ring of permanent magnets with stationary coils. In this instance, there’s no need for brushes.

Additionally, the noise of a brushed DC motor is eliminated and the current flow switches over silently. This means that, unlike the brushed version, brushless motors run quietly.

AssunMotor’s Coreless Brushless DC Motor Diagram

What is Brushless DC Motor Used For?

Since brushless DC motors are so much quieter, they’re ideal for use in applications that will benefit from the quiet operation. Some of these include the following:

• Disk drives
• Electric vehicles
• Computer cooling fans
• Air conditioners
• Washing machines
• Drones
• High-precision servomechanisms

Pros and Cons of DC Motor

As with the servo motors, DC motors also have their set of pros and cons, as listed below.

Pros 

• Easily pairs with gear reducers
• Motors are fast and continuous rotation DC motors
• Ideal for multiple applications
• Higher torque rating
• Variable speeds
• Quick starting and stopping

Cons

• Can have a higher initial cost
• Increased operation and maintenance costs as a result of the commutator & brush gear
• Sparking risk at brush means this motor can’t be used in explosive or hazardous conditions

Important note: AssunMotor’s DC motor (brushed & Brushless) and DC servo motor are coreless in design. You may want to find out more on “What is DC Coreless Motor & How to Choose the Right One?”.

If your project requires high-precision motion, low to no noise in the motor, reliable, long-lasting life, requires high power, high efficiency, high torque, and no cogging, then choose Assun’s motors will be a great choice for you.

Comparing DC Motor & Servo Motor

When it comes to comparing servo motors and DC motors, the DC motors win hands down with sustained output. Unlike DC motors, servo motors offer a more precise rotation for technical applications. It’s important to note that a DC motor will only spin at half of the maximum speed when fully on, meaning the ratio determines the speed of the motor.

Another difference between DC motors and servo motors is that they are generally more costly to buy, install as well as maintain or replace. While they offer superior torque, position control, and speed, their cost can be an issue.

It’s also important to note that servo motors have a rotation limited to 180° whereas a DC motor rotates continuously.

DC Motor Vs Servo Motor

We’ve created a side-by-side view of the key features of DC motors vs servo motors to make a comparison so much easier.

Conclusion

We trust that the brief information we’ve provided regarding the key differences and applications between DC and servo motors will help you choose the right application for your particular project. By considering features such as torque, current, and velocity you’ll identify the strongest motor choice for your application. Whether or not the motor you choose is reliable or not, depends on the maintenance of the various components. Use the info in our article to help you choose the best option!