Speed Control of DC Motor

This image shows Speed Control of DC Motor


Do you want to know the Working and Speed Control of the DC motors? If the answer is yes! then check this blog post which covers the basics of DC motors, their working mechanism, and why speed control is essential. The article covers various speed control methods, including armature voltage control and field flux control, along with practical ways of regulating the speed of a DC motor. Whether you are an engineering enthusiast or simply curious about the topic, this blog is a must-read for everyone interested in understanding DC motors.

What is a DC Motor?

DC motor is an electrical machine that converts electrical energy to mechanical energy. It's called a DC motor because the power supply used is DC (direct current).


Working of DC motor


DC motor works on the principle that when a current-carrying conductor is placed in a magnetic field it experiences a force which is given by Flemming’s Left-hand rule ( When you keep your forefinger, middle finger and thumb perpendicular to each other and forefinger represent the direction of the magnetic field, the middle finger represents the current flowing through the armature then the thumb represents the direction of the force generated on the armature coil.)
As the armature coil rotates it cuts the magnetic flux lines which result in a change in the magnetic field giving rise to back emf according to faradays law of electromagnetic induction. This induced emf is in the opposite direction of the applied voltage. This back emf makes the dc motor self-regulating. Example: When you increase the load on the motor, the speed of the motor gets reduced. This decreases the back emf and increases the current through armature thereby
increasing the torque to compensate for the applied load. Likewise, when you decrease the load, the speed of the motor increases. This increases the back emf and decreases the current through the armature by which the torque is reduced to make up for the load.

Also, read our blog on DC Motor Applications explaining DC motor applications in different industries, products, and types of DC motors.

Why speed control is necessary?

In various applications, such as robotics and electronics, precise speed control of the DC motor is essential for optimal performance.
Imagine you are in a car. To get a comfy ride in traffic, you will need to control the speed of the vehicle. Similarly in electronics, to control the movements of robots or drones so that they won't crash speed control is used. For drones, you get
ready-made Electronic Speed Controllers(ESC) to do this. In this article, we will see how this can be achieved.

The difference between speed control and speed regulation is that speed control is done automatically or manually whereas speed regulation is the measure of the regulation(maintaining) of the constant speed on changing load conditions at the motor shaft.

Speed control methods of DC Motor

The speed of a dc motor is given by the following equation

equation for speed control of DC Motor

N is the speed of the dc motor

V is the voltage across the armature

Ra is the armature resistance

Ia is the current through the armature

K is constant and ϕ is the flux

From the equation we can see that speed control of the dc motor can be achieved by changing flux which is done by changing field current (Flux control method), changing armature resistance(Armature control method) or voltage supply(Voltage control method). Let's see each one of them one by one

How to control the speed of DC motor

1. Flux/Field control method

Here we change the magnetic flux to control the speed of the motor. To achieve this, we change the current through the field winding. So to do this we place a resistor in series with the field winding and vary this resistor to control the current through
which we control the field and then finally the speed of the dc motor. When resistance is set to a minimum, the current through the field winding increases, and thus flux also increases and speed decreases from the equation of speed and below equation.

ϕ = 𝐾fIf
Kf is the magnetic field design constant.

2. Armature control method

In this method, a variable resistor is placed in series with the armature winding.
When there is a change in resistance, the voltage across the armature gets changed, and thus the speed. So, if the variable resistor’s resistance is decreased, the voltage drop across the armature winding is increased according to ohm’s law, and thus speed is increased. Similarly, when the variable resistor is increased, the voltage drop across the armature winding decreases and speed decreases.

3. Voltage control method

This method is the most extensively used method for controlling the speed of the motor. In this method, we change the supply voltage to the motor and vary its speed. So, increasing or decreasing the supply voltage to the motor will increase or decrease the speed of the motor respectively.
The voltage across the motor can be varied by applying a PWM(pulse width modulation) signal. This PWM signal can be generated from any microcontroller or IC 555. The easiest way is by using Arduino by just using the analogWrite(value) function. Thus, varying the width of the pulse speed can be controlled. Decreasing the width will decrease the speed and increasing the width of PWM will increase the speed.



Let us summarize this method with an example:

In this example, we have
DC motor: Converts electrical energy to mechanical or rotational energy. 9V battery: To give power supply to the motor
Arduino Uno: To generate PWM signal to control the speed. L298N motor driver board: To drive the motor.

In this example, as shown in the image, Arduino generates a PWM signal to the motor driver through the command analogWrite(enA, value); which controls the speed of the motor. By changing the parameter ‘value’ we can achieve speed control of DC motor using Arduino. Thereby achieving the speed control of the dc motor.



In this blog post, we have learned that a DC motor is a fundamental device that converts electrical energy into mechanical energy. Understanding its working and the importance of speed control methods is crucial for engineers and enthusiasts alike. By implementing the various speed control techniques discussed in this blog, you can fine-tune the performance of your DC motor to suit your specific needs. So, whether you are building robots, automation systems, or simply tinkering with electronics, mastering DC motor speed control is a must-have skill that will set you apart from the rest. Start exploring the possibilities of speed control of DC motor today!


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Please do check out other blog posts about Popular electronics


Check out other related blog post about DC Motor:  DC Motor Applications and What is the Difference Between Servo Motor vs DC Motor


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Frequently Asked Questions

1. What is the speed control of a DC motor?

The capability to modify the rotation velocity of a direct current (DC) motor by adjusting the applied voltage is known as speed control. To achieve this, several techniques can be utilized, including a variable resistor, pulse width modulation (PWM), or a DC motor controller. Among these methods, PWM has the highest efficiency, whereas a DC motor controller allows for accurate control and safeguards the motor against harm.

2. Why do we control the speed of the DC motor?

DC motors are often subjected to speed control for a variety of reasons, each depending on the particular application. The motor's speed must be regulated to meet the demands of the system it powers in many situations. For example, in a conveyor belt setup, the speed of the motor must match the rate at which products move on the belt to ensure optimal functionality.

In robotics, DC motors are frequently utilized to regulate the motion of robotic limbs or joints. Accurate and smooth movement of these limbs can be achieved by regulating the speed of the motors.

Energy conservation is another motivation for controlling the speed of a DC motor. Running a motor at maximum speed all the time can be wasteful and expensive, consuming significant amounts of energy. By matching the motor's speed to the system's requirements, energy usage can be minimized, resulting in lower operating costs.

3. How speed control of DC motor can be achieved?

The speed control of DC motor can be achieved through

  • Variable Resistors: This approach encompasses utilizing a variable resistor (potentiometer) to alter the voltage applied to the engine. Nevertheless, this approach is not highly effective and may lead to power loss and heat creation.
  • Pulse Width Modulation (PWM): PWM is a superior means of velocity regulation, where the voltage is turned on and off quickly to oversee the average voltage supplied to the engine. This method is frequently exercised in electronic speed regulators (ESCs) for unmanned aerial vehicles (UAVs), remote-controlled cars, and other applications necessitating precision control over the engine speed.
  • DC Motor Controllers: A DC motor controller is an electronic network that monitors the voltage and current conveyed to the engine. This approach offers precise regulation over the engine speed and can protect the engine from overloading or overheating.
  • Field Control Method: This approach adjusts the magnetic field enforced on the engine's armature. The engine's speed can be regulated by altering the field's intensity.
  • Voltage Control Method: This approach alters the voltage delivered to the motor armature. By adjusting the voltage, the motor speed can be governed.
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