The potentiometer can be used in two configurations where it can either vary voltage or vary resistance. 

Your next project might require speed control of a motor.

So, can you use a potentiometer to control motor speed? Yes, you can use a potentiometer to control motor speed. When used to vary voltage, a potentiometer can be connected to a motor and vary the voltage (and therefore power) delivered to a motor which will control its speed. 

I shall discuss the above circuit setup and a couple of other configurations you can use to control the speed of the motor using a potentiometer. 

How a potentiometer can be used to control motor speed

Before we dive into the circuit configurations of controlling the speed of the motor, let’s take a closer look at the Potentiometer. 

If you already know a potentiometer inside out, you can skip this section. 

The potentiometer

Below is the schematic symbol and of a Potentiometer. 

It is a three terminal device with a schematic symbol similar to that of a resistor. This is because it essentially is a resistor which has the ability to vary its resistance. 

The resistance at the both ends of the potentiometer is fixed, while the resistance of the middle pin can be changed by either rotating a knob or sliding a contact depending on its construction. 

However, the potentiometer has the added benefit of being able to vary voltage as well.

Varying resistance

To use a potentiometer as a variable resistor, only two of its terminals are connected (Terminals 1 and 2), while the third terminal (Terminal 3) can be left floating. 

Varying voltage

To use the potentiometer to vary voltage, all three of its pins are connected. 

Pin 1 is connected to the supply voltage, pin 3 is grounded, and Pin 2 is the output voltage. 

Note, the potentiometer is a passive device, therefore it can be used in any direction. Therefore, either of the end pins (1 or 3) can be connected to the supply voltage. 

The input voltage is applied across the entirety of the potentiometer, and the output voltage at Pin 2 is the voltage drop between one of the fixed ends and the sliding contacts.

A potentiometer’s role in speed control of a motor

So, how does the ability of a potentiometer to vary its resistance, and voltage help with controlling the speed of a motor? 

A Motor is a device that rotates when a voltage and current is applied to it.

It converts electrical energy to mechanical energy.

Motors come in a variety of sizes which require different magnitudes of voltages to operate. A smaller motor will require less power to rotate at its maximum speed compared to a larger motor.

The amount of voltage and current that a motor requires is given by its Voltage and Current Ratings. 

These values indicate the nominal maximum voltages and currents required to run at maximum speed. 

But, if you supply a motor with voltages less than its rated values, it is going to run at speeds lower than its maximum speed.

Say you have a motor that is rated for 12V and 1A. 

If we reduce the voltage by 50% (6V), the motor is now effectively going to run at 50% of its top speed. 

Since the potentiometer has the ability to vary voltage, that is how it can be used to control the speed of a motor. 

Circuit configurations to control motor speed with a potentiometer

So, now we have established that a potentiometer can be used to control the speed of a motor, let’s take a look at some circuit configurations.

There are two typical ways to use a potentiometer to control speed; Using the potentiometer by itself, and Using the potentiometer with an Arduino.

How to control motor speed using a potentiometer: Without an Arduino

The first circuit setup is the simplest and only requires a few parts;

• Motor
• Potentiometer
• Power Supply 

In this configuration, the potentiometer will have to be wired so that it can vary voltage (so all three pins will be used).

Below is the circuit schematic to control the speed of a motor using just a potentiometer.

The operation of this setup is simple; as you rotate (or the slide) the potentiometer, the voltage at its output pin (pin 2) which is connected to the motor, is going to vary between values from GND (0V) to the supply voltage (5V in this example).

This change in voltage is going to translate to different speeds of the motor. 

How to control motor speed using a potentiometer: With an Arduino

The second circuit setup will require an Arduino.

An Arduino is needed as it contains a microcontroller which has the capability to produce Pulse Width Modulation (PWM) at some of its designated pins.

Note, you are not restricted to using just an Arduino. As long as you have a microcontroller which can produce PWM you will be fine. 

What is PWM?

PWM is a technique used to vary the average power delivered to electrical and electronic devices. 

It is a digital waveform signal that varies between two values; High and Low.

The amount of time the pin of the Arduino is HIGH vs LOW is known as the Duty Cycle, which ultimately determines the average power.

Below are a couple of different PWM waveforms with different duty cycles. 

Each percentage value of duty cycle for each waveform determines how long the pin is on for, and is also how much percentage of the total power is delivered. 

So, if the duty cycle is 75% and the supply voltage is 5V, the total voltage at the output is now 3.75V (0.75 x 5).

This is great, as we can use PWM to control a motor speed. 

But, where does the potentiometer come in? 

The potentiometer is used to vary the duty cycle of the PWM via the Arduino’s Analog to Digital Converter (ADC) .

So, it directly controls the speed. 

Below is the circuit for using a potentiometer and arduino to control motor speed.

Why you would want to control motor speed using a potentiometer

There are a couple reasons for using a potentiometer to control the speed of a motor.

The main one being that it gives you a much more natural tactile feel when controlling the speed of the motor. 

Say you are building an electric scooter. Accelerating is much more natural by rotating the accelerator (via a potentiometer) than by just pushing buttons. 

How to choose the right potentiometer to control motor speed

As we saw earlier, motors have voltage and current ratings. 

These values determine the maximum voltage and currents they can operate under safely. Going over these values increases the chance of damaging the motor.

A potentiometer is no different. It too has maximum voltage and current rating values within which they operate efficiently. 

When using a potentiometer to control the speed of a motor, you will have to choose a potentiometer that matches the maximum ratings of the motor.

For example, if you have a motor that has ratings of 5V, and 1A, you will have to choose a potentiometer with ratings that are the same (5V, 1A) or higher.

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Unlike a DC motor which just rotates continuously when current is applied to it, a stepper motor can ‘step’ through different positions precisely at certain angles. 

It basically divides up the rotation into a number of steps. 

Their rotation can be controlled through the use of a Motor Controller and a Microcontroller. 

Due to their controlled rotation, they have a number of specific applications where normal DC motors cannot be used.

Applications such as 3D printers, Printers, CNC milling machines, robotics and much more.

But, can a stepper motor run continuously as well? Stepper motors can run continuously. While they are designed for applications that require precise movement, stepper motors can rotate continuously just like a DC motor. They are not restricted to 360 degrees of movement.

A note to be made is that ‘run continuously’ could also mean whether the stepper motor can be powered continuously for long periods of time. The answer here is yes as well. 

I shall cover both scenarios in more detail below. 

Deeper look at the stepper motor

Taking a closer look at the stepper motor will give us a better understanding why it can run continuously.

A quick look at the DC motor

Also, taking a quick look at the DC motor will be beneficial as though they are different, they are similar in their construction. 

Above is a diagram of what the internals of a DC motor looks like. 

The two main parts of a DC motor are its Stator and Rotor. 

The stator is a magnetic housing, and the rotor is a coil of wire. When voltage is applied to the coil of wire, it becomes an Electromagnet. 

The forces created due to the magnetic attraction and repulsion between the stator and rotor, cause the rotor to spin.

This is how a DC motor achieves rotation.

However, this rotation cannot be controlled. When voltage is applied, the rotor will spin continuously until voltage is removed with no specific place that it stops.

The stepper motor 00

Below is the internal construction of a stepper motor. 

It still has a rotor and stator, however they differ in their construction. 

As you can see, instead of having permanent magnets, stepper motors use coil windings (electromagnets) as the wire housing (stator).

The rotor on the other hand is a permanent magnet. 

In order to rotate the stepper motor, coils are energized in opposite pairs which causes the rotor to turn a specific number of degrees. 

One great advantage is that a stepper motor is part of an open loop system. It does not require sensors to know which position it is at. It just needs to count the number of steps it takes. 

Understanding whether a stepper motor can run continuously

Ok, so we took a quick glimpse of the stepper motor and how it works. Now we can answer the question whether a stepper motor can run continuously. 

As mentioned at the start of this article, the question could be viewed as meaning either continuous rotation, or powered to run continuously for long periods of time. 

Let’s look at both cases.

Stepper motor run continuously: Continuous rotation

The first part of the question we are going to discuss is continuous rotation. 

A stepper motor is designed to move in steps through 360 degrees of rotation in either direction.

However, it is not limited to only 360 degrees of movement, it can move continuously just like a traditional DC motor. 

The only difference is that it moves in steps. 

However, achieving continuous rotation comes down to the motor driver and microcontroller, as making a stepper motor run continuously is not as simple as applying power to its terminals. 

It requires switching the power between the different stators in a certain sequence which I will in more detail further below. 

Stepper motor run continuously: Powered to run continuously for long periods of time

So, the stepper motor can rotate continuously.

But, can it be powered to run continuously for long periods of time? 

Yes, a stepper motor can be powered to run continuously for long periods.

This doesn’t just mean rotation continuously for a certain length of time, but also maintaining a certain position.

What I mean by this is that in order for a stepper motor to hold a certain position, it requires power. Unlike servo motors which can hold a position without the need of power. 

One of the many applications of stepper motors is in 3D printers. 

The stepper motors in 3D printers sometimes run continuously for hours on end to print really big objects. 

Is it a good idea to run a stepper motor continuously?

A follow question to whether it can run continuously is, if it is a good idea do so.

If the stepper motor is rotating, most of the electrical energy is converted to mechanical energy (in the form of rotation).

However, when held at a certain position, stepper motors can waste a lot of that power as most of this energy is lost in the form of heat in the stator coils. 

So, if you have to hold a stepper motor in a certain position, do so only for a limited amount of time. 

How to make a stepper motor run continuously

To run a stepper motor continuously requires more than just applying a voltage to its terminals.

It requires energizing and degenerzing coils within the motor in a certain sequence in order to achieve rotation. 

Below are the steps on how to make the stepper motor rotate continuously as per the diagram above;

1. First, Coil A is energized and the rotor is aligned with the magnetic field Coil A produces
2. Then Coil B is energized and Coil A is de-energized 
3. This then causes the rotor to step through a certain angle and align with the magnetic field Coil B produces
4. Finally, Coil C is energized and Coil B is de-energized which causes the rotor to rotate a certain angle and align with Coil C’s magnetic field. 

To make the stepper motor rotate continuously, just keep repeating steps from 1 to 4 indefinitely. 

Doing this requires a motor driver along with a microcontroller which has the ability to energize and de-energize the coils as required. 

When would a stepper motor be used to run continuously?

Even though a stepper motor is designed for precise movements, it can still be used in applications that require it to run continuously whether it be continuous rotation or running continuously for long periods of time.

The added benefit you get of using a stepper motor to run continuously is that you will know how many times it has rotated by counting the number of steps it has taken.

This is great for applications such as 3D printers, and CNC milling machines where precise movement and continuous rotation are both needed.

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Using a robotic arm has many applications and advantages. They can perform repetitive work in hazardous conditions where a human may not be able to do so.

There are many ways of building a robotic arm. One common way is using servo motors.

But, why is a servo motor used in a robotic arm? Servo motors have many reasons for being used in a robotic arm, with the main reason being that the servo motor’s position, velocity and torque can be controlled as required which is necessary when building a robotic arm.

Below are other reasons servo motors are used in a robotic arm:

• Different sizes available
• Inexpensive
• Easy to use
• Readily Available
• Weight (much lighter)

Reasons of using a servo motor in a robotic arm

A robot arm is a great piece of machinery that lends its helping hand (in this case arm) to many situations and applications.

Just like we have joints and muscles in our arms that help us move and position it a certain way, a robotic arm needs something to help it move and perform the tasks it does.

A servo motor is one type of motor that can be used in a robotic arm to perform these movements. 

Reason #1 for using a servo motor in a robotic arm : Different sizes available

The first reason servo motors are used to build robotic arms are there are many different sizes of servo motors available. 

Robotic arms come in a variety of shapes and sizes. Therefore, having a servo motor to match the application is a great advantage.

These servo motors also vary in weight, width and length.

Larger servo motors also tend to have greater torque. Using a small sized servo motor with lower torque on a bigger robotic arm which requires higher torques to move due to its size isn’t the best option.

Below are the different sizes of servo motors.

Reason #2 for using a servo motor in a robotic arm : Inexpensive

To have a greater range of motion, a robotic arm needs to have many moving joints. 

These joints mimic the joints of our arms and a standard robotic arm includes the base, shoulder, elbow, wrist and gripper. 

Another main reason a servo motor is used in robotic arms is because they are inexpensive. 

As you can see 5 servo motors are needed for a standard robotic arm (if more range of motion is needed, more servo motors can be added).

If you have a small budget and your need to build a robotic arm that won’t break the bank, servo motors are a great option.

Reason #3 for using a servo motor in a robotic arm : Easy to use

You saw above that a standard robotic arm can have up to 5 motors to be able to achieve a good range of motion.

Stepper motors are usually the standard motors used for robotic arms. However, stepper motors require external motor controllers as well as a microcontroller to operate and therefore connecting, managing and controlling five of them can be a headache.

Stepper motors can have up to 6 wires to connect!

Servo motors on the other hand do not require a motor controller to operate and only come with 3 wires. All that is needed to operate them is a voltage and Pulse-Width-Modulation.

They are much easier to set up and get going than a stepper motor, which is why it is used for many robotic arms. 

Reason #4 for using a servo motor in a robotic arm : Readily available

The fourth reason why servo motors are used in robotic arms is the fact that they are readily available.

You might know the frustration of wanting to complete a project, whether it be a DIY project or for your work, but parts are not available. 

This can cause a lot of stress, and if you are needing to meet a deadline can cost money too.

Having parts that are readily available can reduce your stress levels, and save on money and time. A servo motor is a type of motor that will surely be available wherever you might be living.

Reason #5 for using a servo motor in a robotic arm : Weight (Lighter)

Compared to stepper motors, servo motors are much lighter.

This is a tremendous advantage when it comes to building a robotic arm. The robotic arm needs to stand upright and maintain its balance when moving.

If the motors used for the robotic arm are too heavy this could potentially cause the robotic arm to topple on itself. 

So, having motors that are lighter that are still powerful can be beneficial when designing a robotic arm. That is where the servo motor comes to the rescue.

How do you select the best type of servo motor for a robotic arm?

Servo motors come in a range of sizes, that provide different torques, speeds, and range of rotation. 

So, which is the best type of servo motor when designing and building a robotic arm?

This all depends on your needs and the application the robotic arm will be used for. 

Larger servo motors have greater torque and range of motion. So, if you’re building a robot arm that needs to pick larger objects and maintain structural integrity, a larger sized servo motor is your best option.

However, if you want to build a robotic arm that is faster and torque isn’t of great concern, a smaller sized servo motor will be the best choice.

Are there industrial servo motors used for robotic arms in industry applications?

There are many applications where bigger sized motors of higher quality are required to build a robotic arm to carry out large scale jobs which could include car manufacturing assembly lines, packaging, welding etc.

You might be more familiar with hobby servo motors that are used by hobbyists, or smaller scale robotic arms.

But, are there servo motors that are higher quality specifically built for robotic arms in manufacturing applications? 

Yes, there are servo motors that are specifically designed for applications with industrial motion control in mind. They are designed with higher torques to meet the rugged needs of these industry applications.

What other alternatives can you be used in a robotic arm instead of a servo motor?

To build a robotic arm you require motors that are capable of movement that mimics joints in our arms such as our wrists, elbows, and shoulder. 

As you have seen, a servo motor is capable of providing rotation that you can control to build a robotic arm. I have briefly mentioned a stepper motor earlier.

A stepped motor is the other motor that is commonly used to build robotic arms. 

It has some notable advantages over using a servo motor. 

The first advantage of using a stepper motor instead of a servo motor is that it has more precise control. The stepper motor has a resolution that can be measured in how many steps it has. 

The most common being 200 steps. However, some stepper motors come with 1600 steps increasing its resolution and therefore accuracy providing greater control.

It also has external motor controllers that allow you to have greater control of the motor as you please.

The next advantage is the range of motion. A stepper motor has a continuous range of motion. A servo motor is limited to a certain range of motion which can be limiting when building a robotic arm.

Everything that has its advantages comes with its disadvantages , and the stepper motor is no different. 

Below are some notable disadvantages:

• More Expensive
• Steeper learning curve
• Requires external circuitry (motor controller) to operate

Why can’t you use DC brushless motors for a robotic arm?

DC brushless motors are used in applications where continuous rotation is required at different speeds. This includes things like drills, fans, heaters, cars etc.

A robotic arm needs to use motors that can have its position controlled with precision.

Due to this, a DC brushless motor cannot be used because it does not have any means of controlling its position.

What are the different parts of the robotic arm where a servo arm is used?

Earlier I mentioned that a robotic arm can have up to five servo motors. These five motors are positioned in places that have great resemblance to the human arm.

The five joints of a robotic arm include:

• The base
• Shoulder
• Elbow
• Wrist
• Gripper

As each joint in your arm plays a crucial role in its movement, so does each joint in the robotic arm.

Applications where a robotic arm uses servo motors

A robotic arm is a useful and versatile piece of technology that can be used in many different applications. 

Below is a list of common applications where you can find its ‘helping hand’

DIY – you might be starting out in the field of embedded systems, or just learning the basics of robots. Building a robotic arm using servo motors is a great way to learn how to use these great motors as well as develop your skills. 

It is also a lot fun and can be used for different projects in your home.

Welding – The Automotive industry utilises the robotic arm to carry out welding on numerous parts of cars. It provides a high value of the finished product while being super efficient.

Painting – Robotic arms are used for larger scaled printing jobs, which can be quite repetitive and hazardous for a human to carry out. Also, robotic arms are more efficient as they reduce the amount of paint needed saving on a lot of money.

Material handling – Many food factories use robotic arms, to handle food and package them as well. 

Assembling – Ever since the invention of the assembly line, robotic arms have played a big role in many areas of manufacturing. One of the biggest areas is assembly. They provide an efficient way of carrying out a repetitive task.

Why use a robotic arm?

Now you know why servo motors are used in robotic arms, and their different applications, you may be wondering, why bother using a robotic arm at all. Why not just have a human carry out these tasks. 

Below are some advantages of using a robotic arm instead of a human.

Hazardous environment – the task that might need to be carried out could take place under hazardous conditions. Conditions like painting, which can contain harmful chemicals. So, a robotic arm can be the perfect candidate for environments such as these as it is not harmed in any way.

Repetitive work – Many assembly jobs are repetitive by nature. When a human performs these repetitive jobs, the quality of the job degrades over time as fatigue sets in. A robotic arm feels not fatigue and requires no breaks, therefore the quality of the job is maintained over a long period of time making it more efficient.

Work beyond capabilities of human physical limitations – The final reason to use a robotic arm instead of a human, is that a human might simply not have the capability of performing the job at hand. Tasks like lifting heavy pieces of material. 

How to build a robotic arm using servo motors

If you are on a lookout for a way to build a robotic arm using servo motors, look no further! The video below is a great tutorial on how to build a  simple robotic arm.

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