Robotic arms might seem like something out of a sci-fi movie, but they are starting to become the norm in many workplaces. 

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.

Servo SizeWeight RangeTypical Servo WidthTypical Servo Length
NanoLess than 8g7.5mm18.5mm
Sub-Micro8g to 16g 11.5mm24mm
Micro17g to 26g13mm29mm
Mini27g to 39g17mm32.5mm
Standard40g to 79g20mm38mm
Large80g and Larger> 20mm> 38mm

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.