A quadcopter is an aircraft lifted and propelled by four horizontal rotors; each rotor consists of two or three rotor blades. Quadcopters are classified as rotorcrafts or a rotary-wing aircraft to distinguish them from fixed-wing aircraft because the quadcopter derives its source of lift from the rotor blades rotating around a mast. They belong to a larger category of aircrafts defined as multicopters.
Multicopters have various names based on the number of propellers mounted on the craft. A four-propeller multicopter is called a quad-copter, a six propeller multicopter is called a hexa-copter, and nowadays we even have octo-copters.
Over the last few years, remote control airborne vehicles have been incredibly popular for hobbyists, academic research groups, and for individuals who are planning for a start-up. The names of these vehicles vary from quadcopters to quadrotors or even drones. However, they refer to the same vehicle and the most appropriate nomenclature for these crafts is quadrotors. For the sake of simplicity, we will call them quadcopters.
This book will cover the basics of a quadcopter and will guide you on how to build a simple and fully functional quadcopter that is equipped with a camera. Hopefully, by the end of the book you will be able to fly your own quadcopter and capture pictures of your favorite places. All the chapters are necessary for a successful flight and some chapters have instructions on how you can fly your quadcopter, where you should fly, and tips about safety. You should follow all the instructions mentioned and do not skip any of them, even if you feel that a chapter is simple and you have nothing to gain from it.
In this chapter, we will cover the following topics:
The basic knowledge to get familiar with quadcopters
Applications of copters
Comparison with other devices
A quadcopter is an aerial vehicle that consists of mechanical and electrical components including the frame, motors, and other electronic parts. It usually consists of the following parts:
Motors
Propellers
Electronic speed controllers (ESC)
Battery and a power distribution board (PDB)
Flight controller (FC)
Frame
More details about the electronic parts, connections, and the frame design will be given in Chapter 2, Hardware Overview, and Chapter 3, Creating a Frame, respectively.
Almost all quadcopters are unmanned aerial vehicles (UAV) or drones. This means that the craft is controlled by a pilot on the ground or in another vehicle. Remotely piloted aircraft (RPA) is another definition that can be used. However, we can separate UAVs into three categories according to the level of artificial intelligence (AI) their craft flight controller has.
This category of craft is fully controlled by a pilot using a ground station. Crafts of this type are preferred by hobbyists.
It is possible to increase the level of intelligence of a UAV so that it will neither be a fully autonomous vehicle, nor a fully remote controlled one. The pilot uses a remote control device to communicate between the quadcopter and the ground station but now the pilot does not fly the craft as if it's an RCV, the only thing that is required now is to set the points that it should pass (navigation points).
This category of craft has no pilot. All we need to do is connect the battery to the electronic system and let it fly. Quadcopters have numerous sensors, such as GPS, accelerometers, cameras, and many more. Every second, the controller gathers data from all the sensors and after calculations it autonomously decides how and where it should go according to the mission plan. These are extremely difficult to build, which is the reason why we prefer hybrid RCVs if we need a craft with autonomous functions.
Usually, any inexperienced hobbyist who is willing to build a quadcopter chooses the X shape, with four motors mounted at the ends. There are plenty of shapes and materials that can be used for this construction. Each has its own advantages and drawbacks, as it will be explained later on in the subsequent chapters. The X shape is the most common and a first attempt for almost everyone. However, a quadcopter can also be created in a Plus or H shape, as shown in the following figure:
Adding more than four motors will result in a different build that might also work. Vehicles like these are defined as hexa-copters or octo-copters depending on the number of motors used. It should be clear that we can only add two motors at a time; adding only one will not work due to the laws of physics, as will be explained later.
A quadcopter consists of four motors. Each motor produces thrust and torque. The quadcopter can hover and stay steady over the ground when all four motors have the same torque and the total thrust of the craft is equal to or greater than m*g, where m is the mass of the craft and g is the gravity constant. Motors one and four spin clockwise, as shown in the following figure:
Motors two and three, on the other hand, spin counter clockwise. Since every motor produces torque, motor one cancels out the torque produced from motor four and motor two cancels out the torque produced from motor three.
Let's have a look at the quadcopter's maneuvers. Assuming that CM is the center of the craft mass; in order to implement a forward movement, all that is needed is to lower the angular velocity of motor one and two. As a result, there will be less thrust produced in the front than the rear resulting in the quadcopter moving forward. Similarly, we can lower the angular velocity of motors one and three or three and four and have either left or right movement. Lastly, there is one more maneuver that a quadcopter can do. In order to have yaw rotation, we need to lower the speed of any of the two opposite motors. Actually, doing this will increase or decrease the total left or right torque. This creates an imbalance in the torque between the motors; thus, causing the quadcopter to have yaw rotation.
The world is in need of something fast, light, and reliable. This technology is already developed but it is not yet reliable. Therefore, it is too early to use quadcopters in our everyday life. However, they can be used in several other ways.
Quadcopters are quite interesting. They are used as a research platform for individual researchers and university research groups, to test and evaluate new ideas in a number of different fields, including flight control theory, navigation, real time systems, robotics, and so on. Researchers usually build, modify, or observe their maneuvers to develop more stable and promising future crafts. Being a researcher for a system like this requires a very good knowledge about the dynamics and mechanics of aerial vehicles. Furthermore, test flights cannot be done in real time. Simulation software is an important tool, so that researchers can test their algorithms and theories. Anything that passes the simulation stage will be tested in the simulation indoor lab where safety is a number one priority.
Swarms of quadcopters can hover in formation autonomously, perform flying routines, such as flips, dart through hula hoops and organize themselves to fly through windows as a group. They are relatively cheap, available in a variety of sizes, and their simple mechanical design means that they can be built and maintained by amateurs.
As they are so maneuverable, quadcopters can be useful in all kinds of situations and environments. Quadcopters capable of autonomous flight can help remove the need for people to put themselves in a number of dangerous positions. This is a prime reason why the research interest has been increasing over the years. For example, a mountain climber can deploy a quadcopter autonomously and check whether he should be more careful or not while climbing. Another idea is to deploy a quadcopter in a house to check whether there are human survivors or not in case of a disaster. Autonomous operations are extremely useful in situations such as earthquakes, fires, and so on.
There are several engineering research laboratories that are currently developing more advanced control techniques and applications for quadcopters. These include mainly MIT's Aerospace Controls Lab, ETH's Flying Machine Arena, and University of Pennsylvania's General Robotics, Automation, Sensing and Perception (GRASP) Lab.
By the end of 2014, quadcopters were released in the market for the general public. As a result, crafts like quadcopters are now used to capture images and videos of areas that are rough or dangerous for humans. There are many off-the-shelf quadcopters that can follow a transmitter bracelet, which can be worn on the arm. There are quadcopters that can follow subjects without bracelets, using image recognition systems such as OpenCV. The most common commercial quadcopter is one of the copters shown in the following screenshot, and is named phantom from DJI and has already made hundreds of thousands of dollars in sales all over the world:
Quadcopters can also save lives! After an earthquake or the collapse of a building, which might cause significant destruction, the response time to search and locate trapped survivors is crucial. Mini and fast quadcopters equipped with cameras can fly among the debris in a safe, cheap, and effective way and locate survivors quickly.
Another scenario worth looking at is people drowning in a sea or lake. Every year, the percentage of accidents is almost the same but now quadcopters can change that. There is already an idea of a quadcopter equipped with three buoys and able to release them over three possible targets. The quadcopters will be fully remote controlled by a pilot that overviews the whole mission. So, in each mission a quadcopter will be able to increase the probability of a rescue.
Lastly, quadcopters are excellent aerial vehicles for transportation of low weight cargo. They can be deployed easily in rough areas or big cities. There is a huge need for a speedy vital organ transportation system in various areas, particularly in Africa where the cost of transportation by road is high and extremely difficult.
There are various other aerial vehicles that can be used. Humans have successfully made helicopters and airplanes for transportation, surveillance, and even war. Can Quadcopters be used for such causes? Are there any other benefits? Obviously, each vehicle has its own advantages and disadvantages.
Quadcopters and almost every other multicopter craft uses its motors and propellers to produce the necessary thrust needed for the lift, whereas airplanes use motors to produce speed. The lift is achieved by the aerodynamic model of the plane and its wings. So the asset of a quadcopter is the stability that it offers; thus providing a great opportunity to capture photos and videos. On the other hand, airplanes are much faster because of their aerodynamic design and as a result they need less power than helicopters and quadcopters, where all the lift is produced by the motors.
The main difference between a quadcopter and a helicopter is the number of blades used for the lift. A helicopter's mechanism is extremely difficult to build and work properly, whereas quadcopters are pretty simple. A helicopter produces all the lift needed, which is equal to its weight, with only one blade. As a result the total mechanism is quite complex. On the other hand, the stability in a quadcopter comes from four motors with their blades and it's quite simple to understand and create. Thus, the mechanism is quite simple. When a blade is spinning, there are two things that happen. First of all, there is thrust, which lifts the craft. Secondly, every motor creates torque, which is why a craft with only one blade would spin around itself. In a helicopter, a rear blade is used to prevent the craft from spinning around itself. On the other hand, in a quadcopter, all the lift is produced by the sum of each motor's lift, which must be equal to the quadcopter's weight. But, instead of a rear motor to prevent the craft from spinning around, each motor eliminates the torque that the opposite motor produces. As a result, the quadcopter hovers steady without spinning around itself.
It can be seen from the preceding analysis that there are numerous applications for a quadcopter. In the upcoming chapters, we will build a quadcopter with four motors mounted on an X-shape frame. Even if almost all the references will be to specific parts, as shown in every figure, any other component with similar characteristics should be fine. In the next chapter, we will go through all the crucial parts of the quadcopter and describe each one's usage in the overall build. By the end of the chapter, it should be clear how the quadcopter works as far as the electronic parts are concerned.
