Chapter 1. Introduction
Some Definitions
Unless you’ve been living under a rock, you’re probably aware that the word drone is frequently in the news. The many headlines about drones have used the term to describe a wide range of aircraft—from small remotely piloted toys, to autonomous flying robots, to full-scale weaponized military surveillance models. This is mainly because different sources have had different definitions of the word drone. Where exactly is the line drawn, or what makes a drone a drone? Let’s start with a basic definition.
Merriam-Webster’s definition of drone is:
an unmanned aircraft or ship guided by remote control or onboard computers
This definition presents a very broad sense of the word, which contributes to the overgeneralizations and misinformation we see when the media reports on a particular type of unmanned aircraft. Let’s be more specific. Terry says he draws the line between radio-controlled (RC) aircraft and drones at the introduction of GPS and autopilots. When an aircraft has the ability to pilot itself, even if it’s just to hold a steady position, that in his eyes is a drone. Throughout this book, we’ll use the following conventions:
- Drone
Unmanned aerial vehicle controlled autonomously using GPS
- Remotely piloted aircraft (RPA)
Model aircraft flown by a pilot on the ground using a radio transmitter or other computer equipment
- UAV
Aircraft that can be flown remotely by a pilot or controlled autonomously using computer software and GPS
- Small Unmanned Aerial Systems (sUAS)
All related processes involved with unmanned aerial technology
Whether we like it or not, the word drone will continue to be used in a sweeping fashion. We are embracing the word and are aiming to help change the negative connotations, by showing the beneficial applications of small UAV technology. With that in mind, we need to increase our own understanding to navigate the media frenzy that is drone-mania. While the US Federal Aviation Administration is trying to settle on comprehensive small UAV commercial use policy, we all need to take our aerial pursuits as responsibly and safely as possible.
Who Is This Book For?
This book is a set of instructions (with additional suggestions along the way) for how to build an autonomous quadcopter. A general understanding of robotics and electronics concepts are a real advantage in pursuing aerial robotics. It also helps to be familiar with basic tools and equipment, including a soldering iron, to have long-term success in designing your own small UAVs.
If you’re a maker who enjoys persevering through trial-and-error problem solving while you’re building something, then you’ll enjoy aerial robotics. Being able to build a flying robot, and view scenes from completely new perspectives, is well worth the time and effort.
The Drone User Community
Sometimes the way to success when you have a problem is knowing the right questions to ask others. Networking with people who share an interest in aerial robotics is an invaluable resource for helping to pinpoint issues and finding solutions. Online forums are a wonderful way to see how others solve similar problems. One site that has been a favorite of Terry’s is MultiRotorForums.com. People on that forum have been incredibly generous in sharing their experience and insights in building and flying small UAVs.
There may also be an organized group of UAV enthusiasts or a model airplane club local to you, either of which would probably appreciate seeing a fresh face at a meeting. Try searching Meetup.com for drone (there’s that word again!) user groups. Another place to look is the Academy of Model Aeronautics. The AMA is the world’s largest model aviation association and has been around since 1936. We have a great group of folks here in the Baltimore and Washington, D.C., area who have contributed greatly to sharing UAV technology in our region. We truly appreciate everyone who has helped us maintain this wild endeavor.
There may also be an organized group of UAV enthusiasts or a model airplane club local to you, either of which would probably appreciate seeing a fresh face at a meeting. Try searching Meetup.com for drone (there’s that word again!) user groups. Another place to look is the Academy of Model Aeronautics. The AMA is the world’s largest model aviation association and has been around since 1936. We have a great group of folks here in the Baltimore and Washington, D.C. area who have contributed greatly to sharing UAV technology in our region. We truly appreciate everyone who has helped us maintain this wild endeavor.
Note
The AMA has a great PDF of best practice guidelines for safe and responsible flight.
Brief History of Autonomous Flight
The top inventions that we believe have contributed most to drone technology include the RC model airplane, microchips, GPS, the Internet, and the smartphone. Let’s take a look.
RC Model Airplane
In 1937, Ross Hull and Clinton DeSoto, officers of the American Radio Relay League, performed the first public demonstration of remote-controlled flights. In the summer and fall of 1937, they designed and built sailplanes with a 13-foot wingspan, completing over 100 successful radio-controlled flights in Hartford, Connecticut. During this era, Hull set the pace for homebrew radio apparatus design. He increased transmitter efficiency by shortening the leads and was the first to describe the much lighter, one-tube on-board receiver for model aircraft. Twin brothers Walter and William Good won first place titles in 1940 and 1947 at the US National Aeromodeling Championships. Their iconic RC model airplane, known as the Guff, is now owned by the Smithsonian National Air and Space Museum (see Figure 1-1).
Figure 1-1. The Good brothers’ RC airplane, the Guff.
The Advent of Microchips
In the summer of 1958, Jack Kilby—a new employee at Texas Instruments and young inventor at the time—revolutionized the electronics industry with the introduction of his integrated circuit. This precursor to the microchip consisted of a transistor and other components on a thin piece of germanium 7/16 × 1/16 inches in size. Knowing that many electronic components, like passive resistors and capacitors, could be made from the same material as the active transistors, Kilby realized they could also be made into configurations to form a complete circuit. Many electronics we use now would not be possible without Kilby’s tiny chip. It transformed room-sized computers into the microcomputers sold today.
The Technology of Drones
At a certain point, model aeronautics reached the maximum height that hardware design, radio signals, and electronic pulses could take it. To go beyond would require the implementation of less tangible technologies that would enable intelligent communication and control.
The Launch of GPS
The official GPS.gov site describes GPS as follows:
The Global Positioning System (GPS) is a U.S.-owned utility that provides users with positioning, navigation, and timing (PNT) services. This system consists of three segments: the space segment, the control segment, and the user segment. The U.S. Air Force develops, maintains, and operates the space and control segments.
The system’s 36 satellites constantly broadcast a stream of time-code and geographical data to users on the ground. Any device with a GPS receiver can use data from any four satellites to calculate its location in relation to those satellites. Maintaining a clear line of site with the GPS satellites is key, and accuracy is improved as you connect to more than the minimum of four. Due to the line-of-site requirement, it can sometimes be difficult to obtain a reliable GPS lock indoors. We will discuss how this affects flying a drone indoors in Chapter 5.
More GPS Information
For additional details, see the following pages from GPS.gov:
Internet
The personal, civilian drone boom would not be where it is today without the Internet. Online shops, social media, and forums enable people to instantly share and learn with people anywhere in the world. Terry got through his initial quadcopter builds by observing other people’s designs and asking questions online. The more intelligent the UAV, the more of a role the Internet will play in future drone applications.
The Smartphone
With the ability to dramatically shrink the size of computer processors and sensors, it was only a matter of time before someone had the idea to use a smartphone’s insides on a model aircraft. When you turn or rotate your smartphone, the orientation of the interface changes direction; the same sensors could be used to control a small drone. As a mobile software engineer, Terry was familiar with developing mobile apps and the capabilities of smartphone operating systems. Currently, he is working on a number of different applications in the drone mapping space.
Small Autopilot Flight Controller
All these things—GPS, the Internet, and the smartphone—have led to the flight controller, essentially the brain of the drone. Civilian autopilots started showing up on hobbyist multicopters around the late 2000s. Early GPS-capable units were available from the German company MikroKopter, and then several Chinese companies copied them. Around that same time, several open source projects started up, such as MultiWii, Ardupilot, and Open Pilot. MultiWii took its name from the interesting fact that the first units were made with sensors hacked from a Nintendo Wii controller. Ardupilot, as you can probably guess, was so called because it was originally Arduino based.
Today, the small autopilots have came a long way, and many include advanced features such as autonomous flight, Return to Home, and Follow Me. Many of these features were only available on top-of-the-line models just a few years ago, but that goes to show you how fast this technology is evolving.
Principles of Flight
The mechanics of flight consist of some simple rules with complex interactions. To understand them well, it wouldn’t hurt to spend some time brushing up on Newton’s laws of physics.
When we talk about a force, what we mean is a simple push or pull. If the forces working on an object are balanced—a push in one direction met by an equal push in the opposite direction—the object is stationary. If the forces are not balanced, the object accelerates in the direction of the stronger force.
Weight/Gravity
Weight is the force on an object caused by gravity. The principle of force is also sometimes called gravity. For something to fly, or even hover, it must somehow continuously balance or overcome the force of gravity (we’ll see how it does that in a moment). Gravity is relentless—even a momentary loss of the opposing force can bring the aircraft crashing to earth. One interesting note about gravity we’ll be dealing with throughout the book: although weight is distributed throughout the aircraft, one point in the aircraft—called the center of gravity—has the most effect on its ability to fly.
Lift
Lift, the opposite of weight, is an aerodynamic force that keeps an aircraft in the air (see Figure 1-2). In the case of winged aircraft, lift comes from air moving across an airfoil shape of a wing or propeller. The air moving above the airfoil is moving faster; therefore, it has lower pressure. Slower-moving air below the wing has higher pressure. Thanks to the lower pressure above the wing, an airplane or helicopter is literally sucked into the sky. To hover or fly level, lift must equal weight; to climb, lift must be greater than weight.
Figure 1-2. As the airfoil form moves forward through the air, it produces lift.
Drag
Have you ever stuck your hand out the window of a moving car on a nice day? The force you felt pushing back is a perfect example of drag. Any object that moves through the atmosphere at any speed will experience some level of drag, and it increases with the speed of the object. Drag is the reason airplanes, locomotives, and sports cars have smooth, sleek lines—that type of streamlining allows air to flow more cleanly around the vehicle, cutting down on drag and making the vehicle more efficient. Drag is also the reason jets retract their landing gear right after takeoff, and it can be a potent force for quadcopters/drones.
Thrust
The thrust principle of flight is the mechanical force that moves an aircraft through the air. The motion must be created in some way by engines, propellers, rockets, muscles (in the case of birds that can fly), or whatever propulsion system is employed. If thrust is greater than drag, the aircraft will increase in speed. Thrust must equal weight and overcome drag.
Figure 1-3 illustrates the four principles or forces of flight.
Figure 1-3. Aircraft illustrating the principles or forces of flight.
Flight Maneuvers: Aircraft Movement with Stick Mapping
Most UAVs are controlled with a standard six-channel (minimum) remote control just like those that model airplanes have used for many years. The remotes have two main joysticks that move both forward and backward as well as left to right. You will also see some combination of switches, knobs, and sliders, depending on your model. Each of these input mechanisms occupies one channel of your radio.
The two main sticks are the most important controllers and occupy four channels total, one for each axis the stick can travel. Outside of the main sticks, we will always need at least one channel to control the aircraft’s flight mode setting. Another common channel requirement is for a feature called Return to Home (RTH). Both of those channels are assigned to and controlled by a switch. We will discuss RTH and flight modes in greater detail later in the book; for now, let’s look more deeply at the channels controlled by your two main sticks (see Figures 1-4 and 1-5).
Figure 1-4. RC transmitter left and right stick command movements for Mode 2.
Note
The controller descriptions here are for Mode 2 radios used in the United States. Other countries may use Mode 1 radios, which simply reverses the movements controlled by each stick. Many modern radios can use either mode, but some are configured one way only at the factory when they are built.
Throttle
Forward/backward motion of the left stick controls the throttle of your aircraft. The throttle essentially acts as the gas pedal for your aircraft, just as its name implies. In most cases, the higher the throttle value, the faster your motors will spin. Of course there are exceptions to that, and we will talk about those in reference to autopilot and autonomous flight. In order for your aircraft to hover above the ground, the throttle must generate enough lift to counter the effects of Weight. During forward flight, the throttle must counter both drag and weight.
Yaw/Rudder
Left-right motion of the left stick is the channel for yaw, which can also be called rudder. Yaw controls rotation across the horizontal axis of a helicopter or multirotor. If you are flying a plane, this channel would be called rudder due to its control of the tail flap by the same name. The effect on flight of the aircraft is the same for both yaw and rudder during forward flight: steering the aircraft in the required direction.
How does any multirotor, with only propellers for moving parts, mimic flight maneuvers that a plane needs flaps and a rudder to achieve? It’s all done through a process called vector thrusting. We will get into it more in the next chapter, but the basic idea is to control the speed of each propeller independently in such a manner to move in any direction. You could, for example, yaw clockwise by increasing the speed of the two clockwise propellers and decreasing the speed of the two counterclockwise props.
Pitch
Forward-backward motion of the right stick is the channel for pitch, which is also referred to as elevator. Pitch tilts the nose of the aircraft up or down. When you move the right stick forward, the nose of the aircraft will pitch down and vice versa. On an airplane, this is achieved by tilting the horizontal tail flaps together in the same direction. Your quadcopter will be able to move in the same manner by the use of vector thrusting, as with yaw. Most autopilots have an autolevel mode that places a limit on how far you can pitch an aircraft. Other modes may not place this limit, allowing the aircraft unlimited pitch. Under the proper conditions, it is even possible to pitch all the way into a forward flip, but you’d better do a little practicing before trying that!
Roll
Left-right motion of the right stick is the channel for roll, also known as aileron. Roll tilts the aircraft to either the left or right in relation to the front of the aircraft. With an airplane, this would happen by tilting the horizontal wing flaps (known as the ailerons), in opposite directions from each other. Vector thrusting is also responsible for handling all roll movement. This attitude change causes the aircraft to fly in the direction of the tilt. Just like pitch, maximum roll is capped off in autolevel modes and is unlimited in manual mode. With the right autopilot settings and a little practice, a small aircraft can do barrel rolls just like a plane.
