This series is a brain dump on everything I have learned about building a radio controlled quadcopter. I started with zero RC knowledge, and through a lot of reading, and even more trial and error. I have built… crashed… and rebuilt…and crashed… my quadcopter several times now— so maybe my trials can help you learn a few things, and save some money, and heartache along the way.
This post is going to be targeted at people who have never flown a multirotor before: what a multirotor is, what are the parts that go into it, how much does it cost, what parts to get and where to buy them, and how to learn to fly.
There are many different types of multirotors. The most popular configurations for beginners are a tri-copter and a quadcopter. They are the easiest and cheapest configurations to built. In this series we will be building an “h-quad” similar to the one pictured. Its cheap and easy to build– and repair. You will crash. A lot. The point is to make it as painless as possible to repair.
I will also suggest some pre-built quads that may be a good choice, and some kits that will allow you to get up and running even faster. The problem with these is that when you crash– it can be more difficult and more expensive to repair.
There are many advanced things you can do with a multirotor. If you can build a quad, learn to fly it, then you might want to take it to the next level and do:
This allows you to attach a small camera to the front of your aircraft and fly it through wireless video goggles as if you were sitting in the cockpit. A lot of people like to challenge themselves to fly under and around objects.
Many people want to attach a gopro (or professional DSLR) to take photos and videos. You may want to have a stabilized gimbal to produce smooth video.
Flips, loops, rolls, spirals. These things defy the laws of physics in practiced hands.
Advanced flight controllers with GPS can be programmed to follow predetermined waypoints at defined altitudes.
Introduction to the Parts of a Quadcopter
Before you start building, you will really need to get a good understanding of the different parts. Don’t worry, its actually pretty simple! I will start off with a brief into of each part, and then in future posts I will talk about each one in detail.
This is the thing you hold that has joyticks and switches. Its often called a “radio” or “transmitter”. Don’t call it a “controller”– that will get confusing when we talk about flight controllers. See my post: Quadcopter Build Series – Radios for detailed information on what a radio does and how to pick the right one.
A “receiver” is the small device that goes in the aircraft that receives wireless input from the transmitter. Some advanced receivers have “telemetry” enabled on them so they can actually talk back to the transmitter as well. This can allow them to report on signal strength, battery levels, gps location, air speed and more. See my post: Building a Quadcopter Series – Radios for more information.
Brushless motors are very efficient, and powerful electric motors. Motors come in different shapes, sizes, and specifications. Smaller motors are meant to spin small props at a faster RPM while large motors spin bigger props at a slower RPM. Generally, the larger the motor and bigger the prop– the more efficient it is at turning electricity into lift. See my post: Quadcopter Build Series – Motors for more information on choosing the right motor.
There are many different types of props. But, for a beginner quad, we will focus on using a design type called “Slow-fly” props. These props are very cheap but work well. A Quadcopter requires using both normal rotation and reverse rotation. A normal rotation prop must spin clockwise. A reverse rotation prop must spin counter-clockwise. See my post: Quadcopter Build Series – Multirotor Propellers
Each motor requires its own ESC. An ESC takes power from the battery, and a signal from the flight controller to determine how fast to spin the motor. An ESC can also provide stepped down voltage to the flight controller. ESCs are rated for a maximum amount of amp draw, so you have to make sure to pick the right one for your quad. See my post: Quadcopter Build Series – ESCs for a more in depth guide.
The flight controller is an essential piece to the quad. It is the brain that allows an inherently unstable airframe to actually fly. Without the flight controller helping out, a multirotor would simply not be able to fly. Flight controllers come in all different shapes, sizes, features, and… price tags. All flight controllers contain gyros and accelerometers. Its basic function is to keep the aircraft stable and translate control inputs from the receiver into the proper outputs for the ESC to adjust motor RPM that make the quad perform maneuvers and stay in the air without tumbling uncontrollably into the ground. Some flight controllers support an electronic compass, GPS, barometer pressure sensors, and optical flow sensors which can add advanced features such as waypoint following, autopilot return to home, altitude hold, and increased stability and ease of flight. See my post: Quadcopter Build Series – Flight Controllers for more information on different flight controller options, features, prices, and where to buy.
Lithium polymer batteries, or LiPos, are the gas tank of your RC aircraft. They range in voltage, amperage rating, and capacity. Selecting the appropriate LiPo is very important to the performance and safety of your aircraft. LiPos are an fire hazard if not used properly. They can, and will explosively ignite if abused. Read my post: Quadcopter Build Series – LiPos and Chargers
How does it work?
Now that we have a basic understanding of what the main parts are, lets explore a little about how they connect together to make a multicopter fly. We will be specifically looking at a quadcopter in the “x” configuration in contrast to the “+” configuration. The difference is that in forward flight two motors are on the leading edge in an “x” configuration where as only one motor is on the leading edge in a “+” configuration.
The diagram to the right shows the proper motor rotation directions. Different flight controllers may require different setups, but they will always alternate directions like this. Notice the rotation directions are the same for the diagonals. Motor rotation and prop rotation direction are very important– and must match.
The reason the motors spin in different directions is to allow the aircraft to “yaw” or… rotate. By increasing the thrust on a diagonal pair of motors, and decreasing the thrust on the other pair– the torque of the motors will cause the craft to yaw. Since they spin in opposite directions we can yaw to the left and to the right by changing which pair we increase and decrease. If all the motors spun the same direction, the craft would spin uncontrollably and would have no yaw control. Most flight controllers cannot deal with this and it will not fly.
To move forward the back 2 motors will increase their thrust to lean the craft forward. This same principal is applied for movement in all the different directions.
It is best to have the motors arranged equidistant from each other. This makes programming the flight controller much simpler. However, it is possible to have the motors oriented in almost any orientation as long as you can balance the center of gravity. To the right we have an example of the “deadcat” orientation (This is where the name comes from). The motors in the front are spaced wider than the ones in the back. This is typically done to allow a video camera to record video without seeing any props. Any orientation that deviates from the equidistant orientation will require additional configuration in your flight controller. It is more difficult to setup.
We will get into some more specifics on flight control– and the math behind it– when we talk about flight controllers later.