To begin to understand how a multirotor operates we need to know what components are required to make it fly, and transmit and receive instructions from the operator.
So what makes up the anatomy of this miniature beast of a machine?
Here is an overview of the basic parts required to build a quadcopter:
- Air frame
- Flight Controller
- ESC's (Electronic speed controllers)
- Radio Transmitter
Lets explain more about the individual components required:
1. The air frame:
This is the frame of the multirotor that will hold all of your components. The frame is usually made from carbon fiber, Carbon/glass fiber composite or G10 Fiberglass and held together using small screws, nuts and spacers.
They come in various sizes but the most common size for racing is around the 250 mark. To get the size of the frame, you measure diagonally from the center of the front motor to the center of the opposite rear motor. They also come in different weights too, but with smaller weights comes a trade-off in strength or an increase in price. Some great frames to look into buying are the Blackout mini H quad, The luminier QAV250 quad and the minion 250 quad. Some local New Zealand frame manufacturers include Boks Quad and the Haste RC n-Armed.
2. Flight Controller:
The flight controller is the brains of the multirotor and is a circuit board of varying complexity. It makes calculations based on what the quadcopter is doing relative to where it should be and will adjust the RPM of the motors to stabilize the craft. It will also relay user input to the motors which enables the user to pitch, roll or yaw the multirotor.
A multirotor without a flight controller would almost be impossible to fly as it would require the operator to control a minimum of 3 different motors simultaneously with enough speed and accuracy to keep it stabilized. Flight controllers were made possible through the invention of smartphones and utilize mini accelerometers and gyroscopes to stabilize the multirotor.
Flight controllers can come with a range of features including GPS capability with return to location and automatic flight features. However for quadcopter racing you only need an accelerometer and gyroscope just to stabilize you mini quad. Any other features will increase the weight of your multirotor.
Common flight controllers used for FPV Quadcopter racing include the Abusemark Naze 32 Acro which is highly popular as well as slightly less popular flight controllers like the Open Pilot projects CC3D board and The KK2.15 mini.
3. Brushless ESC's (electronic speed controllers):
An esc takes the signal from the flight controller and uses this information to increase or decrease the speed of the motors. Kind of like how your muscles receive the commands sent from your brain and convert it into movement. ESC's come in different power ratings e.g 12A, 20A and 30A ratings. It is best to choose an ESC with an Ampere rating higher than the maximum amount of Amperes your motor will draw.
You may also need at least one ESC with built in BEC (battery eliminator circuit) to power your Flight controller and receiver. A BEC will regulate the voltage. For example a Flight controller with a max 5v input rating can be connected to a 12v ESC using its BEC with 5v output.
Some common ESC's include the Afro 12A ESC which can be flashed with BL heli to support oneshot and active braking. As well as other programmeable ESC's. Most motor manufacturers also make ESC's that are tested with their motors.
4. Brushless Motors:
Brushless motors enable the quadcopter to turn electrical energy into rotational kinetic energy. Perched on top of a brushless motor is a propeller which then converts the rotation of the motor into thrust to lift the mini quad into the air. The rate at which the motor spins is governed by the ESC's. 250 quads usually use 2204 2300kv motors to lift their frames into the sky with 5 inch propellers fixed to the motor.
5. LiPo Battery
The battery supplies the electricity to all the components in the quadcopter and can come in a range of different voltages and capacities. Batteries are made up of cells with each cell putting out 3.7v of power. Usually mini quad racers use a 3s (3cell) or 4s (4cell) battery. As an example a 3s battery has 3 cells of 3.7v (3x3.7=11.1v) so has a power output of 11.1v. With a 4s battery, the power output will be 14.8v. While a 1s battery will only be 3.7v. Make sense?
Batteries also come in a range of capacities, which describes how much power the battery can hold. Capacities are displayed in mAh (milli ampere hours) and can help you calculate how long a battery will last before running out of juice.
For instance: a 1500 mAh battery can deliever 1500 mA (1.5A) for 10 hours.
To explain how to calculate how long your battery may last for may be better left for a future post.
There are also C ratings to batteries. A C rating describes how much continuous power you can draw from the battery without doing damage to the battery itself. If you see a 10C rating on a battery, it means that you can discharge that battery at 10 times the amount of its capacity, safely.
Here's the easy way to find your battery's discharge rate, just multiply the number from the C rating by the pack's capacity. Keep in mind that 1000 milliamps equals one amp. Here's an example, using an 11.1V 2000mAh 10C
11.1 volt 2000mAh -10C
2000 milliamps = 2 amps
2 Amps x 10 = 20 amps continuous discharge
It is best to choose a battery with a C rating that can handle the amount of draw from your motors and esc's. Again we will save how to work that out in a later post.
Tip: When buying components (esc's, motors), make sure the power input voltage ranges are compatible with the power output from your battery. e.g dont plug a 5v fpv camera directly into your 3s or 11.1v battery. However its safe to plug a camera with a voltage range from 6v - 14 volts into your 3s battery. But not a 14.8v 4s battery.
The receiver is the component that plucks instructions sent from the mini quad operator out of the air and sends them to the flight controller, or more accurately picks up radio signals from the Transmitter unit. This is how the quadcopter receives its instructions to move forwards, backwards, sideways etc. The receiver unit usually piggy backs its power from the flight controller, so you don't need to wire it separately to the battery. Nothing too complicated here.
When purchasing a receiver, make sure that its compatible with your Radio transmitter.
7. Radio Transmitter:
The transmitter is the remote control you hold in your hand and use to control the multirotor. Any input on the controls of the radio are sent via radio waves to the receiver unit on the quadcopter. The controls include throttle, pitch, roll and yaw as well as a number of auxiliary switches that can be programmed to switch to different flight modes.
These components all work together to create what is known as a multirotor, although these are the main components, what we didn't include in this blog post were the components of an FPV system. A first person view system places a camera in the front of an FPV quadcopter and teleports the user into the cockpit (not literally, but you see what the camera sees) To race FPV properly requires installing a camera and video transmitter into the frame of the mini quad.
We will explain how to install an FPV system in a future post.