The UAV's control system allows the user to control the aircraft remotely from the ground. It is composed of the transmitter and receiver, along with servos and speed controllers. The transmitter takes the user input and sends it to the receiver wirelessly. The receiver interprets the signal and sends control commands to speed controllers and servos. Speed controllers control the speed of brushless electric motors, while servos provide mechanical proportional control which can be used to move control surfaces and other components of the UAV.
The transmitter (sometimes called the radio) is a hand-held controller with joysticks, knobs and switches that takes the user input and transmits it wirelessly to the UAV's receiver. Transmitters can control a determined number of channels, typically 4 to 18. Transmitters have programming functionality which allows for custom mixing and adjusting of the channels, and some models include telemetry capability for displaying real-time data from the UAV. Almost all transmitter systems currently in the market use 2.4 GHz frequency and spread spectrum technology. While previous transmitter technology was prone to interference as it used a single transmission frequency, spread spectrum systems constantly hop between multiple frequencies. This allows for a practically unlimited quantity of transmitters to be used simultaneously without interference.
The receiver is a small electronic component mounted on the UAV that receives the transmitter's signal, interprets it and controls other components in the UAV accordingly. Receivers typically control servos and speed controllers.
A servo is a small rotary actuator that is able to move to a specified angle and maintain that angle. These types of actuators are used to control movable components of a UAV such as control surfaces, retractable landing gears, and camera gimbals.
Battery Eliminator Circuit (BEC)
The battery eliminator circuit is an electronic component that takes power from an UAV's main battery and outputs a voltage suitable for powering electronic components in the UAV. This allows the UAV to use one battery to power both electric motors and electronics, even if they require different voltages.
Electronic speed controllers (ESCs) are electronic boards capable of controlling the speed of a brushless motor. Most ESCs have an integrated BEC circuit, such that they can provide power to the receiver and to all other electronic components connected to the receiver.
There are various ways of connecting control system components. The main difference is the way the receiver is powered on the UAV. The following schematics explain the different options.
Receiver Powered by ESC With Integrated BEC
The most common setup for an electric UAV is to power the receiver using the integrated BEC functionality of the ESCs. In this setup the ESC is connected to the receiver using one cable which provides both power to the receiver and a control signal to the ESC. The receiver then can distribute power other components such as servos.
Receiver Powered by Dedicated Battery
If the UAV does not have an ESC because it is a gas powered aircraft or glider, the receiver must be powered by a dedicated receiver battery. Additionally, even if the UAV has ESCs it might be desirable to power the receiver using a dedicated receiver battery instead. The main advantage of doing this is that in case of an ESC failure, which is not uncommon, the other control systems of the aircraft can continue functioning instead of having a complete system failure. Additionally, if the receiver must distribute power to many servos, or the servos are very power-consuming, they might need more power than the ESC's BEC can provide. If a separate battery is used to power the receiver, the red cable between the ESC and receiver must not be connected.
Receiver Powered by External BEC
Another option is to power the receiver using the main UAV battery, but use an external BEC circuit instead of the integrated ESC BEC. This option can add redundancy to the system, as ESC's fail much more easily than external BEC's. In this setup the red cable between the ESC and receiver must not be connected.