An overview of UAVs and embedded electronics

An overview of UAVs and embedded electronics

Popularly known as drones, Unmanned Aerial Vehicles (UAVs), or even Remotely Piloted Aircraft (ARP), these small aircraft have aroused great interest in recent years, mainly due to their versatility and possible applications. On the other hand, these new and possible applications have, increasingly, approached academia, government, and industry in the search for the reconciliation of ethical, legal and privacy aspects. The most comprehensive definition of this equipment is that of all types of aircraft that do not have human pilots on board.

Various UAV classifications have been proposed, from different points of view, such as operational, commercial, legal and others. One of the most elementary is, however, the classification based on the propulsion topology. This classification is interesting from the point of view of the final application of the UAV. The most common (and from which others are derived) are:

  1. Rotating wings: they are the most popular, whose main characteristic is that the lift is fully generated by the propulsion of a rotating wing system. The biggest advantage of this topology is the ability to take off and land vertically, in addition to the ability to fly static, that is, staying in a point in space (hovering). Such aircraft can also be classified as helicopters (when there is only one propeller) or multicopter (when a set of 3 or more propellers are used). One of the main disadvantages of this type of aircraft is the flight range, since the lift is generated entirely by the engines;
  2. Rotating wings: they are the most popular, whose main characteristic is that the lift is fully generated by the propulsion of a rotating wing system. The biggest advantage of this topology is the ability to take off and land vertically, in addition to the ability to fly static, that is, staying in a point in space (hovering). Such aircraft can also be classified as helicopters (when there is only one propeller) or multicopter (when a set of 3 or more propellers are used). One of the main disadvantages of this type of aircraft is the flight range, since the lift is generated entirely by the engines;

Such aircraft, as the definition itself indicates, do not have “human” pilots on board to carry out their control, which must be performed remotely, or even through automation, in which a pre-programmed mission is used in navigation of the aircraft, which must have a controller board to carry out the mission.

In the case of a remote pilot controlling the aircraft, the configuration of the control is simpler, being typically composed of radio transmitter, engine (s), battery (or fuel), and servo motors (in the case of fixed wing aircraft). This is a configuration widely used in aeromodelling.

If you want to carry out a particular operation in an automated way, it is possible to employ plates known as autopilot, in which a particular route and / or operation is loaded into memory before the flight begins. It is important to remember that the flight is automatic, not autonomous, so that, for safety reasons, the remote pilot must remain in full capacity to regain control of the aircraft at any time.

In general, for a given operation to be carried out automatically, it is necessary that the UAV has the ability to locate itself, in addition to knowing its speed and orientation in space. Such functions are performed by sensors connected to the automatic control board, in order to provide information and provide correction for errors in trajectory, orientation and speed. The most used sensors in the operation of UAVs with automatic control are:

  1. Accelerometer and Gyroscope: They are inertial sensors (that is, they are based on the inertia of a tiny mass inside the chip) of the MEMS class (microelectromechanical systems), and they are intended to measure the angular and linear acceleration of the aircraft, allowing the calculation of the aircraft attitude (ie orientation) and its control and stabilization;
  2. GPS and compass: They are, in general, integrated in a single device, in order to provide the absolute position and orientation on the globe. The GPS (or global positioning system) is a system that was developed in the United States in 1973, and that was made available so that anyone on the globe with a receiver can receive the signals. In order for the position to be determined, a receiver must receive the time and position signals from at least 4 satellites. The compass (or magnetometer) measures the intensity and orientation of the magnetic field, and provides a more accurate UAV orientation than would be possible only with the use of an accelerometer and gyroscope.
  3. Barometer: It is an air pressure sensor, whose function is to determine the altitude of the aircraft, since the pressure is reduced with altitude.
  4. Speedometer: Used in fixed wing aircraft, it is responsible for measuring the aircraft’s speed, generally based on the differential pressure originated in a Pitot tube;
  5. Ammeter and voltmeter: its primary function is to measure the status of the battery, in order to enable the remote pilot to take some action, or even to take an automatic action, such as the return to the starting position (RTL, or return to landing). In general, the device that measures voltage and current, has an internal source for powering the autopilot plate, and is known as a power module.

In addition to these, other sensors can also be incorporated into the UAV for specific applications, such as measuring the distance by ultrasound or laser, and in covered locations with no GPS signal, the optical flow sensor, which uses a small camera facing the ground in order to determine movement (the same principle of operation as the optical mouse).

Another component of great importance in automatic UAVs is the ground station, or GCS. The ground station is software executed on the remote computer, in order to indicate the flight information to the remote pilot, and with the ability to change routes and behaviors during the flight.

In general, three communication links (or links) can exist between the pilot and the aircraft, which are:

  1. Radio Control: it is the main link, responsible for sending and receiving the pilot’s commands in the control of the aircraft. It must also make it possible to start and stop the automatic mode, so that UAV operation is conditioned to the remote pilot.
  2. Telemetry: It is a very desirable item in the aircraft, but not essential, being responsible for the communication between the ground station and the aircraft, primarily for the transfer of information during the flight, such as the sensor data;
  3. Video link: necessary in the case of missions that will be carried out far from the remote pilot, enabling the mode of flight in first person (or FPV) through the computer, or with special glasses.

Several options for autopilot cards are on the market today, it is interesting to highlight the cards compatible with the Ardupilot suite, such as Pixhawk, Navio2, APM2.6, and others, due to the growing community of developers, and the fact that it is based on open source, allowing adaptations and implementations in a flexible way.

Other components can still be part of a UAV, such as the speed controller (ESC), battery eliminators (BEC), gimbal for FPV camera orientation, etc., as in the example in the figure below, which illustrates the case of a four-engine multicopter.