As the world is going through innovations and new developments, technology has risen and things have scaled down to a major extent. Any new technology that arises comes from security and defense requirements and is later integrated into the civil world, and unmanned technology is no different.

Manned systems were too big for intelligence gathering and too risky to be used in gathering intelligence from the enemy. Also, a huge price of man and machine was paid if engaged in combat or ambush. To avoid this situation, unmanned technology was born to cater to this purpose on land, air, and sea, now known as unmanned ground vehicles (UGVs), UAVs, and unmanned water vehicles (UWVs), respectively.

Various unmanned vehicles

UAVs have evolved over time and have taken shape, as we are seeing with day-to-day vehicles. As we have cars and trucks for land, submarines and ships for the sea, and airplanes for the air, similarly, we have unmanned systems for all three domains – land, water, and air – described as follows:

• UWVs: UWVs are uncrewed submarines that are used to travel deep inside the water. They travel up to long ranges deep inside water and are operated by ground crews from far away. These unmanned submarines are autonomously driven water vehicles that travel on a predefined path at a predefined depth and return after completing missions.

  These are used for underwater surveillance using RGB cameras or doing bathymetric surveys using Light Detection and Ranging (LiDAR). The same is being used in defense for reconnaissance and monitoring sea waters.

• UGVs: UGVs are similar to UWVs, with the difference that these vehicles travel on the earth’s surface rather than in air and water. These are operated with the crew members sitting far from the base stations. These are operated in manual and autonomous modes on a predefined path, speed, and route and come back to their original place.
• UAVs: UAVs are vehicles that fly in the air without onboard crews and with the help of onboard sophisticated sensor systems. These unmanned systems are controlled by ground-based controlled systems crews controlled by long-range antennas. These systems are used for civil and military applications such as crowd monitoring, aerial surveys, and agriculture. We will understand more about these systems in the coming chapters.

History and evolution of drones

The history of UAVs, or drones, is quite interesting. The idea of pilotless flying machines dates back to the early 1900s when humans began imagining the chances of an unmanned flight. In their early days, drones were primarily used for military purposes, such as reconnaissance and surveillance, and they proved valuable in situations where sending human pilots was risky.

As development went through advanced phases, drones became smaller and more sophisticated, and various new applications evolved. The evolution of UAVs rose dramatically in the 2000s with the introduction of consumer drones, whose applications were beyond military use. Suddenly, drones became popular among hobbyists, photographers, and filmmakers, offering a new perspective from the sky.

In recent years, drones have been introduced to various other applications as well, where they are now employed in diverse fields, including agriculture for crop monitoring, search and rescue operations, environmental monitoring, and even delivery services. The history of UAVs reflects a journey from military-focused beginnings to becoming versatile tools with widespread civilian applications, showcasing the remarkable evolution of unmanned aerial technology.

Need for an unmanned system

As the era advances, the demand for different datasets and intelligence is growing. Earlier, due to non-availability of the technology, such things were done with the help of man and machines. Now, as technology is rising, drones can reach where man and machine cannot via the ground with less cost and less effort.

The following are key reasons why UAVs have become a key requirement over manned aircraft:

• Easy reach: UAVs have reached remote areas that man or ground vehicles failed to reach easily with less cost and effort.
• Easy transportation: Unmanned systems are highly scalable and available in all shapes and sizes for a variety of work as compared to manned aircraft. Due to their extremely small shape and size, they can be easily transportable in a small form factor, which makes them smaller, simpler, and smarter.
• Less power consumption and easy maintenance: Being small and rough, these devices consume less power, which makes them more economical.
• Economical: Drones prove to be an economical solution for many aerial applications such as surveys and surveillance as compared to other applications.

What are unmanned aerial systems?

An unmanned aerial system (UAS) is an uncrewed aerial platform being operated by an avionics system over a wireless network by a remote crew. It comes in all weights, sizes, and performances. It comes with different types of vehicles that are used for different types of applications. UAVs are also known as remotely piloted aircraft systems (RPAS). In the next section, we will understand the various applications for which UASs are used.

A few of the applications of UAVs in current scenarios include the following:

• Civilian uses of drones:
  • Aerial photography: The use of drones has enabled filmmakers and cinematographers to capture high-quality video from different angles and heights, which was once very difficult and expensive. We can see the use of drones for videography in functions and weddings due to their small size, easy handling, and cost efficiency.
  • Asset inspection: Earlier, the inspection of huge assets such as windmills, pipelines, power transmission lines, bridges, and the like was difficult as the reach of humans was limited and the execution of tasks was costly and time-consuming. After the evolution of drones and their capacity to carry payloads such as Lidar and cameras, the inspection of these assets has become easy and cost-efficient due to the small size of the drones and their reach to places humans can’t. This helps to inspect assets closely and take measures in a timely manner.
  • Wildlife conservation: Drones help to keep an eye on wildlife spread across a larger area within minutes. They give a real-time video feed to the operator of the landmass and aid monitoring in the area. This saves a lot of time and effort compared to when people have to physically monitor the area. Drones also can issue warnings, take a closer look at areas of wild animals, and report if any critical incident has taken place.
  • Agriculture surveys: Special multispectral and hyperspectral camera-equipped drones help to take geotagged imagery of crop fields. These images are later used by software to extract the chemical composition of leaves and provide data about the lack of critical minerals in the plants. The data can be used and analyzed to predict crop health at a particular geolocation and take protective measures against it.
  • Aerial surveys: Drones equipped with high-resolution cameras take geotagged imagery of landmass from the air, and later, these images are used to make high-quality accurate maps to understand the earth’s surface. Drones have made this task easy and time efficient due to their small size and require less human effort.
  • Mosquito repellent: Heavy lift drones are also used to spray mosquito repellent in areas that require efficient mosquito control. Since it’s difficult for humans to spray these insecticides evenly across areas where reach is impossible, drones have made this efficient and cost-effective.
  • Cargo drones: Nowadays, drones are also used in the delivery of goods, which is termed aerial deliveries. Major companies are looking at this as the future of deliveries. Use cases for delivering heavy cargo across remote areas are also being developed.
• Defense use cases of drones:
  • Crowd monitoring: Drones equipped with speakers and cameras have played a pivotal role in crowd monitoring. A drone gives a live feed of the situation, and a person can instruct the crowd with the help of speakers and investigate the situation with the help of a camera without actually going there.
  • Surveillance: Drones equipped with day-night cameras help defense forces keep an eye on critical assets during the day and night. These cameras are equipped with tracking capabilities and lasers to accurately get the geolocation of the target. This helps forces keep a large area under surveillance without any human intervention.
  • Aerial warfare: As we are seeing in the world, drones have become crucial equipment in warfare. This helps to be more lethal without risking human life.
  • Radio relaying: Drones are also used as radio signal boosters and repeaters in remote areas where communication is the key tool. Such drones are used in mountain ranges where line of sight (LOS) is not possible, and a tethered drone is used as a tower for amplifying signals and establishing communications.

The aforementioned are some use cases where drone technology is being used to help reduce the cost and risk of manpower and also reduce the time taken for project completion. We are seeing that different types of drones are being built and used to cater to different application needs. As a fighter plane cannot work as a passenger plane and vice versa, one type of drone does not fit into all applications, hence any system is designed completely from scratch as per the requirements/application/purpose, and so on.

As we have gone through use cases that are catered for by the use of drone technology, here, we will study different types of drones that have been built for the sake of different application requirements such as high endurance, long range, high altitude, and so on. By doing this, we will get to know about the different kinds of drones and later build an understanding of their development. A glimpse at various kinds of drones is covered in the following section.

Types of drones and their specifications

In this section, we will study the various types of drones, their key functionality, and how they are different from each other.

Multirotor

A multirotor is a motor-propeller-based drone. The major elements to produce force and lift in the air are motors and propellers attached to them. This produces thrust in the drone and helps to lift the system’s load.

Based on the number of motors, these drones are classified as follows:

• Two motors or bi-copter: A bi-copter is a multirotor with two rotors placed on each side of the center. These systems are unidirectional systems and capable of lifting less load with low endurance and control. Hence, these systems are not used much:

Figure 1.1 – A bi-copter

• Three motors or tri-copter: A tri-copter has three arms and lift-generating elements at the end of each arm, placed at 120 degrees to each other. These types of drones are small and not load-carrying but can be used for short distances in inspection and surveillance:

Figure 1.2 – A tri-copter

• Four motors or quadcopter: Quadcopters are the most famous drone configurations, used across the world. These are considered the most stable and easy-to-control drones. The dynamics of the drones make them easy to maneuver across the 3D space and give them stability and speed across long ranges and high altitudes. These configurations are also used to carry up to a few kilograms of payload with them:

Figure 1.3 – A quadcopter

• Six motors or hexacopter: Hexacopters are one of the most famous configurations after quadcopters. As the name suggests, they have 6 arms placed at 60 degrees to each other. These configurations are used for more stable flight and are able to carry more load. Eventually, they offer less endurance under the same power than a quadcopter:

Figure 1.4 – A hexacopter

• Eight motors or octocopter: An octocopter, as the name suggests, has 8 arms placed at 45 degrees to each other. It is an extended version of a hexacopter that can lift more weight and comes in large sizes. These are aerodynamically more stable but also more heavy and power-hungry vehicles:

Figure 1.5 – An octocopter

• Eight motors (in Quad) or octa-quad: The octa-quad model is not very famous in the commercial market. It is a good configuration carrying more weight in the small configurations. It’s a quadcopter with four arms and two motors placed on the top and bottom of each arm for producing more thrust in less form factor. These types of drones are mainly used to maintain a good size-to-weight ratio:

Figure 1.6 – An octa-quad

• 12 motors (in Hexa) or deca-hexa copter: The deca-hexa, as the name suggests, has 12 motors on 6 arms placed upside down. These configurations are used for larger drones, such as passenger-carrying drones or heavy cargo drones. These have bigger-sized motors and bigger load capacity and form factor:

Figure 1.7 – A deca-hexa copter

The preceding configuration is used as per the decided payload, load-carrying capacity, and applications.

Fixed-wing drone

A fixed-wing drone, as the name suggests, is a standard airfoil wing-based design where the wing serves as a key lift generator for the system and a single motor (push/pull) helps to cruise in the air. The cruise speed helps to generate adequate lift via wings to travel in the air, and control surfaces work to give direction in the air:

Figure 1.8 – A fixed-wing drone

Fixed-wing VTOL or hybrid drone

Vertical take-off and landing (VTOL) aircraft, also called hybrid aircraft, is assisted by four motors to lift off in the air and later transition into a fixed-wing aircraft. This type of drone does not require a long runway unlike fixed-wing drones. It take off and land like a multicopter from a single place and cruises like a fixed-wing aircraft:

Figure 1.9 – A fixed-wing VTOL

Tilt-rotor drone

A tilt-rotor drone comes under the category of fixed-wing VTOL hybrid drones that take off and land like a multirotor and cruise like a fixed-wing drone. The only difference between these drones and fixed-wing VTOL drones is that these drones work on the principle of differential thrust and have common motors for cruise and take-off. The same motors are used as take-off lifter motors, change their angle from 90 degrees to 180 degrees during transition, and are used as cruise motors.

These drones give much more efficiency than a fixed-wing VTOL since the number of motors is reduced and power consumption is also reduced:

Figure 1.10 – A tilt-rotor hybrid drone

Hence, we have seen different types of drones. These drones can be built in different weight and size categories, but to differentiate them based on their weight profile, the Directorate General of Civil Aviation (DGCA) in India has classified drones into five categories:

• Nano: Any drones less than or equal to 250 grams come under the category of nano drones
• Micro: Any drones between 250 grams and 2 kilograms come under the category of micro drones
• Small: Any drones between 2 kilograms and 25 kilograms come under the category of small drones
• Medium: Drones that are greater than 25 kilograms and less than or equal to 150 kilograms
• Large: Drones that are greater than 150 kilograms

We have now studied different types of drones based on their structure and application, but we haven’t yet studied what’s actually inside the drone and the systems it contains. In the following sections, we will understand the composition of a drone and bifurcate it into different categories.

System composition of a UAV

A UAV has many systems and subsystems that enable it to fly in the air and do missions automatically with safety and precision. These systems are a combination of hardware and software that perform their respective tasks to keep the system under control and stable in the air:

Figure 1.11 – Overview of a drone system

Now that we have seen the system composition of a UAV, let us look at the major mechanical and structural components of drones.

A drone system is a robotic system that is composed of electro-mechanical systems for all its functions. A mechanical system is called a skeleton, the drone under which all the avionics system works. The mechanical system holds the avionics system firmly with it with appropriate strength so that it can take maneuver forces upon it to its limits.

We will study here the major mechanical and structural components of a drone, which are required to hold different parts and have their independent functionalities.

Airframe

The airframe is the main skeleton of a drone, which holds all avionics components in position and helps them to be mounted and fit firmly without any vibrations and loose fitting during the flight. It works as the main body of the drone, which gives the system a proper shape and size, confines all modules, and protects them from direct exposure to the external environment:

Figure 1.12 – A hexacopter carbon fiber airframe

A complete airframe is composed of the following subcomponents:

• Motor mounts: Places to hold the motors using screws or other materials:

Figure 1.13 – A motor mount

• Arms: Tubes/pipes between the main body and motor mounts are called arms. These are used as a stiff mechanical structure to lift the main body and wiring between motors and the main body:

Figure 1.14 – An arm set

• Hub: The hub is the place where the main avionics, such as flight controllers, the Global Positioning System (GPS), and other components, are placed with due interfacing and connection, which helps the system to get the necessary data to process. Arms are attached to the hub and extended outside:

Figure 1.15 – A drone hub

• Landing gear: This is also attached to the hub extending downward. This helps the drone to land on different terrains and also keeps adequate ground clearance for the safety of the payload:

Figure 1.16 – A landing gear

In terms of the features of a mechanical airframe, the following is recommended:

• The airframe should be symmetrical from all aspects on the x, y, and z axes
• Manufacturing of the airframe is to be done from lightweight materials such as carbon fiber, glass fiber, and the like
• A screwless design would be even more helpful for stability and performance

Post the mechanical system comes the avionics system, which is fitted into the mechanical system at appropriate required places to exert thrust and other forces, keeping the center of gravity balanced. These avionics systems include sensors and actuators powered by the power system to exert the necessary force where required and get the necessary task done by the drone:

Figure 1.17 – Avionics components

In the following sections, we will have a glance at the major avionics systems and subsystems of a drone that are interrelated.

The propulsion system or drive train of a drone

The propulsion system is responsible for creating the necessary force to lift the system into the air, maintaining the ratios of lift to weight. This is also a reason to maintain stability in the air, fly at high altitudes, and provide speed to the system. This is the most important part and initial building block of drone systems. It also helps in maintaining electrical stability in the system:

Figure 1.18 – A power train

It consists of the following primary parts:

• Motors: These are the primary components of the propulsion system. These are brushless DC (BLDC) motors, which are far more efficient and lower-power-consumption motors with a long life. These motors rotate at high speed with propellers and produce the necessary thrust to lift the system in the air. Most of the power of the battery is consumed by these motors. These motors are the primary actuators to create motion in the 3D space, travel from one position to another, and lift loads:

Figure 1.19 – A BLDC motor

• Propellers: Propellers are key thrust generators in the multirotor. These are mounted on the motors using screws or other mechanisms. Propellers are manufactured with lightweight materials in such a way that when rotated at high speed, they push the air downward, produce thrust, and lift the system upward. Each propeller produces a set amount of thrust when rotated at a desired RPM, which we will see in the coming chapters:

Figure 1.20 – Propellers

The power system of drones

The power system is the system that is responsible for powering the whole drone with its payload and other peripheral devices. This is the key system that keeps a drone powered, helps in getting the required endurance, and nullifies the effects of high wind or heavy maneuvers. Certain buck-and-boost converters and filters are added to step up and down voltages when required, and current consumption is greater.

These are the major components of the power system of drones:

• Battery: The battery is the most important part of the system. It serves as a key source of power delivery to the system. All systems and subsystems are powered by the battery. The battery must be capable of delivering power as required by the system without failure and serve the current delivery. It is also responsible for deciding the endurance of the drone:

Figure 1.21 – A battery

• Power distribution board: The power distribution board, as the name suggests, helps to distribute power to different systems. High-power-consumption elements such as motors take power through this board, and it is evenly distributed among them. A few more filtering elements are added, such as a capacitor to prevent any part from burning due to surges and extra load current:

Figure 1.22 – A power distribution board

• Buck-and-boost converters: Buck-and-boost converters are used in the circuitry to step up or down the voltage as required by peripheral devices and satisfy the needs of current requirements. These are used as per the power specifications of the payload:

Figure 1.23 – A step-down converter

Command and control system

This is a system that helps connect a drone for command and control and helps to keep the drone in check and in control. It is only due to this system that drones remain in control and can be controlled and operated in the way the pilot wants. This system also helps to keep drone health in check and enables real-time monitoring of sensor data.

The major parts that together make a communication system are the following:

• Remote control (RC): An RC device, or remote controller, is used to fly the drone under the visual LOS (VLOS). It helps to manually fly the system to any place and any orientation. It helps to change the mode of flying and also take control of the system during autonomous missions.

  However, it does not have live monitoring of the system’s sensor data and cannot see the live health of the system:

Figure 1.24 – An RC

• Ground control station (GCS): A GCS is an integrated control station that is used for system configuration and ground testing of systems, as well as to keep a check on system health and sensor data, and for command and control over drones for LOS and beyond VLOS (BVLOS) applications. A GCS is responsible for mission planning and execution in a completely autonomous mode. It is also responsible for the auto-tuning of systems for smoother flying:

Figure 1.25 – A handheld GCS

• Radio modem: A radio modem is a prime device used to communicate between a GCS and a drone. The range of the system depends upon the range at which radio modems communicate. It helps as a key communication link to control and command drones from the GCS. The radio modem helps to provide security to the link and transmit signals on which the GCS and drones communicate:

Figure 1.26 – A radio modem

• Antennas: Antennas play a key role in signal transmission and propagation. The antenna gains and orientation decide the range of the system and the degree to which it can move in the air. The type of antenna is an important parameter in deciding the range of a drone or bird, which we will see in later chapters:

Figure 1.27 – An antenna

• Navigation system: Post power, propulsion, and communication comes the navigation system. This navigation system is only helpful when driving the system in autonomous mode. The navigation system helps the drone to decide the direction and coordinates and moves in a particular direction autonomously or as guided in the mission.

  The drone is able to move in the selected paths and directions with the help of the navigation system, which is supported by built-in sensors. Major components that enable navigation systems are the following:

  • GPS: The GPS is a key component of the navigation system. The GPS used in drones has a GNSS such as Galileo, BeiDou, and other similar navigation systems embedded in it, which helps in getting real-time coordinates of the drone to display in the GCS and helps the pilot in getting real-time maps and locations. The same GPS coordinates are used by mission-planning software to decide the autonomous path of the drone and by the drone to navigate to the provided GPS coordinates. The take-off coordinates are also saved into the drone, which helps the drone to do Return to Launch (RTL) while in failsafe conditions:

Figure 1.28 – A GPS

• Compass or magnetometer: A compass or magnetometer is a crucial component of the drone navigation system. A GPS gives you the coordinates of the system and the desired go-to location, but a compass gives you the direction in which the drone travels. Drones travel to particular coordinates with the guidance of a compass. The compass gives the heading of the drone where the nose of the drone travels. The compass needs to be calibrated with respect to the magnetic field of the space for proper navigation:

Figure 1.29 – A magnetometer

• Processing unit or flight controller: The flight controller is the central processing unit (CPU) of the drone. This is called the brain of the drone. The flight controller receives the sensor data from the inbuilt sensors and peripheral sensors and delivers it to the actuators and motors, thus making the drone fly in manual as well as auto mode.

  The flight controller is programmed to behave in a particular manner in various flying modes and missions and under certain conditions, which we will see in the coming chapters:

Figure 1.30 – A flight controller

• Payload: A flying machine is to be used for some application and work for which it is designed and developed. The device that executes that particular work while being on the drone is called a payload. For example, a day/night camera is a payload for day/night surveillance (see Figure 1.31), a spray tank is a payload for an agriculture spray drone (see Figure 1.32), and an RGB sensor is a payload for a survey drone.

  The payload is the only object that does the job a drone is intended to do. We will see working with similar payloads later in this book for different applications:

Figure 1.31 – A camera payload

Figure 1.32 – A spray tank as a payload

These are some of the main components that are used in a drone system. In a later chapter, we will look at the specifications used for each of the components and how they can be best optimized to build a drone for a particular specification.

Having come to the end of this chapter, we have learned about unmanned systems, their development over time, and their requirements. We moved to UAVs and studied their types, important systems and subsystems, and their functionalities.

In the next chapter of this book, we will cover the dynamics of drones, various forces that act on the system when it’s in the air, and how to make it safe and balanced. We will also go through various aerodynamic terminologies that will help us to understand things better and look at how we use engineering with the aforementioned components to achieve those forces and build a whole flyable system.