Literature Review

CHAPTER TWO 2.1 Literature Review 2.2 Unmanned Aerial Vehicles (UAV) An unmanned aerial vehicle (UAV), commonly known as a drone, as an unmanned aircraft system (UAS), or by several other names, is an aircraft without a human pilot aboard. The flight of UAVs may operate with various degrees of autonomy: either under remote control by a human operator, or fully or intermittently autonomously, by onboard computers. Compared to manned aircraft, UAVs are often preferred for missions that are too "dull, dirty or dangerous “for humans. They originated mostly in military applications, although their use is expanding in commercial, scientific, recreational, agricultural, and other applications, such as policing and surveillance, aerial photography, agriculture and drone racing. Civilian drones now vastly outnumber military drones, with estimates of over a million sold by 2015. Multiple terms are used for unmanned aerial vehicles, which generally refer to the same concept. The term drone, more widely used by the public, was coined in reference to the resemblance of navigation and loud-and-regular motor sounds of old military unmanned aircraft to the male bee. The term has encountered strong opposition from aviation professionals and government regulators. 2.3 Types of Unmanned Aerial Vehicles There is no one standard when it comes to the classification of UAV. Defense agencies have their own standard, and civilians have their ever-evolving loose categories for UAV. People classify them by size, range and endurance, and use a tier system that is employed by the military. For classification, according to size, one can come up with the following sub-classes: 2.3.1 Multi rotor A multirotor is a rotorcraft with more than two rotors. An advantage of multirotor aircraft is the simpler rotor mechanics required for flight control. Unlike single- and double-rotor helicopters which use complex variable pitch rotors whose pitch varies as the blade rotates for flight stability and control, multirotor often use fixed-pitch blades; control of vehicle motion is achieved by varying the relative speed of each rotor to change the thrust and torque produced by each. Are used in Aerial Photography and Video Aerial Inspection. Advantage of Multi rotor     

Accessibility Ease of use VTOL and hover flight Good camera control Can operate in a confined area

Disadvantage of Multi rotor  Short flight times  Small payload capacity

Figure 2.3.1 Multi rotor

2.3.2 Fixed Wing A fixed-wing aircraft is an aircraft, such as an aero plane, which is capable of flight using wings that generate lift caused by the vehicle's forward airspeed and the shape of the wings. Fixed-wing aircraft are distinct from rotary-wing aircraft, in which the wings form a rotor mounted on a spinning shaft, and ornithopters, in which the wings flap in similar manner to a bird. Are used in Aerial Mapping, Pipeline and Power line inspection. Advantage of Fixed Wing  



  



Long endurance Large area coverage Fast flight speed Disadvantage of Fixed Wing Launch and recovery needs a lot of space no VTOL/hover Harder to fly, more training needed Expensive

Figure 2.3.2 Fixed Wing

2.3.3 Single Rotor A single-rotor helicopter has the benefit of much greater efficiency over a multi-rotor, and also that they can be powered by a gas motor for even longer endurance. It is a general rule of aerodynamics that the larger the rotor blade is and the slower it spins, the more efficient it is. This is why a quad-copter is more efficient than an octo-copter, and special long-endurance quads have a large prop diameter. A single-rotor heli allows for very long blades which are more like a spinning wing than a propeller, giving great efficiency. Are used in Aerial LIDAR laser scanning. Advantage of Single Rotor  



VTOL and hover flight Long endurance (with gas power) Heavier payload capability Disadvantage of Single Rotor

 



More dangerous Harder to fly, more training needed Expensive

Figure 2.3.4 Single Rotor 2.3.5 Hybrid VTOL(Vertical Take-Off and Landing) Fixed-wing UAVs with the ability to hover is a new category of hybrids which can also take off and land vertically. Many of these configurations were tried in the 1950s and 60s for manned aircraft, but they proved too complex and difficult to fly, with some disastrous results. With the arrival of modern autopilots, gyros and accelerometers, suddenly these whacky types are feasible because the autopilot can do all the hard work of keeping them stable, leaving the human pilot the easier task of guiding them around the sky. Are used in Drone Delivery. Advantage of Hybrid VTOL 

VTOL and long-endurance flight

Disadvantage of Hybrid VTOL 



Not perfect at either hovering or forward flight Still in development

Figure 2.3.5 Hybrid VTOL (Vertical Take-Off and Landing)

2.4 Configuration of Unmanned Aerial Vehicles 2.4.1 Quad Rotor Configuration A quadcopter has 4 motors mounted on a symmetric frame, each arm is typically 90 degree apart for the X4 config. Two motors rotate CW (clockwise), and the other two rotate CCW (counter clockwise) to create opposite force to stay balance. Quadcopter is the most popular multirotor configuration, with the simplest mechanical structure.

Figure 2.4.1 Quad Rotor Configuration 2.4.2 Hexa Rotor Configuration The hexacopter has 6 motors mounted typically 60 degree apart on a symmetric frame, with three sets of CW and CCW motors/propellers. Hexacopters are very similar to the quadcopters, but they provide more lifting capacity with the extra motors. There is also improvement in redundancy: if one motor fails, the aircraft can still remain stable enough for a safe landing. The downside is that they tend to be larger in size and more expensive to build.

Figure 2.4.2 Hexa Rotor Configuration

2.4.3 Octo Rotor Configuration A typical octocopter has 8 motors on the same level with four sets of CW and CCW propellers. Octocopters are similar to quadcopters and hexacopters. It’s like an upgrade version of the hexacopter with even more lifting capacity and redundancy. However the large number of motors means they draw more current, and you will probably need to carry multiple battery packs. Also it’s going to be expensive .They are very popular as aerial photography platforms and carrying heavy, professional filming gears.

Figure 2.4.3 Octo Rotor Configuration

2.4.4 X8 Rotor Configuration An X8 octocopter uses 8 motors that are mounted on four arms, on an “X” shaped frame with four sets of CW and CCW props.

Figure 2.4.4 X8 Rotor Configuration

2.4.5 Y8 Rotor Configuration An Y8 octocopter uses 8 motors that are mounted on eight arms, on an “Y” shaped frame with four sets of CW and CCW props.

Figure 2.4.5 Y8 Rotor Configuration

2.6 Mechanism of Flying An advantage of quadrotor over a traditional helicopter is fixed rotor propulsion mode, which uses rapidly spinning rotors to push air downwards thus creating a thrust force keeping the helicopter aloft. Helicopter configurations require complicated machinery to control the direction of the motion for which a swashplate is used to change the angle of attack on the main rotor. The complicated design of the rotor and swashplate mechanism presents some problems, increasing construction costs and design complexity. In case of quadrotors the controlling is quite different and also difficult as in helicopter, but interesting problem which has six degrees of freedom (three translational and three rotational) shown in Figure 2.6. It has four independent inputs (rotor speeds), and in order to achieve the six degrees of freedom, rotational and translational motions are coupled (19). To remain stable in its position while flying it should have its own damping because it has very little friction. Each rotor is aligned such that, to have opposite two rotors in one direction and other two in opposite direction. This movement cause the torque from each rotor to cancel by the corresponding motor rotating in opposite direction (Figure 2.14).

Figure 2.14 Flight dynamics Let us consider the quadrotor moving in counter clockwise from the front propeller and F i be the force of each rotor’s, where i= 1,2,3 and 4 respectively as shown in Figure 2.14, such that the rotors F1 and F3 rotate in counter-clockwise and F2 and F4 rotate in clockwise. As mentioned earlier to perform the stationary hover, all the four rotors rotate at the same rate and the total thrust of the craft is equal to its mass, m (21). The total thrust can be represented by u= F1+F2+F3+F4 and Fi is the force of rotor i. Yawing, moving left and right, pitching and rolling is shown in Table 2.1,

S. No Movement

Description

Result

1.

Yaw movement – F1 and F3 are sped up Net torque on the craft is Counterclockwise inversely proportional to F2 negative and it will yaw while and F4. remaining in same altitude.

2.

Upwards downwards

3.

Yaw movement Clockwise

F2 and F4 must increase Net torque on the craft is proportionally to F1 and F3 negative and it will yaw while decrease. remaining in same altitude.

4.

Roll to left

Decreasing the speed of F2 Roll towards left is achieved, and increasing the speed of Note: Both the decreasing and increasing should be done at the F4 same rate, to maintain the zero net torque.

5.

Roll to right

Increasing the speed of F2 Roll towards right is achieved. and decreasing the speed of F4

6.

Pitching forward

Decreasing the speed of F1 Pitch towards left is achieved. and increasing the speed of F3

7.

Pitching to right

Increasing the speed of F1 Pitch towards right is achieved. and decreasing the speed of F3

and F1 and F3 do not increase Craft will move in z-direction, proportionally to F2 and F4 because the net thrust will be no decreasing. longer equal to zero.

Table 2.1 Dynamics of the quad-rotor

Figure 2.15 Quadrotor dynamics.

2.3 Parts of Unmanned Aerial Vehicles Unmanned Aerial Vehicles are made with different parts with respect to the need of the designer to meet the demands. The necessary parts of the UAV are as follows; 2.3.1 Frame Every quadcopter or other multirotor aircraft needs a frame to house all the other components. Things to consider here are weight, size, and materials. We recommend the DJI Flame Wheel F450 or one of the many clones. These are great quadcopter frames. Check out our review of the Flame Wheel F450 here. They’re strong, light, and have a sensible configuration including a built-in power distribution board (PDB) that allows for a clean and easy build. There are also a ton of spare parts and accessories available from many different websites. There are also a ton of clones out there, most of which include the same built-in PDB and durable construction as the original. Parts and accessories are 100% compatible and interchangeable.

Figure 2.3.1 Frame of quadrotors

2.3.2 Motors The motors have an obvious purpose: to spin the propellers. There are tons of motors on the market suitable for quadcopters, and usually you don’t want to get the absolute cheapest motors available, but you also don’t want to break the bank when some reasonably priced motors will suffice. Motors are rated by kilovolts, and the higher the kV rating, the faster the motor spins at a constant voltage. When purchasing motors, most websites will indicate how many amps the ESC you pair it with should be and the size of propeller you should use.

Figure 2.3.2 Motor for quadrotor 2.3.3 Electronic Speed Controls The electronic speed control, or ESC, is what tells the motors how fast to spin at any given time. You need four ESCs for a quadcopter, one connected to each motor. The ESCs are then connected directly to the battery through either a wiring harness or power distribution board. Many ESCs come with a built-in battery eliminator circuit (BEC), which allows you to power things like your flight control board and radio receiver without connecting them directly to the battery. Because the motors on a quadcopter must all spin at precise speeds to achieve accurate flight, the ESC is very important. These days if you are building a quadcopter or other multirotor, it is pretty much standard to use ESCs that have the SimonK firmware on them. This firmware changes the refresh rate of the ESC so the motors get many more instructions per second from

the ESC, thus have greater control over the quadcopter’s behavior. Many companies sell ESCs that have the SimonK firmware already installed.

Figure 2.3.3 Electronic Speed Controller 2.3.4 Flight Controller The flight control board is the ‘brain’ of the quadcopter. It houses the sensors such as gyroscopes and accelerometers that determine how fast each of the quadcopter’s motors spin. Flight control boards range from simple to highly complex. A great flight control board for first time quadcopter builders is the Hobby King KK2.0. It is affordable, easy to set up, and has strong functionality. It can handle just about any type of multirotor aircraft so if you later want to upgrade to a hexacopter or experiment with a tricopter, you won’t need to purchase another board. Update: There is a newer version of the KK flight control board – the KK2.1.5

Figure 3.3.4 Flight Controller 2.3.5 Radio Transmitter and Receiver The radio transmitter and receiver allow you to control the quadcopter. There are many suitable models available, but you will need at least four channels for a basic quadcopter with the KK2.0 control board. We recommend using a radio with 8 channels, so there is more flexibility for later projects that may require more channels. The Turnigy 9x is a great choice for a first radio. It’s inexpensive yet still has some advanced functionality. There is also a large community of 9x users out there, so troubleshooting is easier. Chances are any problem you have has been experienced and solved before, or someone on a forum like rcgroups will be able to help you out. Update: there is a newer model of this radio out – the Turnigy 9xR Pro

Figure 2.3.5 Radio Transmitter and Receiver

2.3.6 Propellers A quadcopter has four propellers, two “normal” propellers that spin counter-clockwise, and two “pusher” propellers that spin clockwise. The pusher propellers will usually be labeled with an ‘R’ after the size. For the quadcopter configuration in this post, we’re using 9×4.7 props. This is a good size for the motors and ESCs we’re using. Propellers are available at a lot of websites.

Figure 2.3.6 Propellers

2.3.6 Battery Quadcopters typically use LiPo batteries which come in a variety of sizes and configurations. We typically use 3S1P batteries, which indicates 3 cells in parallel. Each cell is 3.7 volts, so this battery is rated at 11.1 volts. LiPo batteries also have a C rating and a power rating in mAh (which stands for milliamps per hour). The C rating describes the rate at which power can be drawn from the battery, and the power rating describes how much power the battery can supply. Larger batteries weigh more so there is always a tradeoff between flight duration and total weight. A general rule of thumb is that doubling the battery power will get you 50% more flight time, assuming your quadcopter can lift the additional weight. For this quadcopter.

Figure 2.3.6 Battery

2.3.7 Battery Charger Charging LiPos is a complex process, because there are usually multiple cells within the battery that must be charged and discharged at the same rate. Therefore, you must have a balance charger. There are many chargers on the market that will do the job, but be careful of cheap or off-brand chargers as many of them have faulty components and can cause explosions or fires. In general, you should absolutely never leave LiPo batteries charging unattended. Many people charge batteries outside on a cement area or in a fireproof LiPo bag (although the effectiveness of these is up for debate). We recommend the IMAX B6 AC Balance Charger. It is affordable but reliable. Be wary of knock-offs.

Figure 2.3.7 Battery Charger 2.3.8 Video system Camera or video setup is an optional part of a quadrotor. Today’s development in video technology has brought camera, as an important part of a quadrotor. The quality of the systems is based on the quality of the video transmitter and the image quality of the goggles or monitor display. Quad’s used commercially have FPV (First Person View) camera as shown in Figure 2.12, which uses its own quad power. But military or heavy clearance area quadrotors uses intelligent cameras which uses separate power box for operating systems.

Figure 2.3.9 FPV Camera's (Google search on Sony FPV cams)

2.4 Technical limitations of Unmanned Aerial Vehicles (UAV) The first limitation of is in their flying time. You can expect between eight and 15 minutes in the air before the battery needs changing. Operators usually carry plenty of batteries and will probably look for ways of charging them on location too. Drone batteries use lithium polymer technology which allows considerable energy to be stored in a small package. But they are associated with fire risk and have been known to spontaneously catch fire while charging or if punctured. Most airlines restrict the numbers of batteries on board. Check with your airline for their policy on transporting batteries. It is recommended never to leave them unattended while charging, and to transport and store them in a fireproof box. Most Small Unmanned Aerial Vehicles (UAV) have a maximum speed of 30mph, which restricts their use to weather with wind speeds of less than 20mph. It is not recommended to fly drones in rain, snow, or even in drizzle. Apart from any physical effects on the aircraft, there is a danger the electronics will be damaged, and communication between the controller and the drone can be affected when there is any kind of precipitation in the air. Manufacturers may claim the controller can communicate with the aircraft up to 1km distance, but your effective operating distance will be less than that - because of the requirement for line of sight to the drone, because legal maximum distances are lower (see legal section) and, on occasion, because communication with the drone may be compromised by the presence of signals from mobile phone masts or towers. Cold temperatures reduce battery life and give shorter flying times. Altitude can be a factor: the thin air in the mountains means that special rotors are needed and battery life is reduced. Finally, The conditions that may be unusually hot or cold for a certain amount of time; and their eyes will often need protection if the work consists of close watching of a UVA in the distance in very sunny conditions.

REFFERENCE

[1] Quad Rotorcraft Control: Vision-Based Hovering and Navigation Luis Rodolfo García Carrillo, Alejandro Enrique Dzul López, Rogelio Lozano, Claude Pégard Springer Science & Business Media, 12 Aug 2012 - Technology & Engineering