Battery

The most commonly used battery in quadcopter is LiPo batteries, which is available in many different configurations and sizes. The battery that is normally used is 3S1P batteries, which

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stands for (3 cells in one parallel, connected in series). The battery rating is 11.1 volts; each cell is 3.7 volts, having the power rating in mAh (milliamps per hour) and a C rating. The C rating stands for “the rate at which the power can be drawn from the battery”; also, it tells how much power the battery can supply. There is always a trade-off between the total weight and the endurance as the larger batteries weigh more. Hence, per the general rule of thumb if one, doubles the battery power, 50% more endurance is achieved, knowing that the quadcopter will be able to lift with the extra weight. (Tech 2014)

3.1.1.6

Flight Controller

This is what is called the brain of the quadcopter “The Flight Controller”. The sensors such as accelerometers and gyroscope are housed here, which helps to decide how fast each motor of the quadcopter should spin. There are various types of flight control boards available depending upon the type of controller is needed and the affordability.

Figure 3-6: Flight Controller (Anon 2015)

The functions the flight controllers can perform many functions which may include the following (Maria 2014)

 “Self-Levelling – the ability to let go of the pitch and roll stick on the transmitter and have the quadcopter stay level.

 Gyro Stabilization – the ability to easily keep the quadcopter stable and level under the pilot’s control. This is a standard feature of all flight control boards.

 Altitude Hold – the ability to hover a certain distance from the ground without having to manually adjust the throttle.

 Care Free – The pilot can control the copter as if it is pointing in its original direction as the orientation of the copter changes.

 Return Home – the ability to automatically return to the point where the copter initially took off.

 Waypoint Navigation – the ability to set specific points on a map that copter will follow as part of a flight plan.”

29  Position Hold – the ability to hover at a specific location.

3.1.1.7

Optical Components

If one is still not broke after purchasing all the necessary part, then might consider looking toward some optical components such as the barometers, GPS module, ultrasonic sensor and so on. These components can improve the performance of the quadcopter and bring in more features.

 Barometer – barometer can be used when one is higher up in atmosphere. This sensor can help measure the altitude by measuring the pressure and humidity.

 Ultrasonic Sensor – “this sensor can be used to measure the distance between the

quadcopter and the ground. It comes handy when the one wants to keep the quadcopter at a certain altitude without having to adjust the height flying constantly our self”.

 GPS Module – it can help retrieve precise location by using the satellite, which can be used to determine the speed and path of the quadcopter. This is especially useful for autonomous flying vehicles as they need to know the path they must fly on as well as the exact position.

3.2 Mechanics of Quadcopter

In order to learn how to control a quadcopter, firstly, it is essential to learn about the mechanics involved with it. i.e. how the quadcopter can fly by varying the speed of the propellers. As described in previous chapters that quadcopters flight mechanics is different to that of conventional aircraft (which includes aeroplanes and helicopters). They have a vertical take-off and land (VTOL) system like the helicopters, but flight mechanics and attitude is poles apart. The helicopter has two propellers, one which is the stabilizer tail propeller and the other provides attitude and lift changes to roll and pitch, which is considered the main propeller. The torque forces coming from the main propeller makes the aircraft unsteady, therefore the tail rotor is used to stabilize it from these forces as well as to control the yaw. On the other hand, aircraft having multi-rotors or propellers (four or more) rely on them to act together to perform roll and pitch movements. The on-board flight controller is responsible for analysing the attitude by using the pilot control or other on-board sensors, so it can control the motors. The quadcopter is moved faster or slower depending on the tilt position. It must be taken into consideration that if the tilt angle is not much and the quadcopter will move very slowly and if the tilt angle is very steep the quadcopter will flip and crash. The attitude change is accomplished by varying the speed of motors with less thrust and more thrust (front and back, respectively) and this is all done by the flight controller. The details are later in this chapter.

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3.2.1

Flight Orientations

Since quadcopter are symmetrical, therefore they can fly in two different configurations (i.e. Plus (+) and x). In x configuration, the front two motors/propellers will provide power, while in plus (+) configuration only one of the front motor/propeller will provider power. It is discussed further in the next section.

3.2.1.1

Axis Representation

For each of the two configurations (+, x), the coordinate system is the same. The quadcopter will ascend and descend along z-axis, move forward and backward along x-axis and move left and right along y-axis. (Khan 2014)

 “Yaw is the rotation around z-axis, which turns the quadcopter right or left by changing

the heading as well as the direction it flies in.

 Pitch is the rotation around y-axis, which allows forward and backward flying along x- axis.

 Roll is the rotation around x-axis, which allows right and left flying along y-axis.”

Figure 3-7: Axis Representation(Khan 2014)

3.2.1.2

Attitude Changes

Flight controller comes into play when attitude changes are required by the quadcopter. It changes the speed of the motors per the user’s requirements received from the transmitter. Helicopters and quadcopter have the same principle when it comes to stabilization and yaw control. There are a set of each clockwise rotating motors and counter clockwise rotating motors. Figure 3-8 shows; motor 1 & 3 are rotating clockwise and 2 & 4 are rotating counter clockwise. The rotating counter clockwise motors recompenses for the torque and it helps the quadcopter control in yaw rotation around the z-axis.

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Since the motors are rotating in two different directions, that’s why two different types of propellers are used so they can provide thrust whilst propellers being in different rotating direction. Else, if the propellers are providing thrust in the same directions (i.e. a set of them pushing air upwards and the other set downwards). Due to this reason, another name for these propellers are pullers and pushers. The details of the two configurations are detailed below:

X Configuration Plus (+) Configuration

Pitch Down (forward

flight)

M1 & M2 thrust decreased M1 thrust decreased

M3 & M4 thrust increased M3 thrust increased

Pitch Up (backward flight)

M1 & M2 thrust increased M1 thrust increased

M3 & M4 thrust decreased M3 thrust decreased

Roll Left (left flight)

M2 & M3 thrust increased M2 thrust increased

M1 & M4 thrust decreased M4 thrust decreased

Roll Right (right flight)

M2 & M3 thrust decreased M2 thrust decreased

M1 & M4 thrust increased M4 thrust increased

Yaw Left (turn left)

M2 & M4 thrust increased M2 & M4 thrust increased M1 & M3 thrust decreased M1 & M3 thrust decreased

Yaw Right (turn right)

M2 & M4 thrust decreased M2 & M4 thrust decreased M1 & M3 thrust increased M1 & M3 thrust increased

Table 3-1: X & Plus (+) flight configurations (Digg 2014) Figure 3-8: Plus (+) flight orientation (left) & X flight orientation (right)

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The flight controller uses the motor out configurations to control the motors depending upon the user controls (Digg 2014)

X Configuration Plus (+) Configuration

M1 = T + P + R – Y M1 = T + P + Y

M2 = T + P - R + Y M2 = T - R – Y

M3 = T - P - R – Y M3 = T - P + Y

M4 = T - P + R + Y M4 = T + R - Y

Table 3-2: X & Plus (+) motor out configurations (T=Throttle, P=Pitch, R=Roll, Y=Yaw) (Digg 2014)

The user changes the controls from positive to negative to change the direction, hence if the above configurations is used, one can increase and decrease the thrust depending on the value which is received by the receiver. Motor out configurations as well as attitude configurations will vary depending on clockwise/counter clockwise rotating propellers and motor positioning on different quadcopters. (Maria 2014; Digg 2014; Khan 2014)