Working Principle and Components of Drone

 

How do drones fly in air? Which drone is more popular?

1. Introduction to Drone or UAV

  • Any aircraft or flying machine operated without a human pilot such machines is called as an unmanned aerial vehicle (UAV). It can be guided autonomously or remotely by human operator using on board computers and robot.
  • During surveillance or military operation, UAV can be a part of an unmanned aircraft system (UAS)., Drones are separately for air and water

 Subjects for Drone or UAV

Understanding and development of drones depend on many subjects. Design of drone for particular application comprises many factors like aerodynamic shape of propellers, strength and weight of drone parts, electric motor, electric speed controller, radio transmitter or receiver, and software interface on mobile or computer for monitoring and data analysis

  • Fluid Dynamics or Aerodynamics:
    • Fluid dynamics plays an important role to decide the forces acting on body on drone
    • Shape, size and speed of propeller and drone depend on aerodynamics of propellers or blades
    • CFD modelling helps for flow dynamics of air flow over drone
    • Wind tunnel testing of aero foil blade of drone is still important for testing of CFD results
  • Mechanical Design
    • Rigid body dynamics to study the motion and forces acting on drones
    • Strength of materials
    • Low weight and rigid materials are selected for drone
  • Electronics and Electrical Components:
    • Electric motor with and without brush is required to drive the propellers
    • Electronic Speed Controller
    • Flight controller unit and computer processors
  • Radio Communication: transmitter and receiver for radio signals
  • Battery: Low weight and high-power wattage battery is important
  • Software based interface: data collection and analysis using mobile or computer

2.Working Principle of Drone and Flow Pattern

  • The subject of Fluid dynamics plays a significant role for design and development of aircraft and drones. This subject consists of working principle of aerodynamics of aircrafts.
  • A sufficient amount of upward force is required to lift the vehicle against the gravity which is names Lift.
  • A force created to move the vehicle or body in motion is called thrust. These forces can be studied using laws of fluid flows

  • When air flows over an aerofoil and  pressure, viscous and drag force act on the profiles
  • Force is directly proportional to the velocity air at the inlet

  • Flow pattern around the cross-section of aerofoil or propeller is shown below. High fluid pressure at the bottom and low pressure at the top of propeller cause an up ward force which is called as lift. This force is responsible for lifting the weight of aero-plane or drone.
  • The amount of lift force depends on the angle of inclination of aerofoil or propeller.

  • Based on the principle of conservation of energy in fluid flow (Bernoulli’s principle, the sum of all forms of energy in a fluid is constant along the streamline
  • When air flows over an aero foil or wing, its velocity increases at the top portion. But the pressure of air decreases.
  • In contrast, the air velocity decreases and pressure increase at the bottom side of blade. The next pressure difference across the aero foil results in an upward force which is called as lift
  • CFD modeling of flow over an aero foil has been important in many vehicular and aero-space industries

4. Types of drones based on number of propellers

Number of propellors are provided to drones. The more propellors improve the stability of drones and load carrying capacity but such drones need more battery power to drive more motor to get high power. A quadcopter is more popular drone.

    • Bicopter (2 propeller)
    • Triplecopter (3 propeller)
    • Quadcopter (4 propeller)
    • Hexacopter (6 propeller)
    • Ocptacopter (8 propeller)

Working  Principle of Quadcopter

  • A quadcopter has four propellers at four corners of the frame
  • For each propeller, speed and direction of rotation is independently controlled for balance and movement of the drone
  • In a traditional quadrotor, all the four rotors are placed at equal distance each othe
  • To maintain the balance of system, one pair of rotors rotates in clockwise direction and other pair rotate in anti-clockwise direction
  • To move up (hover), all rotors should run at high speed. By changing the speed of rotors, the drone can be move forward, backward, and side-to-side

5. Dynamics of Quadcopter

  • Movement of drone are classified into four types based on relation motion between four propellers: 1) throttle, 2) Pitch, 3) Roll, and 4) Yawn

  • Throttle/ Hover: up and down movement of drone is called throttle
    • If all four propellers run at normal speed, then the drone will move down
    • If all four propellers run at higher speed, then the drone will move up. This is called hovering of drone
  • Pitch: movement of drone about lateral axis (either forward or backward) is called pitching motion
    • If two rear propellers run at high speed, then the drone will move in forward direction
    • If two front propellers run at high speed, then the drone will move in backward direction
  • Roll: movement of drone about the longitudinal axis is called rolling motion
    • If two right propellers run at high speed, then the drone will move in left direction
    • If two left propellers run at high speed, then the drone will move in right direction
  • Yawn: the rotation of the head of the drone about vertical axis (either the left or right) is called Yawning motion
    • If two propellers of right diagonal run at high speed, then the drone will rotate in anti-clockwise direction
    • If two propellers of left diagonal run at high speed, then the drone will rotate in clockwise direction

 

6. Forces and Moments Acting on a Drone

6.2 Major forces acting on a Drone

When a drone moves in air, various forces acts on its. The resultant force will decide its movement. There are major force acting on a drone

  • Weight
    • Due to the mass of drone, the body mass force always acts in the direction of gravity
    • Higher the weight of drone, more power is required to lift and move the drone
    • Weight of drone = mass of drone × acceleration due to gravity
  • Lift:
    • The vertical force acting on the drone is called lift
    • This force is due to pressure difference across the drone (in vertical direction). Hence, speed, size and shape of propeller blade decide the amount of lift force
    • Lift is essential to lift the body against the gravity
    • To create this force, all four propellers run at high speed to lift the drone
  • Thrust
    • The force acting on the drone in the direction of motion is called thrust. However, for drone dynamics it is normal to the rotor plane.
    • During hovering, the thrust is purely vertical. If thrust is inclined then the drone will tilt forward or backward.
    • This force is essential to move the drone in desired direction at equal speed
    • To get desired motion, two propellers have given high speed
  • Drag
    • The force acting on the drone in the opposite direction of motion due to air resistance is called drag
    • This may be because of pressure difference and viscosity of air
    • To reduce the drag, aerodynamic shape of drone is selected

6.2 Kinematic for Quadcopter

  • The thrust produced by each propeller is perpendicular to the plane of rotation of propellers. It is directly proportional to square of angular velocity of propeller

Fi = kf ×ωi2

  • If L is defined as the distance between two motors or propellers for any diagonal of drone, then the reaction moments about the X-axis and Y-axis

Mx = (F3 – F4) × L

My = (F1 – F2) × L

  • Newton’s second law of motion
    • For linear motion: Force = mass × linear acceleration
    • For rotational motion: Torque = inertia × angular acceleration

a) Hovering Motion

    • Equilibrium Conditions for hovering

mg = F1 + F2 + F3 + F4

All moments = 0

    • Equation of motion

m = F1 + F2 + F3 + F4 – mg

m = 0

  b) Rise or Fall Motion (Throttle up)

    • Conditions for hovering (rise)

mg < F1 + F2 + F3 + F4

All moments = 0

    • Conditions for Fall

mg > F1 + F2 + F3 + F4

All moments = 0

    • Equation of motion

m = F1 + F2 + F3 + F4 – mg

m > 0

c) Yaw Motion

    • Conditions for hovering

mg = F1 + F2 + F3 + F4

All moments ≠ 0

    • Equation of motion

mass* linear acceleration = F1 + F2 + F3 + F4 – mg

Izz *angular acceleration@ Z-axis = M1+ M2+M3+ M4

d) Pitch and Roll Motion

    • Conditions for hovering

mg < F1 + F2 + F3 + F4

All moments ≠ 0

    • Equation of motion

mass* linear acceleration = F1 + F2 + F3 + F4 – mg

Ixx * angular acceleration @ x-axis = (F3 – F4)×L

7. Rigid-body dynamics

  • To calculate individual speeds and forces acting on drone, the three-dimensional rigid-body dynamics should be modelled
  • The first step is to identify the reference coordinates, direction of rotor speed and forces acting the drones
  • For rigid body we have to consider the effect of aerodynamic, inertial, gravitational and gyroscope
  • Aerodynamic Forces:   rotation of the propellers in air causes various forces such as friction and drag
  • Secondary aerodynamic effects: blade flapping, ground effect and local flow fields
  • Inertial counter torques: gravitational forces acting at the centre of drone affect the rotation of propellers
  • Gyroscopic effects: change in the orientation of drone body and plane rotation of propellers.

  • Based on Newton-Euler equations, all forces and moments acting on quadcopter are combined and results in a complete model of the drone dynamics
  • This physical model is useful to control the desired motion of quadcopter

8. Major Components of Drones

The following are major parts of drone.

  1. Frame:
  • It should have sufficient strength hold the propeller momentum and additional weight for motors and cameras
  • Sturdy and less aerodynamic resistance
  1. Propellers:
    • The speed and load lifting ability of drone depends on shape, size and number of propellers
    • The long propellers create huge thrust to carry heavy loads at a low speed (RPM) and less sensitive to change the speed of rotation
    •  Short propellers carry less loads. They change rotation speeds quickly and requires a high speed for more thrust.
  2. Motor
    • Both motors brus less and brushed type can be used for drones
    • Brushed motor is less expensive and useful for small-sized drones
    • Brushless type motors are powerful and energy very efficient. But they need Electronic Speed ​​Controller (ESC) to control their speed. These brushless motors are widely used for racing freestyle drones, traffic survey and aerial photography drone.
  3. ESC (Electronic Speed Controller)
    • ESC is used to connect the battery to the electric motor for power supply
    • It converts the signal from the flight controller to revolution per minted (RPM) of motor
    • ESC is provided to each y motor of the drone
  4. Flight Controller (FC)
    • It is the computer processor which manages balance and telecommunication controls using different transmitter
    • Sensors are located in this unit for accelerometer, barometer, magnetometer, gyrometer and GPS
    • The distance measurement can be carried out by ultra sound sensor
  5. Radio Transmitter sends the radio signal to ESC to pilot to control motor speed.
  6. Radio Receiver: Received the signal from the pilot. This device is attached to the quadcopter
  7. Battery: High-power capacity, Lithium Polymer (LiPo) are used for most drones. The battery can have 3S (3 cells) or 4S (4 cells).

 

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