Quadrotor

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					                                   Quadrotors-The Flying Robots
                 B. Hari kiran (EK112332), B. Karthik (EK114160), G. Siva kumar(EK114199)
                            EEE Department, V.R.Siddhartha Engineering College
                                     Kanuru, Vijayawada, Krishna Dist;
          harikiranbavineni.9@gmail.com,pittu3030@gmail.com,sivakumarg2009@gmail.com
Abstract: Quadrotors also called as                                The more recent generation of
Quadcopters, Quadrocopter or Quadrotor                     Quadrotors are commonly designed to be
helicopters are emerging as the best spying                unmanned aerial vehicles (UAVs). These
devices and also found useful in areas of                  vehicles use an electronic control system and
Science and Technology. Due to the increase in
                                                           electronic sensors to stabilize the aircraft. With
Integrated Electronics Technology and the
application of Microprocessors has made                    their small size and agile maneuverability, these
Quadrotor technology bounce ahead. This                    Quadrotors can be flown indoors as well as
paper provides the basic Information about                 outdoors
Quadrotor working, its components and its
applications in various fields.

Introduction: A Quadrotor, also called a
Quadrotor helicopter or quadrocopter, is an
aircraft that is lifted and propelled by four
rotors. They can also be classified as
helicopters, though unlike standard helicopters,
Quadrotors use fixed-pitch blades, whose rotor
pitch does not vary as the blades rotate. Control
                                                                          New Generation UAV
of vehicle motion can be achieved by varying
the relative speed of each rotor to change the            History: Many designs were proposed that
thrust and torque produced by each.                       dated back to 1920’s.In 1920 Etienne
                                                          Oehmichen proposed a model which consisted
        The quadrotor designs can be divided              of four rotors run by a single engine with eight
in to two generations. The first generation               propellers. The model was a little complex but
Quadrotors were designed to carry one or more             showed a better stability.
passengers. These vehicles were among the first
successful heavier-than-air vertical take off and                   Later in 1922 Dr. George de Bothezat
landing (VTOL) vehicles. However, early                   and Ivan Jerome proposed another model in the
prototypes suffered from poor performance,                shape of ‘X’ with six rotors. Two small
and latter prototypes required too much pilot             propellers with variable pitch are provided to
work load, due to poor stability augmentation.            gain roll and yaw control. This model seemed a
                                                          little better over the Oehmichen’s model but
                                                          lacked stability. The highest it ever reached was
                                                          about 5m. Although demonstrating feasibility, it
                                                          was,          underpowered,         unresponsive,
                                                          mechanically complex and susceptible to
                                                          reliability problems.
            De Bothezat Quadrotor, 1923.
         Again in 1950 a design was developed        adjacent ones are in reverse direction. Here it
featuring two engines driving four rotors with       can be observed in the figure shown here.
wings added for additional lift in forward flight.
No tail rotor was needed and control was
obtained by varying the thrust between rotors.
This unique helicopter was intended to be the
prototype for a line of much larger civil and
military quadrotor helicopters. But due to a lack
of orders for commercial or military versions
however, the project was terminated.

         The most recent designs were
Unmanned Aerial Vehicles(UAV’s) which has
overcome all the defects that earlier designs
suffered. These designs make use of
microprocessor with on board memory to
control the relative speed of four rotors there
by controlling the translatory, rotatory and
vertical motion i.e. roll, pitch and yaw.The                    Directions of motor rotation
figure shows the roll, yaw and pitch directions.
                                                     Each propeller run by the rotor produces both
                                                     the torque and thrust at the centre of the
                                                     design. Both the thrust and the torque depend
                                                     on the square of the velocity of the propeller.
                                                     So motion of the Quadrotor can be controlled
                                                     by changing the relative speed of the rotors.

                                                         When all the rotor speeds are equal
                                                          then the quad moves vertically upwards
                                                          or downwards depending on the thrust
            Direction of Roll, Yaw, Pitch                 produced
 Using other sensors like IR sensor, Altimeter           When both rotors on either axes rotate
sensor, IMU 6 DOF (Degree Of Freedom) sensor,             with the same velocity but with
etc. allowed flexibilities for autonomous flight          difference in velocities between the
systems.                                                  two axes then this produces rotation
                                                          about the centre
Quadrotor Dynamics:                                      When both the rotor speeds on one axis
                                                          are equal and the velocities of the
Quadrotor gains its flight from the thrust
                                                          rotors on the other axis are unequal
produced by the four rotors. The important
                                                          then it produces linear or translatory
design feature in quadrotor is that opposite pair
                                                          motion.
of rotors rotate in the same direction while the
                                                   speed controllers for varying the speed of the
                                                   motors.
The above points can be explained in this figure


                                                   DC Motors

                                                   An electric motor converts electrical energy into
                                                   mechanical energy. Most electric motors
                                                   operate through interacting magnetic fields and
                                                   current-carrying conductors to generate force,
                                                   although a few use electrostatic forces. Motors
                                                   with high rpm (rotations per minute) are
                                                   required for creating necessary thrust to lift
                                                   both the quad and the extra load i.e. payload.
                                                   The best option is to use the Brushless Motors
                                                   which are more reliable and can rotate with a
                                                   very high rpm. On the other hand using the
                                                   brushed motors is degraded as the brushes
               Quadrotor Dynamics                  would burn out on continuous usage. Generally
                                                   DC motors with rpm greater than 6000 are
The complete dynamics of quadrotor requires
                                                   good. But for carrying extra loads Motors with
the knowledge of Aerodynamics Engineering.
                                                   more rpm are preferred.
But by considering the basic forces acting on a
body the required equations can be derived and     Propellers
a control loop can be designed for stabilizing,
movement and hovering the quadrotor.               A propeller is a type of fan that transmits power
                                                   by converting rotational motion into thrust. A
Quadrotor Assembly:                                pressure difference is produced between the
                                                   forward and rear surfaces of the airfoil-shaped
Quadrotors are embedded systems whose
                                                   blade, and air or water is accelerated behind
actions are controlled by microprocessors or
                                                   the blade. The propeller type used in case of
microcontrollers. Generally the basic units of
                                                   quadrotors is counter rotating type propeller.
the quad consist of Controlling Unit and the
                                                   The equations of thrust and torque in the
Controlled Unit.
                                                   following equations suggest that both of them
         The controlling unit can be made of       depend on square of the velocity.
Microprocessor with on board memory i.e.
simply a Microcontroller or by using Field
Programmable Gate Array (FPGA).The best
option is to use the Microcontroller because of
its easy interface and ease in programming. The
controlled unit consists of small DC motors with   Where T=thrust, Q=Torque.
Thus from the above equations it is clear that a     best alternative is the MCU (Micro Controller
propeller of larger diameter produces larger         Unit).
thrust at the same time it also increases the
load torque on the motor. Thus a motor               Microcontroller Unit
propeller set of proper rating must be
                                                     A microcontroller (sometimes abbreviated µC,
considered for maximum efficiency.
                                                     uC or MCU) is a small computer on a single
Electronic speed controllers (ESC’s)                 integrated circuit containing a processor core,
                                                     memory, and programmable input/output
An electronic speed control or ESC is an             peripherals. Program memory in the form of
electronic circuit with the purpose to vary an       NOR flash or OTP ROM is also often included on
electric motor's speed, its direction and possibly   chip, as well as a typically small amount of RAM.
also to act as a dynamic brake. The rapid            Microcontrollers are designed for embedded
switching of the transistors is what causes the      applications, in contrast to the microprocessors
motor itself to emit its characteristic high-        used in personal computers or other general
pitched whine, especially noticeable at lower        purpose applications. Microcontrollers are used
speeds. It also allows much smoother and more        in automatically controlled products and
precise variation of motor speed in a far more       devices, such as automobile engine control
efficient manner than the mechanical type with       systems, implantable medical devices, remote
a resistive coil and moving arm once in common       controls, office machines, appliances, power
use. DC ESCs in the broader sense are PWM            tools, and toys. The best open source
controllers for electric motors. Usually, back       electronics prototyping platform based on
EMF from the motor is used to detect this            flexible, easy-to-use hardware and software is
rotation. The below figure shows the images of       Arduino
motor, ESC and propellers




                                                                       Arduino UNO
             Motor, ESC and Propellers
                                                     It can sense the environment by receiving input
          Coming to the control unit as discussed    from a variety of sensors and can affect its
earlier it may consist of either a Microcontroller   surroundings by controlling lights, motors, and
or FPGA (Field Programmable Gate Array). The         other actuators. The microcontroller on the
                                                     board is programmed using the Arduino
programming language (based on Wiring) and
the Arduino development environment (based
on Processing). Arduino projects can be stand-
alone or they can communicate with software
on running on a computer.

Sensors A sensor is a device that measures a
physical quantity and converts it into a signal
                                                                  Ultra sonic distance sensor
which can be read by an observer or by an
instrument. The use of sensors in case of             IMU 6 DOF (Degrees Of Freedom) The 6DOF
quadrotors is very essential to control the flight,   provides 3 axes of acceleration data, 3 axes of
stabilize and also to have autonomous flight          gyroscopic data, and 3 axes of magnetic data.
systems. The various essential sensors that may       Each independent channel is user selectable, as
be included are                                       is the sampling frequency. This sensor can
                                                      replace all the other sensors required for
Accelerometer-is a device that measures the
                                                      stability.
proper acceleration of the device.




           Triple axis accelerometer sensor

Gyro sensor-is a device for measuring or
maintaining orientation, based on the principles
of conservation of angular momentum.

Altimeter-is an instrument used to measure the
altitude of an object above a fixed level.
                                                      Controlling the Quadrotor:
Ultrasonic sensors generate high frequency
sound waves and evaluate the echo which is            A quadrotor can be controlled from a ground
received back by the sensor. Sensors calculate        system by wireless communication means.
the time interval between sending the signal          Different types of wireless communication
and receiving the echo to determine the               techniques can be used like using a simple
distance to an object.                                transmitter and receiver kit, using Wi-fi with a
                                                      router-client transfer protocol, using Bluetooth
                                                      and various others.
        The simple method is using the                 Controlling theory:
traditional transmitter and receiver kits. But
their range is limited to a maximum of 10-             PID Techniques
100m.                                                  In the industrial area the most used linear
                                                       regulators are surely the PID. The reasons of
                                                       this success are mainly three :

                                                       • Simple structure,

                                                       • Good performance for several processes,

                                                       • Tunable even without a specific model of the
                                                       controlled system.

                                                       In robotics, PID technique represents the basics
                                                       of control. Even though a lot of different
                                                       algorithms provide better performance than
                                                       PID, this last structure is often chosen for the
                                                       reasons expressed above. The traditional PID
                                                       structure is composed of the addition of three
             Transmitter and receiver kit
                                                       contributes, as shown in figure and equation
Power Requirements:

The essential power required to the quadrotor
is derived from the constant battery source.
Generally high energy density batteries are
required for the quad. A voltage of about 12V
and current of about 18-20 amperes are
                                                       The blocks ”1/s” and ”s” represents the
required. So the best available option is the
Lithium Polymer Battery. Lithium-ion polymer           integration and derivation operations.
batteries, polymer lithium ion, or more
commonly       lithium     polymer        batteries
(abbreviated Li-poly, Li-Pol, LiPo, LIP, PLI or LiP)
are rechargeable batteries (secondary cell             Where u is a generic controlled variable, e is the
batteries). They are connected in proper               error between the task r and the process output
combination to get the required rating.                y, KP is the proportional coefficient, KI is the
                                                       integral coefficient and KD is the derivative
                                                       coefficient. The first contribute (P) is
                                                       proportional to the error and define the
                                                       proportional bandwidth. Inside this interval the
                                                       output will be proportional to the error while
                                                       outside the output will be minimum or
             Zippy flight max Lipo Battery
                                                       maximum. The second contribute (I) varies
according to the integral of the error. Even        Applications:
though this component increases the overshoot
and the settling time, it has a unique propriety:   With the extent in the features of the quadrotor
it eliminates the steady state error. The third     its applications in various fields are increasing.
contribute (D) varies according to the derivate     Quadrotors fly because they have very fast
of the error. This component helps to decrease      accelerometers and motor control-systems
the overshoot and the settling time.                keeping the platform stable. This has been
                                                    enabled by the consumer electronics
Following this algorithm, algorithms for            development of MEMs accelerometers and
different flight mechanisms can be developed        gyroscopes, and the ever-decreasing price of
using the equations here                            embedded processors. As these technologies
                                                    become cheaper and more powerful, they are
                                                    accessible to a much broader range of
                                                    innovators. Furthermore, we begin to see cheap
                                                    and robust commercial platforms gaining
                                                    general acceptance as they prove themselves in
                                                    real world applications.

                                                         Some applications currently using
                                                          quadrotor UAVs include inspection of
                                                          power lines, oil rigs or wind turbines,
                                                          law enforcement surveillance or
                                                          military reconnaissance.
                                                         And the military is considering sending
                                                          groups of quadrotor UAVs that can
                                                          perch on powerlines, rocks and rooftop
Where       =acceleration in the X-direction              edges ahead of convoys for advanced
                                                          surveillance, which may also allow
                                                          automatic pin-pointing of sniper
    =acceleration in the Y-direction                      locations using sound triangulation.
                                                         Future applications include robotic
    =acceleration in the Z-direction                      security guards that can rapidly react to
                                                          a triggered alarm by autonomously
                                                          providing surveillance of a specific site
   =angular acceleration about X-axis
                                                          or area.
                                                         Other tasks centre around autonomous
    =angular acceleration about Y-axis                    border patrol and perimeter search.

                                                    And much more
     =angular acceleration about Z-axis
References:

http://evarobotics.com/_webapp_465998/
Quad-Rotor_UAV_Primer

http://wikipedia.org/

http://www.control.lth.se/publications/

http://www.sparkfun.com/categories/23

http://www.arduino.cc/

www.aeroquad.com

http://www.rcgroups.com/forums/showthread.
php?t=1060552

				
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