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Transcript of QUADROTOR
Pranav Maheshwari Minor Project - I
QUAD-ROTOR INTRODUCTION Flight Control Ground Station Mechanical Flight Control Control of quad-rotor helicopters is achieved by varying the thrust of two sets of counter-rotating rotor pairs. Altitude is controlled with the total thrust of all rotors, and lateral acceleration is controlled through the pitch and roll of the aircraft. Attitude is controlled through differential actuation of opposing rotors, with yaw controlled using the difference in reaction torques between the pitch and roll rotor pairs. Aerodynamics Blade Flapping: Total Thrust Variation in Translational Flight: A rotor in translational flight undergoes an effect known as blade flapping. The advancing blade of the rotor has a higher velocity relative to the free-stream, while the retreating blade sees a lower effective airspeed. This causes an imbalance in lift, inducing an up and down oscillation of the rotor blades. In steady state, this causes the effective rotor plane to tilt at some angle off of vertical, causing a deflection of the thrust vector. If the rotor plane is not aligned with the vehicle’s centre of gravity, this will create a moment about the centre of gravity that can degrade attitude controller performance. For stiff rotors without hinges at the hub, there is also a moment generated directly at the rotor hub from the deflection of the blades. Total thrust variation encompasses two related effects:•
1)Effective Translational Lift
2)Change in Thrust due to Angle of Attack
As a rotor moves translationally, the relative momentum of the airstream causes an increase in lift. This is known as translational lift. The angle of attack (AOA) of the rotor with respect to the free-stream also changes the lift, with an increase in AOA increasing thrust, as in aircraft wings. A rotor generates thrust by inducing a velocity on the air that passes through it. Objectives
1.Centre of Gravity should be in the center and below the plane of the four motors.
2.Adequate protection is provided to propellers.
3.Thrust/Weight ratio should be greater than 2.
4.Hub should be able to withstand high impacts.
5.Vibration from motors is minimized.
6.Frame should be capable enough for further additions planned to be done in future. Designs 3D models of the designs were a necessity for clear understanding of the complexities and irregularities related to the design.
Google SketchUp™ was used for 3D modelling.
Two designs were made for indoor and outdoor capabilities respectively keeping in mind the constraints and requirements. The selection of material was done on the basis of four following factors:
Materials considered for the construction of frame were:
• Aluminium Square Rods
• Carbon fibre
Carbon fibre is well known for its strength to weight ratio but it is very costly.Aluminium Rod on the other hand is cost effective, easy to use and provides average strength to weight ratio.Due to a limited budget, Aluminium was selected.
Construction of hub required very small amount of material so cost was not playing a role in selection. It could’ve been done with:
•Medium Density Fibre
Medium Density Fibre and Wood are easy to use but tend to crack on application of Pressure and defeat the objective of constructing an impact resistant hub.
Glass Fibre is a very strong, lightweight and easy to use material but its in-house creation requires high level of expertise.
Styrofoam is a very light, moderately strong and easy to use material.
It was selected due to the ease of functioning and strength.
Aluminium Sheet and Wood were used at many small places due to ease of availability. Hardware Selection PROPULSION Thrust(Kg) = P(in) x D(in)^3 x RPM^2 x 10^-10 x 0.02835
General thrust equation for propellers It is a means of creating force which leads to movement. In a Quad-Rotor, motor and propeller together form the propulsion system. Selection of motor and propeller is a very critical decision to be made while construction of a Quad-Rotor.With the above designs, motors, batteries, ESCs, and propellers were researched and tested based on equation: THRUST REQUIREMENT As mentioned in objectives, the thrust/weight ratio should be a minimum of 2.
Adding the weight of battery and control system components, a total weight of 600gms was reached for the indoor quad and 1480gms for the outdoor quad; which required a minimum thrust of 1200gms and 2960gms respectively.
It was calculated that the weight to thrust ratio would not be possible to achieve, for the indoor quad, with the current materials therefore it was shelved. MOTOR & PROPELLER SELECTION Three classes of motors were investigated: brushless out-runner, brushed and brushless in-runner motors.
A brushless out-runner motor has a stationary core and windings. The outer shell has magnets on it and is free to rotate. The electronic speed controller creates a coil switching sequence that results in a rotating magnetic field. With the attraction of the field and the magnets on the outer shell, the shell rotates. Since the only contact points are the shaft in the bearings, these motors are extremely efficient. These motors are perfect for a direct-drive propeller setup.
Brushed motors operate in a similar manner except the inner core rotates with respect to the outer shell. With these motors, the inner shaft is in contact with commutators. These motors are inherently less efficient due to friction and provide less torque than a brushless out-runner.
In-runner motors operate similar to brushed motors. They still have a rotating inner core, but it is held in place with a magnetic field. These motors are more efficient than a brushless out-runner and operate at extremely high RPM but create little torque. In-runners are generally used to operate small propellers at high rates of speed or used in a geared propeller system.
Motors Used: •1560Kv 49W •1300Kv 149W MOTOR SELECTION PROPELLER SELECTION Propellers vary mainly according to their Diameter and Pitch, with different manufacturers having slightly different designs, and are denoted by diameter x pitch.
Diameter of a propeller has to be decided according to the frame size. Pitch of a propeller is the distance it would travel forward in the air on one complete revolution.
A wide variety of propellers were tested.
•7 x 3.5
•8 x 4.3
•8 x 4 Slow Flyer
•10 x 4.5 TESTING A thrust stand was required for measuring accurate amount of thrust generated from each pair of motor and propeller tested.
It consisted of two arms of equal length joined perpendicular to each other having a pivot point at the point of intersection. One of the arm rested on a weighing scale and the other had motor mounted on it.
Thrust generated by motor created moment equal to:
M = T * L (where M = moment, T = thrust and L = length of the arm)
As the length of the arms is equal; the reading displayed on the weighing scale is exactly equal to the thrust generated from the propeller. The data generated from the thrust stand for different combinations was plotted using MATLAB™ as follows:
The final configuration of motor and propeller selected were:
Motor: 1300kV 149W(with a 3 Cell battery)
Propeller: 10 x 4.5 RESULT TILL NOW TILL NOW What is Ground Control Station ? A Ground Control Station (GCS) is a land or sea-based control center that provides the facilities for human control or overview of the statistics of an unmanned vehicles in the air or in space. This is the unit on the ground that sends and receives signals from one or several airborne units. A GCS could be used to control unmanned aerial vehicles or rockets within or above the atmosphere.These are normally very complicated systems that require many personnel and a lot of computing power. The main goal of our Ground Control Station is:
1. To design a ground control station software, which classifies
the data feed and other useful information from UAV in a
2. Display the gathered information in the GUI of the software.
3. Key points are the software design, software development
process of the Ground Control Station (GCS). When considering the layout of the flight data display, one has been aware that there is limited screen space and all of the data needs to fit on one screen. Yet it needed to remain clear and easily readable. Layout Programming the Displays There isn’t a lot of complicated programming behind the displays on the flight data screen. The displays are simply standard Qt functions. Objectives Flight Data Display Special Features Future Objectives 1. Ability to receive live video feed from the UAV to
Ground Control Station. 2. A 3-D Visualization of the quad-rotor to be added to
the Software. 3. Quad-rotor to be controlled by an Android Phone through
an application. 4. A GPS is planned to be harnessed to know real time
position of the Quad - rotor. 5. Different types of Indicators like Heading Indicator,
Airspeed Indicator etc. to be added to the GUI of
the software for ease in its operation. The software gives a warning when the recorded voltage of battery is lower than critical value. The software will be able to calculate the Estimated Flight Time on the basis of recorded battery voltage. The software has the ability to warn the user in cases of mechanical instability. The main functionalities of the software include:
1. Monitoring and Displaying the Roll, Yaw and Pitch values of the quad-rotor.
2. Simultaneously plots the graphs in real time for the values of Roll, Yaw, and Pitch with reference to time.
3. Displaying values of Flight Time, Battery Voltage, Altitude, Loop Rate etc. Functionalities Operating System: Windows 7 & other versions
Software Used: Qt Creator
Language Used: C, C++
Processor: Pentium (IV) & above
RAM: 256 MB
Hard-Disk: More than 100 MB Software and Hardware Tools I followed SDLC (System Development Life Cycle) for project development phases.
Systems Development Life Cycle(SDLC) is defined as a software development process, although it is also adistinct process independent of software or other Information Technology considerations.It is used by a systems analyst to develop an information system, including requirements,validation, training, and user ownership through investigation, analysis, design,implementation, and maintenance. Methodology Control and Stability Augmentation 1. The Control and Stability Augmentation System (C.S.A.S.) is a subsystem of the vehicle that is responsible for providing the user with good control over the motion of the vehicle, while maintaining a stable attitude. 2. Our strategy, is to first design and implement a robust CSAS, that can allow a sufficient bandwidth of control over the vehicles motion. Subsequently we can add long range autonomous navigation The Generic Feedback Loop 1. A typical control system is implemented via a feedback loop that returns the output variable of the system (plant) for comparison with the reference, and the error is fed to a transfer function called the “controller” . 2. The outputs of the system are different from the state variables. 3. The CSAS can consist of many SISO control loops, one for each controlled variable. Attitude Measurement Since a reliable measurement of the attitude is needed to control it, we need to select suitable sensors for attitude measurement. 1. I.R. Thermopiles 2. M.E.M.S. Gyroscopes 3. M.E.M.S. Accelerometers Our strategy is to use a sensor fusion algorithm that combines the accelerometer and gyroscope data to give the best possible, all-pass, estimate of the attitude. The algorithm we use is the Complementary Filter on SO(3). Attitude Representation There are many ways to represent the attitude ( i.e. the orientation ) of a rigid body. 1. Tait-Bryan angles 2. The Quaternion Form 3. The Direction Cosine Matrix or the Rotation Matrix Fusion of Accelerometer and Gyroscope
Data 1. We use an Inertial Measurement Unit consisting of a three axis accelerometer, one two axis gyroscope and one single axis gyroscope. Such a measurement setup is called a “Strap-down IMU”. 3. Accelerometers can be used for long term correction of the Gyroscope data. 4. Thus, these can be used for long term drift correction of the Gyroscope data. 2. These sensors can provide a good measurement of the attitude for short intervals of time. Avionics System Design Experimental Results