DESIGN AND FABRICATION OF FLAPPING WING MAV

A Project Report

Submitted to

MATS UNIVERSITY AARANG, RAIPUR (C.G.), INDIA

in the partial fulfillment for the award of the Degree of

Bachelor of Engineering in

Aeronautical

by ANKIT CHAKRADHARI (MU11BEAE006) ANKIT CHANDRAKAR (MU11BEAE007)

Under the Guidance of

Mr. KALPIT P. KAURASE ASSISTANT PROFESSOR

Department of Aeronautical Engineering School of Engineering & I.T.

MATS University, Aarang, Raipur (C.G.), India June 2015

DECLARATION BY THE CANDIDATE

I the undersigned solemnly declare that the report of the project work entitled DESIGN AND FABRICATION OF FLAPPING WING MAV is based on my own work carried out during the course of my study under the supervision of MR. KALPIT P. KAURASE, Assistant Professor, Department of Aeronautical Engineering, School of Engineering & I.T., Aarang, Raipur.

I assert that the statements made and conclusions drawn are an outcome of my study of research work. I further declare that to the best of my knowledge and belief the report does not contain any part of any work which has been submitted for any award of any other degree/diploma/certificate in this University or any other University of India or abroad.

_________________ _________________

(Signature of the Candidate) (Signature of the Candidate) Ankit Chakradhari Ankit Chandrakar

MU11BEAE006 MU11BEAE007 School of Engineering & I.T., School of Engineering & I.T.,

Aarang, Raipur (C.G.) Aarang, Raipur (C.G.)

CERTIFICATE BY THE SUPERVISOR

This is to certify that the report of the project entitled DESIGN AND FABRICATION OF FLAPPING WING MAV is a record of research work carried out by ANKIT CHAKRADHARI bearing Roll No. MU11BEAE006 & Enrolment No. 111133 and ANKIT CHANDRAKAR, Roll No. MU11BEAE007 & Enrolment No. 111134 under my guidance and supervision for the submission of Project work of Bachelor of Engineering in Aeronautical of MATS University, Raipur (C.G.), India. To the best of my knowledge and belief the report i) Fulfils the requirement of the Ordinance relating to the B.E. degree of the

University and ii) Is up to the desired standard both in respect of contents and language for being

referred to the examiners.

____________ __________________

(Signature of HoD) (Signature of the Supervisor) Mr. Brijesh Patel, Mr. Kalpit P. Kaurase, School of Engineering & I.T., School of Engineering & I.T., MATS University, Raipur MATS University, Raipur

Forwarded to MATS University, Raipur

_______________

(Signature of the Director) School of Engineering & I.T.,

MATS University, Raipur

CERTIFICATE BY THE EXAMINERS

The project entitled DESIGN AND FABRICATION OF FLAPPING WING MAV submitted by ANKIT CHAKRADHARI, Roll No. MU11BEAE006, Enrolment No. 111133, and ANKIT CHANDRAKAR, Roll No.MU11BEAE007, Enrolment No. 111134 has been examined by the undersigned as a part of the examination and is hereby recommended for the completion of project work of the degree of Bachelor of Engineering in Aeronautical, School of Engineering & I.T., MATS University, Aarang, Raipur (C.G.), India.

.. Internal Examiner External Examiner

Date: Date:

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ABSTRACT

In recent years the subject of flying vehicles propelled by flapping wings, also known as ornithopter, has been an area of interest because of its application to micro aerial vehicles (MAVs). These miniature vehicles seek to mimic small birds and insects to achieve never before seen agility in flight. This renewed interest has raised a host of new problems in vehicle dynamics and control to explore.

In order to better study the control of flapping wing flight we have developed a large scale ornithopter called the Phoenix. It is capable of carrying a heavy (400 gram) computer and sensor package and is designed especially for the application of controls research. The design takes special care to optimize payload capacity, crash survivability, and field repair abilities.

This project aims at the development of a bio-mimetic propulsion mechanism for a Flapping Wing Micro Aerial Vehicle, without considering the aerodynamics of the wings in the design. This artificial bird will be the size of approximately 10-20cm. Therefore the aerodynamic phenomena in flapping flight are studied and summarized.

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ACKNOWLEDGEMENT

We welcome this opportunity to express our heartfelt gratitude and regards to our project guide Mr.Kalpit P. Kaurase, Assistant Professor, Department of Aeronautical Engineering, School of Engineering & I.T. for his unconditional guidance. He always bestowed parental care upon us and evinced keen interest in solving our problems. An erudite teacher, a magnificent person and a strict disciplinarian, we consider ourselves fortunate to have worked under his supervision. I feel motivated and encouraged every time I meet him. Without his encouragement and guidance this project would not have been materialized.

We are highly grateful to Mr. Brijesh Patel, Head of Department, Department of Aeronautical Engineering, School of Engineering & I.T. for providing necessary facilities during the course of the work. He has willingly provided the resources necessary in completing this project and has dedicated his time to ensure my success.

I would also like to acknowledge with much appreciation the crucial role of the staff of Aeronautical Department, who gave the permission to use all required machinery and the necessary material to complete the Differential Simulation Rig.

We greatly appreciate & convey our heartfelt thanks to my family and friends, flow of ideas, dear ones & all those who helped us in completion of this work. A special thanks to our parents, who taught us the value of hard work by their own example and who instilled us the free thinking and the joy of making researches.

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TABLE OF CONTENT

Title Page No. ABSTRACT i ACKNOWLEDGEMENT ii TABLE OF CONTENTS iii LIST OF FIGURES v LIST OF SYMBOLS vi CHAPTER 1: Introduction 1-12

1.1 General

1.2 Ornithopter 1.3 Different from an airplane or helicopter

1.4 Flapping Wing Aerodynamics 1.5 Flapping Wing Worldwide 1.6 Different Layouts

1.7 Applications of Ornithopter CHAPTER 2: Literature Review 13-16 CHAPTER 3: Problem Identification 17-18 CHAPTER 4: Methodology 19-23 4.1 Theoretical Model 4.2 Mechanical Modeling CHAPTER 5: Selection of Design Parameter 24-29 5.1 Gear Arrangement 5.2 Wings 5.3 Overall Parameters CHAPTER 6: Design and Fabrication 30-38 6.1 Body

6.2 Wings and Tail 6.3 Drive Train 6.4 Battery 6.5 Motor

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6.6 Actuators and Receiver 6.7 Transmitter 6.8 Microcontroller 6.9 Final Assembly

CHAPTER 7: Experimental Section 39-40 7.1 Motor Testing

7.2 Drive Train Testing

7.3 Electrical Component Setup and Testing 7.4 Actuator Testing

CHAPTER 8: Result and Discussion 41-43 8.1 Result 8.2 Discussion

CHAPTER 9: Conclusion and Future Work 44-46 9.1 Conclusion 9.2 Future Work

References 47

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LIST OF FIGURES

S. NO. TITLE PAGE NO. FIG. NO. 1 Leading edge vortex 05 1 2 Clap and Fling mechanism 06 2 3 Wing rotation over one flapping cycle 07 3

4 DelFly 08 4 5 Robotic insect 08 5 6 Flapping wing at ETH 09 6 7 Direct actuation 10 7 8 Actuation with mechanism 11 8

9 Mechanism combine with torsional spring 11 9 10 Process flow diagram 23 10 11 Strut type gear 25 11 12 Plate type gear 26 12 13 Chain drive 26 13 14 Body design 32 14 15 Main wings design 33 15 16 Tail wing design 33 16 17 Originally intended flapping mechanism 34 17 18 Gear arrangement 34 18

19 150mAh 3-7V Li-Po battery 35 19 20 Solarbotics GM15A 35 20 21 Microstrain 3DM-GX1 IMU 36 21 22 Arduino microcontroller 37 22

23 Final assembly 38 23

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LIST OF SYMBOLS

Tm Number of teeth on the main gear Tp Number of teeth on the pinion gear G Gear ratio Nn Nominal speed of the main motors Na Actual speed of the motors V Voltage of the Li ion battery KV KV rating of the main motors

Loss coefficient of the motor owing to frictional forces Rotational speed of the rotor W Weight force on the ornithopter body Mb Mass of body FL Lift force on the rotor blade CL Coefficient of lift

h Rotational speed of rotor at hover condition vb Linear speed of the blade A Area of rotor disk FL(t) Total lift force acting on tail

FL(b) Lift force acting on body FD Drag force

CD Coefficient of drag FC Centripetal force

R Radius of rotor disk

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CHAPTER ONE INTRODUCTION

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CHAPTER 1 INTRODUCTION 1.1 General

The research on Micro Aerial Vehicles (MAV) is a comparably young field, which has emerged over the past few years. The ongoing miniaturization of electric components such as electric motors and the improvements in microelectronics made it possible to build miniature planes and helicopters at relatively low costs. This development also made it possible to start imitating insect and bird flight, which need a sophisticated miniaturized actuation chain for their flapping wing motion. The goal of this research is to come up with small aerial vehicles that can operate independently from ground stations, performing certain operations such as surveillance or measurement, especially in environments that are hardly accessible or even dangerous for people. The United States Air Force has been pursuing design projects for surveillance vehicles that have the ability to disguise themselves in plain sight. One of these avenues has been the research and development of micro aerial vehicles, or MAVs. These vehicles often mimic the flight characteristics of hummingbirds and dragonflies because of their size and unique hovering capabilities (AeroVironment Inc. Nano Hummingbird) MAVs will be used as miniature surveillance instruments and will aid the soldiers and civilians of the future.

The micro aircrafts are designed based on the three ways for lift generations. They are fixed, rotary and flapping wings. Among of these methods the flapping wing propulsion systems occupy a special place because so many living species have developed them. For comparison of man-made objective and flying creatures, researchers use the relative speed parameter (Ratio of the speed of flying to maximum length of an object). The birds and insects have relative speed between 60 and 170, while this value for jet airplanes is between 4 and 9. These notes demonstrate the importance of flapping crafts to design of more efficient airplanes to reach to higher relative speeds.

A successful design of flapping-wing crafts requires the contribution of different disciplines including aerospace and biology. It is known that flapping flight of birds is a coupled pitching and plunging oscillation with a phase difference between these two motions. This concept has led engineers to design the next generation of flapping-wing

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crafts. A typical flapping-wing craft which is preliminary composed of a fixed body, two flapping-wings and a controlled tail. The fixed body typically consists of battery, flapping mechanism and motors, electrical controlling systems.

Many experimental, theoretical and computational works have been conducted for understanding the flapping-wing aerodynamics. It is still not clearly known how to distribute the pitching angle and plunging velocity over the flapping cycle to achieve a desired mean thrust and lift and at the same time to minimize the required power for flapping the wings at realistic frequencies and amplitudes.

1.2 Ornithopter An ornithopter (from Greek ornithos "bird" and pteron "wing") is an aircraft that

flies by flapping its wings. Those machines are driven by rotating airfoils. In an ornithopter, the driving airfoils have an oscillating motion instead. This imitates nature, because no animals have any rotating parts.

The ornithopter works on the same principle as the airplane. The forward motion through the air allows the wings to deflect air downward, producing lift. The flapping motion of the wings takes the place of a rotating propeller. The wing design is designed with the spar as far forward of the airfoil but still having acceptable dimensions of strength. Engineers and researchers have experimented with wings that require carbon fiber, plywood, fabric, ribs, and the trailing edge to be stiff, strong, and for the mass to be as low as possible. Any mass located to the aft or empennage, reduce the wings performance and hinder the design of the ornithopter. In order to calculate the performance of the ornithopter, the wings lift is determined by the lift of the wing versus weight, drag and thrust. A smooth aerodynamic surface with a double-surface airfoil is more efficient then a single-surface airfoil to produce more lift.

1.3 Different from an airplane or helicopter Unlike airplanes and helicopters, the driving airfoils of the ornithopter have a

flapping or oscillating motion, instead of rotary. As with helicopters, the wings usually have a combined function of providing both lift and thrust. Theoretically, the flapping wing can be set to zero angle of attack on the upstroke, so it passes easily through the air.

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Since typically the flapping airfoils produce both lift and thrust, drag-inducing structures are minimized. These two advantages potentially allow a high degree of efficiency.

In propeller- or jet-driven aircraft, the propeller creates a relatively narrow stream of relatively fast moving air. The energy carried by the air is lost. The same amount of force can be produced by accelerating a larger mass of air to a smaller velocity, for example by using a larger propeller or adding a bypass fan to a jet engine. Use of flapping wings offers even larger displaced air mass, moved at lower velocity, thus improving efficiency. In order to create an effective ornithopter, it had to be able to flap its wings to generate enough power to get off the ground and travel through the air. Efficient flapping of the wing is characterized by pitching angles, lagging plunging displacements by approximately 90 degrees. Flapping wings increase drag and are not as efficient as propeller-powered aircraft. To increase efficiency of the ornithopter, more power is required on the down stroke than on the upstroke. If the wing on the ornithopter was not flexible and flapped at the same angle while moving up and down, it would act like a huge board moving in two dimensions, not producing lift or thrust. The flexibility and move-ability of the wing let it twist and bend to the reactions of the ornithopter while in flight.

1.4 Flapping Wing Aerodynamics Lift is the force that utilizes the fluid continuity and Newton's laws to create a

force perpendicular to the fluid flow. It is opposed by weight, which is the force that pulls things towards the ground. Thrust is the force that moves things through the air while drag is the force of flight that is an aerodynamic force that reduces speed.

The ornithopter wing is attached to the body at sight angle, which is called the angle of attack; the downward stroke of the wing deflects air downward and backward

generating lift and thrust. Also the wing surface is flexible, this causes the wing to flex to the correct angle of attack we need in order to produce the forces that we want to achieve flight.

The mechanics of flapping flight are far more complicated than that of fixed -wing flight. For an aircraft with fixed wings, only forward motion is necessary to induce aerodynamic lift. But for flapping flight wing not only has to have a forward motion, but

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also must travel up and down. This additional dimension means the wing constantly changes shape during flight.

The air flow field in flapping wings cannot be assumed as steady. A large angle of attack would lead to flow separation and turbulences too. Obviously, there must be phenomena producing extra lift. This unsteady aerodynamics cant be explained by common airfoil theory and are illustrated below.

1.4.1 Unsteady Aerodynamics The highly difficult fact is that lift production of flapping wing mechanisms are

explained with unsteady aerodynamic effects is the reason for the emerging and so far not yet fully explored field of FWMAVs. In the following the most important effects are listed.

Leading edge vortex Clap and fling mechanism Rotational lift Wing-wake interactions A leading edge vortex (LEV) is created at a high angle of attack. A high angle of

attack would normally lead to flow separation. But the LEV is responsible for the flow to stay attached to the wing. At the beginning of the down stroke, a strong vortex flowing from the base to the tip is formed at the leading edge and helps to generate high lift force. This is best seen in the right part of the next figure.

Fig.1 Leading edge vortex [10]

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In the left part another effect of the LEV is shown. The vortex generated in the down stroke is separated after it reaches the tip of the wing. This vortex works as a support for the upstroke and helps to produce even more lift force. In the clap and fling mechanism the wings come together dorsally at the end of the upstroke to perform a clap (A).

Fig.2 Clap and fling mechanism [10]

After the clap the wings fling apart (B). Air is sucked in (C) as the wings start to move downwards creating a bound vortex on each of the wings which produces an instantaneous lift force (D). At the end of each half stroke, the wing performs a rotation around a span wise axis which allows an insect to maintain a positive angle of attack during both down stroke and upstroke.

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Fig.3 Wing rotation over one flapping cycle [10] This rotation guarantees continuous lift production over the whole flapping cycle.

The wings operate with the surrounding flow in specific ways. Used air interacts positively into the flapping process. This phenomenon is also referred to as wake capture.

1.5 Flapping Wing Worldwide Birds inspired Leonardo da Vinci when he designed his ornithopter in 1490.

Leonardo da Vinci was interested in flying during 14881514. He never saw his dream of flight take place because his ornithopter was too heavy and required too much energy to produce lift or thrust. In 1929, the human-powered ornithopter constructed by Alexander Lippisch was towed into the air and glided around. In 1959, in England, another ornithopter was towed into the air and demonstrated the ornithopter being a birdlike machine. By the 1960s, there were powered unmanned ornithopter flights of various sizes demonstrating how ornithopter flew. In 1991 Harris and DeLaurier flew the first successful engine-powered remotely piloted ornithopter in Toronto, Canada. By 1999, there was an ornithopter design that was designed to take off from a level pavement.

1.5.1 DelFly DelFly is a MAV developed at TU Delft in the Netherlands. It has four wings,

which are actuated by one electric motor. The wings are arranged in pairs, with the right upper wing connected to the left lower wing and vice versa. Via a small gear train the wing pairs are connected to the electric motor so that the upper and the lower wing flap

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towards each other. In forward flight, the course can be controlled with rudders installed at the tail of the vehicle. DelFly also carries a camera onboard that sends images to a ground computer from where the vehicle is controlled.

Fig.4 DelFly [6]

1.5.2 Robotic Insect Another interesting project is the so called Robotic Insect, being developed at the

Harvard Microrobotics Laboratory. The underlying concept is the flapping motion of small insects such as flies. For the actuation of the wings of this very small scale MAV a

piezoelectric cantilever is used, inducing an oscillation of the wings at their resonance frequency, in order to produce high amplitude. The joints are integrated in the structure as flexible parts. The power supply however is not included in this vehicle, which means that despite of already producing remarkably high lift it is not yet able to actually fly.

Fig.5 Robotic Insect [6]

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1.5.3 Flapping Wings at ETH The autonomous system lab (ASL) at ETH also aims to develop a MAV of bird

size that is based on the aerodynamic principles used in insect flight and by small birds. Unlike other developments in this area, the intended MAV at ETH shall be able to hover like insects or Humming birds, and so it is supposed to become an interesting alternative to helicopters as currently being developed at ASL. Furthermore, such an aerial vehicle should be large enough to carry some payload such as a camera, but still small enough to have high agility. Hovering is closely connected to unsteady aerodynamic effects at small Reynolds numbers used in nature by insects and small birds. With a wingspan of 280mm and a weight of about 20g the Giant Hummingbird is one of the largest species in nature that can hover, and therefore had been selected as natural ante type. The goal, hover, is not to copy nature but to adopt the basic principles.

Fig.6 Flapping wing at ETH [6] In the last few years, comprehensive researches have been conducted on the

kinematic optimization of flapping-wing vehicles and on its influence on aerodynamics involved in propulsion.

The experimental and numerical analyses conducted by Triantafyllou et al.

showed that a Strouhal number between 0.2 and 0.4 leads the propulsive efficiency to be maximized. With respect to the numerical study by Pedro et al. the appropriate pitch amplitude is also around 3040.

Based on the observations from natures, observations by Taylor et al. demonstrate the obtained results by experimental and computational works.

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For more descriptions, Amiralaei et al. developed the 2D Navier-Stokes which is associated with Finite Volume Method simulating the flapping-wing in low Reynolds Number flows. They have demonstrated that the importance of pitch amplitude and phase angle difference between plunging and pitching is more than Reynolds and Strouhal numbers. They also announced that the best aerodynamic performance occurs in symmetrical oscillations.

1.6 Different Layouts One of the most important criteria that the mechanism should fulfill is simplicity.

Hence the number of components needs to be limited and the entire design should be compact. In the following sections, three possible layouts for the actuation mechanism are presented.

1.6.1 Direct Actuation Starting with an electric motor and a wing, the mechanism to be found will define

how the movement from the motor is translated to the wing. The simplest way to connect motor and wing is to attach the wing directly to the motor (figure 7).

In order to obtain flapping of the wing, the motor can be fed by an alternating input signal, which is intended to result in a periodic oscillation of the wing within certain amplitude. This design is quite simple, no additional parts and joints would be needed which means that the weight can be kept low. Another positive effect of direct actuation is that the possible flapping amplitude of the wing is not predefined, but can be varied by the input signal. The possibility to vary the flapping amplitude and to set the frequency can be seen as two degrees of freedom. Over all it can be said that this design brings very high flexibility.

Fig.7 Direct Actuation [10]

1.6.2 Actuation with Mechanism Another possibility for transferring the motion from the motor to the wing is to

use a lever (figure 8). The wing is articulated at a fixed joint, and a lever is attached directly to the motor's shaft, so that the end of the shaft rotates around the motors center of rotation on a circular path. A second lever connects the end of the motor lever with the

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wing, and translates the rotation from the motor to an oscillatory motion at the wing. The wing now follows a clearly defined motion with constant amplitude. The value of this amplitude as well as the transfer characteristics between motor motion and wing depend on the geometry of the levers. Compared to concept A, this mechanism only has 1 degree of freedom, which is the rotational speed of the motor

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Fig.8 Actuation with Mechanism [10]

1.6.3 Mechanism combined with torsional spring The mechanism in this concept is basically the same as in concept B, but with the

addition of a torsional spring in series at the wing's center of rotation (figure 9).The idea of the torsional spring is that the flapping amplitude gets amplified if the wing is actuated at resonance.

During one oscillation cycle, the motor has to accelerate the wing into one

direction, then stop it and accelerate it into the opposite direction. This needs energy because the motor is not operated at constant conditions. The idea of the torsional spring is that it supports the motor by storing energy when the wing is stopped and releasing this energy in the acceleration phase. Therefore it should have a positive effect on the flapping motion and make the mechanism run smoother. Also, higher amplitudes than without spring are possible.

Fig.9 Mechanism combined with torsional spring [10]

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1.7 Applications of Ornithopter Practical applications capitalize on the resemblance to birds or insects. The

Colorado Division of Wildlife has used these machines to help save the endangered Gunnison Sage Grouse. An artificial hawk under the control of an operator causes the grouse to remain on the ground so they can be captured for study.

Because ornithopters can be made to resemble birds or insects, they could be used for military applications such as aerial reconnaissance without alerting the enemies that

they are under surveillance. Several ornithopters have been flown with video cameras on board, some of which can hover and maneuver in small spaces. In 2011, AeroVironment, Inc. demonstrated a remotely piloted ornithopter resembling a large hummingbird for possible spy missions and they can also used for-

Defense applications Wild life study and photography Traffic monitoring Tracking criminal and illegal activities Inspection of pipes Border surveillance Reconnaissance Surveillance Seismic detection

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CHAPTER TWO LITERATURE REVIEW

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CHAPTER 2 LITERATURE REVIEW Baker, N. S., et al1

This paper describes the fabrication, development, and testing results for a proof-of-concept bio-inspired flapping wing Micro Air Vehicle (MAV) actuation system. This paper also discusses proposed EAP configurations as well as the electrical power supply and methods employed for controlling the actuation system.

Esfahani, M. A., et al2 In this paper the optimization of kinematics, which has great influence in

performance of flapping foil propulsion, is investigated. The purpose of optimization is to design a flapping-wing micro aircraft with appropriate kinematics and aerodynamics features, making the micro aircraft suitable for transportation over large distance with minimum energy consumption. In this paper the optimization of flapping-wing micro

aircraft based on the kinematics of flying is conducted using the multi-objective genetic algorithm. A rectangular NACA0012 airfoil with high aspect ratio is specified and according to manipulation of pitch amplitude, wing reduced frequency and phase difference between plunging and pitching the optimization is done. The optimization procedure is performed based on the both propulsive efficiency and thrust. The aerodynamic model used for simulation of flapping foil follows 2D quasi-steady approximation.

Floreano, D., et al3

In this article they explained how flapping micro air vehicles (MAVs) can be designed at different scales, from bird to insect size. The common believe is that micro fixed wing airplanes and helicopters outperform MAVs at bird scale, but become inferior to flapping MAVs at the scale of insects as small as fruit flies. Here they present our

experience with designing and building micro flapping air vehicles that can fly both fast and slow, hover, and take-off and land vertically, and they present the scaling laws and structural wing designs to miniaturize these designs to insect size.

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Hsu, C. K., et al4 In the paper, they discussed about an approach they used to design flapping wing Micro Air Vehicles (MAV). The approach makes use of the conventional precision machining methods, such as Rapid Prototyping 3D printing, Electrical Discharge Machining and Laser Micromachining techniques, to manufacture the MAV parts.

Malik, M. A. and Ahmad, F.5 In this paper Modified Strip Theory based on blade elemental analysis has been used to develop the aerodynamic model for semi-elliptical wing form. Parametric study has been carried out to show the effect of different parameters on lift, thrust and drag forces for better understanding of ornithopter flight.

Patil, R., et al6 The main objective of this paper is to introduce one of the promising Rapid

Prototyping (RP) technology as a potential application for the fabrication and development of a Flapping Wing Micro Air Vehicle (a rubber band powered Ornithopter). The conventionally constructed Ornithopter of Balsa Wood has been compared with an Ornithopter of ABS-M30 constructed using RP technology (Fused Deposition Modeling). An assessment of their flight time, cost and time involved in the construction, demonstrated the significance of RP technology in the development of MAVs. Further, it is concluded that RP technology can be a right choice to make aerodynamic body parts or airframe structures either hollow or porous which in turn would help in weight reduction with enhanced strength and further with improved flight characteristics.

Pornsin-Sirirak, T. N., et al7 This paper reports the successful development of Microbat the first electrically

powered palm-sized ornithopter. This first prototype was flown for 9 seconds in October 1998. It was powered by two 1-farad super capacitors. Due to the rapid discharge of the capacitor power source, the flight duration was limited. To achieve a longer flight, a rechargeable battery as a power source is preferred. The second prototype houses a small

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3-gramrechargeable Ni-Cad battery. The best flight performance for this prototype lasted 22 seconds. The latest and current prototype is radio-controlled and is capable of turning left or right, pitching up or down. It weighs approximately 12.5 grams. So far, the best flight duration achieved is 42 seconds.

Tandon, A., et al8 In this paper to better study the control of flapping wing flight they have researched

and modeled a large scale ornithopter called the Garuda. The Garuda is capable of carrying a microcontroller, sensor package and an on board surveillance camera to transmit live video feed to the receiver in real time. The design takes special care to optimize payload capacity, crash survivability, and field repair abilities. This model has applications in the field of defense spy surveillance over enemy territories without being detected or arousing suspicion.

Wood, R.J.9 In this article an elegant manufacturing paradigm is employed for the creation of a

biologically inspired flapping-wing micro air vehicle with similar dimensions to insects. A novel wing transmission system is presented which contains one actuated and two passive degrees of freedom. The design and fabrication are detailed and the performance of the resulting structure is clarified highlighting two key metrics: the wing trajectory and the thrust generated.

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CHAPTER THREE PROBLEM IDENTIFICATION

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CHAPTER 3 PROBLEM IDENTIFICATION

Many studies have been able to model and simulate insect control mechanisms and grasp an understanding of the aerodynamics behind the flight mechanism but very few have designed methods of controls in mechanical design. Therefore there is a need for mechanical designs for control mechanisms in flapping wing micro aerial vehicle. Practicality is also an issue, many prototypes that are small in size but require an external power source, without the ability to fly independently and without control they cannot fly effectively and efficiently.

As mentioned earlier, the project was motivated by the work of the DelFly. DelFly is a MAV developed at TU Delft in the Netherlands. It has four wings, which are actuated by one electric motor. The wings are arranged in pairs, with the right upper wing connected to the left lower wing and vice versa. Via a small gear train the wing pairs are connected to the electric motor so that the upper and the lower wing flap towards each other. Due to the lack of appropriate testing measures, it was determined that a testing mechanism for flapping wing MAV prototypes would need to be developed in addition to the creation of a framework for ornithopter design. Upon consideration of these issues, the project goal was established.

Based on the goal, the project called for the creation of two separate components: a theoretical model and ornithopter prototype. The theoretical model provides the framework for the development of ornithopter designs and the physical prototype provides a device on which to conduct test experiments.

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CHAPTER FOUR METHODOLOGY

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CHAPTER 4 METHODOLOGY The methodology which we used in our project completion is divided into two sections that match the goals set for the project. Section 4.1 outlines the theoretical model, how it was modeled and considerations that were taken into account for the mechanical design. Section 4.2 describes the steps taken in manufacturing and creating the flapping wing MAV prototype based upon considerations from the theoretical model and it shows in detail the experiment used to analyze the physical prototype and validate the theoretical model. It should be noted that hereafter, the term airfoils will be referred to as wings.

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Fig.10 Process flow diagram

Selection of Project Area

Literature Review

Literature Review on Selected Projected Title

Title Finalization

Problem Identification

Selection of Design Parameter

CAD Design

Material Selection

Result and Discussion

Experimental Section

Conclusion and Future Work

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4.1 Theoretical Model A theoretical model is a description technique which applies mathematical and

scientific concepts to engineering disciplines for the purpose of explaining systems, studying the effects of different components within the system, and predicting component behavior. Theoretical modeling is a highly beneficial pre prototyping measure that allows for a better understanding of the needs and capabilities of a system physical model prior to construction. This concept was utilized to aid in the creation of the flapping wing MAV prototype component of the test platform.

This section comprises of Selection of project, Literature review, Title finalization, Literature survey on selected topic, problem identification and selection of design parameter. They are further explained.

4.1.1 Selection of project Among the 5-8 project topics we choose flapping wing micro aerial vehicle as our

final project. The first step of this process, identification, requires a clearly defined and communicated strategy. The best option would be to set up a strategy development process that contains project identification and project selection as an integral part. 4.1.2 Literature review

In the literature review we read about as possible as literatures on different topics. After reading the entire papers, we decided to make flapping wing micro aerial vehicle.

4.1.3 Title finalization After the literature survey we found that this topic is under our criteria, we

decided to make this topic as our final year project. 4.1.4 Literature survey on selected topic

Then finally we read literatures on selected topic and problem identification is carried out in the project. 4.1.5 Selection of design parameter

In this section the required parameters like weight, size, shape etc. are taken or calculated.

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4.2 Mechanical Modeling The flapping wing MAV proposed design utilized an electric motor to transfer

power to the wings and thus produce lift. For this reason, most of the theoretical modeling focused on the mechanical system that transfers that power. To simplify the model, the system was divided into three subsections; the drive mechanism (slider crank and motor), the double rocker mechanism, and the wing component. To begin, the slider-crank two bar linkage converts the rotational motion of the motor into linear motion that moves the wings. The velocity and position of the slider can be determined through knowing the motors speed. The next component is the double-rocker two bar linkage. This linkage amplifies the angular displacement of the wing relative to the slider-cranks linear movement from the slider-crank.

This mechanism also serves as the pivot position and shoulder joint for wing motion. Finally, the wings are modeled as flat plates with a given attack angle during the forward and backstroke.

The overall goal in creating a theoretical model to acquire an understanding of the lift forces acting on the ornithopter. Accordingly, known aerodynamic concepts for lift of a fixed plate were incorporated within the model to assist in analyzing these forces. By understanding the kinematics of actuation, the transmission of force from the motor to the wing was tracked. An understanding of the typical forces was developed using the equations for lift.

This section comprises of CAD design, material selection and experimental section.

4.2.1 CAD design On the basis of design parameters a CAD design is made with the help of CATIA

or other design software.

4.2.2 Material selection Then the required materials are also select for the fabrication of flapping wing

micro aerial vehicle.

4.2.3 Experimental section Finally the experimental section will be carried out and results are taken, than the

conclusion of project report will be declared.

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CHAPTER FIVE SELECTION OF DESIGN

PARAMETER

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CHAPTER 5 SELECTION OF DESIGN PARAMETER

The design of the Flapping Wing MAV is carried out with a thorough understanding of the working of the various mechanical elements and parts used in the fabrication of the system. The various mechanical elements of the system are:

Gear arrangement Wings The electrical components are of equally vital significance in the fabrication the

flapping wing MAV. The different electrical components used during the course of fabrication are as follows:

Power supply (LiPo Battery) Micro controller Electric motors

5.1 Gear Arrangement Unless we use an electric motor, we'll need to gear down the motor speed, so that it

gives enough torque to flap the wings. In designing the flapping wing aircraft, gearbox can be one of the most challenging parts of the ornithopter to build. There are different types of gear mechanisms; few of them are:

5.1.1 Strut Type Gearbox This type of gearbox is recommended for micro-sized Ornithopters because it is

very simple. In a strut type gearbox, the gear axles are spaced along a linear rail of strut as shown in figure 10. The strut type gearbox has no bearings and since the large ornithopters require bearings to support the loads, so this type of gearbox is not suitable for large ornithopters.

Fig. 11 Strut type gear [11]

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5.1.2 Plate Type Gearbox The plate type gearbox is recommended for larger ornithopters, because of its

compatibility with bearings. It has dual crank mechanisms and is a more complex design. Figure 12 shows a plate type gearbox that consists of two or more plates with spacers between them, with bearings to support the gear axles.

Fig. 12 Plate type gear [11]

5.1.3 Chain Drive This type of gearbox is also used for large ornithopter because it reduces the

weight of the system by distributing load onto more of the gear teeth.

Fig. 13 Chain drive [11]

5.2 Wings When fabricating ornithopter, an efficient wing design can make the difference

between failure and success. This is where we talk about aerodynamics to check where the lift comes from. The wings are the main lifting body, which can make the flight success, so the wing consideration is very important. An effective ornithopter must have the wings, which are capable of generating thrust and the lift to keep the aircraft airborne. Since, there will be drag and the gravitational force (weight) pulling the aircraft backward and downward respectively, so the thrust and lift must overcome the drag and weight.

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5.2.1 Geometric Similarities The concept of geometric similarity can help relate different physical quantities

by means of the dimensional argument. If flyers are assumed to be geometrically similar, the weight W, lift L, and mass m for un-accelerated level flight, can be expressed with respect to a characteristic length l as

W = L= mg .Eq. 1 Here, L=lift

The wing area S and weight are expressed as S = l2 .Eq. 2

W = l3 .Eq. 3 5.2.2 Wing Span

When we are studying the flapping birds or ornithopter, parameters of interest are related to the body mass m of the bird or ornithopter. We can relate the wingspan and mass by using geometric similarity. Liu (2006) suggests that, over a large range of the weight, birds and aircraft basically follow the power law as given below:

l = 1. 654m1/3 (for aircraft) .Eq. 4 l = 1.704m1/3(for birds) .Eq. 5

5.2.3 Wing Area The historical data shows that there is a large variation in the wing area (Norberg,

1990). Greenewalt studied different species of the birds and then categorized the birds into three categories (Greenewalt, 1975). He gave the relationship of the wing area and mass for big birds as:

S = m0.78 .Eq. 6 5.2.4 Aspect Ratio

The AR is a relation between the wingspan b and the wing area S: = 2 .Eq. 7 Generally, decreasing AR. increases the maneuverability and induced drag tends to decrease with higher AR. Similarly; the lift to drag L/D (glide ratio) increases with increasing AR.

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5.2.5 Frequency The frequency by the birds or the ornithopter flaps their wings depends on the size

of the ornithopter. The flapping frequency is an important parameter in the ornithopter

design. There is an upper limit and lower limit of this frequency. The upper and lower frequency limits means that the body cannot flap the wings with the frequency higher or lower (respectively) than the specified frequency due to structural and power limitations. In an updated study, Pennycuick (1996) studied different species of the birds and made a detailed analysis of the frequency, leading to the following expression:

f = m3/8g1/2b23/24S1/3 3/8 .Eq. 8 Where

m = Mass of the bird (kg) g = Acceleration due to gravity (m/s2) b = Wingspan (m) S = Wing area (m2) = Air density (kg/m3). The above equation can be used to predict the wing-beat frequency of species thats mass, wingspan, and wing area is known.

The following design parameters were used to guide project development. 5.3 Overall Parameters 5.3.1 Cost

The total cost of the theoretical model and ornithopter prototype may not exceed 5000/-. 5.3.2 Theoretical Model Parameters 1. Functionality:

The theoretical model must be input customizable and allow for the performance prediction for any desired ornithopter weight, dimension, or angle of attack.

The theoretical model must be able to predict expected ornithopter prototype lift and airfoil flapping frequency for a given set of input variables.

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5.3.3 Ornithopter Prototype Parameters 1. Weight:

The prototype cannot exceed 500g in total weight 2. Dimension:

The prototype chassis must be no larger than 20cm in either width or length and cannot exceed 8cm in height.

The prototype airfoils may be no larger than 6cm in either length or height. 3. Functionality:

The prototype must allow for synchronous flapping of the airfoils. The prototype must allow for interchangeable airfoils. The prototype must be powered by an electronic speed controller (ESC), RC

Transmitter, and receiver.

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CHAPTER SIX DESIGN AND FABRICATION

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CHAPTER 6 DESIGN AND FABRICATION

Regarding the design of the mechanism it needs to be considered that it is intended to actually fly, but only be used for further studies and measurements. Hence the mechanism is not optimized for lightweight but nevertheless kept as simple as possible, allowing room for improvement towards a future mechanism that will be able to fly.

The main purpose of this effort is to present an idea about how to fabricate a flapping wing MAV. Here are few design considerations, which are useful and necessary for designing and fabrication of an ornithopter.

The course of action for this chapter included a detailed design of the individual mechanical components of the flapping wing MAV and then fabricating by assembling all the mechanical and electrical components at the required places. The detailed design of the mechanical components of the flapping wing MAV is carried out using CATIA V5 software.

CATIA (Computer Aided Three-dimensional Interactive Application) is a multi-platform CAD/CAM/CAE commercial software suite developed by the French company Dassault System, in 1977 by French aircraft manufacturer Avions Marcel Dassault. CATIA is PLM (Product Lifecycle Management) software. CATIA enables the creation of 3D parts, from 3D sketches, sheet metal, composites, molded, forged or tooling parts up to the definition of mechanical assemblies. The software provides advanced technologies for mechanical surfacing. It provides tools to complete product definition, including functional tolerances as well as kinematics definition. CATIA provides a wide range of applications for tooling design, for both generic tooling and mold.

CATIA can be applied to a wide variety of industries, from aerospace and defense,

automotive, and industrial equipment, to high tech, shipbuilding, consumer goods, plant design, consumer packaged goods, life sciences, architecture and construction, process power and petroleum, and services. CATIA V4, CATIA V5, Pro/ENGINEER and Solid Works are the dominant systems.

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6.1 Body Because weight is a significant design constraint, the group eliminated metals as

an option for the body material and instead decided to research composites and polymers. The group eventually narrowed the field to two different materials. The first, balsa wood, had been used in previous flapping wing MAVs. The group also found a polymer, Polymethacrylimide foam that is often used in sandwich construction and less dense than balsa wood. This foam is easy to shape, as it can be sliced with a hot-wire foam cutter, and also adhesive to epoxy, which would aid in the construction of the MAV. However, this foam is less widely available than balsa wood, and thus more expensive. Balsa wood would be easy to customize in-house, for it can be easily cut and sanded to the desired size and shape. Although balsa is denser than the polymer foam, the body is small enough for this weight difference to be minimal. Because balsa wood is cheap, customizable, and durable, the group selected it to build the body of the MAV.

The shape of the body was designed to be simple and lightweight. There is a solid piece running from the tail to the nose, where there is another section designed to mount the drive train and hinge. The length of the body was designed to match the wing span, thus keeping the MAV as small as possible while making control feasible as well. The body shape was finalized for ease of manufacturing and for simplicity as well. The finalized drive train was used to design the front part of the body, and a very simplistic final design was chosen. Minimizing the frontal area mitigates drag losses due to the frontal profile. To connect the slim body structure to the front portion, a simple approach was taken. Milling out a section on the front piece that the back section could be slotted into and glued gave the body stability and strength. The finalized body was rather simplistic, and its design can be seen in Figure 14.

Fig. 14 Body design

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6.2 Wings and Tail For a design involving two wings, it is crucial for each wing to be as lightweight

as possible. For this purpose, the group decided to research thin polyester films to comprise the wing, and lightweight spars to provide support and allow for the flapping effect.

While researching different wing shapes, the group took previous MAVs and manufacturing techniques into consideration. The design, mostly rectangular in shape, was selected to mimic that of the DelFly. This design will prevent the wing spars from being overly complicated and flimsy, while still keeping much of the surface area necessary for lift. The design is tapered at the outer edge of the trailing edges, allowing for the support spar to bed closer to the leading edge and preventing the backside corners of the wings from being unstable during flapping.

Fig. 15 Main wings

The group also researched multiple designs for the tail structure. The first option considered was an inverted V-tail. This requires only two control surfaces; however the MAV would not be highly maneuverable. This is demonstrated by the DelFly, where the V-tail was abandoned due to inadequate control of longitudinal motion in wake of the flapping wings.

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Fig. 16 Tail wing

6.3 Drive Train The motion of the hinge will be created by a drive train connected to the motor.

The group considered a single drive train options. The first contained gears that would spin parallel to the axis of forward movement (with their axels perpendicular). Although this design has been successfully implemented onto previous MAVs, it was dismissed due its complicated drive train and the effect that gyroscopic forces would have on flight. Instead, the group chose a method involving counter-rotating gears, spinning perpendicular to the forward movement of the MAV (with their axels parallel). Mechanically, this design is more simple and easier to construct, and due to the counter-rotation, the gyroscopic forces would be minimized.

Fig.17 Diagram of the originally intended flapping mechanism

From our motor tests we discovered that a drive train ratio of 70:7 would be desirable, and we ordered gears to match this design. This would give us an acceptable drive train

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assembly, and this drive train can be seen in Figure 17. This drive train is simplistic and secure, so we are anticipating minimal issues with its assembly.

Fig.18 Gear arrangement

For the design of the drive bar and the other design parameters, we used CATIA V5R16 to create and test the kinematics of the drive train.

6.4 Battery Lithium polymer batteries are commonly used in remote controlled planes and

MAVs. These batteries are fairly cheap and lightweight, which allows for longer and smoother flights. After researching many lithium polymer batteries, the group settled on a one cell, 160 milliampere-hour, and 3.7 volt battery from the vendor DraganFly (rctoys.com). The group researched both batteries and motors together, for the battery must have the ability to run the motor. The battery voltage is crucial, for if it is below the nominal voltage of the motor, the motor will not start. The electrical charge of 160 mAh is comparable to batteries used in other small ornithopters. This battery was also selected for its small mass of 4.1 grams and slender profile that will allow it to fit nicely into the

body of the MAV.

Fig.19 150mAh-3-7V-Li-PO-Battery [8]

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6.5 Motor The group researched different types of motors and decided that a brushless DC

motor would be most appropriate for this project. Brushless motors have several advantages over brushed motors. They have more torque per weight, and more torque per watt, making them more efficient. Brushless motors have increased reliability, leading to a longer lifetime. The group narrowed the motor selection down to two: the Hobby King AP-02 Brushless Micro Motor and the Micromo Series 1307 004 BH brushless geared motor, each of which weigh less than 2.5 grams.

Fig.20 Solarbotics GM15A [8]

6.6 Actuators and Receiver Because the tail will have three separate control surfaces, it will require three

actuators to control these movements. The group initially settled on the Toki Biowire servos from HobbyKing. Weighing only 1 gram each, these servos are fairly light, and their slender shape would allow for easy integration with the rear end of the fuselage. These servos would be able to rotate the elevators and rudders 30 in both directions. However, after further research, the group discovered PlantracoMicroflights 1.1 gram magnetic actuators. With the same range of motion and weight, this became the groups primary choice. These actuators also cost half as much as the Biowire servos, which will

make an effective difference when purchasing three. Because these actuators are magnetic, the original plan to use small metals brads to fasten them to the body was replaced with the design of three actuator mounts. These mounts, made from PEEK, could be cut using the Washburn Shops laser cutter.

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Fig.21 MicroStrain 3DM-GX1 IMU [8]

6.7 Transmitter The group encountered issues with finding a transmitter suitable for this project.

The receiver is designed to operate on a 900 MHz frequency. The group sought to find a 900 MHz transmitter on campus; however all of the transmitters owned by WPI professors unfortunately operate on either 2.4 GHz or 72 MHz. These are the most

common frequencies for RC aircraft in the US and 900 MHz is hard to find. This is because in the USA, 900 MHz is right on the edge of the cell phone band, so amateur radio applications like RC planes stay away from that range. However, our receiver was manufactured in Canada where the cell phone band ends at 850 MHz, allowing RC applications to extend further.

Some older transmitters made for robotic applications have been made to operate on the correct frequency. One such transmitter was obtained by the group from the local FIRST robotics chapter. This transmitter was designed to plug into a computer and simply serve as a transmitter for a ground station. Finding documentation for the controller, cable to attach to a computer, and programming a ground station would have been very difficult for the limited time available to our group. The group decided to pursue other options.

The group decided to purchase a transmitter from plantraco, the same vendor for the actuators and receiver. This circumnavigated the problem entirely as this transmitter is 900 MHz and designed to work specifically with Plantraco products. The transmitter has controls for throttle, rudder, elevators, and ailerons. Since this design calls for two separately moving elevons and a rudder the aileron and elevator control will both be used to control the flaps.

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6.8 Microcontroller The group originally planned on programming the MAV to run autonomously. If

this is the case, a microcontroller is necessary. However, the group determined autopilot is not a primary objective of this project, and using a transmitter to control the MAV remotely is a much more practical option. In future developments and experiments with autopilot, the group recommends a microcontroller such as the Arduino Pro Mini, which has several analog and digital inputs and has been widely used at WPI. This MAV, however, will not contain a microcontroller as it is outside the scope of this project.

Fig.22 Arduino microcontroller [8]

6.9 Final Assembly After manufacturing the individual parts, assembly was rather straightforward.

The hinge, gears, drive bars, and control discs could all be fastened to the body with small metal brads. Super glue is very effective in attaching the spars to the hinge, as well as the actuators to the mounts and subsequently, the mounts to the body. A photograph of this assembly is shown below in Figure 23.

Fig.23 Final assembly

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CHAPTER SEVEN EXPERIMENTAL SECTION

39

CHAPTER 7 EXPERIMENTAL SECTION 7.1 Motor Testing

The group performed a test on the motor to verify that it operated as intended and its power output was as stated by the manufacturer. For ease of testing, the receiver/transmitter was replaced with an Arduino Uno board. This allowed for far greater throttle control over the motor. Based on documentation for the motor controller, it was established that the correct duty cycle at full throttle had pulse duration of 2ms and the low throttle was 1.1ms. This was programmed into the Arduino and an oscilloscope was used to verify the signal clarity. Because the Arduino nominally outputs 5V, a voltage divider was created to lower the voltage to 3.7V. A 4k and a 3k resistor were used to reduce this voltage while still maintaining a clear signal to the motor. In order to start a brushless motor, the throttle must first be set at full, then zero, then some middle throttle. The board was programmed to output this and then run at 80% throttle continuously. To test the total output of the motor system, enough torque was applied to stall the motor while the total current draw was measured, based on the formula W=AV The group was able to determine at 3.7V and full throttle the motor draws 0.3A, giving a total of 1.1W of power.

7.2 Drive Train Testing After assembling the drive train, a test was performed to ensure that the gears and

drive bars would perform properly. Because the motor had not yet been mounted to the body, this was done through the use of a drill. The drill, with the smallest gear attached to the drill tip and locked into one of the larger gears, was spun at increasing speeds. The drive train functioned properly, moving the hinge so that the wings flapped in a

symmetrical manner.

7.3 Electrical Component Setup and Testing The electrical components operate in two basic control loops that are then

connected together. The first control loop is the actuators, transmitter and receiver working together to provide stability and control. The actuators are plug and play with

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the receiver and respond well to controls from the transmitter. The receiver has magnetic points where a power supply can be attached. At rest the receiver draws 40 mA of current and when the actuators are moving the current draw peaks at 200mA. The second control loop involves the motor and electronic speed controller or ESC. All brushless motors require an ESC to function. The ESC takes signals from the receiver and coverts them into a pulse with modulation signal (PWM). A PWM signal is an analog signal that behaves similar to a digital signal. It fluctuates between high and low voltages and the ratio between the time it is high and the time it is low is known as the duty cycle. Our receiver outputs a signal known as Pulse Position Modulation. This signal is very similar to a PWM signal except it outputs a larger magnitude of voltage. The ESC is capable of converting between the two automatically and the motor will be directly connected to the receiver.

7.4 Actuator Testing Before mounting the actuators to the body of the MAV, tests are conducted to

ensure that the actuators function properly and can be controlled in tandem by the dual joystick transmitter. Each of the three actuators is wired into the receiver so that the two actuators corresponding to the left and right elevators could be controlled with horizontal movements of the left and right joystick, respectively, and so the rudders actuator could be controlled with vertical movements of the right joystick. This would leave the vertical axis of the left joystick to interact with the motors speed controller. Because this test was successful, the group attached the actuators to the body using the PEEK mounts. Next, a test is performed to ensure that the actuators were powerful enough to move the tail structure. Unfortunately, with the current design, the actuators were unable to spin the control discs and move the tail. A solution to this is to design control discs with larger

moment arms, thus allowing for the same actuators to move the tail.

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CHAPTER EIGHT RESULT AND DISCUSSION

42

CHAPTER 8 RESULT AND DISCUSSION

Many test flights were conducted with the finished flapping wing MAV, first with an equivalent weight and distribution payload under manual control to determine whether the machine would actually be able to fly. Initial tests showed that sustained flight was possible but the robot was exceedingly difficult to control and quickly crashed. Later tests with a PD control on the elevator to stabilize pitch qualitatively showed promise but difficulties with gearbox and wing spar reliability plagued the testing process.

This process of breaking things during testing is an essential part of the design process and leaps of progress were made during this time in tracking down problems and implementing design solutions to them. Parts of the gearbox like the connection between the final rocker link and the shoulder were a common point of failure and received stopgap design revisions until enough changes accumulated for a full design iteration of the machine. Changes were incorporated into the gearbox design, the electronics package switched over to the much lighter Gumstix based system, and the frame was reconfigured to balance the new weight distribution properly.

8.1 Result The design process detailed by this report began with an examination of the

project objective. This is to build a flapping-wing micro air vehicle capable of takeoff, hover, and forward horizontal flight. After a thorough literary review, it was decided that the wing movements of most birds and insects is very complex with twists and other motions that are not yet fully understood by experts. This allows for the design of a vehicle capable of flight with a simplified wing motion. These wings are attached to a symmetric hinge that is powered by a motor. A battery powers the motor, allowing for

free flight with an onboard power source. Aside from the main wings, the design also includes a tail structure. Allowing full movement in each component of the tail structure simplifies both the design and manufacturing processes.

8.2 Discussion The flapping wing MAV made using gear drive which was rotated through the

DC motor and it was tested for its flying capability. The flight time of the Ornithopter (the time between the hand launch and its landing on the ground) was recorded for many

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trials. For a 150 mAh LiPo battery rotations of gear train an average flight time of 5 minutes was observed. Whereas, for the same rotations the balsa wood Ornithopter gave an average flight time of 5 minutes 10 seconds. This limitation of flight travel time mainly is because of the change in the weight of body material. However, considering the fabrication method, balsa wood Ornithopter is significant since the total time taken for the fabrication procedure is found very short. The total time to transform CAD models to physical models took only a time of 30 minutes.

Special light-weight material like balsa wood which is generally used for building the MAVs is rarely available in few places in the world. Cost and time factor for building the MAV from these kinds of wooden materials also is comparatively high. Other materials like fiberglass epoxy composite also exhibits high strength and low weight to suit the MAV construction. However, there have been difficulties to hold the desired aerodynamic shapes with these materials.

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CHAPTER NINE CONCLUSION AND FUTURE

WORK

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CHAPTER 9 CONCLUSION AND FUTURE WORK 9.1 Conclusion

The goal of this thesis was to develop a Flapping Wing MAV capable of hovering flight. The focus was also in the improvement in wing design and controllability. These goals were, except of the controllability, fully reached.

The chosen mechanism for turning rotation of the DC-motors into a flapping

movement of the wings is accurate and leads to error free functioning. By decreasing the amplitude even smoother behavior of the motor can be expected.

Through more than 20 tests the wings were optimized in angle and chord length and yield to enough lift generation for hover flight. The weight of the MAV is about 250g and therefore could be extended by additional hardware such as electronic or batteries or sensors.

The static behavior with respect to controllability was not fully characterized. It was shown that by changing the inputs to the motors the applied torques can be changed also but there was no reduction of the torques to the center of gravity of the MAV. The motor controller that allows independent inputs to each motor is essential for control issues. These input scan easily be mapped to the wished behavior through a coupled gamepad.

9.2 Future Work In order to achieve more lift generation the search space for finding the optimal

wing and mechanical configuration can be extended by a smoother discretization and including also the wing shape. There were no improvements on the motors so far. Many suppliers have the same size of DC-Motors but with different parameters, such as velocity constant.

Also there should be betterment in the controllability by calibrating the motors and reducing play in the structure.

Concluding it can be said that the flapping wing MAV designed and developed in this thesis is capable of hovering flight. Yet it is not controlled and yields to torque in the

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pitch and roll axis. The gained knowledge can be used for further improvements and opens the way toward an autonomous flapping wing MAV.

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9. Wood, R.J.,design, fabrication and analysis of a 3DOF, 3cm flapping wing MAV, School of engineering and applied sciences, Harvard University, Cambridge, ma02138,pp.106-114,2010.

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