Synopsis
Content
MICROCOPTER
Submitted by: SURAJ WANKHEDE ROHAN POWALE PRASHANT SANNAKKI SHASHANK CHAUREY JIGNESH MISRTY
Department of Electronics
Vidyalankar institute of technology Wadala(E), Mumbai 400 037
University of Mumbai
2009-10
Department of Electronic Engineering
CERTIFICATE
MICROCOPTER
Submitted by: SURAJ WANKHEDE ROHAN POWALE PRASHANT SANNAKKI SHASHANK CHAUREY JIGNESH MISRTY GUIDED BY: PROF: Dr. ANJALI DESHPANDE A project report submitted to
the University of Mumbai in partial fulfillment of degree course in Electronics Leading to bachelor’s degree in engineering.
Signature of guide
Head of department
Principal
2009-10
Department of Electronic Engineering
ABSTRACT
Historically, helicopters with four rotors (quadrotors) have not been very common, mainly because most of the usual payloads could be lifted using one or two rotors. However, the quadrotor possesses some special characteristics that make it attractive. One, of course, is the superior payload capacity. The other is the simplicity of its control system: just by independently adjusting the speed of each rotor it is possible to control both the attitude and the horizontal/vertical motion. This system is particularly suitable for small UAVs, because it reduces the mechanical complexity of the rotors (saving volume and weight) and simplifies the control algorithms. In order to be successful in selecting the appropriate control algorithms it is essential to have a complete understanding of microcopter flight dynamics. The microcopter relies on standard helicopter theories, although these have been severely modified to account for the particularities of the microcopter.
A microcopter consists of four brushless dc outrunner motors. This is because it mainly requires stationary thrust rather than high speed. The rotation speed of the motors are controlled by the respective ESC(electronic speed control). As the microcopter is controlled wirelessly it also consist of transmitter–receiver section. A RF transmitter-receiver using ASK(Amplitude shift keying) modulation is considered for microcopter. Modulation is carried out using four channels. Number of propellers used are four and they are selected as such to get same thrust as the takeoff weight at about 3000-4500rpm. Accordingly size of the propeller is selected. Propellers are available in size of (10" x 4,5") , (10’’x3.8") and (12"x3.8") etc. LIPO i.e. Lithium polymer battery is used to supply power to the microcopter. They have a voltage of 11,1 V or 14,4 V.Normal sizes are 1200mAh/20C to 5000mAh/30C batteries. The microcopter can be successfully applied to applications like Camera Surveillance in which mobile surveillance is accomplished using aerial platform. Other applications include Remote Volcano Sensing, Air Pollution Sensor (Inner-city), Microwave Cavity Resonator ,etc.
Department of Electronic Engineering
ACKNOWLEDGEMENT
We are very grateful to numerous individuals for their assistance and co-operation. We can’t express our gratitude to all those who encouraged, supported and guided us.
We are especially grateful to our project guide Dr. Anjali Deshpande for her valuable advice, timely advice and constant support in design of this project.
We are also grateful to our principal Mr.Prashant Sonare and Our Head of Electronics Department, Prof. Shrikant Velenkar for their constant support.
Finally we are thankful to our staff members and colleagues for their constant support.
Department of Electronic Engineering
CONTENTS
Sr.No 1 2
Page Title List of figures and tables Introduction 2.1 Helicopter Technology 2.2 Quadcopter Technology 2.3 Advantages of Quadcopter Technologg
Page No 1
2 2 3
3
Basic theory of motors
4 3.1. Brushed motors and its disadvantages 3.2. Brushless motors 3.3 Inrunners and Outrunners 3.4 motor specifications 3.5. Comparison between Brushed & Brushless Motors 9 5 6 7 8
3.6. Why brushless outrunner motors are used in Microcopterr
4
Electronic speed controller
10
4 5 6 7
Transmitter & Recevier Propellers Battery Principle and Operation
7.1
Diagrammatic Representation of layout
7.2 Operation and flight control 8
Stages of Development 9 10 Applications of Microcopter Conclusion
Department of Electronic Engineering
5 6 7 8
Transmitter & Recevier Propellers Battery Principle and Operation
12 15 16
8.1 Diagrammatic Representation of layout 8.2 Operation and flight control 9 Project status
17 18
9.1 Work planned 9.2 Work completed 10 11 12 Applications of Microcopter Conclusion References
20 21 22 23 24
1.0 List of figures and tables Sr.no.
1. 2.
Title
Figure of brushless motor Comparison table: brushless dc motor vs. brushed motor
Page no. 5 6
3. 4. 5. 6. 7. 8.
Block diagram of transmitter and receiver Block diagram of ASK modulation Waveform of ASK modulation Propellers Diagrammatic representation of microcopter Block of microcopter
12 13 14 15 17 18
1
2.0
Introduction
2.1 Helicopter technology
A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter achieves lift with the rotor blades which rotate around a mast. The primary advantage of a helicopter is from the rotor which provides lift without the aircraft needing to move forward, allowing the helicopter to take off and land vertically without a runway. For this reason, helicopters are often used in congested or isolated areas where fixed-wing aircraft cannot take off or land. The lift from the rotor also allows the helicopter to hover in one area more efficiently than other forms of vertical takeoff and landing aircraft, allowing it to accomplish tasks that fixed-wing aircraft cannot perform.
2.2
Quadcopter /Microcopter technology
A quadrotor, also called a quadrotor helicopter, is an aircraft that is lifted and propelled by four rotors. Quadrotors are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is derived from four rotors. They can also be classified as helicopters, though unlike standard helicopters, quadrotors are able to use fixed-pitch blades, whose angle of attack does not vary as the blades rotate. Control of vehicle motion can be achieved by varying the relative speed of each rotor to change the thrust and torque produced by each. Here exist two generations of quadrotor designs. The first generation quadrotors were designed to carry one or more passengers. These vehicles were among the first successful heavier-than-air vertical take off and landing (VTOL) vehicles. However, early prototypes suffered from poor performance, and latter prototypes required too much pilot work load, due to poor stability augmentation. The more recent generation of quadrotors are commonly designed to be unmanned aerial vehicles (UAVs). These vehicles use an electronic control system and electronic sensors to stabilize the aircraft. With their small size and agile maneuverability, these quadrotors can be flown indoors as well as outdoors.
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2.3
Advantages of Quadcopter / microcopter technology
The advantages of the current generation of quadrotors, versus comparably scale helicopters, are as follows. First, quadrotors do not require mechanical linkages to vary rotor angle of attack as they spin. This simplifies the design of the vehicle, and reduces maintenance time and cost. Second, the use of four rotors allows each individual rotor to have a smaller diameter than the equivalent helicopter rotor, for a given vehicle size, allowing them to store less kinetic energy during flight. This reduces the damage caused should the rotors hit any objects. For small scale UAVs, this makes the vehicles safer to interact with in close proximity. Finally, by enclosing the rotors within a frame, the rotors can be protected during collisions, permitting flights indoors and in obstacle-dense environments, with low risk of damaging the vehicle, its operators, or its surroundings.
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3.0
Basic theory of motors
3.1 Brushed motors A standard brushed motor is often referred as a canned motor. Every canned motor consists of the following parts: Armature- The rotating portion of the motor. It consists of the poles, terminals, and the commutator. Poles- Copper wires wound around a piece of metal forming an electromagnet. The poles are attached to the armature. Most motors have 3 or more poles Terminal- Point at which the copper wire of a poll attaches. Commutator- A switch on the armature that reverses the current to the poles every 1/2 rotation so that the magnetic fields of each will always maintain rotation. Brushes- Tabs in the motor cap that are wired to the battery and make contact with the plates on the commutator as the armature rotates. Magnets- The outer shell (or can) of the motor is lined with two permanent magnets, of opposite polarity. This non-rotating portion of the motor is also referred as the motor stator. The battery is wired directly to the brushes. The brushes make contact with the plates of the commutator as the motor turns. There are the same number of plates on the commutator as there are poles on the armature. When the brushes come in contact with the appropriate plates of the commutator, a particular pole (electromagnet) is charged. When a pole is charged, it is attracted to one of the magnets in the can and repelled by the other. The commutator acts as a switch by switching the polarity of each pole every time the pole passes a magnet. When the polarity is switched, the pole is attracted to the next magnet in the can while being repelled by the one it just passed. This process repeats as long as power is supplied to the motor.
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Disadvantages of Brushed Motors
• • • • •
The brushes and commutator wear out The brushes and commutator must be cleaned periodically Friction from the brushes slow the motor down Friction from the brushes lead to shorter flight times and battery life. Friction from the brushes cause lower power to weight ratio
3.2 Brushless motors
Figure:1 brushless motor Brushless RC motors work on the same principle as brushed motors, except the electromagnets(poles) are stationary and the permanent magnets are on the spinning portion of the motor. Since the electromagnets are stationary, there is no need for brushes! The electronic speed controller(ESC) takes care of switching the voltage of the electromagnets. It's important to know that a brushless speed controller and a brushed speed controller can not be used interchangeably. They perform completely different tasks. The quickest way to tell the difference between a canned motor and a brushless motor is to count the number of wire leads. All brushless RC motors have 3 wires. Canned motors have 2 wires. The third wire is used for feedback. Switching any two of these wires will change the rotation of the motor. 5
3.3
Inrunner and outrunners
There are two types of brushless motors. Inrunners
Inrunner brushless motors are set up very similar to the canned motor explained above, except the permanent magnets and electromagnets are in opposite positions. The faster a motor spins, the more efficient it is. Inrunner motors turn very fast and are much more efficient than outrunner motors. Inrunner brushless RC motors require a reducing gearbox between the motor and propeller of your RC airplane. For this reason, the output speed and torque of the propeller can easily be "tweaked" to facilitate different flying characteristics by using different size gears. The downside is added parts that can and do fail. The gears get stripped, and the gearbox shafts are easily bent. It can also be an obstacle when mounting the gearbox motor combination for your RC airplane neatly, especially under a cowling. Outrunners An outrunner brushless motor has the permanent magnets on the outside of the electromagnets. the outer hub holding the permanent magnets has the output shaft attached in the center.
Outrunners
• • • • •
Inrunners
• • • • •
Low RPM's, high torque Less efficient than inrunners No gearbox required Narrow prop selection Silent
High RPM's, low torque More efficient than outrunners Require a gearbox Wide prop selection Noisy
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3.4 Motor Specifications Voltage Constant Kv is the "Voltage Constant". This is how many RPM's the motor turns for each volt applied. Actually, it's a tad less because even brushless motors aren't 100% efficient.For example, if you apply 12volts to a 200Kv motor, it will turn at just under (12 x 200) 2400 RPM's Torque Constant Kt is the "Torque Constant". For all motors, Kt= 1355/Kv. In a nut shell, this means the faster the motor spins for a given voltage (Kv), the lower the output torque will be (Kv). Outrunners generally have a lower Kv, which in turn produces more torque at a slower speed for spinning those larger props. The opposite is true with inrunners. No Load Current Io is the "No Load Current". This is the amount of current it takes to spin the motor with no prop. For example, if your motor is pulling 25Amps, and the Io is 2Amps, then you really only have 23Amps turning the prop. Terminal Resistance Rm is the "Terminal Resistance". This is the internal resistance of the motor measured in Ohms. The higher the Rm, the less efficient the motor is. Current and Power The maximum current and power is what determines how large of a prop and what size plane can be used with the motor. Simply multiply the current by the battery voltage to get power. The larger the propeller's diameter and pitch, the more current the motor will draw for a given RPM. For example, the 200Kv motor will run at 2400 RPM's regardless of whether it has a 10x6 prop or a 11x5 prop. But, the 11x5 propellers
cause the motor to draw more current. Drawing too much current will destroy the motor. 7
3.5
Comparison Table: Brushless DC Motor vs Brushed DC Motor BLDC Motor Brushed DC Motor Electronic commutation based Brushed commutation on Hall position sensors Less required due to absence Periodic maintenance is of brushes required Longer Shorter Flat - Enables operation on all Moderately flat - At higher speeds with rated load speeds, brush friction increases, thus reducing useful torque High - No voltage drop across Moderate brushes High - Reduced size due to Moderate/Low - The heat superior thermal produced by the armature is characteristics. Because dissipated in the air gap, thus BLDC has the windings on the increasing the temperature in stator, which is connected to the air gap and limiting specs the case, the heat dissipation on the output power/frame size is better Low, because it has Higher rotor inertia which permanent magnets on the limits the dynamic rotor. This improves the characteristics dynamic response. Higher - No mechanical Lower - Mechanical limitations limitation imposed by be the brushes brushes/commutator. Low, because it has Arcs in the brushes will permanent magnets on the generate noise causing EMI in rotor. This improves the the equipment nearby dynamic response.
Feature Commutation Maintenance Life Speed/Torque Characteristics
Efficiency Output Power/ Frame Size
Rotor Inertia
Speed Range
Electric Noise Generation
Cost of Building
Moderate - Since it has Moderate - Due to increases in permanent magnets, building steel & copper. ( with wound cost may be higher. However, field stator) steel & copper prices are up
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3.6
Why brushless outrunners are used in microcopter
The choice of the motor models heavily depends on purpose and takeoff weight of microcopter or quadcopter. Since a tri- or quadrocopter needs mainly stationary thrust and not a high maximum speed, its ideal to use slow running, big propellers with a low pitch. To avoid gearboxes (weight, clumsy, inefficient, noisy) it is highly recommended to use brushless outrunner motors with a low "kv" (RPMs per volts, about 1000kv are fine) rating. The revolutions per minute should be in the range of 3000 to 4500 when hovering. Due to above reasons we are using brushless outrunners in microcopters/quadcopters.
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4.0
Electronic Speed Controller
An Electronic speed controller (ESC) is what controls how fast the motors turns. The ESC plugs into the throttle channel of the receiver. The factors that determine what ESC to use include the type of motor you have, the size of the motor, and the type of batteries. Selection of Motor ( Brushless or Canned ) ESC’s designed specifically for brushed motors will only work with brushed motors. Likewise, electronic speed controllers designed specifically for brushless motors will only work for brushless motors. There are a few ESC’s that are designed to work with both. A brushed ESC simply turns the voltage on and off very rapidly(several times a second). To increase the speed, the ESC increases the amount of time that the voltage is on while decreasing the amount of time that the voltage is off. This is called “chopping” the voltage. To slow the motor down, this process is reversed. The brushes on a brushed motor determine how the electromagnets are energized to keep the motor spinning. A brushless ESC has the added task of determining how each pole needs to be energized at any given time to keep the motor spinning. The brushless ESC needs to have feed back from the motor in order to perform this task. The brushes on a brushed motor are in a fixed position relative to the permanent magnets. When the armature rotates, the brushes contact the plates of the commutator at the perfect spot each revolution to keep the motor turning. Without feedback, the ESC on a brushless motor has no idea where the permanent magnets are in relation to the electromagnets(poles).
All brushless motors and brushless ESC’s have three wires. Only two of the three wires are energized by the ESC at any given time. The pole that is not energized (coasting) will actually generate a small amount of voltage that is proportional to how fast the motor is turning. This small voltage is used by the ESC to determine how fast and in what direction the motor is turning at any given time. Size of motor Electronic speed controllers are rated for a maximum current. The more current an ESC is rated for, the more expensive and heavier it will be. Choose an electronic speed controller that is rated for slightly more than what your motor will pull at full throttle. Too much current will damaged an electronic speed controller very quickly. 10 Battery Eliminator Circuit (BEC) The motor requires much more power than the receiver and speed controller. A battery eliminator circuit (BEC) converts the voltage from the motor battery to a lower voltage for the receiver and ESC. This eliminates the need for a separate low voltage battery for the receiver and ESC. The BEC also senses when the battery is getting low and cuts power to the motor while allowing the servos to function for a safe landing. The BEC is usually incorporated circuit board of the ESC for small to medium size electric airplanes. Large RC airplanes that require larger voltages to power the motor will require a stand-alone BEC, which is called a voltage regulator.
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5.0
RF transmitter & receiver
Figure:2 transmitter and receiver block diagram
Four channel ASK transmitter and receiver Special ASK transmitter and receiver modules are used to transmit and receive digital code. It has carrier frequency of 433.92 MHz and operating range of around 100-150 meters. Amplitude Shift Key Modulation Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. The level of amplitude can be used to represent binary logic 0s and 1s. We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given.
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Like AM, ASK is also linear and sensitive to atmospheric noise, distortions, propagation conditions on different routes in PSTN, etc. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light. Laser transmitters normally have a fixed “bias” current that causes the device to emit a low light level. This low level represents binary 0, while a higher-amplitude light wave represents binary 1. The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation). More sophisticated encoding schemes have been developed which represent data in groups using additional amplitude levels. For instance, a four-level encoding scheme can represent two bits with each shift in amplitude; an eightlevel scheme can represent three bits; and so on. These forms of amplitude-shift keying require a high signal-to-noise ratio for their recovery, as by their nature much of the signal is transmitted at reduced power. Here is a diagram showing the ideal model for a transmission system using an ASK modulation
Figure:3 ASK modulation block diagram. In this method the amplitude of the carrier assumes one of the two amplitudes dependent on the logic states of the input bit stream.
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A typical output waveform of an ASK modulator is shown in the figure below. The frequency components are the USB and LSB with a residual carrier frequency. The low amplitude carrier is allowed to be transmitted to ensure that at the receiver the logic 1 and logic 0 conditions can be recognized uniquely as shown in figure below
Figure :4 Amplitude Shift Key Modulation waveforms
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6.0 Propellers
A propeller is a type of fan which transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and air or water is accelerated behind the blade. A pressure difference between the forward and rear surfaces of the airfoilshaped blade is produced and air or water accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's principle and Newton's third law. We should choose propellers to get the same thrust as the takeoff weight at about 3000 to 4500 RPMs. If propellers are too small, the RPMs will be too high, and efficiency and payload weight suffers. Also, flight time will decrease significantly, because of too high current consumption. If propellers are too big, the hovering RPMs are too low, so flight stability suffers.. Propellers are available in size of (10" x 4,5") , (10’’x3.8") and (12"x3.8") etc.If we have a good motor on a light frame then we can also use 3 blade propellers.
Figure:5 two blade propeller
Figure:6 Three blade propeller
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7.0 Battery
Lithium polymer battery (Lipo battery) Lithium-ion polymer 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 batteries). Normally batteries are composed of several identical secondary cells in parallel addition to increase the discharge current capability. As batteries usually Lithium-Polymer batteries or LiPos are used. These types of batteries differ from other types by a light weight combined with high capacity. Handling these batteries is not without any danger, so some rules have to be kept in mind. These types need a special kind of charger, because the charging procedure differs a lot from other types (like NiCad and NiMh). The cells should not be overcharged, neither should they be unloaded to deeply. To keep the charge difference between cells to a minimum, a balancer must be used. This balancer might be integrated in the charger, or a separate balancer should be attached to the charger. All LiPo-packs have a connector for a balancer. For a Quadcopter LiPo-packs with three or four cells are used. They have a voltage of 11,1 V or 14,4 V. Depending on our Brushless Motors we will need a bigger or smaller battery. Normal sizes are 1200mAh/20C to 5000mAh/30C batteries.
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8.0 Principle and Operation
8.1 Diagrammatic Representation
Figure :7 Quadcopter showing direction of each propeller
As all the propellers are spinning at the same angular velocity, a yaw stabilising tail rotor like the one found on a standard helicopter is not needed. Yaw is achieved by increasing the torque produced by a pair of rotating motors either the clockwise pair or the anti-clockwise pair and decreasing the torque produced by the other pair. Similarly the pitch of the rotors need not be altered. Instead, movements in the pitch (forward/backward) and roll (left/right) axes can be achieved separately, simply by altering the thrust produced by a pair of motors and all this can be done without affecting the yaw of the vehicle. The front and rear propellers control the pitch of the vehicle while in flight and the right and left propellers control the roll of the vehicle.
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Motors , electronic speed controllers, and battery are connected as shown blow.
Figure: 8 Microcopter connections 8.2 Operation and flight control The Flight Control (FC) is the main controlling board on the quadcopter and all the necessary sensors and microprocessors used to achieve and maintain stable flight are located on this board. Due to the nature of the project a strict power to weight ratio budget was designed. From initial estimations, maximum payload for the vehicle would be approximately 500-700 grams. The motors used in RC vehicles vary greatly so it was desired to find a light motor with low power consumption. The main requirement was that it provided 1000 rpm V^-1. A Brushless motor fulfils the specifications. Brushless motors are more complicated to operate because they need to changethe DC supply voltage of the battery into a phased AC (usually three phase) with controlled power output so that the speed of the motors can be accurately controlled. In total there are four Brushless Controllers (BL-Ctrl) one for each motor.
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To achieve a very stable level of flight it is desired to change the throttle value very rapidly (<0.5m). Control of the vehicle is achieved through use of a RF transmitter and receiver pair. A transmitter with a minimum of four channels is required to control the quadcopter in the various planes.. The receiver demodulates the instructions given by the pilot and converts them into electrical signals. A receiver with a summing signal is required for the MikroKopter (MK). This signal contains all of the channels sent by the transmitter and is made available to the FC for processing. The design of the frame is only limited by one factor: it must be as light as possible. The frame designed took on a basic cross shape similar to many open source projects . Bearing in mind that the frame must be lightweight some of the materials considered include: aluminium , carbon fiber or polystyrene; it is possible to have a combination of these. The most cost effective material for this project is aluminium or wood because it is readily available and cheap. The batteries needed to power all the onboard electronics have to have a low weight to power ratio so that maximum flight time may be achieved. The different types of battery considered suitable for use in RC vehicles are: Lithium polymer (Lipo), Nickel-cadmium (NiCd) and Nickel metal hydride battery (NiMh). The Lipo types are the most advanced and offer the most power. They are volatile and must be handled with care but they can have a capacity of over 10,000 mAh. NiMh batteries are a slightly older technology but they are still capable of capacities around 5000 mAh. However if a poor quality of battery is purchased then bad cells can develop quickly when the capacity is increased. NiMh batteries are cheaper than Lipo batteries and are also less volatile. NiCd batteries are the cheapest overall and have similar characteristics to that of NiMh but are unable to achieve an equal capacity. A decent flying time is desired to test the software and hardware which will be added and due to the powerful motors and large propellers the best weight to power ratio with a high capacity can be achieved using the Lipo batteries. The propellers play a major role on the takeoff weight and the speed that the vehicle will fly at. The diameter of the propellers as well as their pitch must be considered. Due to the slow spinning motors a low pitch is desired.
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9.0 Project status
9.1 Work planned
STAGE I: Determining the project and assessing the availability of the components of the hardware & deciding upon the feasible software for the purpose. STAGE II: Procurement of literature & literature review. STAGE III: Hardware: Designing the circuit diagrams Software: Designing basic flowcharts & algorithms. STAGE IV: Finalizing the basic design of the hardware Designing the PCB: PCB design is ready, components selected. STAGE V: Hardware: Testing & troubleshooting Software: Algorithms finalized. Coding begins. Code tested & troubleshooting solved. STAGE VI: Assembling the entire project, testing & troubleshooting it in entirety. Stage VII: Annexed features of levels, synchronization and flight control tested and troubleshooting solved. STAGE VIII: Entire unit encompassing all the features is tested & troubleshooting is solved, project is ready for display.
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9.2
Work Completed
• • • • • • • •
Microcopter basic block diagram was designed and hence accordingly detailed research was done. Different designs of microcopter like tricopter and quadcopter were studied in detail. After thorough research we came to the conclusion that quadcopter design with four rotors is more stable. Components and their specifications were decided according to the requirement of the project. Theory of brushless motors and electronic speed controllers (ESC) were studied. Different circuits of ESC were searched and simulated on multisim. Different motors and propeller combinations were considered. Transmitter and Receiver circuits were decided which uses ASK modulation at frequency 433.92 MHz.
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10.0 Applications
A number of options were considered as a possible applications for quadcopter below is a list of some of the applications investigated and the reason why they were eliminated. 1] Camera Surveillance Possibly the most obvious use for an aerial platform would be as a mount for a camera so that it may be used as a mobile surveillance device. A decision was made to build the quadcopter/microcopter for use as a platform for a camera which would be wireless. The standardized connection could then be used to attach different devices and essentially enable the quadcopter to be used for a multitude of applications. 2] Remote Volcano Sensing Andrew McGonigle, a Scottish scientist working for the University of Sheffield, has developed a novel means for determining whether or not a volcano is due to erupt.It involves sending a Radio Controlled (RC) helicopter/microcopter into the crater of a volcano and measuring the level of various gases. This information can then be processed once the Helicopter returns. The sensors were the main reason this idea was abandoned. They were found to be too expensive and there was nowhere to test the vehicle i.e. a local active volcano. 3] Air Pollution Sensor (Inner-city) It was thought that the vehicle could be used to navigate a pre-determined flight path and measure several air pollutant levels en route. The resulting measurements could then be used as an indication of the air pollution in a particular area of a city. However, the idea was abandoned due to a problem with the measurement sensors i.e they were either both large and bulky or a passive measurement was needed. The passive measurement would once again be affected by the moving vehicle and is usually taken over a longer period.
4] Microwave Cavity Resonator An idea put forward by Dr. Ian Glover a strathclyde lecturer involved testing the reflectivity of a content in the boundary layer. The boundary layer is the first few hundred meters above the earth surface. The reflectivity of air affect the transmission of radio waves. The proposed method of measurement included building a microwave cavity resonator. The resonator chamber would allow to
pass through it and by testing the capacitance of the air the reflectivity could be determined. The rotating propellers posed a problem because they would force air pass the cavity thus affecting the measurement. A different method was to actively monitor the temperature and humidity of the surrounding air and perform a calculation using the two variables. The problem with this is obtaining an Instantaneous and accurate measurement of the humidity. Once again the rotating blades would affect the measurement
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11.0 Conclusion
The control system demonstrates in simulation that reliable and controlled flight can be achieved. Tests have confirmed the functionality and range of wireless transmission. Theoretical calculations have determined that the desired amount of lift can be achieved. Experimental tests must be completed to verify these calculations. A complete and thorough test plan has been provided and can be used by subsequent design teams to complete this project. This plan includes assembly diagrams and instructions as well as a complete bill of materials. Reflecting on this project, it was very aggressive for a five person design team. This project required an extreme amount of engineering to be done in a short amount of time. With respect to this aggressive nature of the project, its status at this point can be deemed a mild success. Since we have completed the entire study and research required for this project; our next step would be to design a working prototype. It includes building a light weight frame for microcopter, design of electronic speed controller circuit, and and mounting these components on microcopter frame with motors, battery and receiver circuit, and then performing test flights.
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12.0 References
1. 2. 3. 4. 5. 6. 7.
8. 9. http://aeromodelling.nitc.googlepages.com/links 10. http://www.electric-rc-helicopter.com/article/gyroconfusion.php 11. http://www.anglia.com/newsarchive/261.asp?article_id=921 12. http://www.microchip.com/ParamChartSearch/chart.aspx?
branchID=8093&mid=14⟨=en&pageId=75
http://www.mikrokopter.de/ucwiki/en/MikroKopter http://www.quadcopter.org/index.php5?title=Quadcopter_Home http://www.rcgroups.com/forums/showthread.php?t=768115 http://radiocontrol.wikia.com/wiki/Brushless_motor http://www.himodel.com/electric/1290KV_Outrunner_Brushless_Motor_Type_FC2 830-9T.html http://www.rentron.com/rf_remote_control.htm http://www.himodel.com/electric/1290KV_Outrunner_Brushless_Motor_Type_FC2 830-9T.html http://mikrokopter.de/ucwiki/KategorieNachbauten
Submitted by: SURAJ WANKHEDE ROHAN POWALE PRASHANT SANNAKKI SHASHANK CHAUREY JIGNESH MISRTY
Department of Electronics
Vidyalankar institute of technology Wadala(E), Mumbai 400 037
University of Mumbai
2009-10
Department of Electronic Engineering
CERTIFICATE
MICROCOPTER
Submitted by: SURAJ WANKHEDE ROHAN POWALE PRASHANT SANNAKKI SHASHANK CHAUREY JIGNESH MISRTY GUIDED BY: PROF: Dr. ANJALI DESHPANDE A project report submitted to
the University of Mumbai in partial fulfillment of degree course in Electronics Leading to bachelor’s degree in engineering.
Signature of guide
Head of department
Principal
2009-10
Department of Electronic Engineering
ABSTRACT
Historically, helicopters with four rotors (quadrotors) have not been very common, mainly because most of the usual payloads could be lifted using one or two rotors. However, the quadrotor possesses some special characteristics that make it attractive. One, of course, is the superior payload capacity. The other is the simplicity of its control system: just by independently adjusting the speed of each rotor it is possible to control both the attitude and the horizontal/vertical motion. This system is particularly suitable for small UAVs, because it reduces the mechanical complexity of the rotors (saving volume and weight) and simplifies the control algorithms. In order to be successful in selecting the appropriate control algorithms it is essential to have a complete understanding of microcopter flight dynamics. The microcopter relies on standard helicopter theories, although these have been severely modified to account for the particularities of the microcopter.
A microcopter consists of four brushless dc outrunner motors. This is because it mainly requires stationary thrust rather than high speed. The rotation speed of the motors are controlled by the respective ESC(electronic speed control). As the microcopter is controlled wirelessly it also consist of transmitter–receiver section. A RF transmitter-receiver using ASK(Amplitude shift keying) modulation is considered for microcopter. Modulation is carried out using four channels. Number of propellers used are four and they are selected as such to get same thrust as the takeoff weight at about 3000-4500rpm. Accordingly size of the propeller is selected. Propellers are available in size of (10" x 4,5") , (10’’x3.8") and (12"x3.8") etc. LIPO i.e. Lithium polymer battery is used to supply power to the microcopter. They have a voltage of 11,1 V or 14,4 V.Normal sizes are 1200mAh/20C to 5000mAh/30C batteries. The microcopter can be successfully applied to applications like Camera Surveillance in which mobile surveillance is accomplished using aerial platform. Other applications include Remote Volcano Sensing, Air Pollution Sensor (Inner-city), Microwave Cavity Resonator ,etc.
Department of Electronic Engineering
ACKNOWLEDGEMENT
We are very grateful to numerous individuals for their assistance and co-operation. We can’t express our gratitude to all those who encouraged, supported and guided us.
We are especially grateful to our project guide Dr. Anjali Deshpande for her valuable advice, timely advice and constant support in design of this project.
We are also grateful to our principal Mr.Prashant Sonare and Our Head of Electronics Department, Prof. Shrikant Velenkar for their constant support.
Finally we are thankful to our staff members and colleagues for their constant support.
Department of Electronic Engineering
CONTENTS
Sr.No 1 2
Page Title List of figures and tables Introduction 2.1 Helicopter Technology 2.2 Quadcopter Technology 2.3 Advantages of Quadcopter Technologg
Page No 1
2 2 3
3
Basic theory of motors
4 3.1. Brushed motors and its disadvantages 3.2. Brushless motors 3.3 Inrunners and Outrunners 3.4 motor specifications 3.5. Comparison between Brushed & Brushless Motors 9 5 6 7 8
3.6. Why brushless outrunner motors are used in Microcopterr
4
Electronic speed controller
10
4 5 6 7
Transmitter & Recevier Propellers Battery Principle and Operation
7.1
Diagrammatic Representation of layout
7.2 Operation and flight control 8
Stages of Development 9 10 Applications of Microcopter Conclusion
Department of Electronic Engineering
5 6 7 8
Transmitter & Recevier Propellers Battery Principle and Operation
12 15 16
8.1 Diagrammatic Representation of layout 8.2 Operation and flight control 9 Project status
17 18
9.1 Work planned 9.2 Work completed 10 11 12 Applications of Microcopter Conclusion References
20 21 22 23 24
1.0 List of figures and tables Sr.no.
1. 2.
Title
Figure of brushless motor Comparison table: brushless dc motor vs. brushed motor
Page no. 5 6
3. 4. 5. 6. 7. 8.
Block diagram of transmitter and receiver Block diagram of ASK modulation Waveform of ASK modulation Propellers Diagrammatic representation of microcopter Block of microcopter
12 13 14 15 17 18
1
2.0
Introduction
2.1 Helicopter technology
A helicopter is an aircraft that is lifted and propelled by one or more horizontal rotors, each rotor consisting of two or more rotor blades. Helicopters are classified as rotorcraft or rotary-wing aircraft to distinguish them from fixed-wing aircraft because the helicopter achieves lift with the rotor blades which rotate around a mast. The primary advantage of a helicopter is from the rotor which provides lift without the aircraft needing to move forward, allowing the helicopter to take off and land vertically without a runway. For this reason, helicopters are often used in congested or isolated areas where fixed-wing aircraft cannot take off or land. The lift from the rotor also allows the helicopter to hover in one area more efficiently than other forms of vertical takeoff and landing aircraft, allowing it to accomplish tasks that fixed-wing aircraft cannot perform.
2.2
Quadcopter /Microcopter technology
A quadrotor, also called a quadrotor helicopter, is an aircraft that is lifted and propelled by four rotors. Quadrotors are classified as rotorcraft, as opposed to fixed-wing aircraft, because their lift is derived from four rotors. They can also be classified as helicopters, though unlike standard helicopters, quadrotors are able to use fixed-pitch blades, whose angle of attack does not vary as the blades rotate. Control of vehicle motion can be achieved by varying the relative speed of each rotor to change the thrust and torque produced by each. Here exist two generations of quadrotor designs. The first generation quadrotors were designed to carry one or more passengers. These vehicles were among the first successful heavier-than-air vertical take off and landing (VTOL) vehicles. However, early prototypes suffered from poor performance, and latter prototypes required too much pilot work load, due to poor stability augmentation. The more recent generation of quadrotors are commonly designed to be unmanned aerial vehicles (UAVs). These vehicles use an electronic control system and electronic sensors to stabilize the aircraft. With their small size and agile maneuverability, these quadrotors can be flown indoors as well as outdoors.
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2.3
Advantages of Quadcopter / microcopter technology
The advantages of the current generation of quadrotors, versus comparably scale helicopters, are as follows. First, quadrotors do not require mechanical linkages to vary rotor angle of attack as they spin. This simplifies the design of the vehicle, and reduces maintenance time and cost. Second, the use of four rotors allows each individual rotor to have a smaller diameter than the equivalent helicopter rotor, for a given vehicle size, allowing them to store less kinetic energy during flight. This reduces the damage caused should the rotors hit any objects. For small scale UAVs, this makes the vehicles safer to interact with in close proximity. Finally, by enclosing the rotors within a frame, the rotors can be protected during collisions, permitting flights indoors and in obstacle-dense environments, with low risk of damaging the vehicle, its operators, or its surroundings.
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3.0
Basic theory of motors
3.1 Brushed motors A standard brushed motor is often referred as a canned motor. Every canned motor consists of the following parts: Armature- The rotating portion of the motor. It consists of the poles, terminals, and the commutator. Poles- Copper wires wound around a piece of metal forming an electromagnet. The poles are attached to the armature. Most motors have 3 or more poles Terminal- Point at which the copper wire of a poll attaches. Commutator- A switch on the armature that reverses the current to the poles every 1/2 rotation so that the magnetic fields of each will always maintain rotation. Brushes- Tabs in the motor cap that are wired to the battery and make contact with the plates on the commutator as the armature rotates. Magnets- The outer shell (or can) of the motor is lined with two permanent magnets, of opposite polarity. This non-rotating portion of the motor is also referred as the motor stator. The battery is wired directly to the brushes. The brushes make contact with the plates of the commutator as the motor turns. There are the same number of plates on the commutator as there are poles on the armature. When the brushes come in contact with the appropriate plates of the commutator, a particular pole (electromagnet) is charged. When a pole is charged, it is attracted to one of the magnets in the can and repelled by the other. The commutator acts as a switch by switching the polarity of each pole every time the pole passes a magnet. When the polarity is switched, the pole is attracted to the next magnet in the can while being repelled by the one it just passed. This process repeats as long as power is supplied to the motor.
4
Disadvantages of Brushed Motors
• • • • •
The brushes and commutator wear out The brushes and commutator must be cleaned periodically Friction from the brushes slow the motor down Friction from the brushes lead to shorter flight times and battery life. Friction from the brushes cause lower power to weight ratio
3.2 Brushless motors
Figure:1 brushless motor Brushless RC motors work on the same principle as brushed motors, except the electromagnets(poles) are stationary and the permanent magnets are on the spinning portion of the motor. Since the electromagnets are stationary, there is no need for brushes! The electronic speed controller(ESC) takes care of switching the voltage of the electromagnets. It's important to know that a brushless speed controller and a brushed speed controller can not be used interchangeably. They perform completely different tasks. The quickest way to tell the difference between a canned motor and a brushless motor is to count the number of wire leads. All brushless RC motors have 3 wires. Canned motors have 2 wires. The third wire is used for feedback. Switching any two of these wires will change the rotation of the motor. 5
3.3
Inrunner and outrunners
There are two types of brushless motors. Inrunners
Inrunner brushless motors are set up very similar to the canned motor explained above, except the permanent magnets and electromagnets are in opposite positions. The faster a motor spins, the more efficient it is. Inrunner motors turn very fast and are much more efficient than outrunner motors. Inrunner brushless RC motors require a reducing gearbox between the motor and propeller of your RC airplane. For this reason, the output speed and torque of the propeller can easily be "tweaked" to facilitate different flying characteristics by using different size gears. The downside is added parts that can and do fail. The gears get stripped, and the gearbox shafts are easily bent. It can also be an obstacle when mounting the gearbox motor combination for your RC airplane neatly, especially under a cowling. Outrunners An outrunner brushless motor has the permanent magnets on the outside of the electromagnets. the outer hub holding the permanent magnets has the output shaft attached in the center.
Outrunners
• • • • •
Inrunners
• • • • •
Low RPM's, high torque Less efficient than inrunners No gearbox required Narrow prop selection Silent
High RPM's, low torque More efficient than outrunners Require a gearbox Wide prop selection Noisy
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3.4 Motor Specifications Voltage Constant Kv is the "Voltage Constant". This is how many RPM's the motor turns for each volt applied. Actually, it's a tad less because even brushless motors aren't 100% efficient.For example, if you apply 12volts to a 200Kv motor, it will turn at just under (12 x 200) 2400 RPM's Torque Constant Kt is the "Torque Constant". For all motors, Kt= 1355/Kv. In a nut shell, this means the faster the motor spins for a given voltage (Kv), the lower the output torque will be (Kv). Outrunners generally have a lower Kv, which in turn produces more torque at a slower speed for spinning those larger props. The opposite is true with inrunners. No Load Current Io is the "No Load Current". This is the amount of current it takes to spin the motor with no prop. For example, if your motor is pulling 25Amps, and the Io is 2Amps, then you really only have 23Amps turning the prop. Terminal Resistance Rm is the "Terminal Resistance". This is the internal resistance of the motor measured in Ohms. The higher the Rm, the less efficient the motor is. Current and Power The maximum current and power is what determines how large of a prop and what size plane can be used with the motor. Simply multiply the current by the battery voltage to get power. The larger the propeller's diameter and pitch, the more current the motor will draw for a given RPM. For example, the 200Kv motor will run at 2400 RPM's regardless of whether it has a 10x6 prop or a 11x5 prop. But, the 11x5 propellers
cause the motor to draw more current. Drawing too much current will destroy the motor. 7
3.5
Comparison Table: Brushless DC Motor vs Brushed DC Motor BLDC Motor Brushed DC Motor Electronic commutation based Brushed commutation on Hall position sensors Less required due to absence Periodic maintenance is of brushes required Longer Shorter Flat - Enables operation on all Moderately flat - At higher speeds with rated load speeds, brush friction increases, thus reducing useful torque High - No voltage drop across Moderate brushes High - Reduced size due to Moderate/Low - The heat superior thermal produced by the armature is characteristics. Because dissipated in the air gap, thus BLDC has the windings on the increasing the temperature in stator, which is connected to the air gap and limiting specs the case, the heat dissipation on the output power/frame size is better Low, because it has Higher rotor inertia which permanent magnets on the limits the dynamic rotor. This improves the characteristics dynamic response. Higher - No mechanical Lower - Mechanical limitations limitation imposed by be the brushes brushes/commutator. Low, because it has Arcs in the brushes will permanent magnets on the generate noise causing EMI in rotor. This improves the the equipment nearby dynamic response.
Feature Commutation Maintenance Life Speed/Torque Characteristics
Efficiency Output Power/ Frame Size
Rotor Inertia
Speed Range
Electric Noise Generation
Cost of Building
Moderate - Since it has Moderate - Due to increases in permanent magnets, building steel & copper. ( with wound cost may be higher. However, field stator) steel & copper prices are up
8
3.6
Why brushless outrunners are used in microcopter
The choice of the motor models heavily depends on purpose and takeoff weight of microcopter or quadcopter. Since a tri- or quadrocopter needs mainly stationary thrust and not a high maximum speed, its ideal to use slow running, big propellers with a low pitch. To avoid gearboxes (weight, clumsy, inefficient, noisy) it is highly recommended to use brushless outrunner motors with a low "kv" (RPMs per volts, about 1000kv are fine) rating. The revolutions per minute should be in the range of 3000 to 4500 when hovering. Due to above reasons we are using brushless outrunners in microcopters/quadcopters.
9
4.0
Electronic Speed Controller
An Electronic speed controller (ESC) is what controls how fast the motors turns. The ESC plugs into the throttle channel of the receiver. The factors that determine what ESC to use include the type of motor you have, the size of the motor, and the type of batteries. Selection of Motor ( Brushless or Canned ) ESC’s designed specifically for brushed motors will only work with brushed motors. Likewise, electronic speed controllers designed specifically for brushless motors will only work for brushless motors. There are a few ESC’s that are designed to work with both. A brushed ESC simply turns the voltage on and off very rapidly(several times a second). To increase the speed, the ESC increases the amount of time that the voltage is on while decreasing the amount of time that the voltage is off. This is called “chopping” the voltage. To slow the motor down, this process is reversed. The brushes on a brushed motor determine how the electromagnets are energized to keep the motor spinning. A brushless ESC has the added task of determining how each pole needs to be energized at any given time to keep the motor spinning. The brushless ESC needs to have feed back from the motor in order to perform this task. The brushes on a brushed motor are in a fixed position relative to the permanent magnets. When the armature rotates, the brushes contact the plates of the commutator at the perfect spot each revolution to keep the motor turning. Without feedback, the ESC on a brushless motor has no idea where the permanent magnets are in relation to the electromagnets(poles).
All brushless motors and brushless ESC’s have three wires. Only two of the three wires are energized by the ESC at any given time. The pole that is not energized (coasting) will actually generate a small amount of voltage that is proportional to how fast the motor is turning. This small voltage is used by the ESC to determine how fast and in what direction the motor is turning at any given time. Size of motor Electronic speed controllers are rated for a maximum current. The more current an ESC is rated for, the more expensive and heavier it will be. Choose an electronic speed controller that is rated for slightly more than what your motor will pull at full throttle. Too much current will damaged an electronic speed controller very quickly. 10 Battery Eliminator Circuit (BEC) The motor requires much more power than the receiver and speed controller. A battery eliminator circuit (BEC) converts the voltage from the motor battery to a lower voltage for the receiver and ESC. This eliminates the need for a separate low voltage battery for the receiver and ESC. The BEC also senses when the battery is getting low and cuts power to the motor while allowing the servos to function for a safe landing. The BEC is usually incorporated circuit board of the ESC for small to medium size electric airplanes. Large RC airplanes that require larger voltages to power the motor will require a stand-alone BEC, which is called a voltage regulator.
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5.0
RF transmitter & receiver
Figure:2 transmitter and receiver block diagram
Four channel ASK transmitter and receiver Special ASK transmitter and receiver modules are used to transmit and receive digital code. It has carrier frequency of 433.92 MHz and operating range of around 100-150 meters. Amplitude Shift Key Modulation Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave. The amplitude of an analog carrier signal varies in accordance with the bit stream (modulating signal), keeping frequency and phase constant. The level of amplitude can be used to represent binary logic 0s and 1s. We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given.
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Like AM, ASK is also linear and sensitive to atmospheric noise, distortions, propagation conditions on different routes in PSTN, etc. Both ASK modulation and demodulation processes are relatively inexpensive. The ASK technique is also commonly used to transmit digital data over optical fiber. For LED transmitters, binary 1 is represented by a short pulse of light and binary 0 by the absence of light. Laser transmitters normally have a fixed “bias” current that causes the device to emit a low light level. This low level represents binary 0, while a higher-amplitude light wave represents binary 1. The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero. This type of modulation is called on-off keying, and is used at radio frequencies to transmit Morse code (referred to as continuous wave operation). More sophisticated encoding schemes have been developed which represent data in groups using additional amplitude levels. For instance, a four-level encoding scheme can represent two bits with each shift in amplitude; an eightlevel scheme can represent three bits; and so on. These forms of amplitude-shift keying require a high signal-to-noise ratio for their recovery, as by their nature much of the signal is transmitted at reduced power. Here is a diagram showing the ideal model for a transmission system using an ASK modulation
Figure:3 ASK modulation block diagram. In this method the amplitude of the carrier assumes one of the two amplitudes dependent on the logic states of the input bit stream.
13
A typical output waveform of an ASK modulator is shown in the figure below. The frequency components are the USB and LSB with a residual carrier frequency. The low amplitude carrier is allowed to be transmitted to ensure that at the receiver the logic 1 and logic 0 conditions can be recognized uniquely as shown in figure below
Figure :4 Amplitude Shift Key Modulation waveforms
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6.0 Propellers
A propeller is a type of fan which transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and air or water is accelerated behind the blade. A pressure difference between the forward and rear surfaces of the airfoilshaped blade is produced and air or water accelerated behind the blade. Propeller dynamics can be modeled by both Bernoulli's principle and Newton's third law. We should choose propellers to get the same thrust as the takeoff weight at about 3000 to 4500 RPMs. If propellers are too small, the RPMs will be too high, and efficiency and payload weight suffers. Also, flight time will decrease significantly, because of too high current consumption. If propellers are too big, the hovering RPMs are too low, so flight stability suffers.. Propellers are available in size of (10" x 4,5") , (10’’x3.8") and (12"x3.8") etc.If we have a good motor on a light frame then we can also use 3 blade propellers.
Figure:5 two blade propeller
Figure:6 Three blade propeller
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7.0 Battery
Lithium polymer battery (Lipo battery) Lithium-ion polymer 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 batteries). Normally batteries are composed of several identical secondary cells in parallel addition to increase the discharge current capability. As batteries usually Lithium-Polymer batteries or LiPos are used. These types of batteries differ from other types by a light weight combined with high capacity. Handling these batteries is not without any danger, so some rules have to be kept in mind. These types need a special kind of charger, because the charging procedure differs a lot from other types (like NiCad and NiMh). The cells should not be overcharged, neither should they be unloaded to deeply. To keep the charge difference between cells to a minimum, a balancer must be used. This balancer might be integrated in the charger, or a separate balancer should be attached to the charger. All LiPo-packs have a connector for a balancer. For a Quadcopter LiPo-packs with three or four cells are used. They have a voltage of 11,1 V or 14,4 V. Depending on our Brushless Motors we will need a bigger or smaller battery. Normal sizes are 1200mAh/20C to 5000mAh/30C batteries.
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8.0 Principle and Operation
8.1 Diagrammatic Representation
Figure :7 Quadcopter showing direction of each propeller
As all the propellers are spinning at the same angular velocity, a yaw stabilising tail rotor like the one found on a standard helicopter is not needed. Yaw is achieved by increasing the torque produced by a pair of rotating motors either the clockwise pair or the anti-clockwise pair and decreasing the torque produced by the other pair. Similarly the pitch of the rotors need not be altered. Instead, movements in the pitch (forward/backward) and roll (left/right) axes can be achieved separately, simply by altering the thrust produced by a pair of motors and all this can be done without affecting the yaw of the vehicle. The front and rear propellers control the pitch of the vehicle while in flight and the right and left propellers control the roll of the vehicle.
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Motors , electronic speed controllers, and battery are connected as shown blow.
Figure: 8 Microcopter connections 8.2 Operation and flight control The Flight Control (FC) is the main controlling board on the quadcopter and all the necessary sensors and microprocessors used to achieve and maintain stable flight are located on this board. Due to the nature of the project a strict power to weight ratio budget was designed. From initial estimations, maximum payload for the vehicle would be approximately 500-700 grams. The motors used in RC vehicles vary greatly so it was desired to find a light motor with low power consumption. The main requirement was that it provided 1000 rpm V^-1. A Brushless motor fulfils the specifications. Brushless motors are more complicated to operate because they need to changethe DC supply voltage of the battery into a phased AC (usually three phase) with controlled power output so that the speed of the motors can be accurately controlled. In total there are four Brushless Controllers (BL-Ctrl) one for each motor.
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To achieve a very stable level of flight it is desired to change the throttle value very rapidly (<0.5m). Control of the vehicle is achieved through use of a RF transmitter and receiver pair. A transmitter with a minimum of four channels is required to control the quadcopter in the various planes.. The receiver demodulates the instructions given by the pilot and converts them into electrical signals. A receiver with a summing signal is required for the MikroKopter (MK). This signal contains all of the channels sent by the transmitter and is made available to the FC for processing. The design of the frame is only limited by one factor: it must be as light as possible. The frame designed took on a basic cross shape similar to many open source projects . Bearing in mind that the frame must be lightweight some of the materials considered include: aluminium , carbon fiber or polystyrene; it is possible to have a combination of these. The most cost effective material for this project is aluminium or wood because it is readily available and cheap. The batteries needed to power all the onboard electronics have to have a low weight to power ratio so that maximum flight time may be achieved. The different types of battery considered suitable for use in RC vehicles are: Lithium polymer (Lipo), Nickel-cadmium (NiCd) and Nickel metal hydride battery (NiMh). The Lipo types are the most advanced and offer the most power. They are volatile and must be handled with care but they can have a capacity of over 10,000 mAh. NiMh batteries are a slightly older technology but they are still capable of capacities around 5000 mAh. However if a poor quality of battery is purchased then bad cells can develop quickly when the capacity is increased. NiMh batteries are cheaper than Lipo batteries and are also less volatile. NiCd batteries are the cheapest overall and have similar characteristics to that of NiMh but are unable to achieve an equal capacity. A decent flying time is desired to test the software and hardware which will be added and due to the powerful motors and large propellers the best weight to power ratio with a high capacity can be achieved using the Lipo batteries. The propellers play a major role on the takeoff weight and the speed that the vehicle will fly at. The diameter of the propellers as well as their pitch must be considered. Due to the slow spinning motors a low pitch is desired.
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9.0 Project status
9.1 Work planned
STAGE I: Determining the project and assessing the availability of the components of the hardware & deciding upon the feasible software for the purpose. STAGE II: Procurement of literature & literature review. STAGE III: Hardware: Designing the circuit diagrams Software: Designing basic flowcharts & algorithms. STAGE IV: Finalizing the basic design of the hardware Designing the PCB: PCB design is ready, components selected. STAGE V: Hardware: Testing & troubleshooting Software: Algorithms finalized. Coding begins. Code tested & troubleshooting solved. STAGE VI: Assembling the entire project, testing & troubleshooting it in entirety. Stage VII: Annexed features of levels, synchronization and flight control tested and troubleshooting solved. STAGE VIII: Entire unit encompassing all the features is tested & troubleshooting is solved, project is ready for display.
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9.2
Work Completed
• • • • • • • •
Microcopter basic block diagram was designed and hence accordingly detailed research was done. Different designs of microcopter like tricopter and quadcopter were studied in detail. After thorough research we came to the conclusion that quadcopter design with four rotors is more stable. Components and their specifications were decided according to the requirement of the project. Theory of brushless motors and electronic speed controllers (ESC) were studied. Different circuits of ESC were searched and simulated on multisim. Different motors and propeller combinations were considered. Transmitter and Receiver circuits were decided which uses ASK modulation at frequency 433.92 MHz.
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10.0 Applications
A number of options were considered as a possible applications for quadcopter below is a list of some of the applications investigated and the reason why they were eliminated. 1] Camera Surveillance Possibly the most obvious use for an aerial platform would be as a mount for a camera so that it may be used as a mobile surveillance device. A decision was made to build the quadcopter/microcopter for use as a platform for a camera which would be wireless. The standardized connection could then be used to attach different devices and essentially enable the quadcopter to be used for a multitude of applications. 2] Remote Volcano Sensing Andrew McGonigle, a Scottish scientist working for the University of Sheffield, has developed a novel means for determining whether or not a volcano is due to erupt.It involves sending a Radio Controlled (RC) helicopter/microcopter into the crater of a volcano and measuring the level of various gases. This information can then be processed once the Helicopter returns. The sensors were the main reason this idea was abandoned. They were found to be too expensive and there was nowhere to test the vehicle i.e. a local active volcano. 3] Air Pollution Sensor (Inner-city) It was thought that the vehicle could be used to navigate a pre-determined flight path and measure several air pollutant levels en route. The resulting measurements could then be used as an indication of the air pollution in a particular area of a city. However, the idea was abandoned due to a problem with the measurement sensors i.e they were either both large and bulky or a passive measurement was needed. The passive measurement would once again be affected by the moving vehicle and is usually taken over a longer period.
4] Microwave Cavity Resonator An idea put forward by Dr. Ian Glover a strathclyde lecturer involved testing the reflectivity of a content in the boundary layer. The boundary layer is the first few hundred meters above the earth surface. The reflectivity of air affect the transmission of radio waves. The proposed method of measurement included building a microwave cavity resonator. The resonator chamber would allow to
pass through it and by testing the capacitance of the air the reflectivity could be determined. The rotating propellers posed a problem because they would force air pass the cavity thus affecting the measurement. A different method was to actively monitor the temperature and humidity of the surrounding air and perform a calculation using the two variables. The problem with this is obtaining an Instantaneous and accurate measurement of the humidity. Once again the rotating blades would affect the measurement
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11.0 Conclusion
The control system demonstrates in simulation that reliable and controlled flight can be achieved. Tests have confirmed the functionality and range of wireless transmission. Theoretical calculations have determined that the desired amount of lift can be achieved. Experimental tests must be completed to verify these calculations. A complete and thorough test plan has been provided and can be used by subsequent design teams to complete this project. This plan includes assembly diagrams and instructions as well as a complete bill of materials. Reflecting on this project, it was very aggressive for a five person design team. This project required an extreme amount of engineering to be done in a short amount of time. With respect to this aggressive nature of the project, its status at this point can be deemed a mild success. Since we have completed the entire study and research required for this project; our next step would be to design a working prototype. It includes building a light weight frame for microcopter, design of electronic speed controller circuit, and and mounting these components on microcopter frame with motors, battery and receiver circuit, and then performing test flights.
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12.0 References
1. 2. 3. 4. 5. 6. 7.
8. 9. http://aeromodelling.nitc.googlepages.com/links 10. http://www.electric-rc-helicopter.com/article/gyroconfusion.php 11. http://www.anglia.com/newsarchive/261.asp?article_id=921 12. http://www.microchip.com/ParamChartSearch/chart.aspx?
branchID=8093&mid=14⟨=en&pageId=75
http://www.mikrokopter.de/ucwiki/en/MikroKopter http://www.quadcopter.org/index.php5?title=Quadcopter_Home http://www.rcgroups.com/forums/showthread.php?t=768115 http://radiocontrol.wikia.com/wiki/Brushless_motor http://www.himodel.com/electric/1290KV_Outrunner_Brushless_Motor_Type_FC2 830-9T.html http://www.rentron.com/rf_remote_control.htm http://www.himodel.com/electric/1290KV_Outrunner_Brushless_Motor_Type_FC2 830-9T.html http://mikrokopter.de/ucwiki/KategorieNachbauten
