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A Small Semi-Autonomous Rotary-Wing

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1. Pitch rate 200 Pitch input 150 100 Angular rate degrees second Time seconds Figure 5 8 The pitch rate gray and pilot input for pitch rate black during a quadrotor flight are shown quadrotor then remained over a stationary point on the ground while its pitch and roll rates oscillated around zero The quadrotor also rotated about its yaw axis while hovering over this stationary point The pilot then reduced the thrust input and the quadrotor landed The quadrotor stayed within three feet of the ground during this flight Since the quadrotor flew so close to the ground there may have been some attitude stabilization from ground effect that would not have been present for a flight at a greater height above the ground Figure 5 9 shows the pitch rate of the quadrotor during this flight The quadro tor motors were turned on about one and a half seconds into the test when the small oscillations in pitch rate started After the quadrotor lifted off the ground at a time of about five seconds there was a positive pitch rate for a short amount 94 Pitch rate degrees second 150 Time seconds Figure 5 9 A graph showing the pitch rate in degrees per second of the quadrotor during a flight of time Between six and seven seconds into the test the quadrotor experienced a negative pitch rate and the pilot gave an input to increase the pitch rate This input caused the pitch rat
2. Change A D channel to read the next gyroscope Has each gyroscope been sampled Figure 4 1 A flowchart describing the interrupt service routine used to sample the gyroscope timers on the PIC microcontroller would need to be used To avoid this situation and leave timers available for other tasks an algorithm was written to record one input pulse at a time using only one timer timerl The four input pulses are read consecutively pitch thrust roll and yaw and then this order is repeated continuously An interrupt service routine ISR was written for each CCP pin Figure 4 2 shows a flowchart illustrating the structure of the code written in each ISR In capture mode the CCP hardware can be configured to cause an interrupt on either the rising or falling edge of a pulse When the rising or falling edge 74 occurs the current value of the timer being used with the CCP pin is copied to a 16 bit integer unique to the current CCP pin A simple method to measure a pulse length is to configure the CCP hardware to cause an interrupt on a rising edge In the interrupt service routine for this CCP pin the timer value at the time of the interrupt that was copied to the 16 bit integer for the current CCP pin can be saved as a variable riseTime for example the CCP hardware can be configured to cause an interrupt on a falling edge and a flag can be set to indicate that the rising pulse edge has occurred When the fallin
3. enough to provide intelligent control with sensor data of limited quality Quadrotor Background and System Design A quadrotor is a rotary wing UAV that has been the subject of several recent re search projects Small quadrotors have many exciting potential missions including flight indoors and in dense urban areas However the development of the control systems needed to fly these vehicles can be very challening 2 1 Quadrotor Description A quadrotor has four rotors and requires no cyclic or collective pitch A quadrotor UAV can be highly maneuverable has the potential to hover and to take off fly and land in small areas and can have simple control mechanisms 20 21 However because of its low rate damping electronic stability augmentation is required for stable flight A quadrotor has four motors located at the front rear left and right ends of 28 a cross frame as shown in figure 2 1 The quadrotor is controlled by changing the speed of rotation of each motor The front and rear rotors rotate in a counter clockwise direction while the left and right rotors rotate in a clockwise direction to balance the torque created by the spinning rotors The relative speed of the left and right rotors is varied to control the roll rate of the UAV Increasing the speed of the left motor by the same amount that the speed of the right motor is decreased will keep the total thrust provided by the four rotors approximately the same In
4. 2003 Office of the Secretary of Defense Unmanned Aerial Vehicles Roadmap 2002 2027 December 2002 http www noaanews noaa gov stories2005 s2508 htm October 24 2005 Phillip McKerrow Modelling the Draganflyer four rotor helicopter In Pro ceedings of the 2004 IEEE International Conference on Robotics and Automa tion 2004 11 12 13 14 17 18 19 20 21 103 Huai yu Wu Zhao ying Zhou and Dong Sun Autonomous Hovering Control and Test for Micro Air Vehicle In Proceedings of the 2003 IEEE International Conference on Robotics and Automation 2003 http www yamaha motor co jp global business sky index html November 28 2005 http www honeywell com November 18 2005 William J Pisano Dale A Lawrence and Scott E Palo Low Cost UAV Avionics for Autonomous Antenna Calibration In AJAA InfotechQ Aerospace Conference 2005 Eric N Johnson Daniel P Schrage and J V R Prasad Flight Test Results of Fault Tolerant Control Systems on Small and Micro Rotorcraft In AHS International Specialists Meeting on Unmanned Rotorcraft 2005 Joseph K Conroy Paul D Samuel and Darryll J Pines Development of an MAV Control and Navigation System In AIAA Infotech Aerospace Confer ence 2005 Joseph Conroy Paul Samuel and Darryll Pines The Evaluation of Optic Flow Data using a Wireless Telemetry System for Micro Air Vehicle Applications In AHS International Specialists Meeting
5. Radioplane which was bought by Northrop LAA ES rE D A Figure 1 5 Reginald Denny and one of Radioplane s target drones 2 in 1952 continued to develop unmanned aircraft after World War II adding film cameras to their target drones in 1955 to make world s first reconnaisance UAV and producing 48 000 aircraft between 1946 and 1984 2 Germans used V 1 cruise missiles or buzz bombs to attack England during the last year of World War II 1944 1945 Only 2400 of the 10 500 missiles launched hit their targets Four thousand of the missiles launched were destroyed by British defenses illustrating the dangerous nature of these attacks and the benefits of using unmanned systems for these attacks In addition 2900 Allied soldiers were killed defending against these V 1 attacks The success of these buzz bombs encouraged the use of cruise missiles in future conflicts 2 1 1 4 Cold War Reconnaissannce missions during World War II resulted in large numbers of lost pilots One reconnaisance group lost over 25 of its pilots flying missions over North Africa in the first months of fighting there in 1942 By comparison only 5 5 of American pilots were lost during bombing flights over Germany in day time from 1943 1945 2 Even during fairly peaceful times reconnaisance can be a deadly mission Twenty three aircraft and 179 airmen were lost flying reconnais sance missions from 1946 1990 not including losses during the Viet
6. proportional integral and derivative and optimal LQ linear quadratic control in simulations Both control algorithms were then used on a quadrotor mounted on a testbed that included a 3D universal joint that contrained height and allowed only angular rotations An expensive almost 2000 euros commercial IMU 39 that uses accelerometers and magnetic references to eliminate sensor drift and a Kalman filter were used to determine the position and orientation of the quadrotor An offboard PC was used to send orders to the testbed and a PIC microcontroller was used on the testbed for control calculations The classic PID control was more successful than the optimal control even allowing an automous flight with cables supplying power from the ground A possible explanation for the poor performance of the optimal control is because the actuator dynamics were not included in the analysis used to determine the control gain matrix 40 2 3 7 University of Technology in Compi gne France A research team from France used the commercial Draganflyer quadrotor to study the stabilization of a quadrotor 40 The gyroscopes that come with the Dragan flyer were left onboard and used for an inner control loop intended to stabilize the quadrotor A 3D electromagnetic tracking system 41 was used to measure position and orientation of the Draganflyer at a rate of 14 Hz A sensor was placed on the Draganflyer frame that allowed the 3D position and orientatio
7. shown in figure 3 2 weighs three grams is about 1 inch long by 0 5 inches wide and costs 50 This board is also available in a surface mount chip that measures 7 mm x 7mm x 3mm and costs 30 However the evaluation board does not require any external resistors or capacitors for the gyroscope to be used Also the difficult soldering of the gyroscope s ball grid array that is necessary when using the surface mount chip has already been performed on the evaluation board The sensor uses a resonator gyro that senses Coriolis motion and is capable of measuring 150 degrees per second of angular velocity The gyroscope includes signal conditioning electronics to help preserve the signal in noisy environments The bandwidth of the surface mount chip can be set using external resistors and capacitors The bandwidth of the evaluation board is fixed and set at 40 Hz The chip produces an analog voltage output between 0 25 and 4 75 volts for a 5 volt 51 Figure 3 2 A picture of the gyroscope evaluation board with two rulers inches on the top ruler and centimeters on the bottom ruler source that is proportional to the angular velocity about the axis normal to the top surface of the gyroscope package The voltage increases for clockwise rotation while looking down at the top of the chip of the gyroscope The noise density of the gyroscope which is defined as the average noise at any frequency f in Hz in the bandwidth of the part is
8. 0 05 degrees per second per Vf The initial null point is 2 5 volts but this can change by a maximum of 300 millivolts for a temperature range of 40 to 85 degrees Celsius The sensitivity of the gyroscope varies from 11 25 to 13 75 millivolts per degree per second over the gyroscope s operating temperature range 52 3 4 Accelerometer A dual axis accelerometer from Analog Devices Inc ADXL210EB was also in terfaced with the PIC microcontroller 47 The evaluation board shown in figure 3 3 is 3 4 inch by 7 8 inch weighs 5 grams and costs 30 This accelerometer is capable of sensing accelerations of 10 g s in two perpendicular axes and is also available in a 14 pin dual inline surface mount package that is about 8 mm x 10 mm x 5 mm and costs about 15 The sensor chip produces a digital pulse proportional to its acceleration along two axes by using a duty cycle modulator that is included as part of the sensor chip The noise density of the accelerometer is 500 micro g s ug s per Vf where f is the frequency in Hz The accelerometer s initial offset at rest 0 g s can be between 2 and 2 g s and also changes with temperature at a rate of 0 002 g s per degree Celsius between 40 and 85 degrees Celsius Temperature drift can also change the accelerometer measurements during motion by 0 05 of the accelerometer output 3 5 R C transmitter and receiver An R C transmitter and receiver were used to send pil
9. Servo Controller The Mini SSC II a serial servo controller from Scott Edwards Electronics Inc can control multiple servo motors through serial communication 50 A SSC circuit board figure 3 6 is 1 4 inches by 2 1 inches weighs 0 6 oz and costs 60 The board contains a PIC microcontroller eight servo connectors connectors for supplying power to the microcontroller and connectors for the data and ground pins used for serial communication There are three settings that can be configured using jumpers on the circuit board the baud rate used for serial communication 2400 or 9600 the range of motion for servos 90 or 180 degrees and the numbers of the motors to be controlled 0 7 or 8 15 SSC boards with different motor numbers can be ordered so that 255 motors can be controlled using a single serial 59 Figure 3 5 A picture of the R C receiver with two rulers The top ruler is in inches and the bottom ruler is in centimeters input The power requirements for the PIC microcontroller on the SSC board are 7 15V and 10 milliamps mA The servo motors that are controlled by the board also need to be supplied with power and these requirements vary depending on the motor application The SSC board must receive a specific three byte sequence of serial data to control a servo motor The first byte called the sync byte must be set to 255 and tells the SSC that a three byte servo command sequence has started The second byte
10. and European airspace authorities The Global Hawk became the first UAV to cross the Pacific Ocean in April 2001 flying from California to Australia The 7267 mile trip was completed in 23 hours when the UAV landed within feet of the center of the runway in Australia Global Hawks have been flying combat missions in Iraq and Afghanistan since November 2001 2 17 1 2 2 Small Fixed wing UAVs Small unmanned air vehicles UAVs can be deployed at the front lines of combat to provide situational awareness to small units of troops through real time information about surrounding areas 8 Small fixed wing unmanned and micro air vehicles such as the Dragon Eye Aerosonde Hornet and Wasp have become prevalent and have demonstrated impressive flight abilities and levels of autonomy 1 The Marine Corps uses the Dragon Eye manufactured by AeroVironment at the company platoon squad level for reconnaisance surveillance and target aquisition missions with a range of 10km The Dragon Eye shown in figure 1 11 weighs 4 5 pounds can carry a one pound payload has a 3 8 foot wingspan and is powered with a battery 1 Figure 1 11 A picture of a soldier holding the Dragon Eye 8 The FPASS Force Protection Aerial Surveillance System from Lockheed Mar tin shown in figure 1 12 is used by Air Force security to increase situational awareness through surveillance the patrol of base perimeters and runway areas and watching over
11. cables must be installed between the radio receiver and the PIC microcontroller The Y cables consist of three wires ground power and input signal similar to a standard servo cable and allow the pilot input to reach both the microcontroller and the flight data recorder These cables allow the recorder to receive its power from the battery used to power the microcontroller 3 11 Hardware Integration and Circuit Design A circuit board was designed and fabricated to connect the PIC development board gyroscopes R C receiver battery and electric speed controllers Figure 3 9 shows a schematic of these connections A freeware version version 4 13 of the Eagle layout editor was used to create the circuit board which is shown in figure 3 10 55 The software has a tool that allows circuit schematics to be created using the software library of parts as well as components created by the user Once the schematic has been created the parts can be placed on a circuit board using the board editor The software program has an auto router tool which places copper traces connecting the parts in the manner specified in the schematic Files to send to a circuit fabrication shop for production of the circuit 63 Rechargeable Battery Pack Circuit board with gyroscopes ESC x 4 one for each motor RIC Transmitter amp Receiver PIC
12. convoys The system has six aircraft and a ground station 18 Figure 1 12 A picture of the FPASS system 8 Each aircraft is powered with a battery and has a seven pound weight a one pound payload and a 4 3 foot wingspan 1 The Pointer from AeroVironment is a hand launched UAV that is battery pow ered and can be carried in a packpack The Pointer figure 1 13 weighs 8 3 pounds can carry a one pound payload has a nine foot wingspan and can be easily as sembled from six parts 1 6 One hundred Pointers have been bought by the Figure 1 13 A picture of the Pointer UAV in flight 8 Marines Army and Air Force since 1989 and the United States Special Opera tions Command has purchased 60 UAVs Pointers were used in Desert Storm and are currently in use in Iraq and Afghanistan These UAVs have also been used 19 by the Drug Enforcement Agency and the National Guard 1 Pointers have al lowed surveillance and reconnaisance missions to be performed quickly and safely The Pointer s television camera can be used to obtain real time high resolution images while keeping the UAV operator safe 6 A Global Positioning System GPS night vision sensors and IR imaging technology have also been used on the Pointer and have allowed for night flying and have eliminated the need for visual contact of the Pointer by its operator These sensors have also helped re duce the interaction the operator must have with the flyin
13. has been estimated to do the work of 15 laborers and the helicopters cover 10 of the land on which rice is grown in Japan These R C helicopters have also been used in civil applications in Japan 2 After Mount Usu erupted in 2000 manned aircraft were not permitted to fly over the volcano to monitor the advance of ash and mud towards communi ties at the base of the volcano To obtain this important information the Japanese Ministry of Construction used modified versions of the robotic helicopters that had been used in agricultural applications to fly these reconnaisance missions Many vertical takeoff and landing VTOL UAVs such as the Fire Scout Hum mingbird and Maverick are currently being developed or used by the U S mili tary 1 The Fire Scout figure 1 19 from Northrup Grumman has a length of 22 9 feet a wingspan of 27 5 feet a weight of 3150 pounds and a payload capacity of 600 pounds Over one hundred flight tests have been performed using multiple Figure 1 19 A picture of the Fire Scout UAV 1 flight modes including autonomous flight 1 8 In addition to these large rotary wing vehicles DARPA and the Army are sponsoring a micro air vehicle called the MAV from Honeywell 1 The goals for the MAV figure 1 20 are to make a system that can be operated by a single person and can fit in a backpack The 24 current ducted fan design weighs 15 pounds has a payload of two pounds and has a duct diameter of 13 in
14. in the 1950 s This vehicle had rotors over 19 feet in diameter and wings to create lift in forward flight Two engines were used in the design and the vehicle was controlled by varying the thrust provided by each rotor The Convertawings quadrotor was flown successfully but production was stopped because of a lack of interest in this aircraft 25 26 31 2 3 Recent Quadrotor Research There have been a large number of papers in recent years describing the dynamics and controls of quadrotor UAVs as well as efforts at constructing and flying these vehicles Some projects have focused on modeling the dynamics of quadrotors or testing control strategies in simulations 10 27 30 while the following section describes projects that have attempted to fly quadrotors 2 3 1 Draganflyer A well known quadrotor is the Draganflyer figure 2 3 a commercial product from RC Toys 10 31 The Draganflyer is flown using an R C transmitter and its Figure 2 3 A picture of the commercially available Draganflyer quadrotor onboard electronics The pilot can control the collective throttle setting for the four motors and the yaw pitch and roll rates of the quadrotor The electronics onboard the Draganflyer include a receiver for pilot inputs three piezo gyroscopes to sense the angular velocity of the system a microcontroller to perform control calculations and motor drivers The most recent version of the Draganflyer also 32 includes f
15. pitch direction are shown in figure 5 3 The differential motor output in the pitch axis was defined as the output to motor three minus the output to motor one At the beginning of the test the pitch rotation and error in pitch rate are equal to zero and the differential motor output is also zero A little after two seconds into the test the quadrotor frame was rotated about its pitch axis This pitch rotation caused the pitch gyroscope to sense an angular rotation resulting in an error in pitch rate The control law calculations then increased the output to motor three and decreased the output to motor one in an attempt to minimize the error in pitch rate Figure 5 3 shows the differential motor output for the motors on the pitch axis increasing during the pitch rotation After the pitch rate and error return to zero shortly before four seconds the effect of the integral term in the PI control law can be seen Although the error in pitch rate was very close to zero the integral of the pitch error was not zero because the integration of the previous pitch error was 88 greater than zero Therefore a difference in the two motor outputs remained Similar results were obtained for the test of roll rotations figure 5 4 The quadrotor frame was briefly rotated about its roll axis first in the negative direc tion for a very short amount of time and then in the positive direction For this test the differential motor output was defined as the
16. quadrotor helicopters at the beginning of the twentieth century The Br guet Richet Quad Rotor Helicopter figure 2 2 was built in 1907 and had a large 8 1 meter rotor placed at each of the four corners of its horizontal cross shaped frame 23 Two of the rotors rotated in a clockwise di rection while the remaining two rotated in a counter clockwise direction The pilot sat in the center of the cross below a single engine that drove the rotors through a belt and pulley transmission The only control input available to the pilot was the throttle and the helicopter did not have sufficient stability Photographs taken 30 Figure 2 2 A picture of the Br guet Richet helicopter 23 during flight attempts show men at each corner of the frame helping to stabilize and maybe even lift the quadrotor Although unaided flight was not achieved the idea of using both clockwise and counter clockwise rotating propellers is a key feature of the quadrotor developed in this research Another large quadrotor helicopter was built for the U S Army Air Service in Dayton Ohio in 1921 by George de Bothezat 24 The helicopter s four rotors were each 26 feet in diameter All four rotors were turned by a single engine More than 100 test flights were performed on the de Bothezat helicopter but the helicopter could not be well controlled in flight and did not meet U S Army performance specifications Convertawings built a quadrotor in Amityville New York
17. quadrotor is a challenging problem because of the small payload capability of these small UAVs Small lightweight and low cost sensors and mi crocontrollers can be used to control a quadrotor and make the vehicle easier to fly while adding minimal weight but have limitations such as sensor performance and computing power when compared to larger and more expensive computers and sensors that are used in most flight control applications The overall goal of this project is to implement these lightweight and low cost sensors and microcon trollers so that they will be useful in the development of a small semi autonomous or autonomous quadrotor UAV A microcontroller has been interfaced with MEMS gyroscopes a radio control R C transmitter and receiver and motor drivers A single angular degree of freedom test system with two rotors has been developed to test these electronics Pilot input from the R C transmitter and receiver was converted into the desired angular velocity of the system and a desired thrust The angular velocity of the system is measured with a gyroscope and pilot in the loop PI proportional and integral control has been implemented using the microcontroller to calculate the speed of each of the two rotors to maintain the desired angular velocity The PI control resulted in a decrease in the difference between the angular velocity of the test system and the desired angular velocity In addition the amount of pilot input ill ne
18. rate during a quadrotor flight 93 5 9 A graph showing the pitch rate of the quadrotor during a flight 5 10 A graph showing the roll rate of the quadrotor during a flight 5 11 A graph showing the yaw rate of the quadrotor during a flight 5 12 A graph of the roll angle of the quadrotor during a flight 94 95 96 97 5 13 A graph of the pitch angle 0 of the quadrotor during a flight 98 5 14 A graph of the yaw angle w of the quadrotor during a flight 99 List of Tables 3 1 Table of costs for the quadrotor xl Acknowledgments I would like to thank my wife Mandy and my family for their love and support I would also like to thank Dr Long my advisor and Dr Horn for allowing me to work with them and for all their help and guidance during this project I would like to acknowledge the National Defense Science and Engineering Graduate Fellowship and the National Science Foundation Graduate Research Fel lowship programs and the Penn State Rotorcraft Center of Excellence for their financial support xii Introduction The Department of Defense Dictionary defines an unmanned air vehicle UAV as A powered aerial vehicle that does not carry a human operator uses aerodynamic forces to provide vehicle lift can fly autonomously or be piloted remotely can be expendable or recoverable and can carry a lethal or non lethal payload 1 There are many potential missions for which UAVs can be useful Missions
19. rates 2 4 6 Two missions performed by the Lightning Bug helped illustrate the potential of UAVs In October 1965 a cooperative mission was performed by the Lightning Bug and two manned aircraft a U 2 and a RB 47 During the mission the Lightning Bug intentionally drew fire from surface to air missiles while the other two aircraft observed the defense tactics used to attack the Lightning Bug In the second mission a Lightning Bug intentionally flew to a known missile site and relayed data on the electronic parameters of the missile s radio guidance and fusing systems until the bug was hit The data obtained during these two missions helped make important improvements in U S equipment saving many manned aircraft during the rest of the war One challenge that arose during the Vietnam War was the resistance from pilots to the use of UAVs Pilots did not like their jobs being taken away and the pilots that were flying the UAVs felt like they were being underutilized A change was made to call the UAVs remotely piloted vehicles to help convince crews that 10 were operating them they were still performing a pilot s function As the war continued the Lightning Bug was used in more ways Two im portant developments were the Navy beginning to operate the UAVs from aircraft carriers in 1969 1970 and the use of a real time video link instead of camera film in 1972 2 The demand for the first rotary wing UAV the QH 50 DASH arose w
20. started to use a five gram inertial measurement unit and optic flow sensors to make these UAVs more autonomous 16 17 Auburn University has worked with the Techni cal University of Delft in Holland on a small ducted fan design that uses adaptive aerostructures 18 19 Rotary wing UAVs and specifically small rotary wing UAVs with VTOL and hover capabilities can have many applications Small rotary wing UAVs could be especially useful for indoor flight or for urban missions Urban combat areas can change very quickly making it very difficult for soliders to maintain situational awareness Using UAVs for reconnaisance is also challenging in these situations because of the short line of sight distances and many obstacles These challenges of the urban combat environment could be met by small autonomous rotary wing UAVs that are able to fly in areas with many obstacles poor quality GPS signals and where communication between the UAVs and their operators are difficult 1 Incorporating a reliable semi autonomous or autonomous control system in these small vehicles so that the operator does not have to constantly monitor their performance or location will be very challenging since they will only be able to carry the smallest microprocessor systems and power supplies along with very lightweight and inexpensive sensor systems The software will have to be very 26 compact to fit in the available memory of the small microprocessors but powerful
21. systems were passive not required to emit signals and independent did not need external inputs A professor of aeronautics and astronautics at the Massachusetts Institute of Technol ogy Charles Stark Draper was the leader in advancing the theory and technology needed to develop manufacture and implement inertial navigation systems in sev eral types of vehicles including aircraft submarines and space vehicles Draper developed the first INS for an aircraft in 1949 Draper s INS allowed a vehicle s navigation to remain accurate even in the presence of turbulence or during aircraft maneuvers without external inputs INS continued to improve navigational accu racy to such a degree that an INS was able to guide man to and from the moon in the 1960s Currently technology such as GPS receivers are often used in UAVs to supplement inertial navigation systems that use ring laser gyroscopes These systems can achieve navigational accuracies of less than 20 feet during a 24 hour flight 2 1 1 5 Vietnam 1964 1975 The use of UAVs continued in the Vietnam War during which UAVs proved their abilities particularly in the large number of wartime reconnaissance missions that the UAVs flew The Ryan AQM 34 Lightning Bug or Firefly was the most used UAV during this conflict 1016 Lightning Bugs flew 3435 combat missions with a survival rate of 84 By 1971 two missions were being flown per day and by 1972 UAVs were acheiving 90 success
22. the cross after the notches have been placed together and the two pieces have been epoxied together holes The motors were then secured by drilling small screws through both the plastic mount and the wood frame figure 3 13 Hole drilled into front End of quadrotor frame being face of plastic mount slid into hole in plastic mount Figure 3 13 The picture on the left shows the hole that was drilled into the plastic mount of each motor The picture on the right shows an end of the quadrotor frame being slid into the hole in the plastic mount After the frame was slid into the hole in the plastic mount small screws were used to secure the motor to the wood frame Lightweight strong carbon fiber sheets from The Robot Marketplace 57 and half inch thick foam rubber were used to mount the electronics to the quadrotor 68 frame while isolating the sensors from vibrations in the frame One carbon fiber sheet was attached to the top of the quadrotor frame using Dual Lock fastener from 3M Then the bottom of the foam rubber was fastened to this carbon fiber sheet and a second carbon fiber sheet was fastened to the top of the foam rubber The electronics were fastened to the top of the second carbon fiber sheet also using Dual Lock fastener The lithium polymer battery was attached to the bottom of the quadrotor frame using Dual Lock fastener To help protect the quadrotor frame and electronics during landings additional pieces of p
23. the error in roll rate is shown on the vertical axis on the left and the scale for the differential motor output is shown on the vertical axis on the right The results for the test of the control law for rotation about the yaw axis are shown in figure 5 5 The differential motor output for this test was defined as the output to the counter clockwise rotating motors motors one and three minus the output to the clockwise rotating motors motors two and four One and a half seconds into the test the quadrotor was rotated about its yaw axis and the control law increased the differential motor output between the counter clockwise rotating and clockwise rotating motors After the yaw rotation decreased to zero at four and one half seconds the differential motor output remained non zero because of the integral term in the PI control law 90 140 70 Yaw rate error 120 60 Differential motor output Yaw rate error degrees second Differential motor output digital counts Time seconds Figure 5 5 This graph shows the yaw rate gray of the quadrotor in degrees per second and the differential motor output in digital counts black for the yaw axis calculated during a test of the control system The scale for the error in yaw rate is shown on the vertical axis on the left and the scale for the differential motor output is shown on the vertical axis on the right 5 3 Quadrotor flights Several quadr
24. vehicles RPVs with radar reflectors to draw fire from ground defenses and then used other RPVs with explosives to determine the location of the radar source and destroy these defenses This weakened the air defense systems making them vulnerable to attacks from manned aircraft while decreasing the risk of the pilots performing these manned missions 6 The use of UAVs in Lebanon in the early 1980s by the Israeli military helped reintroduce U S Navy to the capability of UAVs 2 This led to the use of the Pioneer UAV figure 1 6 which was produced cooperatively between Israeli and U S companies by the U S Navy in 1986 and its continued use today in the Marine Corps 7 The Figure 1 6 A picture of the Pioneer UAV in flight 8 Israeli military and industry have helped Israel become one of the world s leaders in UAV production and innovation and have helped demonstrate tactics such as using unmanned and manned systems together as force multipliers 2 12 1 1 7 Recent UAV Military Missions Five models of UAVs were used in the Gulf War Operation Desert Storm and although these systems did not play a critical role they once again showed the possiblities of UAVs in combat 4 The U S Navy successfully used the Pioneer in a fire spotter role during this war Iraqi troops learned that an air attack would follow the appearance of a Pioneer and even surrendered to a Pioneer on one occasion 2 Surveillance and re
25. which are dull dirty or dangerous are considered ideal for UAVs Long endurance flights such as the 30 hour missions that were flown from the United States to Kosovo in 1999 can qualify as dull Pilots flying these missions must deal with issues such as sustained alertness and fatigue that could be avoided through the use of UAVs 1 A historical example of UAVs performing dirty missions is the collection of radioactive samples after nuclear test explosions in 1946 1948 After 1948 pilots flying manned aircraft while wearing 60 pound lead suits for protection were used to perform this mission However these pilot were put at risk when they were trapped by their heavy suits after crashes or from long term radioactive effects 1 UAVs can also perform dangerous missions and go in harm s way without risking a pilot s life Reconnaisance has been a dangerous mission throughout history accounting for the highest loss rates for pilots and aircraft during the Vietnam War and is a good mission for UAVs to perform 1 In addition to manned reconnaisance missions being dangerous the failure of these missions can also be damaging politically When a U 2 was shot down over the U S S R in 1960 and its pilot was captured it was an expensive loss not only in terms of money invested in the aircraft and the capture of the pilot but also politically as treaty negiotiations between the U S and the Soviet Union were harmed by the incident 2 1 1
26. 2 2 Small Fixed wing UAVs 17 1 2 3 Rotary wing UAVs ned ey Ge a de ew ee he ae Se ek 22 Chapter 2 Quadrotor Background and System Design 27 2 1 Quadrotor Description nas ee a a 27 2 2 Early quadrotor designs miso a 29 2 3 Recent Quadrotor Research oaa a 31 2 3 1 Draganflyer 2 2 22 aa aaa 4 44 0 od ae ee Ee eS 31 2 32 AQUMATOCOPUCE s e iy tect ee te ae Be ad Da 32 io Oy A Flyet ss dE ee ea ee e e 33 2 3 4 University of Pennsylvania 23902 booed ke eke SS eS 35 2 3 5 Cornell University s s 4 2 4 2 44 422 6 8 2 8 26d ates 37 2 3 6 Swiss Federal Institute of Technology 39 2 3 7 University of Technology in Compi gne France 40 2 3 8 Stanford University eye da ld le da ed 41 2A System Approach amp sid ese ela et i a ch PSone gh lose 42 Chapter 3 Quadrotor Hardware 45 go Microcontroller e EA A a a E A 45 3 2 Development Kb A AA a 49 3 3 ON TOSTOPE e e ts we en Gy en o O A 50 3 4 Accelerometer ss A ed Oe o a A 52 3 5 R C transmitter and receiver ese E le als Ae aos 52 3 6 Serial Servo Controller ar a A AA 54 3 7 Electric speed controller o oo aa ns deb Ri Bene BR Pod 56 3 8 Quadrotor Powerplant wd a a 58 3 9 A GE A IO a a E a a a a ta 60 3 10 Flight Data Recorder Gta eo Gnas eck A Oe EA 61 3 11 Hardware Integration and Circuit Design 62 3 12 Quadrotor anme Lea o a uhh SA be BA De IS a 66 Chapter 4 System Integration and Software 70 a sranie Boe Ba va
27. 3 In total there was two billion dollars spent on UAVs worldwide in 2002 Although the majority of UAV spending and operation occurs in the United States Western Europe and Japan 52 countries around the world either develop manufacture operate or export UAVs Forty one of these countries actively fly 80 of the available 250 models of UAVs UAVs are generally separated into three classes high altitude long endurance aircraft small aircraft with conventional configurations and vertical takeoff and landing UAVs 6 This section describes a few of the current UAVs in each of these classes 14 1 2 1 Fixed wing High Altitude Long Endurance Aircraft By the 1960s developments in air defense systems forced reconnaisance aircraft to fly at higher altitudes to ensure they were out of the range of these defense systems The necessity of flying at these higher altitudes forced aircraft to their limits The U 2 had to be flown one knot from both stalling and overstressing the airframe The limitations of orbiting satellites were another difficulty being faced in reconnaisance missions Orbiting satellites can only provide short glimpses of targets of interest at regular intervals not the ability to continuously watch these targets This allowed the subjects of interest to learn when to stop activity to avoid being seen by the orbiting satellites 2 UAVs are well suited for high altitude gt 40 000 50 000 feet missions and long endurance g
28. 4 Flyer indicate the new design has slow unstable dynamics that may be easily flown by a human pilot or an autopilot The control electronics are largely the same as the previous version of the X 4 Flyer but the authors anticipate that the more favorable dynamics of the current X 4 Flyer will allow the control algortihm to be performed with the 39 Figure 2 5 A picture of the X 4Flyer 21 onboard processor eliminating the need for the ground computer used in the first X 4 Flyer Flight tests had not been attempted at the time of the paper 2 3 4 University of Pennsylvania A research group at the University of Pennsylvania is developing a quadrotor using a commercially available model the HMX 4 that is similar to the Draganflyer as a testbed 20 34 In the first paper both onboard and offboard computers were used to combine information from inertial sensors and cameras to control the quadrotor 20 Three onboard gyroscopes are used to stablize the quadrotor in an inner control loop A camera placed on the ground is used as the primary sensor Five 2 5 cm colored markers placed on the base of the quadrotor are tracked by the camera and a marker tracking algorithm is used to obtain positions and areas of markers on the image plane The algorithm then computes the pitch roll and yaw angles and the position of the quadrotor Due to weight limitations of the HMX 4 no GPS or additional accelerometers could be placed on the quadrot
29. Australia and has been documented in two papers 21 22 The electronics used in this project are detailed in the first paper The use of two inertial measurement units IMU were investigated The first was a commercial IMU from Crossbow that weighed about 475 grams and the second IMU the Embedded inertial Measurement Unit or EiMU was developed by a robotics group in Australia 33 and weighed less than 100 grams The authors stated that the greater weight of the commercial IMU negatively affected the performance of the X 4 Flyer so the EiMU was used in the final prototype An onboard computer with two processors is used to record pilot input from an R C receiver at 45 Hz a serial interface to the IMU allows data from the IMU to be recorded at 120 Hz this data is then downsampled to 45 Hz and a second serial interface is used for asynchronous serial communication to send the pilot input and IMU data to the ground computer at a rate of 45 Hz This second serial interface is also used to receive control signals from the ground computer and send signals to the speed controllers used to drive the motors A non linear dynamic model of the X 4 Flyer is also presented This model is linearized about a hover condition and transfer functions relating pilot control inputs to Euler angles yaw pitch and roll are obtained for this linearized model These transfer functions were used to develop a pilot augmentation system that 34 included an inner loo
30. D converters and CCP channels Read all 3 gyroscopes for 5 seconds while quadrotor is stationary to determine zero angular rate reading for each gyroscope ME Control loop calculations Print saved variables 20 ms Figure 4 3 A flowchart showing the entire program structure The control loop is the next part of the program This loop executes until a button on the PIC development board is pressed The control loop is designated to be 20 ms long Once the code in the control loop has been executed the loop 77 timer is repeatedly checked until 20 ms have passed The next iteration of the loop is then started The servo pulses from the SSC board are sent every 20 ms so updating their length more often than 20 ms is unneccesary The time spent waiting for 20 ms to pass before starting the loop s next iteration could be used to communicate with additional sensors or perform additional calculations Once the button to exit the control loop is pressed the serialOut function is used to turn the motors off and the variables that have been saved during the program execution are printed to a computer monitor 4 4 Control loop The structure of the control loop is given in figure 4 4 For each iteration of the control loop the current angular rates and pilot inputs are determined the control calculations are performed and signals are sent to the motors 4 4 1 Determining angular rates First the sum of the gyroscope readi
31. Development SSC Serial Board 9V Board Battery Figure 3 9 Schematic of the components connected using the fabricated circuit board board can also be made in this software program The circuit board for the UAV was fabricated by Advanced Circuits at a cost of 40 56 The circuit board was designed so that three individual circuit boards were fabricated on a single board which was cut using a band saw into the three smaller boards The three circuit boards were needed so each of the three gyroscopes could measure angular velocity about a different perpendicular axis Each of the three boards have holes for right angle male pin headers that permit the boards to be soldered onto the headers so that the three boards are perpendicular to each other A picture of the circuit before it was populated with gyroscopes and other cables and connectors is shown in figure 3 11 The two small boards are the two vertical boards in figure 3 11 and both hold a gyroscope The large board is 2 25 inches by 3 inches and holds the following components Gyroscope A twenty pin dual inline socket was soldered to the board to hold the gyrscope evaluation board 64 X GYROZBOARD X GYRO3BOARD Scott Hanford amp GYROZCONNECTOR vt NN ewag Le E a o ura 2 O Figure 3 10 This picture shows the circuit board layout designed with the Eagle software program Connections to the two small boards For each of the tw
32. Dual Axis Accelerometer with Duty Cycle Data Sheet 2004 Mini SSC II Serial Servo Controller User s Manual July 2000 http www futaba rc com radios index html July 11 2005 http www seetron com ssc htm July 11 2005 Astro Flight Inc Aircraft Speed Control Model 217D Data Sheet http www motocalc com July 11 2005 http www mpjet com August 9 2005 http www eagletreesystems com July 11 2005 http www cadsoft de July 11 2005 http 4pcb com May 20 2005 106 57 http www robotmarketplace com May 20 2005 58 J Lowen Shearer Bohdan T Kulakowski and John F Gardner Dynamic Modeling and Control of Engineering Systems Prentice Hall 2nd edition 1997 59 Brian L Stevens and Frank L Lewis Aircraft Control and Simulation John Wiley and Sons Inc 2nd edition 2003
33. Even the lightest fixed wing models must fly fairly fast to provide sufficient lift for flight 10 These fixed wing aircraft also need space to turn and although research has demonstrated their capability to fly in small circles over a specified area they are difficult to fly in confined places such as urban environments and small indoor spaces 10 11 It can be difficult flying fixed wing UAVs from aircraft carriers and rotary wing UAVs can allow unmanned flight capabilities from these carriers 6 Rotary wing unmanned air vehicles have the potential to be very useful in these situations and this potential has resulted in the development of many of these vehicles The most widespread use of rotary wing UAVs is the use of R C helicopters figure 1 18 for agriculture in Japan 2 There is 100 million worth of commercial Figure 1 18 A picture of an R C helicopter performing an agricultural mission 5 sales of these UAVs annually and companies such as Yamaha have developed in dustrial unmanned helicopters 12 There are 6000 licensed operators for the 1565 UAVs that provide one third of the agricultural aviation in Japan This wide spread use of UAVs occured as a result of the decreasing number of rice farmers in Japan After a government competition to determine a feasible way to deal with this labor shortage robotic helicopters were selected and their development was 23 initially subsidized by the government Each helicopter
34. I controller intended to represent the control of one of the three angular rates of the quadrotor The input signal r respresents the input from a pilot This input is converted into a desired angular rate wg A summing junction subtracts the measured angular rate Wm from the desired angular rate to determine the error e equation 4 3 The measured angular rate is calculated from the gyroscope output y as described in equation 4 1 81 Calculate desired rate from pilot intput Convert gyro output to angular rate Figure 4 5 A block diagram describing a system with a PI controller e Wd Wm 4 3 The integral of the error el is then found by adding the product of the current error and the current time step to the integral of the error calculated at the previous timestep equation 4 4 The integral of the error could also by found using more accurate numerical integration techniques such as trapezoidal integration with a minimal increase in computation time el el timeStep e 4 4 82 This integral is represented by the z term in figure 4 5 The PI controller uses the proportional kP and integral kI gains the current error e and the integral of the error el to calculate the motor outputs u as described in equation 4 5 u kP x e kl el 4 5 A motor output is calculated for each of the three angular rates uPitch uRoll and uYaw using equation 4 5 and for the collective thrust
35. MUs are often expensive heavy and output sensor data that has been previously filtered by proprietary filters 33 These units may also be too expensive to replace or repair if they are damaged in a crash 44 Using a commercial quadrotor as a testbed for the control electronics can result in limitations on the payload the vehicle could carry and it could be expensive to repurchase the frame if a crash occurred The payload limitation could be especially important if an increased payload is necessary to increase the quadrotor s level of autonomy in the future Quadrotor Hardware This chapter discusses the hardware used in the development of the quadrotor The commercially available hardware components used in this research and how the parts were physically integrated with each other are described The system used to test the efficacy of using these hardware components for the quadrotor and the steps used to construct the quadrotor frame are also discussed 3 1 Microcontroller The PIC 18F8720 Microchip Technology Inc 8 bit microcontroller was chosen to obtain data from sensors input from a pilot perform control calculations and control the motors on the quadrotor UAV This microcontroller has a 25 MHz processor the current compiler runs the processor at 20 MHz 68 input output I O pins 128 Kbytes of Enhanced FLASH program memory 4 Kbytes of RAM 1 Kbytes of data EEPROM A Guassian elimination code was used to test the nu
36. PIC18F6520 microcontrollers an ultrasonic sonar sensor a differential GPS unit Trimble Lassen LP and a Class II Bluetooth device that has a range of 150 300 feet and is used to communicate between the quadrotor and the ground station that includes a cluster of personal computers and a laptop with a standard joystick for manual flight The IMU uses data from its sensors angular rate gyros accelerometers and magnetometers to estimate the attitude and attitude rate of the quadrotor The IMU outputs these estimates which are susceptible to high noise levels and degra dation in accuracy when there are large vibrations in the quadrotor frame at high thrust levels Acceleration data was noisy for all thrust levels and attitude in formation was used instead of acceleration measurements to estimate translational accelerations A Kalman filter was used to estimate the vehicle altitude since read ings from the ultrasound sensor were unreliable An infrared distance sensor was added to the system to supplement the sonar measurements during limited parts of the quadrotor flight envelope Another Kalman filter used GPS measurements 42 velocity measurements and attitude information to estimate position and velocity estimates The GPS data was also used to correct the translational acceleration estimates A single quadrotor has performed well in outdoor hover tests during which manual attitude inputs were used in response to wind disturbances while th
37. The Pennsylvania State University The Graduate School A SMALL SEMI AUTONOMOUS ROTARY WING UNMANNED AIR VEHICLE A Thesis in Aerospace Engineering by Scott D Hanford 2005 Scott D Hanford Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science December 2005 I grant The Pennsylvania State University the non exclusive right to use this work for the University s own purposes and to make single copies of the work available to the public on a not for profit basis if copies are not otherwise available Scott D Hanford The thesis of Scott D Hanford was reviewed and approved by the following Lyle N Long Professor of Aerospace Engineering Thesis Advisor Joseph F Horn Assistant Professor of Aerospace Engineering George A Lesieutre Professor of Aerospace Engineering Head of the Department of Aerospace Engineering Signatures are on file in the Graduate School Abstract Small semi autonomous rotary wing UAVs have many potential military and civil ian applications A quadrotor one such UAV with four fixed pitch rotors has become popular in recent years This UAV can be highly maneuverable has the potential to hover and to take off fly and land in small areas and can have simple control mechanisms However a quadrotor is unstable and can be difficult to fly Although electronic stability augmentation can result in stable flight implement ing this in a small
38. UAV history UAVs or platforms very similar to UAVs have a long history and have been called many different names including aerial torpedos drones remotely piloted vehi cles unmanned aircraft unmanned aerial vehicles and remotely operated aircraft throughout their history 2 Several aviation pioneers used unmanned versions of their aircraft to test these vehicles in flight 2 3 These models helped in realizing the benefits of wing dihedral and camber Kites could even be considered the first reconnaisance UAV as they were used to take pictures during Spanish American War 4 Although UAVs were being used before the Wright brothers achieved the first powered heavier than air flight a lack of technology in the three areas of automatic stabilization remote control and autonomous navigation allowed manned aviation to progress more quickly than unmanned flight Later technology improvements in all three of these areas were critical for the development of successful UAVs 1 1 1 The Beginning Nikola Tesla is credited with developing the concept of a remote controlled flying machine Tesla claimed he was capable of inventing a remote controlled aircraft that could change its direction in flight explode at will and never make a miss 2 Tesla demonstrated what he called teleautomation in 1898 by making a four foot long boat stop go turn left or right and blink its lights by using different radio signals Tesla a
39. addition the total torque created by these two rotors will remain constant Similarly the pitch rate is controlled by varying the relative speed of the front and rear rotors The yaw rate is controlled by varying the relative speed of the clockwise right and left and counter clockwise front and rear rotors The collective thrust is controlled by varying the speed of all the rotors simultaneously A quadrotor has some advantages over other rotary wing UAVs It is mechan ically simple and is controlled by only changing the speed of rotation for the four motors 21 Since the yaw rate is controlled by changing motor speed a tail rotor is not required to control yaw rate and all thrust can be used to provide lift A quadrotor may also be able to fly closer to an obstacle than conventional helicopter configurations that have a large single rotor without fear of a rotor strike 10 21 The vehicles dynamics are good for agility and its four rotors can allow increased payload 20 Another advantage of a quadrotor is that minimal cross coupling simplifies the quadrotor dynamics However the dynamics of the quadrotor and specifically its low rate damping can make the vehicle difficult to control 20 The challenge of controlling the vehicle can be even more difficult for a small low cost quadrotor 22 29 Figure 2 1 A drawing of a quadrotor showing direction of motor rotation 2 2 Early quadrotor designs There are a few examples of manned
40. cessing and three gyroscopes were used onboard to stabilize the quadrotor The new two camera visual feedback system decreased the errors in quadrotor position and orientation from the group s earlier research The use of a ground camera to determine the attitude of the quadrotor is useful 37 for experiments in quadrotor control but can only be used in unique circumstances on a practical aircraft For example the two camera method decribed above could be useful for automated takeoffs and landings at a prescribed location with a stationary ground camera at a location where a mobile ground robot can be placed or for other missions that require cooperation between air and ground robots 2 3 5 Cornell University Two quadrotor projects have been performed at Cornell University The goal of the first research project was to develop a method to estimate the attitude of a quadrotor by using an offboard vision system and three onboard gyroscopes 35 Four LEDs were mounted on the corners of the quadrotor frame and were tracked by three cameras that made up the offboard vision system The system used an onboard computer which sent data from the gyroscopes to the offboard computer and sent the motor commands received from the offboard computer to the motors and an offboard computer which used the gyroscope and vision data to calculate motor inputs and send the inputs to the computer onboard the quadrotor A tether was used to provide power to t
41. cessor having to ask if something needs to be done 44 An example of a situation where interrupts can be useful is when a task needs to be performed when a digital input pin undergoes a transition from low 0 volts to high 5 volts An interrupt can be set to occur when the transition takes place The task that needs to be performed when the pin undergoes a transition can be placed in the interrupt service routine As soon as the pin transition occurs the interrupt will happen the program will be paused and the interrupt service routine will be executed Without interrupts the status of the pin would have to be repeatedly checked in the main program to see if there had been a transition to high Interrupts allow the response to the transition to be fast and do not require that computational time be used to repeatedly check the state of the pin There are five built in timers called timers 0 4 in the PIC 18F8720 that can 48 be used with a great deal of flexibility All of the timers can use the internal microcontroller clock that increments every 0 2 microseconds as an input The number of increments before the timer resets or overflows and starts counting from zero again can be programmed for each timer The timer input can also be divided by specified integers This means that if the internal clock is chosen to be the input and is divided by 2 the timer will increment every 0 4 microseconds instead of the normal 0 2 microseconds The t
42. ches Figure 1 20 A picture of the MAV from Honeywell 13 University research groups including those at Georgia Tech Maryland Col orado and Auburn have also developed rotary wing UAV systems Research at the University of Colorado has studied adding low cost avionics to an R C he licopter for autonomously calibrating antennae 14 This group incorporated a custom made inertial measurement unit with rate gyroscopes and accelerometers and a GPS unit with the goal of achieving autonomous hover using a commercially available R C helicopter Researchers at the Georgia Institute of Technology have developed two rotary wing UAVs the GTMax which uses a Yamaha R C heli copter airframe has a 10 2 foot diameter rotor and weighs about 157 pounds and the GTSpy which uses the MASS Helispy airframe weighs six pounds and has a 11 inch diameter duct 15 Using a wide array of sensors tests have demonstrated many flight capabilities including fault detection and accomodation fault tolerant 25 flight control vision based navigation vision based obstacle avoidance and even launching of the GTSpy from the GTMax during flight The University of Mary land has also developed two rotary wing micro UAVs 16 The MICOR vehicle has two counter rotating coaxial rotors and weighs 140 grams and the GIANT vehicle has a single rotor and weighs 220 grams These two vehicles have been flown using an R C transmitter and receiver and recent research has
43. connaisance were provided by UAVs in both Bosnia and Kosovo 2 4 The Predator was the primary UAV used in Bosnia It was flown from a base in Hungary and flew 2700 hours during 332 flights 4 The Pioneer was used in both Bosnia and Kosovo to provide reconnaisance for Marines in these areas 2 1 2 Present day UAVs UAVs have continually become more prevalent and in the world today there are about 2400 UAVs in operation 2 Figure 1 7 displays the weight of several of these UAVs versus their wingspans The use of UAVs can be divided into these areas 66 of all UAVs are used for commercial activities 31 for military uses 2 in non military or civil applications and less than 1 for both academic and nonprofit or nongovernment such as the Red Cross and United Nations purposes About 65 of these UAVs are used for agricultural purposes in Japan Western Europe has the next largest collection of UAVs which are used for military reconnaisance The United States has roughly 160 UAVs in operation or evaluation The military 13 o gt Dragon Warrior Spectre H Asrosonde aa Fotal Weight k 0 Wing Span m Figure 1 7 This figure shows a graph of weight versus wingspan for many present day UAVs 8 This graph shows the relative small number of small UAVs compared to UAVs with larger weights and wingspans owns most of these UAVs and spent over one billion dollars on UAVs for the first time in 200
44. d for the controller to be activated and allow the motor to turn on 3 8 Quadrotor Powerplant In choosing the components to be used for the quadrotor s powerplant the soft ware program MotoCalc version 7 09 from Capable Computing Inc was used to determine the combination of components that would meet the desired require ments for flight length aircraft weight and thrust production 52 A flight length of 15 minutes a time considered adequate to perform a worthwhile mission was required A thrust to weight ratio of 1 5 2 1 was deemed high enough to lift the quadrotor and provide sufficient control effort A rechargeable battery was selected to provide power to the motors and the SSC board It was important for the battery to be lightweight have enough capacity for the desired flight length and be able to provide high amounts of current that may be drawn by the motors A rechargeable lithium polymer battery from Thunder Power met all of these requirements and was selected for use on the quadrotor The battery has 3 cells for a total voltage of 11 1 volts has a capacity of 2100 59 milliAmp hours mAh and weighs 5 1 oz It can provide a continous discharge of 21 25 Amps and a burst discharge of 33 Amps The battery costs 85 The motors and gearboxes used for the quadrotor were purchased as a single unit from Grand Wing Servo for about 10 The GW EPS 100C DS BB power system with a gear ratio of 6 60 1 was chosen Each power
45. e alti tude command remained constant Once the design for the individual quadrotor is completed the future goal for this research group is to use new multi agent control techniques to allow several quadrotors to act as individual agents in a sys tem The potential for using vision based navigation and control for the individual quadrotors is also mentioned 2 4 System Approach Quadrotors will be most useful when they are semi autonomous or autonomous so that their operator does not have to constantly monitor their performance or location and is able to perform other tasks while flying the vehicle The short term goal of this research is to develop a stability augmentation system for a lightweight and low cost quadrotor that will permit manual flight and to test this system on a quadrotor This stability augmentation system must be implemented in such a way that the components used in this system will be useful in the development of an autonomous or semi autonomous quadrotor UAV The long term goal of this research is to add additional sensors to increase the autonomy of this inexpensive quadrotor Implementing an inexpensive semi autonomous control system that can be flown on a small quadrotor is a challenging problem because of the small pay 43 load capability of these small UAVs Small lightweight and low cost sensors and microcontrollers can help reduce the instability of quadrotors and make it easier to fly while adding minimal we
46. e output signal changes by 12 5 milliVolts for a change in angular velocity of one degree per 79 second 4 4 2 Determining pilot inputs The pilot inputs are then calculated using the length of pulses from the R C re ceiver determined using the CCP channel interrupt service routine ISR described earlier in section 4 2 2 Equation 4 2 is used to convert the measured pulse lengths to the desired angular rates 4 2 I lse 1 h nput pus ength _ 1500 wa Input gain x The pulse lengths measured by the CCP channel ISRs are in microcontroller ticks which must be divided by 5 to get the pulse lengths in microseconds The three sticks on the R C transmitter corresponding to the three angular rates of the quadrotor are spring loaded and rest in the middle of their range This means that with no input applied to the sticks the pulses from these three channels are about 1500 microseconds us long Fifteen hundred us are subtracted from the length of the pulse in microseconds so that when no force is applied to the sticks on the transmitter the desired angular rates are zero To ensure that the range of possible desired angular rates corresponds to most of the range of measured angular rates 150 degrees per second the input gain was set to 0 1 This means that when the transmitter stick is pressed to its positive limit the pulse length will be about 2000 us and the desired angular velocity will be about 100 degrees per second W
47. e performed by this UAV In addition to the integration of more sen sors future projects can also implement more advanced control schemes including sensor data fusion and state estimation methods on the quadrotor Control algo rithms that can overcome any performance shortcomings of the sensors or that can adapt to sensor failures could be especially useful The current quadrotor could also provide a testbed for research in cooperative control of UAVs or in cooperative efforts between UAVs and unmanned ground vehicles Bibliography Office of the Secretary of Defense Unmanned Aircraft Systems Roadmap 2005 2030 2005 Laurence R Newcome Unmanned Aviation A Brief History of Unmanned Aerial Vehicles AIAA 2004 John D Anderson Jr Introduction to Flight McGraw Hill Companies Inc 5th edition 2005 Paul G Fahlstrom and Thomas J Gleason Introduction to UAV Systems Paul G Fahlstrom and Thomas J Gleason 2nd edition 1998 Robert C Michelson and Laurence R Newcome AIAA short course in 21st Century Aerial Robotics Roger W Gallington Harry Berman John Entzminger Michael S Francis Patrick Palmore and Jay Stratakes Future Aeronautical and Space Systems chapter 6 AIAA 1997 Unmanned Aerial Vehicles S Tsach J Chemla and D Penn UAV Systems Development in IAI Past Present amp Future In 2nd AIAA Unmanned Unlimited Systems Technolo gies and Operations Aerospace Land and Sea Conference
48. e powered by a DC voltage source between 7 and 15 volts The development circuit board from CCS Inc can be bought separately for 60 The PIC 18F8720 microcontroller can be bought by itself for 17 oo ee IA Figure 3 1 A picture of the PIC development board The PIC microcontroller is the chip labeled 18F8720 The top ruler is in inches and the bottom ruler is in centimeters This board contains the PIC microcontroller a header with two rows for ac cessing the microcontroller input output pins two serial ports a connector for the In Circuit Debugger ICD and other hardware including a voltage regulator and oscillator crystal There are also three LEDs a potentiometer and a push button 50 to help with programming and debugging The ICD connects the PIC development board and a PC through a USB connection and allows program variable values to be watched and statements to be printed to the computer monitor a break point to be inserted into the program and programs to be stepped through line by line The two serial ports provide built in buffering for sending and receiving serial data and MAX232 hardware to convert serial data from the PIC to the RS 232 protocol These serial ports can also be used to print information to a computer monitor without the use of the ICD 3 3 Gyroscope A single chip rate gyro evaluation board ADXRS150EB from Analog Devices Inc can be used to measure angular velocity 46 The evaluation board
49. e specifications of the battery 60 pack The flight time at full power is less than the desired length but when the power supplied to the motors is decreased to generate only the thrust needed to hover 32 ounces the estimated flight time is increased to about 23 minutes 3 9 Test Setup A two rotor test system shown in figure 3 8 was developed to test the hardware components described earlier in this chapter by implementing a pilot in the loop control law A motor gearbox system and a propeller were mounted to each end Figure 3 8 A picture of the setup used to develop and test the electronics for this project of a piece of wood that was constrained to rotate in one degree of freedom at its 61 midpoint Pilot input from the R C transmitter and receiver was converted into the desired angular velocity of the system and a desired thrust The gyroscope described in section 3 3 was used to measure angular velocity and the PIC micro controller was used to determine the motor output from the control law calculations that will be described in section 4 4 3 10 Flight Data Recorder An onboard flight data recorder from Eagle Tree Systems was used to record pilot inputs during tests using the two rotor test system 54 The data recorder can be used to monitor altitude airspeed battery level and four channels of pilot controls The flight data recorder is both lightweight and small it weighs less than 3 o
50. e to reach a peak magnitude of about 130 degrees per second seven seconds into the test but the PI control law decreased this high pitch rate by the time the quadrotor landed The roll rate during this flight is shown in figure 5 10 After the quadrotor lifted off of the ground five seconds into the test the quadrotor experienced a brief positive roll rate and then a larger negative pitch rate Between six and seven seconds into the test the pilot gave an input to increase the roll rate Similar to the input for pitch rate this roll input resulted in a peak magnitude of roll rate about 120 degrees per second The roll rate also decreased by the time the 95 150 Roll rate degrees second 150 Time seconds Figure 5 10 A graph showing the roll rate in degrees per second of the quadrotor during a flight quadrotor landed Figure 5 11 shows the yaw rate of the quadrotor during this flight The magni tude of the yaw rate stayed relatively small lt 20 degrees per second during the first two seconds of the flight between five and seven seconds of the test Then the yaw rate increased and had a large magnitude for most of the rest of the test The yaw rate is controlled by the moment created by the difference in propeller torques between the counter clockwise rotating and clockwise rotating motors while the pitch and roll rates are controlled by the moment resulting from the difference in propeller thrusts bet
51. e used for the R C receiver input signals and two pins were used for power and ground Battery and Power The main board was designed to power the quadrotor mo tors and the SSC board all with one battery Two different types of con nectors for powering the circuit boards were included in the design A Molex high current connection and a simple 0 1 inch pitch two pin header were included Four single row straight male headers with two pins each provide the connections for powering the electric speed controllers from the battery An eight volt regulator 7808 with 0 1 microfarad bypass capacitors is used to provide 8 volts to the PIC board 3 12 Quadrotor frame The main goals when designing and building the quadrotor frame were to create a frame that was lightweight but strong enough to survive rough landings and simple to build in case damage was sustained upon landing The frame was made of two pieces of 3 8 inch by 3 8 inch square poplar Each piece was 26 inches long A notch was cut in the middle of each piece and the pieces were attached with epoxy to form a cross figure 3 12 To attach the motors to the quadrotor frame holes were drilled into a plastic mount that comes attached to the motors These holes were drilled so that each end of the wood quadrotor frame could be slid into the Figure 3 12 The picture on the left shows the notch that was cut into each piece of the cross The picture on the right shows the two pieces of
52. ecord value of timer when interrupt occurred as fallTime Subtract riseTime from fallTime to determine pulse length Configure CCP channel to cause interrupt on rising edge Reset flag to indicate that rising edge has not been seen Change input channel Figure 4 2 A flowchart describing the interrupt service routine used to measure the length of one input pulse from the R C receiver servo pulse 4 3 Program structure Figure 4 3 is a flowchart of the body of the program used to control the quadrotor vehicle The first part of the program declares all of the variables needed through out the program as well as variables that were used for troubleshooting during code development and for storing results during quadrotor flights The serialOut function and interrupt service routines for timerl timer3 each of the four CCP 76 channels and timer4 for gyro reading are then defined The serialOut function is then used to arm the ESCs by sending 1 ms long servo pulses to all the ESCs for one second Next the CCP channels timers and A D converter are set up and the interrupts are enabled For the next five seconds each of the three gyroscopes are sampled while the quadrotor is stationary to determine the reading for each gyroscope when there is zero angular velocity Declare variables Define functions and interrupt service routines Arm ESCs with serialOut function Set up hardware features interrupts timers A
53. ed for the current gyroscope pitchNumGyroReadings for example is incremented Then the channel to be used for the next A D conversion is set When the results for each gyroscope are averaged in the control loop the variables that store the sum and the number of the gyroscope readings are reset to zero so the variables will be ready for the next iteration of the control loop 4 2 2 R C receiver and Capture Compare Pulse width mod ulation channels The capture compare pulse width modulation CCP hardware was set to capture mode to obtain four inputs from the R C receiver by measuring the pulse lengths from the receiver Each input channel to be read from the receiver has three pins as described in section 3 5 The positive voltage and reference ground pins were connected to the PIC positive voltage 5 volts and the PIC reference ground The signal from each channel was connected to one of the CCP pins on the PIC microcontroller Although all of the CCP pins can measure pulse lengths simultaneously this would require a timer to be used for each individual CCP pin Since four CCP pins are used to measure pulse lengths from the R C receiver four out of the five 73 Perform A D conversion on current gyroscope store 10 bit number in value Add value to sum of previous A D conversions for current gyroscope sum value Increment variable storing number of conversions for current gyroscope numberOfReadings
54. eded to maintain the desired angular rate of the system was decreased using PI control A quadrotor has been developed using commercially available inexpensive parts for the UAV s frame brushed motors electric speed controls and propellers The electronics and control system developed for the single degree of freedom test system were extended in this design Three gyroscopes were used to measure the roll pitch and yaw rates of the quadrotor Four pilot inputs the desired thrust and the desired roll pitch and yaw rates were sent to the quadrotor s microcon troller using the R C transmitter and receiver An inexperienced R C pilot was able to successfully fly the quadrotor for short periods of time The quadrotor has shown promising characteristics and has the potential to be useful in several future research projects Table of Contents List of Figures viii List of Tables xi Acknowledgments xii Chapter 1 Introduction 1 Lied UAV OIE y Pk a eS a AL ee ee AA AA 2 Idt ThetBeginhing ia a mesen aieea ia ae tid TA i SY p aS f 3 1 1 2 Aerial Torpedos soc O AA CR eS 4 1 1 3 Target Drones and World War II UAVsS 5 LEA Cold Wak cee arn a geet gi mas e ee eee IA A yg 7 1 1 5 Vietnam 1964 1975 atico dy dr dr 9 LLO Israeli UAVS re a Pt ea AAA ei pia eo 11 1 1 7 Recent UAV Military Missions 12 a Presentada UAVS 50 a i bs a A E 12 1 2 1 Fixed wing High Altitude Long Endurance Aircraft 14 1
55. en to fly the quadrotor is described in this chapter The features of the C compiler used to program the PIC microcontroller and the interfaces to each piece of hardware are discussed The structure of the program written to fly the quadrotor and the characteristics of the control law used in this program are then explained 4 1 CCS C compiler CCS Inc has developed a C compiler called the PCWH for the PIC 18F8720 microcontroller 45 This compiler is easy to use with CCS s Windows based IDE integrated development environment and its C aware editor This editor highlights C syntax features with colors has tab control can search for matching brackets or parentheses and has other features This is not an ANSI compliant C compiler and it has some differences from a traditional C compiler because of separate code and data segments in the PIC hardware This compiler does have some of the standard ANSI library and math functions and has many extensions 71 that are useful when working with the PIC hardware The compiler has built in libraries for working with RS 232 serial input and output digital input and output and precision delays and makes hardware features such as timers and A D conversion easy to use with C functions In addition to 1 8 16 and 32 bit integer types 32 bit floating point numbers and floating point math which is very important for the control calculations used in this research are also supported The IDE a
56. fter the rotation begins the pilot gave two inputs first a shorter input and then a longer one in response to the pitch rotation This pilot input and the control law created a differential motor output to the motors on the pitch axis motors one and three that resulted in a decrease in the magnitude of the negative pitch rotation about seven seconds into the test A little after seven seconds into the flight the pilot also decreased the input for thrust causing the quadrotor to land on the ground about eight seconds into the test causing the large spike in pitch rate seen at eight seconds 5 3 2 Angular rates during a flight The yaw pitch and roll rates of the quadrotor were stored in the microcontroller s RAM during another flight At the completion of the flight these rates were printed to a computer monitor using the PIC development board s serial port The three rates recorded during this quadrotor flight are shown in figures 5 9 5 11 The quadrotor lifted off the ground about five seconds into the test and landed on the ground a little after ten seconds into the test The rates during landing were not recorded because the microcontroller on the quadrotor ran out of memory to store the angular rates shortly before landing occurred During this flight the quadrotor lifted off the ground while tilted in its pitch and roll axes and flew in the direction of its tilt until pilot input was given to correct for this tilt The 93 250
57. g Pointer allowing the operator to perform other tasks while flying the UAV 6 The Raven figure 1 14 from AeroVironment is a reeingineered Pointer that is smaller than the Pointer weighs four pounds and has a one pound payload and a 4 3 foot wingspan thanks to battery and electric motor technology improvements The Raven requires minimal operator skill and maintenance and was first used in Iraq for over the hill and route reconniasance 1 Figure 1 14 A picture of the Raven UAV in flight 1 The Aerosonde shown in figure 1 15 is a small 33 pound weight 12 pound payload capacity 9 4 foot wingspan long endurance 30 hours UAV 1 It was the first UAV to complete a transatlantic flight when it flew from Newfoundland 20 Figure 1 15 A picture of the Aerosonde UAV in flight 1 Canada to Scotland in 26 hours and 45 minutes in August 1998 2 The Aerosonde is too small to carry a satellite data link so the UAV must be autonomous when it is over the horizon from its ground station which it was for most of its flight across the Atlantic Ocean The Aerosonde has flown in many harsh environments including Alaska In September of 2005 the Aerosonde was flown into Hurricane Ophelia 9 The ScanEagle is a small low cost UAV that is capable of 20 hour flights weighs 39 6 pounds can carry a five to seven pound payload and has a ten foot wingspan 1 It has a near vertical recovery system and a pneumatic catapult
58. g edge occurs and causes an interrupt the value of the timer is copied into a 16 bit integer as described above The variable fallTime can be set equal to this value The value of fall Time minus the value of the variable riseTime will be equal to the length of the pulse in CPU ticks Since the PIC is run at a processing speed of 20 MHz five CPU ticks correspond to 1 microsecond This technique can be used to determine the amount of time that any digital pulse is high or low 4 2 3 Serial Servo Controller and serial communication As described in section 3 6 the Serial Servo Controller must receive a three byte sequence to send a servo pulse 48 The pins on the PIC through which the serial data is sent and the baud rate at which the data is to be sent are defined in the C program A function called serialOut was written to send the three bytes sequences to the SSC through one of the serial ports on the PIC development board The serialOut function uses the C command putc to accomplish the serial communication There are two arguments that must be passed to this function the number of the motor the data should be sent to and the desired length of the 75 Record value of timer when interrupt occurred as riseTime Has rising Configure CCP channel to Is this CCP pin oe t edge of pulse cause interrupt on falling channel Set flag to indicate that rising edge has been seen No R
59. h t 640 poe gow be Poh od e The weaponized Predator Sse eB aa ee eS A picture of the Global Hawk in flight The Dragon Eye dado ee te I ae ed Oe The PLASMA oh ee ne oe Ye de Sag Be Fee BS ea The Pointer UAV cee e a O a a ape le Nes eel eo OS The Raven AAA eM ko Ge A oan es Sade hg Ge ahd The Aerosonde UAV a oer dh aera seers ok Seg aig oR eG ey RC The Acrovironment Wasp lt lt 6 su re aes ais als Deals The Aerovironment Hornet 0 0 0000 ee eee A picture of an R C helicopter performing an agricultural mission The rotary wing Fire Scout UAV The MAV from Honeywell 0080 da em a ds ed A drawing of a quadrotor showing direction of motor rotation The Br guet Richet helicopter acne a ee The Dragantlyer quadrotor said e ow be a da ate The EADS Quattrocopter cil i Mi A Doan Sam See abo as Ga AP Bonsante Sug Se 24 A picture of a modified Draganflyer vill 3 1 The PIG development board ua bate Be he ee GD 3 2 A picture of the gyroscope evaluation board 3 3 A picture of the accelerometer evaluation board 3 4 An R C transmitter 44 2 8 34 Be Od ake Gd a ee Bae An R O receiver Cats deinen ace eta el Sd ese Gs Sas 3 6 The Mini SSC b oard Ode 2 oe a o dee ia 3 7 A diagram of connections to the ESC gro Hime A eee 3 9 Schematic of the components connected using the fabricated circuit Oar 614 4 6 2 A cd dle
60. hat are shown in figure 3 7 One is to receive the input signal one is for a battery to drive the motor and one is to output the voltage specified by the input signal to the motor The connection from the input signal is the same as a servo connector and has three pins a positive voltage a reference ground and the signal The connections with the motor and the battery to drive the motor both have positive and negative terminals Rechargeable Battery Pack Electric Speed Controller Servo Signal Figure 3 7 A diagram of connections to the ESC The voltage supplied to the motor is varied by turning the motor on and off very quickly at a frequency of 2 8 kHz a frequency faster than the time constant of the motor helps keep the motor speed constant This is the same technique used by the microcontroller s PWM channels For example for the motor to run 58 at approximately half of its full speed the motor is turned on and off for equal amounts of time To increase the speed of the motor the percentage of time that the motor is on is increased There is a safety feature on the speed controller that prevents the controller from activating until it receives a radio signal corresponding to a short pulse 1 ms high for a duration of one second When the speed controller is being used on an aircraft with a single motor this means that the throttle control on the radio transmitter must be held in its lowest position for one secon
61. he quadrotor send the motor commands to the quadrotor and send the gyroscope data to the ground computer A Kalman filter was used to provide a real time estimate of the quadrotor s attitude The goal of this filter was to provide an estimate that had the low rate qualities of the vision system 10 Hz and high rate qualities of the gyroscopes 300 Hz This filter kept the high frequency data from the gyroscopes and the low frequency data from the vision system and attempted to minimize the negative qualities of the gyroscope sensor drift and bias and the cameras low data rate 38 and latency The estimate obtained using the Kalman filter showed that the filter was successful in eliminating bias from the gyroscope and the estimate was able to capture high frequency data more quickly than the vision system alone The second project at Cornell University was performed as a master s thesis project 36 This project concentrated on the four thrust producing units and structure of a quadrotor These two areas were especially important since this quadrotor was heavier 6 2 kg than the previously mentioned quadrotor designs The quadrotor frame was designed using Matlab and ANSYS finite element soft ware to determine the appropriate size and strength of the structural components Despite their expense and the complicated nature of their driving circuitry brush less motors were chosen for their high power to weight ratios Propellers with la
62. hen the range of destroyer sonar systems became greater than the range of the destroyer antisubmarine weapons The DASH which evolved from a small one person he licopter was designed to extend the range of these antisubmarine weapons by taking off from the deck of a destroyer and attacking hostile submarines using two homing torpedoes carried by the DASH The date of the first unmanned DASH flight was August 12 1960 and the DASH was deployed in January of 1963 In addition to antisubmarine warfare this unmanned helicopter was used in surveil lance gunfire spotting bombing cargo transfer smokescreen laying and rescue operations The DASH s capabilities were increased with the additions of a tele vision camera and video data link Later additions included low light television a laser rangefinder and target designator and a moving target indicator radar These payloads allowed the DASH to find and fire on targets in all weather and permitted the DASH to be used against troops and convoys at night in an effective manner Almost 50 of the 810 unmanned helicopters used in Vietnam were lost but the DASH represented a major milestone for rotary wing UAVs 2 11 1 1 6 Israeli UAVs Although the U S experienced a decrease in interest in UAVs after the Vietnam War the level of activity with UAVs in Israel was high and eventually helped to recapture U S interest in UAVs 2 During the Yom Kippur War in 1973 Israel used remotely piloted
63. hen the transmitter stick is pressed to its negative limit the pulse length will be about 1000 us and the desired angular velocity will be about 100 degrees per second This input gain can also be decreased to give more sensitivity 80 for a smaller range of desired angular rates 4 4 3 PI control law A proportional and integral PI control law is used to calculate motor outputs to minimize the error between each of the quadrotor s three desired angular rates and the measured angular rates The error for each of the three angular rates is calculated by subtracting the measured angular velocity that was calculated from the gyroscope readings from the desired angular velocity determined from the pilot inputs The proportional term of the controller produces a signal proportional to the error in angular rate Increasing the effect of this term which is accomplished by increasing the gain kP associated with this term decreases the response time of the system being controlled Increasing the gain too much can have an adverse effect on the stability of the system The integral term of the controller results in a signal that is proportional to the integral of the error in angular rate This term can be used to eliminate steady state error in angular rate Increasing the gain kI associated with this term too much can lead to oscillations of the system about its desired angular rate 58 Figure 4 5 shows a block diagram of a system with a P
64. ht graph shows the oscillations in the roll angle that occurred during this flight The first two peaks were equal to 20 degrees and 30 degrees and then the remaining peaks decreased in magnitude Figure 5 13 shows the pitch angle 0 recorded during the quadrotor flight Similar to the result for the roll angle there were large peaks in the pitch angle at the beginning of the flight and the peaks in the pitch angle at the end of the flight 98 Theta degrees 40 Time seconds Figure 5 13 A graph of the pitch angle theta 0 of the quadrotor during a flight were smaller in magnitude Figure 5 14 shows the yaw angle Y recorded during this flight The yaw angle was very small until seven seconds into the test when it increased from about zero degrees to roughly 150 degrees This increase in the yaw angle occurred during the oscillations of the quadrotor over a stationary point The graphs of the Euler angles in figures 5 12 5 14 match well with the behavior of the quadrotor observed during this flight Psi degrees Time seconds Figure 5 14 A graph of the yaw angle psi 4 of the quadrotor during a flight 99 Conclusions A lightweight quadrotor system has been designed with an emphasis on using inexpensive commercially available components These components have been in tegrated with a custom designed circuit board and software has been developed to interface these co
65. ight but have limitations such as sensor performance and computing power when compared to larger and more expensive computers and sensors that are used in most flight control applications Since weight is such an important consideration for a small quadrotor a careful matching of batteries electric motors and rotors will be essential These components will have to be sized to allow the necessary payload to be carried on the quadrotor To accomplish the short term goal of this research the use of commercially available hardware was emphasized and the design was kept as simple as possible The microcontroller and MEMS sensors used in this research are both lightweight and low cost Microcontrollers do not have a traditional operating system have no moving parts such as fans or disk drives have very low power requirements and are very compact and lightweight The MEMS sensors are low cost lightweight and commercially available They can be purchased for as low as 15 30 dollars Although the sensors can be of high quality the noise bias and drift properties are not as good as those of gyroscopes and inertial measurement units typically used for flight controls Inexpensive brushed motors were used to keep the cost low and were controlled using electronic speed control units The rotors were off the shelf wood propellers from Zinger Propeller In addition commercial IMUs and commercial quadrotor frames were not used in this project Commercial I
66. imers can also be set up to generate interrupts when timer overflows occur Timers 0 1 and 3 can also use an external pin as their input When this input is chosen the timer increments once for every time the pin undergoes a cycle from low to high to low and acts as a counter There are five capture compare pulse width modulation channels on the PIC Each channel can be set to perform one of the three functions The compare function monitors an analog input voltage When this input voltage is equal to a specific reference voltage a digital output pin can be set to 0 or 5 volts an interrupt can occur or a timer can be reset The capture setting is valuable for measuring the length of a digital pulse An interrupt can be generated on the falling or rising edges of digital pulses or after every 4 or 16 pulses The value of a timer is copied to a variable unique to each CCP channel when the interrupt occurs The pulse width modulation PWM mode is used to generate a square wave a digital pulse whose signal is high for varying lengths of time PWM signals are often useful for driving motors 49 3 2 Development kit The CCS C compiler and Embedded C Language Development Kit with its In Circuit Debugger Programming Unit ICD U40 was used to program the PIC 18F8720 microcontroller 45 The development kit which cost 120 includes a development circuit board shown in figure 3 1 that is 2 5 inches by 4 13 inches weighs 1 6 ounces and must b
67. in Bosnia in May of 1995 to provide real time video surveillance While in use during the conflict in Kosovo in 1999 the delay in time between the Predator finding a target and a fighter attacking the target allowed many of the vehicles the Predator helped identify as targets to escape A laser designator and antitank missiles were added to the Predator allowing a single Predator to find designate and attack targets A Predator equipped with weapons is shown in figure 1 9 This system was tested in 2001 and has been used in Afghanistan and Kuwait to attack terrorists vehicles 2 The Predator has a ceiling of 25 000 feet but the larger Predator B 33 foot length 66 foot wingspan and 10 500 pound gross weight has a ceiling of 50 000 feet 1 The Air Force s Global Hawk figure 1 10 from Northrop Grumman has two different model sizes The lengths of the two model sizes are 44 4 and 47 6 feet the 16 Figure 1 9 A picture of the weaponized Predator in flight 8 wingspans are 116 2 and 130 9 feet and the gross weights are 26 750 and 32 250 pounds 1 Five test vehicles had repeatable and reliable performance from 1998 Figure 1 10 A picture of the Air Force s Global Hawk in flight 5 2000 reaching an altitude of 66 400 feet and demonstrating an endurance of 31 5 hours Half of the hours flown by these test vehicles were in civilian airspace providing valuable experience for flying UAVs with the approval of the FAA
68. indicates the servo motor to which the current three byte sequence is being sent the motor numbers can range from 0 to 254 The third byte is the desired position of the servo motor which can also range from 0 to 254 The numbers sent to the SSC board must be sent as individual byte values not the text representation of these numbers To monitor serial communication with the SSC board a green LED on the SSC board can be used This LED turns on 56 Figure 3 6 A picture of the Mini SSC board and two rulers The top ruler is in inches and the bottom ruler is in centimeters after successful initialization of the SSC s microcontroller After initialization the LED turns on after the first two bytes are received and then will turn off after the third byte the position byte is received This LED can provide useful information about the status of the SSC board serial communication 48 3 7 Electric speed controller Electric speed controllers ESCs are used to convert an input signal such as from the SSC board or an R C receiver with low current into a voltage and current 57 capable of driving a motor The 217D from AstroFlight Inc was used for the quadrotor 51 This ESC is rated for a continuous current of 40 Amps weighs one ounce and costs about 20 This versatile ESC can be powered by battery packs that have 6 16 nickel cadmium cells or 2 5 lithium polymer cells These controllers have three sets of connections t
69. launcher that allow it to be operated from a variety of take off or landing locations These UAVs have been sent to Iraq for force protection of the 1st Marine Expeditionary Force Its ground station also allows the operator to have the ScanEagle operations integrated with more sophisticated UAVs such as the Predator 1 The Hornet and Wasp are small fixed wing micro air vehicles from AeroVi ronment 1 The Wasp figure 1 16 weighs six ounces and has a wingspan of 13 inches This micro UAV has demonstrated autonomous flight modes such as GPS 21 Figure 1 16 A picture of Aerovironment s Wasp Notice the size of the Wasp compared to the pencil in the picture 1 waypoint navigation loiter and altitude and heading hold It also has forward and side looking cameras Future goals for the Wasp include adding an optic flow based collision avoidance and navigation system that can be used in areas with poor GPS signals and in urban areas 1 The Hornet figure 1 17 has a weight of six ounces and a wingspan of 15 inches It was the first UAV to be completely powered by Figure 1 17 A picture of Aerovironment s Hornet 1 hydrogen The fuel cell serves as the wing demonstrating the important idea of using single components to serve multiple functions in very small UAVs 22 1 2 3 Rotary wing UAVs Rotary wing UAVs can have capabilities that may allow missions to be performed that can not be considered with fixed wing UAVs
70. lk we fa ee Seen eee igh eee ee a i 70 4 2 System Integration Liso is so e Sel okt aig See eg Bs 71 4 2 1 Gyroscope and A D Converter 71 4 2 2 R C receiver and CCP channels 72 4 2 3 Serial Servo Controller and serial communication 74 ALS Propran Structure sebo ate Oi a E AA 75 ZA COmrol loopy a oe oy Se e ee DER EE E A ee TT 4 4 1 Determining angular rates ooa oaa a TT 4 4 2 Determining pilot inputs aise a ee a 79 WA P eontro law Ma sed aa a A TO AE 80 4 4 4 Driving the motors tea e o a 82 vi Chapter 5 Results Dele ESSE VELEN co sare ak bse Saat at bie Secs Es A a a 5 2 PI Control Law 5 3 Quadrotor flights 5 3 1 Pitch rate and input during a flight 244 2624 4 h04124 5 3 2 Angular rates during a flight 5 3 3 Euler angles during a flight Chapter 6 Conclusions Bibliography vii 84 84 87 90 92 92 96 100 106 List of Figures 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 1 10 1 11 1 12 1 13 1 14 1 15 1 16 1 17 1 18 1 19 1 20 2 1 2 2 2 3 2 4 2 5 2 6 A demonstration of automatically stabilized flight in 1914 The Curtiss Sperry Aerial Torpedo A line of Kettering Bugs 400 ii di RO OR eS The Queen Bee target drone from Great Britain Reginald Denny and one of Radioplane s target drones The Pioneer UAV in flight AS A graph of weight versus wingspan for several UAVs The Predator in flig
71. lso described his idea for a remote controlled flying machine to Peter Cooper Hewitt who later would pass the idea on to Elmer Sperry 2 Elmer Sperry is often credited for establishing the field of unmanned avia tion Sperry was able to use his experience developing gyroscopes to implement automatic stabilization of an aircraft allowing stabilized flight without any pilot control and also worked on the problem of remote control Sperry used three gyroscopes to determine a horizontal reference for any flight attitude In 1914 Sperry s son Lawrence Sperry publicly demonstrated this automatic stabilization in France by flying a seaplane without touching the controls while a mechanic Emile Cachin climbed out on the seaplane s wing figure 1 1 2 Figure 1 1 A picture showing Lawrence Sperry s demonstration of automatically sta bilized flight in 1914 This picture shows a person walking out on the wing to test the seaplane s automatic stabilization 2 1 1 2 Aerial Torpedos The development of automatic stabilization led to interest in using unmanned aircraft as flying bombs or aerial torpedos 2 Elmer Sperry and Charles Kettering both worked on the development of aerial torpedos the Curtiss Sperry Aerial Torpedo figure 1 2 and the Kettering Bug figure 1 3 The Curtiss Sperry Aerial Figure 1 2 This picture shows the Curtiss Sperry Aerial Torpedo 2 Torpedo experienced problems stabilizing itself after launch a
72. mber of floating point operations per second FLOPS that the PIC is capable of performing When solving a system of 29 equations consisting of 32 bit float 46 ing point variables which used over 90 of the chip s RAM 24 kFLOPS were achieved The PIC does not have an operating system but simply runs the pro gram in its memory when it is turned on An important characteristic for using the PIC in an unmanned air vehicle is that the microcontroller requires low current 12 mA typical current draw with a maximum of 20 mA 43 This PIC micro controller also has other hardware features such as an analog to digital converter ADC interrupts timers and capture compare pulse width modulation CCP channels that are very useful for simplify the interfacing of sensors and motors with the microcontroller The PIC 18F8720 has 16 channels capable of performing 10 bit analog to digital conversions These channels are used to convert an analog voltage between 0 and 5 volts to an integer between 0 and 1023 proportional to the amplitude of the analog voltage 44 The ADCs on this microcontroller perform their conversions using successive approximation 43 Successive approximation is accomplished with a digital to analog converter DAC and a comparator For a 10 bit ADC a 10 bit integer is sent to the DAC which converts this integer to an analog voltage between 0 and 5 volts This analog voltage from the DAC is then compared to the analog v
73. mponents with a microcontroller A single degree of freedom test system was built to test the integration of these components and a pilot in the loop control law was successfully implemented on this system The quadrotor was constructed with the electronics needed to develop a stability augmentation system for the quadrotor for about 760 A stability augmentation system was successfully developed for the pitch roll and yaw axes of the quadrotor The quadrotor has been successfully flown by an inexperienced R C pilot demonstrat ing that low cost components can be used to create a control system that allows manual flight of a quadrotor The quadrotor that has been developed for this research can be used in several future research projects The hardware and software used for this quadrotor can easily be integrated with additional sensors such as cameras sonar and optic flow 101 sensors that will allow the level of quadrotor autonomy to be increased An in crease in autonomy will allow operators to be able to learn how to fly the quadrotor very quickly and could allow the operator to perform other tasks while simulta neously flying the quadrotor A semi autonomous or autonomous quadrotor has the potential to fly in very confined spaces such as urban environments or even indoors with minimal operator interaction Sensors such as cameras or biological and chemical detectors could also be added to the quadrotor and allow meaningful missions to b
74. n of the Dra ganflyer to be measured by the Polhemus measuring device on the ground The device communicated with a computer on the ground using RS 232 protocol The computer calculated angular and linear velocities numerically from the Polhemus data and then determined control inputs for throttle pitch roll and yaw that were sent to the Draganflyer through an R C radio The Draganflyer was able to successfully follow both vertical and horizontal trajectories and is shown hovering in figure 2 6 This research using the Polhemus sensor is useful for practical ex Figure 2 6 A picture of a modified Draganflyer hovering 40 periments investigating control of a quadrotor but to be able to perform useful missions the quadrotor will need onboard sensors 41 2 3 8 Stanford University A modified Draganflyer is being used at Stanford University for the Stanford Test bed of Autonomous Rotorcraft for Multi Agent Control STARMAC 42 The quadrotor was chosen over conventional helicopters and fixed wing aircraft as the vehicle for outdoor testing and validation of multi vehicle control schemes The electronics that come with the Draganflyer have been replaced with a printed cir cuit board that was designed and assembled at Stanford This board performs all of the sensing and communication that is needed for autonomous flight of the quadro tor and has the following components a commercial IMU called the MicroStrain 3DM G two Microchip
75. nam War In addition the Soviet shooting down of a U 2 in 1960 and the trial of its pilot was politically embarrassing and harmed U S Soviet treaty negotiations The Cold War era marked the beginning of UAV use for surveillance in the U S military by the Air Force Army and Marines 2 The Cold War also motivated the need for robotic weapons that were capable of traveling the long distances separating continents while maintaining accuracy high enough to hit their desired targets The two competing technologies were intercon tinental ballistic missiles ICBMs and unmanned aircraft used as intercontinental cruise missiles Early nuclear bombs were too heavy for ICBMs to carry but ICBMs had the benefit that their high flight speeds 10 000 mph allowed them to reach their targets quickly limiting the accumulation of navigation errors The unmanned aircraft could carry the weight of the early nuclear bombs because of the aerodynamic lift produced by the aircraft but their slower flight speeds 500 mph resulted in long flight times over which navigational errors were accumulated Al though the ICBM became the dominate technology for transporting nuclear bombs once these bombs became lighter the attempts to achieve high accuracy navigation systems greatly benefitted the field of unmanned air vehicles 2 In the attempts to improve the accuracy of navigation systems inertial naviga tion systems INS became the favored concept because these
76. nd a catapult was developed to fix this problem A distance gear was used to have the aircraft dive towards its target at a prescribed distance Flight tests demonstrated that this aerial torpedo had an accuracy of 2 miles for a 30 mile flight The Kettering Bug gt AA lt 3 CEA lt 4 ia Sy ae T Figure 1 3 This picture shows several Kettering Bugs which were the first production cruise missiles 5 had several innovative flight controls The altitude was measured by an aneroid barometer until the aircraft reached its desired altitude at which point the altitude was maintained with a gyroscope linked to the elevator Another gyroscope was used to maintain heading and an anemometer was used to determine distance A subtracting counter was used to determine the distance at which the Bug should dive at its preset target either by releasing its detachable wings or short circuiting the ignition 2 4 Lawrence Sperry was working on an Army contract to use Messenger biplanes as aerial torpedoes when it was recognized that the unmanned aircraft were nav igating as accurately as possible given the current technology The difficulty in compensating for unpredictable changes in wind conditions was limiting the accu racy of the aircraft navigation This realization helped result in the first use of a radio to control an aircraft in May of 1922 Heading corrections were sent by radio to the Messenger from an escorting aircraft that flew wi
77. nd compiler allow viewing of C and assembly code side by side and insertion of assembly code that may reference C variables anywhere in the source code The compiler also comes with many ready to run example C programs written for the PIC 18F8720 microcontroller that demonstrate how some built in functions can be used 4 2 System Integration This section describes the C code that was written to interface the PIC microcon troller with the hardware used in this project 4 2 1 Gyroscope and A D Converter The 10 bit analog to digital converter was used to convert the output voltage from the gyroscope that represents angular velocity to an integer between 0 and 1023 An interrupt service routine ISR and a timer on the PIC timer4 were used to sample each of the three gyroscopes yaw pitch and roll every millisecond The readings for each individual gyroscope were then averaged in the main control loop which is executed every 20 ms Timer4 was set to overflow every millisecond and 72 to cause an interrupt when each overflow occurred The code inside the ISR that was executed at each interrupt is shown in figure 4 1 As shown in the figure an A D conversion for the current gyroscope is performed the 10 bit value from the conversion is added to a variable that stores the sum of the current gyroscope s readings pitchGyroReadings for the gyroscope that measures pitch rate and a counter to keep track of the number of readings obtain
78. ngs since the last iteration of the control loop is divided by the number of readings since the last iteration of the control loop to find the average angular velocity over the last 20 ms This calculation is repeated for all three gyroscopes The variables storing the sum of the gyroscope readings and the number of gyroscope readings then must be reset to zero for all three gyroscopes The angular rates are then obtained using equation 4 1 78 Setup variables functions hardware for control loop Average gyroscope readings taken in ISR Calculate the 3 angular rates Calculate desired angular rates using pulse lengths from R C receiver Control Calculate error in angular rates for current time step loop Calculate motor output using PI control algorithm Check to make sure motor output is not outside limits Send motor output to SSC board Print saved variables exit program Figure 4 4 A flowchart describing the steps used in the control loop ma average gyro reading zero gyro reading Angular velocity 0 0125 4 1 The value of the gyroscope reading when there is zero angular velocity is sub tracted from the average gyroscope reading that was just calculated This differ ence in gyroscope readings is multiplied by 5 the output from the gyroscope is 0 5 volts and divided by 1023 the A D conversion is 10 bit so the range of the result is 0 1023 This number is then divided by 0 0125 because the gyroscop
79. o small circuit boards five holes were placed for connecting the boards using single row right angle male pin headers The main circuit board was soldered to one end of the header and the small board was soldered to the other end resulting in a right angle between the two soldered boards The five holes and the header are used to connect the boards both electrically and mechanically Two header 65 4 Figure 3 11 A picture of the main circuit board with the two small circuit boards attached at 90 degree angles Two rulers are shown in this picture the top ruler is in inches and the bottom ruler is in centimeters pins are used to supply the gyroscope on the small board with 5 volts and a ground A third header pin carries the signal from the gyroscope to the main board The two header pins that do not have electrical connections are used to strengthen the mechanical connection between the small and large boards R C receiver Four single row straight male pin headers with three pins each were soldered onto the main circuit board to connect with the R C receiver The receiver can be connected to these headers using standard servo connectors three pins one signal one ground one positive voltage 66 Connection with PIC development board A dual row straight male header was soldered to the main board to provide a connection from the main board to the PIC development board Three pins were used for the gyroscopes four pins wer
80. oltage of the signal to be digitized using the comparator Usually this process is started by setting the most significant bit of the integer high and this value 512 for a 10 bit integer is sent to the DAC The analog voltage output from the DAC is then compared with the signal s analog voltage If the DAC output voltage is higher than the signal voltage the most significant bit is left high If the signal voltage is higher than the DAC output voltage the most significant bit is reset to low Then this process is repeated for each of the remaining bits 47 from the second most significant bit to the least significant bit At the end of the conversion the 10 bit number represents the analog voltage of the input signal 44 A single analog to digital conversion takes about 20 microseconds on the PIC18F8720 microcontroller This microcontroller is capable of generating interrupts which cause the pro gram execution to be paused while a user defined interrupt service routine ISR is executed Program execution then resumes where it was paused after the execu tion of the interrupt service routine has finished Examples of events that can be set to cause an interrupt are digital input pins undergoing a transition 5 to 0 volts or 0 to 5 volts a timer overflowing and resetting to zero or an incoming RS 232 character The main advantage of interrupts is that they allow the processor to be told when something needs to be done instead of the pro
81. on Unmanned Rotorcraft 2005 R M Barrett Adaptive Aerostructures Improving High Performance Sub scale Military UAVs In 45th AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference 2004 Ron Barrett Roelof Vos Paolo Tiso and Roeland De Breuker Post Buckled Precompressed PBP Actuators Enhancing VTOL Autonomous High Speed MAVs In 46th AIAA ASME ASCE AHS ASC Structures Structural Dy namics and Materials Conference 2005 E Altug J P Ostrowski and R Mahony Control of a Quadrotor Helicopter Using Visual Feedback In Proceedings of the IEEE International Conference on Robotics and Automation pages 72 7 2002 Paul Pounds Robert Mahony Joel Gresham Peter Corke and Jonathan Roberts Towards Dynamically Favourable Quad Rotor Aerial Robots In Proceedings of the 2004 Australasian Conference on Robotics and Automation 2004 P Pounds R Mahony P Hynes and J Roberts Design of a Four Rotor Aerial Robot In Proceedings of the 2002 Australasian Conference on Robotics and Automation 2002 23 24 26 os 27 28 29 me 30 31 32 33 34 35 36 104 J Gordon Leishman The Br guet Richet Quadrotor Helicopter of 1907 Ver tiflite 47 3 58 60 2002 Z Mohammad Zain N Mohamad and Z Mohamad Ali Redesign of de Bothezat Helicopter The Way Forward For the Rotorcraft Industry In 43rd AIAA ASME ASCE AHS ASC Structures Structural D
82. oplar were attached to the frame to decrease the impact of landing on the quadrotor frame The completed quadrotor is shown in figure 3 14 Figure 3 14 A picture of the completed quadrotor is shown 69 Table 3 1 shows the costs of the individual components that were used to build the quadrotor There a couple of ways to further reduce the cost of the quadrotor Some of the prices shown in this table particularly the custom made circuit board could be substantially lower if the components were purchased in larger quantities A less expensive R C transmitter and receiver could also be used In addition the PIC microcontroller and gyroscopes could be purchased in less expensive packages as discussed in sections 3 2 and 3 3 Table 3 1 This table lists the components used in the construction of the quadrotor the price for each individual component the number of components needed and the total cost for each component The total cost of the quadrotor was about 760 Name of Component Individual Cost Number Needed Total Cost PIC Development Board 60 1 60 Gyroscope Evaluation Board 50 3 150 Electric Speed Controller 20 4 80 Motor gearbox 10 4 40 Set of 2 Propellers 15 2 30 Propeller Adapter 5 4 20 R C Transmitter amp Receiver 180 1 180 SSC Board 60 1 60 Lithium Polymer Battery 85 1 85 Custom made Circuit Board 40 1 40 Quadrotor Frame 15 1 15 Completed Quadrotor 760 System Integration and Software The software writt
83. or 36 The offboard computer receives and processes images from the ground camera sets goal positions for the quadrotor and calculates and sends motor inputs to the quadrotor through its parallel port The onboard computer stabilizes the quadro tor using the gyroscopes and receives motor inputs from the offboard controller through an R C receiver located onboard A model of the quadrotor dynamics was presented and two control strategies feedback linearization and backstepping were tested in simulation The back stepping controller performed better and was implemented experimentally with the quadrotor and a tethering system that prevented excessive translation in the horizontal plane but allowed rotations and vertical translation More recently an onboard camera was added to the quadrotor to develop a two camera method to estimate the position and attitude of the quadrotor 34 In addition to the five markers on the quadrotor that are seen by the ground camera as in the previous paper another marker was placed on the ground camera and viewed by the onboard camera This two camera method had smaller angular and position errors in its estimate of the quadrotor s position and orientation than the other video methods the authors tested in simulations Experiments using the two cameras were performed using the HMX 4 and test system described in the first paper 20 Two separate computers one onboard and one offboard were used for vision pro
84. ot inputs to the quadrotor These components are often used to control servo motors on R C radio controlled airplanes cars and other vehicles The signals sent between the transmitter figure 3 4 and receiver figure 3 5 are pulses that have a frequency of about 50 60 Hz which corresponds to a period of 16 20 milliseconds The high portion of the pulses usually has a range of 1 to 2 milliseconds ms A range in pulse length of 1 2 ms will result in a 90 degree range of motion for a servo motor This range 53 Figure 3 3 A picture of the accelerometer evaluation board with two rulers inches on the top ruler and centimeters on the bottom ruler of motion is often satisfactory for use in many applications because they are often connected to mechanisms that do not need more than 90 degrees of motion 48 The range of motion of some servos can be increased by sending pulses that are high for less than 1 ms or greater than 2 ms The transmitter and receiver are capable of communicating six channels Futaba model 6EXA 49 This model costs about 180 but less expensive models could be used as well The receiver has three pins for each channel a positive voltage pin with a voltage equal to the voltage of the power supply used by the receiver five volts from the PIC development board in the quadrotor setup a reference ground and a pin to carry the servo signal 54 Figure 3 4 A picture of the R C transmitter 3 6 Serial
85. ot was was not giving any adjustments to the desired pitch rate at that moment With Control Without Control Pitch rate input degrees second Time seconds Figure 5 2 This graph shows the pilot inputs for pitch rate of the test system during tests both with gray and without black control feedback In addition to the smaller range of pitch rate measured during the test with feedback less pilot input was needed especially after the first 11 seconds of the test Even during the first 11 seconds of the test that used feedback the changes to the pilot input were smooth and gradual Throughout the test without feedback the pilot input was constantly adjusted 87 5 2 PI Control Law Tests were performed to show the results of the control law calculations for pitch roll and yaw rotations Rotations of the quadrotor were performed manually The angular rates measured using the gyroscope and the motor outputs calculated from the control law equations 4 6 4 9 were recorded throughout the tests for these rotations The desired angular rates for each axis pitch roll and yaw were equal to zero throughout these tests so any rotation resulted in an error with a magnitude equal to the magnitude of the measured rotation The motors were not connected during these tests so any rotations of the quadrotor were a result of the manual rotations The results obtained during the test of the PI control law for the
86. otor flights were successful An inexperienced R C pilot was able to command the quadrotor to lift off the ground using only thrust input keep the quadrotor in the air above a fairly small area 15 feet by 15 feet by providing pitch roll and yaw inputs and gently land the quadrotor Although flight times were short lt 20 seconds a more experienced R C pilot is likely to be able to increase the lengths of these flights easily For the first few tests the proportional and integral gains for the pitch and roll axes were set equal to the gains used for the test system These gains were then adjusted after each flight to make the 91 quadrotor easier to fly Since the quadrotor dynamics of the pitch and roll axes are similar the gains for these axes are similar in magnitude The proportional and integral gains for the yaw axis were harder to tune and were adjusted after flights during which control of the yaw rate was not satisfactory Pictures of the quadrotor in flight are shown in figures 5 6 and 5 7 Figure 5 6 A side view of the quadrotor in flight Figure 5 7 Another picture of the quadrotor in flight 92 5 3 1 Pitch rate and input during a flight Figure 5 8 shows the pitch rates of the quadrotor and the pilot inputs for pitch rate stored in the microcontroller s RAM on the quadrotor during a flight The quadrotor began to rotate in the negative pitch direction a little under seven sec onds into the test Shortly a
87. our infrared heat sensors to allow the quadrotor to level itself while it is being flown outdoors The Draganflyer has a carbon fiber and high impact nylon frame has a length of 30 inches from rotor tip to rotor tip weighs 17 ounces and can lift a payload of four ounces in addition to its onboard electronics A rechargeable battery pack is carried onboard 2 3 2 Quattrocopter The EADS Quattrocopter figure 2 4 is a quadrotor unmanned air vehicle that was intended to be a testbed for developing micro air vehicle flight control but is now being pursued for industrial applications because of its promising performance 32 The onboard electronics include a micro avionics autopilot that has a six degree Figure 2 4 A picture of the EADS Quattrocopter 32 of freedom MEMS inertial measurement unit IMU air data sensors and a GPS receiver a R C receiver a 16 bit analog to digital converter and power amplifiers to drive the motors The Quattrocopter is capable of a 20 minute flight with a single charge of its lithium batteries The vehicle is small length of 65 cm weighs about half a kilogram and has a detachable fuselage so it can be stored in 33 a backpack The electric motors allow this UAV to operate quietly The UAV has a 50 excess power margin to carry out manuevers and to carry small payloads such as a camera radar or acoustic sensors 2 3 3 X 4 Flyer Another quadrotor the X 4 Flyer is under development in
88. output to motor two minus the output to motor four The large positive roll rates caused the control law to increase the differential motor output between the motors in the roll axis The effect of the integral term can again be seen after the roll rate error becomes very close to zero 160 80 Pitch rate error 140 4 70 Differential g z 120 5 motor output 60 3 k o 8 T 8 100 4 50 5 J E 5 gt 80 y 40 2 2 o S 605 30 5 o Oo 2 40 20 3 5 S a 204 10 2 a 0 y 0 0 1 2 3 4 5 20 10 Time seconds Figure 5 3 This graph shows the pitch rate gray of the quadrotor in degrees per second and the differential motor output in digital counts for the pitch axis black calculated during a test of the control system The scale for the error in pitch rate is shown on the vertical axis on the left and the scale for the differential motor output is shown on the vertical axis on the right 89 140 35 Roll rate error 120 5 30 Differential motor output 100 25 o 20 o o fi 15 40 4 10 20 5 Roll rate error degrees second Differential motor output digital counts 20 40 10 Time seconds Figure 5 4 This graph shows the roll rate gray of the quadrotor in degrees per second and the differential motor output in digital counts for the roll axis black calculated during a test of the control system The scale for
89. p to damp the high frequency dynamics of the system and an outer loop to control the slower dynamics of the X 4 Flyer Gyroscope signals from the IMU were high pass filtered to measure angular rates needed for this inner control loop The outer control loop design was eventually abandoned because of the difficulty in obtaining the attitude of the X 4 Flyer from the IMU and the success the pilot augmentation system achieved using only the inner control loop The X 4 Flyer that was built had a weight of 2 kg a 70 cm frame length and 11 inch diameter rotors Flight testing was conducted using a truck battery and tether cord to provide power to the X 4 Flyer However these tests were not successful and the thrust margin of the X 4 Flyer was not large enough to allow controllable flight The stated goals for improvement after this paper were to design a new X 4 Flyer that would be capable of producing more thrust weigh less due to new construction and a lighter IMU have an onboard power supply that would allow flights of two minutes and have a wireless serial link and a camera system In a more recent paper from the same research group the X 4 Flyer was re designed to generate sufficient thrust and manage the unstable dynamics of the X 4 Flyer more successfully 21 The new design which is shown in figure 2 5 included inverted rotors and rotor hubs with a teetering design that have springs to provide torsional stiffness Simulations of the new X
90. rge diameters and low pitch ratios were chosen for their performance in hover zero forward velocity The lack of commercially available pusher propellers that rotate clockwise necessitated that custom made propellers be ordered The use of lithium polymer batteries with their high energy density and the capability to rapidly drain large amounts of current was another important feature of the design of the thrust producing unit This quadrotor had its power supply and sensors onboard These two com ponents took up half of the vehicle s weight An inertial measurement unit from Systron Donner 37 was used The IMU was subject to drift but was sufficient for hover tests conducted with a human pilot Simulations of the full vehicle non linear dynamics including force and torque disturbances sensor bias and sensor noise were used to design tune and test controllers and state estimators Flight tests were performed with a tether to 39 prevent damage to the vehicle or its surroundings There were some successful flights but a crash occurred and damaged the IMU Due to the high cost of the IMU the only option was to repair the damaged IMU preventing further tests before completion of the thesis 2 3 6 Swiss Federal Institute of Technology A team from the Swiss Federal Institute of Technology has worked on the control of angular rates and the height of a quadrotor 38 Dynamic models of the quadrotor were used to test both classic PID
91. roportional and integral gains in equation 4 5 were tuned experimentally so that the test system exhibited a satisfactory response to disturbances To show the importance of using feedback from the gyroscope tests were per formed to try to keep the test system level both with and without pitch rate feedback from the gyroscope The Flight Data Recorder described in section 3 10 85 was used to record the pilot input for pitch rate in both cases and outputs from the gyroscope were saved in the PIC microcontroller s RAM and printed to a computer monitor after the tests Figure 5 1 shows the pitch rates that were recorded by the gyroscope during these tests The pitch rates recorded during the test without feedback control had a much higher range from 80 to 80 degrees per second than the pitch rates for the test with feedback control which had a range of 20 to 20 degrees per second With Control 14 Without Control Pitch rate degrees per second 100 Time seconds Figure 5 1 This graph shows the pitch rate of the test system during tests both with gray and without black control feedback Figure 5 2 shows the pilot inputs for pitch rate recorded using the Flight Data Recorder throughout the two tests A desired pitch rate of zero degrees per second means that the transmitter stick is in its middle position indicating no force on the 86 stick from the pilot This means that the pil
92. system weighs two ounces Two pairs of counter clockwise clockwise wood propellers with diameters of 14 inches and pitches of six inches from Zinger Propeller were used in the quadrotor Each pair of propellers cost 15 A propeller with a large diameter and small pitch was found to provide high static thrust which is very important for the hovering manuevers that the quadrotor will perform The propellers have 1 4 inch diameter holes and the motor gearbox systems have three mm diameter shafts so propeller adapters were needed to secure the propellers on the motor gearbox shafts A collet propeller adapter the MPJ 8031 from MP Jet that fits a motor shaft of three mm and a propeller hole of five mm was found 53 Each propeller adapter cost 5 A plastic tube with a 1 4 inch outer diameter provided a perfect fit between the adapter and the propeller Simulations performed with Motocalc using this combination of battery mo tor gearbox systems and propellers predicted that the requirements for length of flight and thrust to weight ratio would be satisfied At full power a thrust of 49 ounces was predicted The total weight of the quadrotor with the parts used in the simulation was estimated to be 32 ounces Therefore at full power the thrust to weight ratio was predicted to be about 1 5 1 and the flight time was estimated to be about 10 minutes In addition the current being drawn from the battery was estimated to be 12 5 amps which is within th
93. t 12 24 hours because of the advantages they offer over manned air craft performing these missions Special equipment is needed for pilots to fly at these high altitudes and multiple crew members are needed to fly for these long durations to avoid pilot fatigue 2 6 In addition UAVs can loiter over one area for large amounts of time and can fly over an area at unpredictable intervals The area of high altitude long endurance UAVs has seen a high amount of activity since the Department of Defense became interested in this area in the late 1960s 2 Military and scientific applications have encouraged and benefitted from the high altitude and long endurance capabilities The potential of solar powered UAVs to fly for weeks or months has raised the possibility of even more UAV missions and resulted in strong efforts to develop solar powered flight especially by NASA and AeroVironment 2 Two well known high altitude long endurance UAVs currently in use are the Predator and the Global Hawk 15 The Predator figure 1 8 was intended to fulfill military requirements for a UAV that could loiter for 24 hours 500 miles from its base and provide one foot resolution images with a 400 500 pound payload 2 The Predator has a length i Figure 1 8 The Predator UAV in flight 8 of 26 7 feet a wingspan of 48 7 feet and a gross weight of 2250 pounds 1 After achieving an endurance of over 40 hours during testing the Predator was deployed
94. tek Mate tia athe eas Fe 3 10 Design of the circuit board aco a we ba el beh ek 3 11 The main circuit board with the two small circuit boards attached at 90 degree angles e al Se Si a 3 12 Construction of the quadrotor frame 3 13 A picture showing the method used to mount the motors to the quadrotor frame a awe Oe Od Ook hE dl 3 14 The completed quadrotor face Len Oa Di AA 4 1 A flowchart describing the interrupt service routine used to sample the gyroscope 4 2p s gots otara e a a o 4 2 A flowchart describing the interrupt service routine used to measure the length of one input pulse from the R C receiver 4 3 A flowchart showing the entire program structure 4 4 A flowchart describing the steps used in the control loop 45 A block diagram describing a system with a PI controller 5 1 A graph of the pitch rate of the test system during tests both with and without control feedback cercar a a doe 5 2 A graph of the pilot inputs for pitch rate of the test system during tests both with and without control feedback 5 3 Results of control law for rotation about the pitch axis 5 4 Results of control law for rotation about the roll axis 5 5 Results of control law for rotation about the yaw axis 5 6 The quadrotor in flight o tt A ae e kh a 5 7 Another picture of the quadrotor in flight 91 5 8 The pitch rate and pilot input for pitch
95. thin sight of the Messenger during tests on targets 30 60 and 90 miles away Remote control was also used by the Royal Aircraft Establishment in the United Kingdom to provide inputs to aircraft using a pilot in the loop Using this radio control flight speeds of 100 mph and a range of 65 miles were achieved in 1924 2 4 1 1 3 Target Drones and World War II UAVs The British extended their success in remote control to fly Fairey Queen Bee biplanes one of which is shown in figure 1 4 as radio controlled target drones for naval warships 2 4 6 During one of the first demonstrations the British Fleet fired at a drone for two hours without damaging the Fairey Queen A contract Figure 1 4 This picture shows one of the Queen Bees used by Great Britain as target drones 5 for 420 Queen Bee target drones was signed after the demonstration This single drone showed the potential invulnerability of unmanned air vehicles when it was used for four months before a warship was finally able to damage the drone Reginald Denny a Briton who moved to Hollywood to pursue his acting career opened a hobby shop selling model airplanes after his arrival in California and became instrumental in the building of the radio control airplane industry Denny helped start Radioplane which built 15 000 target drones for the U S military from 1941 1945 for training antiaircraft gunners Figure 1 5 shows Denny posing with one of Radioplane s target drones
96. uThrust using the pilot input for thrust 4 4 4 Driving the motors As described in section 2 1 the command to be sent to each motor ul for motor 1 u2 for motor 2 u3 for motor 3 and u4 for motor 4 is a combination of the collective thrust uThrust and the motor outputs for the three angular rates uPitch uRoll and uYaw Equations 4 6 4 9 are used to calculated the value of the output to send to each motor uMotorl uThrust uPitch uYaw 4 6 uMotor2 uThrust uRoll uYaw 4 7 uMotor3 uThrust uPitch uYaw 4 8 uMotor4 uThrust uRoll uYaw 4 9 The final step in the control loop is to check to make sure the outputs that will 83 be sent to the motors ul u4 are within the range of values that are acceptable to the SSC board The serialOut function described in section 4 2 3 is then used to send the motor commands to the SSC board Results This chapter gives results from the test system tests of the control law implemen tation and flights of the quadrotor 5 1 Test System The electronics and PI control law were tested using the two rotor system described in section 3 9 Two pilot inputs from the R C transmitter and receiver were used to determine the desired thrust and pitch rate A gyroscope was mounted on the test system to measure the pitch rate The PI control law was used to calculate the speed of the two motors needed to maintain the desired angular velocity of the system The p
97. unces and its dimensions are 3 15 inches by 1 57 inches by 0 67 inches The flight data recorder is easily interfaced to a personal computer through a USB connection An application is included with the recorder that is used to set the different recording options parameters to be recorded capture rate etc for the flight data recorder After the recorder has been used in flight this application is needed to download the data from the recorder The application can be used to view the recorded data and any error messages generated during the flight The downloaded data can also be saved as a data file which can then be easily opened in Microsoft Excel or similar software The data capture rate is also adjustable and can be set to 5 different settings The recorder automatically adjusts this rate depending on how fast the parame ters that are being recorded are changing When the airplane is performing turns or loops the capture rate will be greater than when the airplane is stationary on 62 the ground The default capture rate is 4 Hz which is intended to give reason able resolution and recording time The recording time depends on the number of parameters being recorded the capture rate and how quickly the parameters change The flight data recorder was used to record the pilot inputs while using the test set up Although only two inputs were recorded the flight data recorder can record up to four inputs To record these inputs Y
98. w G Earl and Raffaello D Andrea Real Time Attitude Estimation Techniques Applied to a Four Rotor Helicopter In Proceeding of the 43rd IEEE Conference on Decision and Control 2004 E B Nice Design of a Four Rotor Hovering Vehicle Master s thesis Cornell University 2004 37 38 39 40 41 42 43 44 45 46 47 48 49 50 l 52 53 54 59 56 105 http www systron com November 14 2005 Samir Bouabdallah Andfe Noth and Roland Siegwan PID vs LQ Control Techniques Applied to an Indoor Micro Quadrotor In Proceedings of 2004 IEEE RSJ International Conference On Intelligent Robots and Systems 2004 http www xsens com November 14 2005 P Castillo A Dzul and R Lozano Real Time Stabilization and Tracking of a Four Rotor Mini Rotorcraft In IEEE Transactions on Control Systems Technology volume 12 pages 510 6 July 2004 http www polhemus com fastrak htm November 14 2005 Gabe Hoffmann Dev Gorur Rajnarayan Steven L Waslander David Dostal Jung Soon Jang and Claire J Tomlin The Stanford Testbed of Autonomous Rotorcraft for Multi Agent Control STARMAC In Proceedings of the 23rd Digital Avionics Systems Conference 2004 PIC18F8720 Data Sheet 2004 Paul Horowitz and Winfield Hill The Art of Electronics Cambridge Univer sity Press 2nd edition 1989 http www ccsinfo com July 1 2005 Angular Rate Sensor ADXRS150 Data Sheet 2004 ADXL210E Low Cost
99. ween the two motors on the pitch and roll axes The yaw rate can be more difficult to control than the pitch and roll rates because the mo ment created by the difference in propeller torques is smaller in magnitude than 96 Yaw rate degrees second 80 Time seconds Figure 5 11 A graph showing the yaw rate in degrees per second of the quadrotor during a flight the moment created by the difference in propeller thrusts resulting in less control authority for the yaw rate than for the pitch and roll rates 5 3 3 Euler angles during a flight Using the angular rates saved during the same quadrotor flight that was described in section 5 3 2 the Euler angles of the quadrotor were calculated after the flight using equations 5 1 5 3 59 P tand Qsind Rcos 5 1 6 Qcos Rsin 5 2 De Qsing Rcos 5 3 cos O 97 In equations 5 1 5 3 P Q and R are the roll pitch and yaw rates measured by the gyroscopes and 6 and w are the time derivatives of the Euler angles 0 and w The Euler angles were assumed to have a value of zero at the beginning of each flight and equations 5 1 5 3 were numerically integrated to calculate the Euler angles of the quadrotor during flight Figure 5 12 shows the roll angle recorded during the quadrotor flight This Phi degrees Time seconds Figure 5 12 A graph of the roll angle phi of the quadrotor during a flig
100. ynamics and Materials Conference 2002 http www cradleofaviation org exhibits jet quadrotor August 9 2005 http avia russian ee vertigo convertawings r html August 9 2005 Tarek Hamel Robert Mahony Rogelio Lozano and James Ostrowski Dy namic Modelling and Configuration Stabilization for an X4 Flyer In FAC 15th Triennial World Congress 2002 Tarek Hamel Robert Mahony and Abdelhamid Chriette Visual servo tra jectory tracking for a four rotor VTOL aerial vehicle In Proceedings of the IEEE International Conference on Robotics and Automation 2002 Marcus Aberg 4xFanSaucer Master s thesis KTH Signals Sensors and Sys tems Stockholm Sweden 2004 Ming Chen and Mihai Huzmezan A combined MBPC 2 DOF H controller for a Quad Rotor UAV In AIAA Atmospheric Flight Mechanics Conference and Exhibit 2003 http www rctoys com draganflyer5 php November 14 2005 Richard K Arning and Stefan Sassen Flight Control of Micro Aerial Vehicles In AIAA Guidance Navigation and Control Conference and Exhibit 2004 Jonathan M Roberts Peter I Corke and Gregg Buskey Low Cost Flight Control System for a Small Autonomous Helicopter In Proceedings of the 2002 Australasian Conference on Robotics and Automation 2002 E Altug J P Ostrowski and C J Taylor Quadrotor Control Using Dual Camera Visual Feedback In Proceedings of the IEEE International Confer ence on Robotics and Automation pages 4294 9 2003 Matthe

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