The University of Texas at Arlington Autonomous Vehicle Laboratory AUVSI Student UAV Competition TEAM AVL

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1 The University of Texas at Arlington Autonomous Vehicle Laboratory 2005 AUVSI Student UAV Competition TEAM AVL Student Team Enrico G. Pianori, Jon Paul Eisenring Venko Damianov Ryan Slater Amen Omoragbon Rolando Castilleja Faculty Dr. Arthur A. Reyes Computer Science and Engineering Dr. Atilla Dogan Mechanical and Aerospace Engineering Dr. Kamesh Subbarao Mechanical and Aerospace Engineering Dr. Brian Huff Industrial & Manufacturing Systems Engineering Michael Youngblood, PhD Candidate Artificial Intelligence

2 TEAM AVL: Journal Report Enrico Pianori 1, Jon Paul Eisenring 2, Venko Damianov 3 Ryan Slater 4, Amen Omoragbon 5, Rolando Castilleja 6 The University of Texas at Arlington, Arlington, TX ABSTRACT This paper describes the development, design philosophy, and implementation of a fixed wing Autonomous Aerial Vehicle to perform autonomous reconnaissance of a pre determined set of locations. The mission objective of the project is to simulate realistic reconnaissance missions performed by Autonomous Aerial Vehicles operating in a controlled autonomous flight mode. In addition, it is required that these unmanned radio controllable aircraft be launched, and under autonomous control navigate a specified course, use onboard sensors to locate and assess a series of man made objects, and possibly land under autonomous control. In this paper, architectures for system design, integration, and autonomous operation of an Almost Ready to Fly fixed wing aircraft, and safety are explored. The vehicle is tested by exhibition of proficiency in control over mission elements which include; autonomous takeoff and landing, autonomous control, waypoint navigation, and mission flexibility (the ability to change missions before and during flight). Safety features such as structural reinforcements, the ability to switch to manual control at anytime during the flight, and other engineering processes that improve safety are evaluated. In accomplishing these objectives, several issues such as airframe selection, method of autonomy, payload configuration, systems integration, and radio signal interference have been successfully addressed. Abbreviation AAV AGL AMA ARF CG GCS GPS GUI IPD Li Poly MP Ni Cad Ni MH PID TO USB Listing of Nomenclature Definition Autonomous Aerial Vehicle Above Ground Level American Model Academy Almost Ready to Fly aircraft Center of Gravity Ground Control System Global Positioning System Graphical User Interface Intelligent Pulse Decoding Lithium Polymer (battery) MicroPilot autopilot system Nickel Cadmium (battery) Nickel Metal Hydride (battery) Proportional, Integral, Derivative (control loops) Take Off Universal Serial Bus 1 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory 2 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory 3 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory 4 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory 5 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory 6 Undergraduate Student, Department of Mechanical and Aerospace Engineering, Autonomous Vehicle Laboratory

3 INTRODUCTION Over the past few decades, research and flight advances have been made which seek to remove the pilot from certain decisionmaking roles so as to expand the capability of aerial vehicles in otherwise hazardous or monotonous roles. With the introduction of Unmanned Aerial Vehicles (UAV), pilots have been removed from the cockpit as well. The development and use of Autonomous Aerial Vehicles (AAV) gives us the ability to gather information and/or data without risk to human life and without the need for constant control by the human operator. These platforms provide a functionality limited only by the capabilities of the specific airframe, control system, payload, and our imagination This technology has widespread military and commercial applications and the 3 rd Annual AUVSI Student UAV Competition, gives students the chance to work with this emerging technology. The UAV under consideration is required to be capable of autonomous flight using GPS coordinates, photo reconnaissance, and must do it all in a given time frame. This paper describes the development of a fully functional UAV that meets those requirements in the next few sections. MISSION REQUIREMENTS The aircraft is required to take off from a paved runway and climb to above 50 ft AGL either by autonomous or radio controlled means. It must autonomously navigate through a pre selected corridor to several GPS locations and photograph the ground in order to identify targets. Finally, the aircraft must land either by autonomous means or by radio control. The aircraft performance is evaluated based on accuracy of photographs, completion time of mission, and ability to stay within the bounds of the course. Extra value is placed on autonomous take off and landing. Aircraft Flight Requirements 1. Flight Duration: 20 minutes minimum 2. Take Off and Landing: 150 ft. with no obstacle. 3. Design vehicle Take Off weight: 14 lbs. max 4. There is no minimum or maximum speed. 5. Flight Altitude: Minimum 50 ft. AGL Maximum 500 ft. AGL AIRCRAFT SYSTEM DESCRIPTION Rationale: The focus of the competition is autonomous flight. Based on previous university experience, it was determined that to design and construct an aircraft for the mission would obstruct the ultimate goal of autonomous flight and would take away from the direction of the competition. The team s energy was instead redirected to system autonomy. Major Aircraft Part Descriptions a. Airframe: Based on the considerations mentioned above, off the shelf ARFs were reviewed due to their short build time, ease of implementation, integration, and reliable construction and flight performance. The ARF selected was a SIG Mfg. Kadet Senior because of its low wing loading, large interior volume, and ease of modification. The stock flying weight is lbs with the recommended engine and 8 oz fuel tank, leaving as much as 8 lbs for additional avionics and payload. Table 1: Senior Kadet Wing Characteristics Wing Area (ft 2 ) 7.92 Aspect Ratio 5.07 Leading Edge Sweep ( ) 0 Taper Ratio 1 Span (ft.) 6.33 Cord (ft.) 1.25 MAC (ft.) 1.25

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5 AGL board. The 0.6 oz., 1.7 inch diameter ultrasonic transducer is mounted facing down on the bottom of the port wing. The connection between the transducer and the board is shielded coaxial cable. Figure 2: AGL Board and Transducer c. GPS Antenna: The MP2028 g is fitted with a San Jose Navigation Inc. MK 4 Mini GPS antenna. The MP2028 g is equipped with an onboard GPS signal decoder, so the antenna need only be connected to the board to provide positioning and altitude information to facilitate autonomous navigation. This information is also relayed to the ground station for tracking purposes. Figure 3: MK 4 Mini GPS Antenna d. Airspeed Pitot Pressure Sensor: The MP2028 g calculates relative wind velocity through a Pitot tube extending from the leading edge of the starboard wingtip. A hose connects the interior of the tube to the MP2028 g board, allowing it to calculate and thus compensate for winds. e. Static Pressure Sensor: In addition to GPS data, the MP2028 g has a static pressure port to which a hose exposes the static pressure inside the aircraft to determine pressure altitude. This is compared to the GPS altitude in order to determine absolute altitude. f. Proportional, Integral, and Derivative Control Loop Gains: MicroPilot uses the PID loop system to monitor and control flight performance. These loops can be adjusted by making changes in the magnitude of their gains by way of HORIZON mp GUI provided by the MicroPilot Company. The PID loops consist of: Aileron from Desired Roll Elevator from Desired Pitch Rudder from Y accelerometer Rudder from Heading Throttle from Speed Throttle from Glide Slope Pitch from Altitude Pitch from AGL Altitude Pitch from Airspeed Altitude Roll from Heading Heading from Cross Track g. Servo Control Board: All control output from the autopilot is ultimately sent through the Servo Control Board, to which all control surface and throttle servos, and camera switches are attached. This serves as the mechanism through which the autopilot controls the plane and payloads GROUND CONTROL STATION (GCS) Ground Control Station Requirements: The GCS must be capable of direct communication with the AAV whether in autonomous or radio controlled flight. It was determined that in addition to the radio transmitter to control the AAV in takeoff, landing, or emergency situations, tracking and situation data acquisition capability must be present. Rationale: A system comprised of two way communication devices was collected and integrated to become capable of control, tasking, and monitoring of AAV and its systems. This was done using a programmable radio control

6 transmitter, a notebook computer and a pair of radios to communicate with the aircraft. In addition, proprietary software was put to use to facilitate the data transfer. Ground Control Station Description: The GCS consists of two entities; the Data and Avionics notebook computer and the Pilot Operated Remote Control Transmitter. The AAV operates in total autonomy between takeoff and landing. In flight, the AAV and GCS will communicate, via radio frequency transmitter / receivers, with two discrete communication systems using 900 MHz band radio modems and a 1.2 GHz band multimedia transmitter / receiver setup. In addition the 72 MHz band Pilot Operated Remote Control Transmitter can communicate with the receiver onboard the AAV. The GCS notebook computer can use two applications to communicate with the autopilot, the HORIZON mp graphical user interface software included in the autopilot purchase and HyperTerminal telnet immulation software to make real time adjustments to the onboard computer. Radio Control Hardware: The remote control transmitter and receiver is a Multiplex Royal Evo 9 channel transmitter and Mulitplex Mini DS IPD 9 channel receiver. These were chosen for their reliability, quality, and versatility (all channels on this particular radio system are user assignable). The computer system used in the Evo 9 is highly versatile. The large LCD display provides easy to read graphics and the control sticks offer adjustable spring tension and length. The transmitter provides automatic fail safe and information update in IPD mode when fail safe is triggered by a loss of signal. [T]he abbreviation IPD stands for Intelligent Pulse Decoding. The intelligence takes the form of a microprocessor which analyses the signals picked up from the transmitter, processes them (where necessary) and then passes them on to the servos. The received signals are not simply passed on directly to the servos, as with conventional FM/PPM receivers, but are checked for interference and validity. (Ref. 10) Figure 4. Multiplex Transmitter and Receiver a. Compaq Presario R3200 PC: The second hardware component of the GCS is a Compaq notebook PC with which data is exchanged via radio modem and multimedia receiver. The following software is used it interface with and monitor the avionics on the AAV. b. MP2028 g HORIZON mp Software: The MP2028 g includes the HORIZON mp for mission creation, parameter adjustment, flight monitoring and mission simulation. The HORIZON mp software offers a GUI for communicating with the MP2028 g. It acts as a setup tool for configuration of the MP2028 g. Its main function is to allow the user to observe and interact with the UAV while it is in flight or on the ground via the RS 232 cable provided by MicroPilot. In flight communication is done via 900 MHz radio modems.

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8 the transmitter. It operates at 1.2 GHz, which causes no conflict with the 900 MHz wireless modems or the 72 MHz Radio Controls and provides clear reception over long distances. specifications listed in Appendix IV. creased the receiver signal gain to 6 db This in Figure 8. Ajoka AJ 9200TN c. Lianyida Receiver RC100A: This multimedia receiver is connected to a custom made 3.5 ft antenna to boost sensitivity. The data from this device is processed by an analog to digital converter which communicates with the notebook computer via a USB connection. The real time video is viewed on the screen during the flight as the HORIZON mp GUI tracks the flight over a still aerial photograph. This is used as a backup in case the still camera misses the target. Video from the flight is captured and saved on the PC hard drive. Figure 9. Lianyida Receiver RC100A The 1 db stock antenna on this receiver provided limited range, even in line of sight. It was replaced with a custom 3.5 ft antenna, constructed as per amateur radio operator Figure 10. Custom Antenna and Stand PAYLOAD Requirements: To complete a reconnaissance mission, the AAV must be equipped with imaging equipment. This can include a still camera which is set to snap a picture a predetermined location, or a video camera which may also be set to turn off and on or can take video throughout the entire flight. Rationale: Both of the above options have their merits and disadvantages. A still camera tends to perform at a higher resolution than a comparably sized or priced video camera. However, if the timing of the capture is not accurate, the photo might miss the target. Conversely, a video camera can capture a stream of images as the aircraft passes over or near the target, so its chances of showing the desired object are greater. However, the image quality is compromised due to the lower resolution. To take advantage of both systems qualities, it was decided to install both video and still digital cameras. Should the camera miss the target, the video should make up for it. Payload Hardware Composition: a. Samsung Digimax A402 4 Mega Pixel Camera: The camera was chosen for image quality, ease of operation, and low cost. Further, the camera did not automatically shut itself off, but went into Suspend Mode

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10 caused the plane to pitch up at every increase in throttle, causing pitch instability. This non zero thrust angle was removed. Also, a quick refueling port and fuel filter were added to the system to increase reliability and ease of operation. b. Landing Gear: Another casualty of the additional weight was the landing gear. The single strut nose gear provided by the manufacturer was only meant to support up to around 8 lbs. It summarily collapsed on the first grassy landing. It was replaced by a double forked gear which provided more lateral stability and strength upon ground roll. Also, the main landing gear, which are constructed of 3 / 16 in wire caused the now heavy aircraft to bounce repeatedly even on the softest landings. This was remedied by stringing a steel wire between the wheel axles which allowed less spring like motion. c. Fuselage Structure: Three mid section fuselage ribs were structurally reinforced with 1 / 16 inch plywood in order to support the Micro Pilot and servo housing harness. The original manufacturer s servo tray was moved to a more aft position in order to allow more room for the electronics. A 3 inch by 3 inch opening was cut in the bottom mid section of the fuselage, 1 reinforced with a / 16 inch plywood frame and covered with a clear Plexiglas door to allow a viewing area for the still picture camera. The nine channel receiver for the manual radio control system was placed in the rear mid section of the fuselage on a 1 / 16 inch plywood mounting tray. d. Autonomous System: The autonomous MP system was enclosed in a small 1 / 16 inch plywood box and then into a 0.04 inch thick copper box. The enclosure was mounted via a quick release mechanism on two foam mounts in order to re duce possible vibrations and placed in front of the CG. The AGL signal generating unit was enclosed in a 1 / 16 inch plywood box over aluminum sheeting and then placed right behind the CG. The AGL piezoelectric transducer was placed on a ¼ inch balsa mounting box on the outer portion of the underside of the right wing. The Pitot tube was also placed on the outer tip of the right wing. The GPS antenna wire was shortened and placed over a copper plate on top of the windscreen. Six switches and charging ports were installed on the airframe in order to operate the appropriate electronics. e. Hard Wired Communications: One USB port was installed on the side of the fuselage to download the mission pictures to the ground station. An RS 232 data port was installed on the fuselage connecting to the communication port of the autonomous system. f. Software: During the course of the project, MicroPilot Company updated the operating system of the MP2028 g ten times leading to continuous learning curves. The most difficult part was learning the operational peculiarities of HORIZON and MP Hyperterminal. These included differences between specified manual instructions and actual operating instructions, as well as a proprietary programming code for tasking. g. Radio Interference: The interior of the aircraft, though considerable for a radio controlled plane, was still limited considering the plethora of components placed on board. This caused substantial interference between the electronic components. Extra care had to be taken to isolate boards, wires and antennae from the emissions of other components. The following are a sample list of modifications that were made: GPS antenna cable shortened Copper bracket supports and shields GPS antenna

11 1mm thick copper box surrounds MP2028 g board Radio modem box sheeted with 1 / 8 inch plywood and aluminum foil Receiver harness lengthened to isolate receiver from MP2028 g board Receiver mounted on 1 / 16 inch plywood and aluminum foil to isolate from radio modem Radio modem cable extension was shielded with copper tape along the entire length AGL box sheeted with 1 / 16 inch plywood and aluminum foil TESTING Components: Testing of the aircraft continuously evolves as new features are brought online. The aircraft s main control surfaces and sensors were tested in parts: on the bench, and during piloted, semiautonomous, and autonomous flight. The bench testing ensures that each control is actuated properly, and has the correct degree of motion to accomplish the task in flight. The above ground level (AGL) sensor, and the global positioning system (GPS), were also calibrated and tested on the bench to ensure nominal behavior. Appendix VI provides a sampling of errors encountered during systems testing, their possible causes, and solutions. These and many other issues had to be addressed prior to attaining radio controlled and fully autonomous flight. Though some problems stood out than others, all had to be approached with equal care and methodically so that the next problem could be remedied. Autonomy: It took a while to achieve autonomy due to component conflicts caused by radio interference. The first autonomous flight was conducted on April 8, 2005 at Benbrook Lake, TX, a local R/C flying site. The initial autonomy was conducted utilizing two waypoints specified by X and Y components with respect to an ori gin. The aircraft followed the input path, yet the controls needed considerable fine tuning. In the following months, a systematic approach was pursued in order to optimize autonomous performance. The inner PID loops controlling bank, pitch, roll, and heading deviation correction needed to be adjusted over the next flights. Gradual 10% adjustments were input into each loop gains until desired effects were achieved. Gradually, the project progressed to more sophisticated command programming and tasking. Later systems were incorporated such as automated picture taking based on GPS coordinates and real time video. As of the submission, more than 15 autonomous flights have been achieved. SAFETY Safety is an important part of engineering design. Considerable thought and planning has to go into ensuring equipment, personnel, and software are well protected before, during and after missions. This is also especially true during implementation and troubleshooting of equipment. This project began in September of 2004 and safety was of the utmost concern throughout its completion. This was addressed to the participating students at the beginning of the project and throughout the daily operation of the equipment in the Autonomous Vehicles Laboratory. The methods included check lists, lab operational safety rules, and safety redundancy procedures which were strictly enforced to prevent or minimize chance of injury. Safety considerations have been characterized in two following sections: Procedures for Accident Avoidance and Hardware Handling Procedures for Accident Avoidance The airplane is de fueled after each flight. Two team members are involved in the starting of the airplane s engine. One secures the plane while the other starts the engine. Prior to each flight a range check of the transmitter and the receiver is performed ac

12 cording to the manufacturer s suggested procedure. All flights are conducted using a skilled pilot covered by AMA insurance. No spectators or operators are allowed to stand in front or to the side of a rotating propeller. All team members must remain behind the airplane while the engine is in motion. All autonomous fine tuning flights are conducted at a minimum altitude of 500 ft. This altitude provides enough time to safely transition from autonomous to manual flight in case of emergency. Also, in the event of an engine failure the conservative altitude provides the pilot with a better chance of safely landing the aircraft than a low altitude. Hardware Handling The tips of the propeller are painted white so that its boundary is seen while in rotation. All battery charging ports and switches are placed either under or on the side of the fuselage opposite to the engine s exhaust port in order to prevent possible short circuiting due to fuel and oil emissions. The Lithium Polymer battery charging port has a distinctive mark in order to distinguish it from the other battery ports. This is done to prevent improper charging which could result in fire or a possible explosion. Fuel is stored in fire proof cabinets. All batteries on board the aircraft are checked for proper charge prior to each take off in order to prevent loss of control or communication during flight. A redundant voltage monitoring switch was installed for the MicroPilot board. All onboard wires were shielded with copper tape and all onboard electronics are isolated by metal sheets to decrease radio frequency emissions that could po tentially lead to possible interference with other electronics. All software files and programs pertinent to the autonomous project including the operating system of the ground station were backed up and saved. This gives us the ability to retrieve the information in case of loss or damage of the originals. Conclusion Many considerations must go into the design of an autonomous aerial vehicle program, from aerodynamics, and structures to electronics and communications. It would seem that the largest obstacles to overcome in a project such as this involve coaxing the various systems to interact in a usable manner. These are not limited to the wood, metal, epoxy, and silicon that go into the AAV itself, but also to the people who must deal with the equipment. Great safety precautions must be upheld to ensure no harm comes to those who come in contact with the project. These prevailing issues must be addressed before any autonomy can be attained. Once a harmonious balance between isolation and communication is reached among the various components, the system can be expected to perform in a manner consistent with its intent. This was shown as the modified ARF completed each autonomous flight along prescribed plans. Acknowledgements Special appreciation goes to the MicroPilot Company for the discounted MP2028 g board used on the project. Also to Reflex XTR for donating a computer R/C flight simulator to use for pilot training. Additional thanks goes to Multiplex giving the team a wonderful dealo on their radios and other electronics. References 1. MicroPilot, MP2028g Installation and Operation nuals/manual MP2028.pdf

13 2. MicroPilot, MP2.4 Radio Modem Installation and Operation MicroPilot, Working with radio modems MicroPilot, Electronic compass user guide MicroPilot, Installing and using analog to digital convertors MaxStream, XStream Wireless OEM RF Module xstream/module/manual_xstream OEM RF Module_v4.29.pdf 7. O.S. Engines, 61FX Owner s Instruction Manual SIG, Kadet Senior ARF Assembly Manual Multiplex, Royal EVO Instructions Multiplex, Operating Instructions RX 9 / RX 12 SYNTH DS IPD receivers. 11. Samsung, Digimax A402 User s Manual Engine Specifications O.S. Model 61 FX (OSMG0561) Displacement (cu in) Bore (in) Stroke (in) RPM 2,000 17,000 Output (HP@rpm) 16,000 Weight (oz) 19.4 Recommended Props 11x8 10, 12x7 11, 12.5x6 7 Flight Characteristics of UTA AVL UTA AVL Cruise Speed (mph) 40 Max Speed (mph) 70 Cruise Altitude (ft) 500 Max TO Weight (lbs) 12 Empty Weight (lbs) 10.5 Range (mi) 5 TO Distance (ft) 60 Landing Distance (ft) 60 Wing Loading (lbs/ft 2 ) Appendices Appendix I: Airframe Characteristics Aircraft Parameters SPECIFICATION UNITS Aspect Ratio 5.07 Wing Area 7.92 ft 2 Wing Span 6.33 ft W/S 0.66 lb/ft 2 Fuselage Length 5.33 ft Fuselage Width 0.42 ft Weight Take Off 12 lbs Weight Landing 11.5 lbs

14 3 7 / / / / / / / / / / / Max Deflection / / / 4 Max Deflection 12 1 / / / 8 or 2 5 /

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16 Appendix IV: Combined Specificaions for Specialty Antennae Custom Antenna Antenna San Jose Navigation Inc. Model: MK 4 Type Mini GPS Receiver Multimedia Signal Receiver Frequency MHz 1200 MHz Size 1.34 x 1 x 0.4 inches LMR 400 Coaxial Cable at 43 inches in length Gain +5 db +6 db

17 4 MP Samsung Digimax A402 Digital Camera Appendix V: Interaction between aircraft components. Jomar E Switch Micropilot Servo Control Board 5 Num Servos 32 San Jose Navigation MK 4 Mini GPS Antenna Jomar E Switch Micropilot MP2028g Auto Pilot SensComp Above Ground Level Sensor and Board Aircraft Control Surfaces and Throttle 6V Ni MH Battery 11.1V Li Poly Battery 8.7V Ni MH Battery 6V Ni MH Battery Ajoka AJ 9200TN 1.2GHz Wireless Video+Audio Transmitter JMC Electron 208C 1.2 MP Video Camera MaxStream 9XStream 900MHz Wireless OEM RF Module Radio Modem Multiplex Mini DS IPD 9 Channel Radio Control Receiver Aircraft Systems Ground Systems Lianyida RC100A 1.2GHz Wireless Video+Audio Receiver 12 V Battery MaxStream 9XStream 900MHz Wireless OEM RF Module Radio Modem Compaq Presario R3200 Laptop PC Ground Control Station Multiplex Royal Evo 9 Radio Control Transmitter

18 Appendix VI. Sample Troubleshooting Chart Problem Possible Cause(s) Solution Positive pitching Negative thrust angle Change the thrust angle to 0 deg moment Radio frequency interference GPS signal is causing an interference Locate the GPS transmitter away from the micropilot in a position in which its wires do not cross the micropilot or servos. Malfunctioning Micropilot. Malfunctioning Radio Transmitter. Airplane making shallow bank turns. Radio waves emitted from wires are causing interference. Radio frequencies from the modem are causing interference. Radio frequency interference. Vibration from the engine is causing an interference Transmitter is out of tune. The PID term roll from heading for is lower than required. Shield wires with copper tape with gap in the shielding and connect all the negatives to a common ground. The same as GPS signal interference. Cover micro pilot with 1mm thick copper box to isolate micropilot from frequencies and follow above solutions. Mount the engine on vibration reduction mounds. Send to the manufacturer for tuning. Increase PID term in order to get required bank angle.