Lightweight Fixed Wing UAV

Transcription

1 Lightweight Fixed Wing UAV Cindy Xiao, Rijesh Augustine, Andrew Jowsey, Michael G. Lipsett, Duncan G. Elliott University of Alberta Abstract The University of Alberta Aerial Robotics (UAARG) is a student vehicle project in the Faculty of Engineering. Funded from both Shell and the University, UAARG designs and builds custom unmanned aerial systems (UAS). Last year s redesign of a lightweight, versatile, fixed-wing unmanned aerial vehicle (UAV) has proven to be a unique and viable system. UAARG has continued this design by further improving its payload, electronics, airframe, and flight operations. This fully autonomous UAV utilizes onboard electronics to perform real-time image capture and transmission via Wi-Fi link. Extensive tests and design reviews have been conducted with UAARG s experienced R/C pilots, club executives, and mechanical/computer engineering professors to ensure that UAARG delivers AUVSI mission requirements with excellence. This report summarizes the designing, building, and testing that has been devoted for a successful year at AUVSI Seafarer Chapter s 13th Annual Student UAS (SUAS) Competition. Table of Contents Introduction System Overview Airframe Design Airframe Customizations Weather Requirements Budget Avionics Power Systems Communications Autopilot Imaging Achievable Competition Objectives Safety Considerations and Approach Safety Design Features Flight Protocols Equipment Firmware Failsafes Conclusion References

2 Introduction UAARG has further refined and tested last year s design to achieve the mission requirements of the AUVSI Seafarer Chapter s Student UAS (SUAS) Competition. Our system design continues the objective of designing a lightweight, cost-effective, and compact UAV. This UAV has a wingspan of 1.8m and weighs only 2.9kg, including its two lithium polymer batteries. Its modular avionics board contains nearly all of the necessary autopilot, R/C, imaging, and communications hardware, providing an efficient assembly procedure and fast troubleshooting. The UAV is designed to fly autonomously through a series of adjustable waypoints, while images are captured onboard, downloaded via a Wi-fi connection, and analyzed on the ground. We are able to provide real time geo-referenced images, allowing us to update our flight plan depending on unexpected targets and scenarios. UAARG plans to accomplish: Autonomous Flight, Target and QR/C Localization, Classification, and Decoding as our primary mission tasks. In addition, the following secondary tasks will be attempted: Actionable Intelligence, Off-Axis Standard Target, Emergent Target, SRIC, Interoperability, and the Search, Detect, and Avoid task. Figure 1: System Block Diagram University of Alberta - UAARG 1

3 System Overview Airframe Design Figure 2: HobbyKing EPP FPV Airframe The airframe chosen was one originally designed by Hobbyking for FPV flying. The large FPV compartment in the front allows extensive cargo space, considering the plane s compact design. It is inexpensive ($69.99 US) and is made of a durable expanded polypropylene (EPP) foam. This allows the overall frame to remain lightweight and easy to retrofit for new avionic components. Furthermore, EPP foam is able to absorb high impacts with little damage or deformation. Thus, maintenance costs and downtime are low after failed flight tests. The large tail boom is ideal for balancing out the weight of additional sensors and equipment within the cargo space. The plane has shown that it is capable of a take off weight up to 3kg, allowing us to carry a heavy payload without sacrificing much flight performance. Overall, the aerodynamics of the aircraft are very forgiving and require very little pilot training. University of Alberta - UAARG 2

4 Table 1: UAARG 2015 Weights and Balance s Flight times vary depending on the weather and payload used in flight. At a weight of kg and using a 5000mAh LiPo battery, our initial design was capable of flying from minutes in clear weather. With the current weight of 2.89 kg, the UAV capable of flying minutes using two 5000mAh LiPo batteries. Airframe Customizations Multiple modifications were made to improve the structural integrity of the stock airframe and to allow the incorporation of various electronic components. Improvements to the airframe includes high failure point reinforcement, fast assembly design, and flight performance repeatability. Cut-outs were made in the wings, fuselage and tail to install sensory and communication components that are essential for UAV operations. An extensive design review was conducted amongst club members and faculty advisors to ensure that structural integrity was not lost in critical structures. Improvements such as a new motor mount, tail boom reinforcement, and wing covers were added to eliminate failure points in the stock airframe. On hard landings, the original basswood motor mount would fracture and detach due to thin wood and low quality adhesives. Furthermore, the long and weight-balancing tail boom snapped due to its inherent high stress zone near the base of the fuselage. As seen in Figure 3, the motor mount was fortified by using a thicker basswood and adding thin wooden extrusions that puncture into the fuselage. A balsa wood rod is now placed within the tail boom and a thicker carbon-fiber tube envelopes the fracture point. These failure points were quickly determined and resolved during early payload flight tests. University of Alberta - UAARG 3

5 Figure 3: Failure-Point Corrections Figure 4: Airframe Improvements Flight performance was optimized in subsequent flight tests. Centre of gravity was no longer ideal after installing the autopilot and imaging electronics within the on-board cargo space. In response, center of gravity was analyzed using Table 1 above and corrected by attaching a servo mount along the plane s tail-boom (Figure 4, left). The mount is constructed out of a carbon fibre sheet and is secured with epoxy. This also allows for more weight to be placed in the cargo space and less stress on servo s control arms. Stress on all servos were reduced by bending control rods to a specific angle. The vertical stabilizer was also improved with an extension that increases surface behind the propeller (Figure 3, left). Modifications to the airframe were also made to simplify operations and decrease deployment time. A detachable tail boom was constructed to improve the transportation of the aircraft without increasing setup time substantially (Figure 4, centre). To prevent changes in the airframe structure between flights, wing struts (Figure 4, centre) and reinforcements for the servo control rods were installed; this greatly reduced the need for re-trimming the aircraft during test flights. The foam body of the aircraft was modified to accommodate hardware components. In the nose, a hole was cut to allow the 900 MHz telemetry antenna to stand upright. In both the fuselage and left wing and holes were cut to embed the R/C satellite receivers. Slices were made in the foam to secure their antennas orthogonally to improve R/C reception. The Wi-Fi adapter is also mounted to the wing. The adapter has a fairly low profile, so it does not greatly degrade the aerodynamics of the wing. Figure 5: Embedded Wifi Module The wings also contain several major sensory components. The airspeed pitot tube is placed so that it meets the air 5cm from the leading surface of the left wing. This ensures that the static port is not at a high pressure system; the port is connected to the actual sensor via rubber tubes. A Canon Powershot A2400IS camera is embedded within the right wing a secured using thin sheets of basswood and University of Alberta - UAARG 4

6 t-nuts. Once again, its mount on only extrudes 1-2mm from the wing, thus maintaining its aerodynamics. Weather Requirements Operations will be carried out during daylight hours using Visual Flight Rules (VFR). The weather criteria to determine whether the flight-testing may proceed are listed below. Table 2: Weather conditions required for flight Budget One of the primary goals of the current system was to develop an inexpensive UAV that duplicated the functionality of our older, more expensive Senior Telemaster system. Parts were primarily sourced from reputable online vendors, with customer reviews considered to ensure that sourced parts are durable and mission adequate. In addition to meeting AUVSI mission specifications, compatibility with the Lisa/MX v2.1 and our existing software was also considered in the purchasing decision for many of these devices. Table 3: Complete UAS budget Air Frame Imaging Autopilot Ground Station EPP-FPV Frame $90 Odroid Processor Board $70 Lisa/M (v2.0) $210 Imaging Laptop N/A Motor $30 Imaging Camera $100 GPS $20 Autopilot (Paparazzi) Laptop N/A Servos/ESC $60 2 USB Wi-Fi Cards $40 XBee $40 XBee $40 Battery (2) $100 Power Supply $15 Power Supply $15 High Gain Wi-fi Antenna $15 Propeller $10 Cables/Connectors $30 Wi-Fi Router $100 Cables/Wires/ Connectors $30 Battery Charger $150 Total: $1165 University of Alberta - UAARG 5

7 Avionics Figure 6. Layout of all aircraft avionics systems The avionics of the UAV are designed in a highly modular fashion. The majority of the avionic hardware is laid out on a cut out perforated board. Components are primarily secured to this avionics board using M3 screws, spacers and bolts. This allows components to be swapped on and off with ease without disrupting other hardware. The laid out design also allows for quick and easy troubleshooting, as all components are visible and easily accessible. The avionics board is designed to slide easily into the front of the plane, as seen at the top of Figure 6. There are two primary contact points at the front and back of the board that are used to ensure alignment of the avionics board with the fuselage; the board is shaped to the fuselage at these points. Pressure from the batteries and fuselage wall provide lateral stability to the avionics board. Components on the avionics board include power switches, autopilot computer, onboard imaging computer, telemetry radio, logic level converter and switching power regulators (Figure 7). A printed circuit board (PCB) was designed for additional modularity. The PCB is used for power distribution for University of Alberta - UAARG 6

8 avionics hardware and telemetry data communication. The PCB houses two Murata 5V 2A switching regulators, the Digi Xbee Pro telemetry radio, and a logic level converter. The logic level converter pulls the telemetry data from the autopilot computer from a 3.3V logic level to a 1.8V logic level that the imaging computer is rated for. The avionics board also houses 4 switches used to fully power on the plane. Two of the switches are used to power on/off the autopilot board and the onboard imaging computer. The remaining two are used to regulate power flow to the servos and the motor. All connections are at the back of the avionics board. This includes USB connections, autopilot module connections, servo connections, and power connections. Figure 7: Avionics board layout Peripheral hardware that connects to the avionics board include two DSM2 Orange RX satellite receivers, an airspeed sensor, a current sensor, a GPS sensor, 2 Wi-Fi modules, a camera, and an ESC. The autopilot computer is the Lisa/MX V2.1 (Lisa), an STM32 microcontroller based board that is compatible with the Paparazzi autopilot system. The Lisa is capable of outputting up to 8 PWM signals to control up to 8 servos. Radio Control (R/C) data is received via satellite receivers that directly interface with the Lisa; up to two satellite receivers may be used. This allows for improved R/C reception at longer ranges and varying attitudes. The Lisa has multiple built in analog-to-digital converters (ADC). This allows for analysis and processing of data from various sensors and incorporating the information into autonomous navigation and geo-referencing. A 10 degree of freedom (DOF) Aspirin Inertial Measurement Unit (IMU) is integrated as part of the Lisa, limiting the need to have additional onboard sensors. The IMU has a 3 axis gyroscope, 3 axis accelerometer, 3 axis magnetometer, and a barometer. All these sensors come pre-calibrated, but custom calibrations can be made. For accurate geo-referencing and autonomous navigation, the magnetometer has to be calibrated for variation, deviation and current generated magnetic fields. The gyroscope, accelerometer and magnetometer provide additional attitude and orientation data. The barometer provides altitude data. All these sensors not only help the aircraft fly autonomously, but are also crucial for accurate geo-referencing. Additional components that interface with the Lisa are the airspeed sensor, current sensor, and GPS module. An Eagle Tree airspeed sensor provides airspeed by measuring pressure differences across a pitot tube mounted in the wing. This data is used in autopilot control loops to help the UAV fly in windy conditions. A current sensor inputs real-time current draw. This is not only used University of Alberta - UAARG 7

9 for energy calculations, but also for magnetometer calibration. The GPS module, a Ublox NEO-6M mounted in the UAV s tail, is responsible for determining the plane s current location in 3D space to 5m of accuracy. The onboard imaging computer is an Odroid U3, a single-board Linux computer. This computer has a 1.7 GHz quad core processor and 2GB of RAM; its compact size and high performance allows for easy integration into the UAS. The Odroid is responsible for capturing images, tagging images with autopilot data and transmitting images to the Ground Imaging Station (GIS), as well as performing the data transfer required for the SRIC task. Image capture is performed by a wing-mounted Canon Powershot A2400IS. Images are then transferred to the GIS via a high power Alfa n Wi-Fi module. A second n Wi-Fi module interfaces with the Odroid; this is used exclusively for the SRIC task. Power Systems The plane is powered by two 4-cell lithium polymer batteries, capable of providing an operating voltage of 14.8V to 16.8V. Batteries are connected in parallel; each battery has a capacity of 5000 mah. A 45A Turnigy electronic speed controller (ESC) is used to convert the DC to three phase AC power to drive the primary motor used for flight. This brushless motor runs at 750kv, and in turn drives a 10x7 slow flyer prop. This setup provides 40 minutes of flight time at a cruising speed of 15m/s. The ESC also contains a battery eliminator circuit (BEC) which outputs 5.5 VDC. This rail is used to power all the servos and runs through the switch on the avionics board. The batteries are also used to power the avionics board. The onboard electronics either operate at 5V or 3.3V. To generate 5 V, two Murata 5 V, 2 A switching regulators are utilized. They provide high efficiency buck conversion, generating little waste heat. The 5 V are directly provided to the autopilot control board and the onboard computer. The 3.3 V is obtained through buck regulators on the autopilot control board. Figure 8: Power Distribution Schematic University of Alberta - UAARG 8

10 Due to weight and space constrictions, no redundant power supply was implemented. Communications The UAS has five different communication links during flight. These include three bidirectional links, including autopilot telemetry/control and 2 Wi-Fi links, and two unidirectional links, GPS and R/C. The main control link is R/C. The safety pilot handles a 2.4GHz Spektrum Transmitter. This links to two onboard satellite receivers, which communicates to the Lisa. The information transmitted is capable of directly controlling the aircraft's flight by manipulating its control surfaces. It is also capable of engaging and disengaging the autopilot. The autopilot telemetry/control link uses the 900MHz spectrum. This spectrum allows for longer ranges, while still allowing for high data transfer rates. Two identical Digi Xbee Pro's work together to form bilateral communication with the plane and GCS. This link is used to send real-time telemetry from the plane to the GCS. This provides constant status and location of the UAV. The GCS can also send data and commands to the aircraft via this link. This includes adjusting different autopilot gains in flight, and modifying the aircraft's autonomous flight plan. The GPS link is vital for autopilot flight and geo-referencing; the onboard GPS has an accuracy of 5m. There are two Wi-Fi adapters on the UAV. The primary adapter is used to allow communication between the GIS and the Odroid. This allows for real-time image transfer from the UAV as well as sending commands to the Odroid. The secondary Wi-Fi adapter is used for connecting to stationary Wi-Fi enabled servers on the ground and retrieving data. Autopilot The system is based on the free and open source Paparazzi autopilot system. This is an open-source autopilot system, allowing it to be altered to meet design requirements. Paparazzi has a big community, with many researchers and hobbyists. It is very easy to learn and implement. There are multiple hardware vendors that produce products compatible with Paparazzi. The autopilot system is able to autonomously control the aircraft, display aircraft position and status at all times, and perform failsafe procedures. The software has two distinct parts, the GCS and the onboard firmware. Paparazzi is prepared for each UAV and mission by modifying XML configuration files. An airframe file is used to define all the hardware of the UAV, autopilot gain parameters, and calibration coefficients. A flight plan file contains mission boundaries, waypoints, navigations routines and failsafes. Once these files have been configured the GCS is then used to generate and upload the firmware to the Lisa. The GCS is then used to establish a data link server and process 2-way communication with the Lisa. University of Alberta - UAARG 9

11 Figure 9: Block diagram of autopilot system components During a mission the GCS displays the current navigation routine the UAV is following as well as telemetry data. A map is available in the GCS to show the location of the plane and waypoints and change the location of waypoints in 3D space. The GCS is also able to switch the UAV to a different navigation routine at any time, involving a predefined block of maneuvers. Autonomous navigation is achieved by using an inertial navigation system (INS) and PID control gains on the Lisa. Raw data from the 10 DOF IMU, GPS and Airspeed sensor is filtered to determine the current state of the UAV. This includes speed, attitude, and altitude. The current state of the UAV is compared to the desired state and PID control loops are used to adjust the control surfaces effectively. When changing to the desired state, each control loop must exhibit positive stability and not cause the UAV to exceed its technical limitations. In order to do this, each control loop has to be tuned independently for its proportional, integral, and differential coefficients. Tuning is done in flight with an experienced pilot at the controls. Navigation routines are defined before flight that will isolate specific control loops. These navigation routines are initiated and the response of the UAV is recorded and contrasted with the desired response. Basic loops for stabilized flight can be a part of more advanced loops for autonomous navigation, so they are tuned first. Figures 10 and 11 below show graphs of the UAV s pitch and roll during a stabilized flight guided by a safety pilot. The desired angle from the autopilot s stabilization loop is plotted against the measured angle from the IMU in both graphs. University of Alberta - UAARG 10

12 Figure 10: Desired Pitch vs. Actual Pitch during a stabilized flight Figure 11: Desired Roll vs. Actual Roll during a stabilized flight Imaging The imaging and networking subsystem is responsible for capturing images and image data from the UAV, relaying it to the ground, and processing that data to obtain target information. There are two major components to the system: - The onboard imaging computer. Responsible for image capture, data tagging, and relaying data to the ground imaging station. - The ground station computer and Wi-fi router. Responsible for initiating image capture, receiving the image data, and marking target locations. University of Alberta - UAARG 11

13 Figure 12. Block diagram of the imaging system The onboard imaging computer is an Odroid U3. This is a single-board computer with an ARM architecture, running a server version of Ubuntu We chose a Linux-based single-board computer for this task due to the availability of image processing libraries and the need to interface with and control many different types of hardware. The Odroid was chosen due to its high performance and low price relative to other single-board computer options on the market at the time (the original Raspberry Pi, the Pandaboard, the Beaglebone). We have one ground-facing camera onboard the aircraft, a Canon Powershot A2400IS. This is a consumer point-and-shoot camera that we have modified with the Canon Hack Development Kit (CHDK), a free and open source firmware upgrade for Canon cameras. CHDK allows us to set shutter speed, ISO and aperture. Additionally CHDK provides custom scripting, remote shooting and download from the camera. A consumer point-and-shoot is a cheaper solution than a specialized scientific imaging camera, but at the same time give us better quality and exposure control than a lower cost solution like a typical webcam would. In order to control the 3 processes of capturing, tagging, and transmitting images taken from this camera, the Odroid runs a custom multithreaded program, called Waldo. The Odroid receives telemetry data through its UART port from the autopilot. Waldo decodes this data and extracts the information about the aircraft s position and orientation, which are required for georectification of the image. Waldo then interpolates this data when the image capture is triggered and tags the resulting image with it. Images are then transmitted to the ground over the Wi-fi link, in parallel with the capturing and tagging processes. Waldo is initiated remotely from the ground imaging station; a user is able to monitor the status of image processing and transmission from the ground station. However, Waldo also runs regardless of whether a Wi-fi connection exists between the aircraft and the ground station; it saves images into a local buffer when link is lost and attempts to re-transmit images upon regaining a Wi-fi link, ensuring its reliability. The Ground Imaging Station, which receives and processes these captured images, consists of a laptop computer and Wi-fi router. The Wi-fi router is configured as an access point to connect both the Ground Imaging Computer and the Odroid on a common wireless network. Image georeferencing is done here, via another custom program called Pigeon. Our system is designed so that a human operator performs target recognition; Pigeon allows the operator to easily browse through images University of Alberta - UAARG 12

14 and mark the position of targets within the image. Pigeon is then able to take those coordinates in addition to the received position and orientation data, and georectify the position of the marker. Target properties, such as shape, orientation, and color, are also entered by the operator upon marking the image. Pigeon also has various export functionality. It is able to export target location via CSV and KML, for easy data processing. Figure 13. The Pigeon ground imaging station GUI. Test image shown, with visible 4 x4 square blue target with 2 wide red letter T oriented north In order to develop a strategy for covering the search area, we have performed calculations that take into account the following properties of our system and the environment. The angle of view produced off the camera-lens combination The effect of camera shutter speed The size of the search area The amount overlap desired on each image From these, we calculate the values of parameters that we can control: Rate of image capture The amount of mission time to spend inside the search area The nominal velocity and altitude for flight, configurable via Paparazzi The number of flight passes to make over the width of the field A spreadsheet with an example calculation is shown below with our Canon Powershot A2400IS. This calculation is performed with an example cruising altitude of 70m and speed of 15 m/s, and shows that we are able to cover a first sweep of a 1km x 0.7km search area in under 10 minutes with ~188 University of Alberta - UAARG 13

15 pictures. This is with a required delay of approximately 3 seconds between images, well within the capture rate achievable by our camera s shutter speed settings and Waldo. Table 4. Example search area calculations Achievable Competition Objectives 1. Autonomous Flight UAARG s aircraft will be capable of performing autonomous waypoint-guided flight. Takeoff and landing will be performed manually. A flight plan containing the provided waypoint sequence, University of Alberta - UAARG 14

16 search area boundaries, a planned flight path within the search area, and no-fly boundaries will be prepared prior to the mission. This flight plan is displayed on the Ground Control Station computer. Once takeoff has been achieved, the aircraft shall navigate autonomously through the waypoint sequence and through the search area. As the aircraft navigates through the airfield, the users and judges will be provided information via the GCS screen regarding its position, speed, and orientation. Images will be taken continuously as the aircraft flies above the waypoints and search areas; waypoints within the search area may be added or moved by the GCS operator in response to detected targets within these images. The autopilot will respond appropriately to unpredictable scenarios such as strong winds, loss of R/C link and loss of telemetry link. 2. Search Area Task Image capture is initiated upon takeoff. The onboard imaging software, Waldo, performs image capture and image transmission in parallel. One operator at the Ground Imaging Station is dedicated to monitoring received images for targets and recognizing target characteristics. This is done via our ground station imaging software, Pigeon, which georectifies marked targets using position and orientation data received from the UAV. 3. Actionable Intelligence If the Wi-fi link is lost, Waldo will continue to capture images; it will attempt to automatically reestablish connection and continue to transmit image data once the Wi-fi link is reestablished. This method allows analysis to begin before landing. As a result, target characteristics are discovered well in advance to mission deadlines. Targets of interest can be further examined once discovered. 4. Off-axis Target We plan to perform a high-altitude roll in order to perform this task. A waypoint in the flight plan near the no-fly boundary will be set up to achieve this. 5. Emergent Target Task The coordinates of the emergent search area shall be programmed into the GCS when it is received. One search pass shall be performed over the area at the same cruising altitude and speed as within the main search area. Once the emergent target s location has been found at the Ground Imaging Station, its waypoint shall be programmed into the GCS; a second flight pass will then be performed at a lower altitude and/or a zoomed camera lens. 6. SRIC Task We have one Wi-fi module dedicated for communicating to the SRIC server, and plan to circle autonomously about the SRIC server point during the mission. However, further testing is required to develop our strategy for this task. 7. Interoperability and SDA Task The Paparazzi autopilot system s ground software components - the GCS, the telemetry link University of Alberta - UAARG 15

17 data, and the control uplink communicate with each other via a common message bus (the Ivy bus). All telemetry information received from the aircraft is broadcast onto the Ivy bus. Additional modules may be written to receive messages from this software bus and to broadcast messages onto it, allowing points in the GCS to be updated automatically. We plan to at a minimum read the UAV position from the Paparazzi Ivy Bus and transport this data to the competition server, as well as download object locations for the SDA task and display them in our GCS. Safety Considerations and Approach Safety is important to both mission success and UAARG members. UAARG has implemented the following three types of safety considerations to ensure no incidents occur during competition: These techniques have been continuously tested and will be presented to competition organizers during the Flight Readiness Review (FRR). Safety Design Features Manual Power Toggling Power toggle switches are conveniently installed in the nose of the airframe to provide easy manual power-down capabilities and prevent accidental shorting during troubleshooting on the avionics board. Figure 14: On board Switchgear Kill Switch A kill switch is installed in addition to the power switches to prevent propellor incidents during assembly, testing, and troubleshooting. This kill switches works by grounding the motor signal going to the electronic speed controller. It will only be turned off at the moment of launch and re-engaged immediately after landing. Risk of Power Loss Due to weight and space constrictions no redundant power supply was implemented. The UAV will lose control if failures occur in the BEC or the 5V regulator that powers the autopilot control board. Although not redundant, the individual power supplies are highly rated and are not nearing maximum power dissipation. University of Alberta - UAARG 16

18 Flight Protocols UAARG has developed specific guidelines for operating the UAV. These guidelines are a combination of checklists, log templates, best practices, and emergency information packages. All UAARG members are responsible for reviewing and understanding the flight protocols prior flights. Individual roles have also been developed to ensure that every member is accountable. The flight commander is responsible for key decisions and communication within the group. He or she will also be in possession of the emergency numbers of local ATC towers, nearby hospitals, police and fire departments. Specific airframe, autopilot, and imaging roles have individualized checklists that correlate to the flight commander s. These not only provide safe practises but ensures systematic preparation prior to flights. Thus, set-up and testing is streamlined. Equipment A fire extinguisher will always be present in the case of fires. For fires directly resulting from a failed LiPo battery, a bucket of sand will be used to isolate the source. A first aid kit will be present in case of any injury. Safety glasses will also be worn by personnel who will take to UAV to the runway and arm the throttle for take-off. The flight commander will constantly monitor the UAV during flight. If there is any danger to either the UAV and its components, or the personnel on the ground, the flight will end through manual R/C landing or termination. Certain conditions for delaying a flight may include: sudden change in weather or wind, UAV performance problems, critical component failure, falling debris, or smoke is seen coming from the UAV. Firmware Failsafes All failsafes are programmed and flashed into the autopilot board prior to flight. These failsafes are derived from both competition requirements in Section 9 and club protocols.the two primary failsafe states that the UAV may enter are Standby and Termination. In Standby state, the UAV will return to a predesignated home waypoint within close proximity to the takeoff area. This state's primary purpose is to postpone the mission until nominal communications return. The Termination state is defined by 0% throttle, full elevator up, full right rudder, and full roll on ailerons. During operations both the pilot and the ground control operator have direct ability to terminate the flight at any time. Furthermore, the pilot and GCS operator have direct radio contact at all times. All members present during the flight can request to end the flight, but must go through the flight commander before the flight can be terminated. University of Alberta - UAARG 17

19 Table 5: Failure scenarios and response actions Failure: Likelihood of recovery: Solution: Lost Telemetry High In the event of losing telemetry communications, the UAV must automatically return home after 30 seconds. Otherwise, the pilot must use R/C override to maintain manual control or land safely. If the UAV does return home but communications cannot not re-established with 3 minutes, the pilot must use R/C override to maintain a manual control or land safely. R/C uplink failure High In the event when R/C uplink is lost for greater than 10 seconds, the flight must be terminated. Lost Telemetry and R/C Uplink Communications In the event of losing telemetry communications, the UAV must automatically return home after 30 seconds. Otherwise, the flight must be terminated. If the UAV does return home but communications cannot not re-established with 3 minutes, the flight must be terminated. Lost GPS Medium In the event that GPS location is lost, the UAV control will return to R/C uplink. If the pilot cannot safely operate the UAV, its flight will be immediately terminated. Outside mission boundary Medium If the UAV leaves the mission boundaries, the UAV will be directed back within boundaries. In the event of loss of control and data link, flight will be automatically terminated To test the safety procedures, all possible scenarios will be simulated on the ground. This can be accomplished by physically disrupting various communication links and observing the reaction. We do this by setting up a test bench and powering off the communications modules responsible for each link, or by walking with the bench out of the wireless link s known range. Once the University of Alberta - UAARG 18

20 simulated failure occurs, the UAS should respond by going into the appropriate failsafe mode as mentioned above. Conclusion By continuing to develop an already highly successful system this year, UAARG have been able to refine and test this UAV to its limits. Many of the remaining considerations from last year s design report have now been resolved. The modular avionics board wiring and hardware has been reorganized to be installation and troubleshooting friendly. Power supplies are now highly rated for the UAV s power requirements and an additional LiPo battery has nearly doubled flight times. Furthermore, the new Canon Powershot camera has proven to integrate well with its CHDK software and provides high quality images. UAARG has achieved these design objectives through rigorous research, review and testing. Test flights have indicated that our unique lightweight and inexpensive design can effectively complete AUVSI s mission requirements. As result, we are confident that UAARG will compete admirably amongst all other university teams. Acknowledgements We would like to thank Peter Cary, the Edmonton Radio Control Society, the University of Alberta, Shell Canada and all members of the University of Alberta Aerial Robotics Group as for their support and guidance. References [1] AUVSI Seafarer Chapter. AUVSI Seafarer Chapter 13 th Annual Student UAS Competition Internet: seafarer.org/documents/2015documents/2015_auvsi_suas_rules_r ev_1.1_final_ pdf Appendix Please find all additional files attached to this pdf document. University of Alberta - UAARG 19