JP University of Toronto UTAT

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2015 Association for Unmanned Vehicle Systems International

Student Unmanned Aircraft System Competition

University of Toronto Aeronautics Team

Technical Journal Paper

May 2015University of Toronto

Canada


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Abstract

This is the technical journal paper the University of Toronto Explorer (UT-X) designed for the 2015Association for Unmanned Vehicle Systems International student UAS competition at the PatuxentRiver Naval Air Station in St. Inigoes, Maryland. The design process is presented following a systemsengineering approach, starting with an operational analysis of the requirements imposed by the com-petition. A design is presented and decomposed into subsystems, whose requirements and designs arepresented. These requirements drive the design of a twin boom pusher prop aircraft equipped with anadvanced autopilot, high resolution camera payload and high rate data link capable of providing timelyand accurate aerial surveillance.

University of Toronto Aeronautics Team II


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Contents

1 Systems Engineering 1

1.1 Mission Requirements Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Design Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Expected Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Programmatic Risks and Mitigation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Technical Design Description 2

2.1 Airframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1.1 Subsystem Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22.1.2 Composite Airframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.1.3 Power & Propulsion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Guidance and Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.2.1 Subsystem Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2.2 Autopilot and Mission Planner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.3 Communication and Data Link . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3.1 Subsystem Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3.2 Data Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.3.3 Frequency List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2.4 Payload . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4.1 Subsystem Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4.2 Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.4.3 Stabilization Gimbal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.5 Ground Control Station and Post Processing . . . . . . . . . . . . . . . . . . . . . . . . . . 72.5.1 Subsystem Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.5.2 Mission Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.5.3 Data Post-Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3 Test and Evaluation Results 10

3.1 Autopilot System Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.1.1 Autonomous Flight Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.2 Payload System Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2.1 Search Area Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

4 Safety Considerations and Approach 11

4.1 Operational Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.1.1 Pre-flight Check List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4.1.2 Ground Crew Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2 Design Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.2.1 Avionics Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124.2.2 Modular Airframe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134.2.3 Emergency Flight Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.3 Risk Management and Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

University of Toronto Aeronautics Team III


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5 Conclusion 14

A UT-X CAD Drawing

B Weight and Balance Table ii

C Project Schedule iv

D Sponsorships v

University of Toronto Aeronautics Team IV


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1 Systems Engineering

1.1 Mission Requirements Analysis

The mission demonstration requirements, limitations, primary and secondary tasks were analyzed, lead-ing to the derivation of the system requirements for UT-X. This section lists the core driving requirementsfor the UT-X unmanned aerial system1. Following the system requirements, the subsystem requirementswere derived and are presented in their respective sections within Section 2.

1-1 The UT-X system shall navigate the search area autonomously following waypoints.1-2 The UT-X system shall provide geo-tagged high resolution aerial photography of the competition area1-3 The UT-X system shall remain within flight boundaries at all times.1-4 The UT-X system shall display vehicle location and altitude at all times during the mission.1-5 The UT-X system shall be capable of manual override into radio control by a safety pilot.1-6 The UT-X system shall terminate flight in the event of extended loss of communication.1-7 The UT-X system shall terminate flight if given a kill signal from the ground control.

1-8 The UT-X system shall have a maximum mission time of 60 minutes.

1.2 Design Rationale

An analysis of the system requirements has led to the design of UT-X, an autonomously flying fixedwing aircraft equipped with a high resolution camera payload. Due to the complexity of the design problem,the system has been broken into five subsystems shown in Figure 1. The required flight endurance, airfieldsize, and payload weight necessitate the design of a custom-built airframe and fuselage, detailed in Section2.1. The requirements of the autonomous flight task drive the need for an advanced autopilot coupled witha versatile ground station software, described in Section 2.2. The communication and data link subsystemin Section 2.3 addresses the need for a reliable and safe aircraft control system as well as a high data

rate link for aerial images. The complexity of the targets in the search area task require UT-X to employa stabilized high resolution payload, shown in Section 2.4. Finally, ground station and post processingsubsystem outlined in Section 2.5 is designed in a response to requirements for real-time telemetry as wellas efficient data extraction from acquired aerial images.

1.3 Expected Performance

The team has performed all flight tests with the flight crew that will be at the competition. A moredetailed discussion testing can be found in Section 3. The rigorous testing of UT-X has confirmed that thesystem will be able to achieve the Threshold and Objective for the primary tasks outlined in Table 1. Inaddition, this year the team will be attempting several of the secondary tasks and aim to achieve thresholdlevel achievement.

1.4 Programmatic Risks and Mitigation Methods

All mission saftey risks and mitigation methods are discussed in detail in Section 4.3.

1‘Shall’ indicates a mandatory requirement, ‘Should’ indicates a strongly recommended requirement

University of Toronto Aeronautics Team 1


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Figure 1: High Level System Block Diagram

Level Task Attempt Threshold Objective

Primary Autonomous Flight √ √ √

Primary Search Area √ √ √

Secondary ADLC √ √ √ Secondary Actionable Intelligence

√ √ √ Secondary Off-Axis Target

√ √ Secondary Emergent Target

√ √ √ Secondary SRIC

√ √ Secondary IR Search-PrimarySecondary IR Search-SecondarySecondary Air Drop

√ √ Secondary InteroperabilitySecondary Sense, Detect, and Avoid

Table 1: Expected Mission Performance

2 Technical Design Description

2.1 Airframe

2.1.1 Subsystem Requirements

Following the mission requirements analysis in Section 1.1, subsystem requirements were derived forthe airframe. Some of the main driving requirements are listed below.

4-1 The airframe shall have a 20 lbs. total lifting capability

4-2 The airframe shall have a nominal airspeed of 38 knots4-3 The airframe shall have an endurance of at least 30 minutes4-4 The airframe shall maintain level flight at an altitude of 500 feet4-5 The airframe shall have a climb rate of at least 10 feet per second4-6 The airframe shall be propelled by an electric motor.



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2.1.2 Composite Airframe

The current UT-X airframe is the latest iteration on the design that has been developed over the past2 years for both the AUVSI and Unmanned Systems Canada (USC) competitions. The main impetusbehind the airframe design was that a lighter and more maneuverable airframe was needed over the seniortelemaster plane that was used previously. The main wing and empennage are constructed from carbonfiber composites. The molding process used allows for the production of smooth and accurate surfaceswhich result in excellent aerodynamic performance. The carbon fiber skin ensures that the wing is durablestiff, and lightweight. While the first iteration of the fuselage design was also made of carbon fiber, amodification was made recently to use a wooden fuselage. While it is aesthetically less appealing, thewooden fuselage offers much easier construction and repairability. In addition, it provides more room andmounting locations for payload and avionics. Due to steering difficulties experienced during autonomoustakeoff last year, this current UT-X frame will use a tricycle landing gear configuration. A detailed CADdrawing of the UT-X airframe can be found in Appendix A. The weight breakdown can be found inAppendix B, showing the mass budget and centre of gravity location.

Configuration Dual-tailboom pusher

Wing Span 77.89 in

Wing Area 748 sq in

Aspect Ratio 8.1

Total Length 74.86 in

Payload Volume 1836 cu in

Cruise Speed 38.9 kn

MTOW 22 lbs

Table 2: Airframe specifications

Figure 2: Photo of UTX aircraft from the 2015 USC Competition

2.1.3 Power & Propulsion

In order to overcome cruise drag, it was determined that the motor had to provide a total static thrustof 12 lbs and a dynamic thrust of 7.7 lbs at the cruise speed of 38 knots. Electric propulsion was chosen



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as it is much easier to start up and control from the autopilot. Using MotoCalc, the optimal motorpropeller, battery combination was found to have the specifications shown in Table 3. In order to satisfythese specifications, the NTM Prop Drive 50-60 Motor was chosen in combination with four Turnigy 6s5000mAh LiPo batteries. Through testing, the Turnigy 16x10 cherokee wood propeller was found to be

the most efficient.

Motor Battery Propeller

RPM/V 380 Voltage (V) 22.2 Diameter (in) 16Max Current (A) 70 Current (A) 20 Pitch (in) 10No Load Current (A) 2

Table 3: Power & propulsion specifications

2.2 Guidance and Navigation


Following the mission requirements analysis in Section 1.1, subsystem requirements were derived forthe guidance and navigation. Some of the main driving requirements are listed below.

3-1 The guidance system shall report aircraft attitude, location, and airspeed to the ground station.3-2 The guidance system shall perform autonomous takeoff of the aircraft.3-3 The guidance system shall perform autonomous landing of the aircraft.3-4 The guidance system shall navigate autonomously to commanded waypoints within 100 ft.3-5 The guidance system shall autonomously maintain airspeed to within 2 knots of commanded values.3-6 The guidance system shall measure ground location to within 10 feet.3-7 The guidance system shall navigate within assigned boundaries at all time during the mission.

3-8 The guidance system shall return the UT-X system to home after 10 seconds of lost contact.3-9 The guidance system shall switch to Radio Controlled (RC) flight once the override command is given

2.2.2 Autopilot and Mission Planner

The mission requires a thorough, timely coverage of the entire competition field. To best meet thisrequirement, UT-X will operate with full flight autonomy for the mission, using autonomous takeoffwaypoint following flight, and landing. The Autopilot subsystem consists of the Pixhawk loaded withthe Arduplane firmware, designed by 3D Robotics. The Pixhawk comes equipped with a gyroscopeaccelerometer, magnetometer, and GPS. It will be outfitted with an airspeed sensor so that the autopilotcan maintain the speeds required to maintain altitude. It also has channels available to output servo signals

for camera stabilization, which are utilized by the payload stabilization system. The autopilot interfaceswith the ground station using the program Mission Planner, shown in Figure 3. It displays telemetryand location in real-time and allows the user to set waypoints and flight commands. Figure 3 shows apreliminary flight plan displayed in Mission Planner’s interface. The interface allows the user to specifyinstructions such as automatic takeoff, landing, as well as the creation of complex search patterns as shownin Figure 3.



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Figure 3: Flight plan from the 2014 AUVSI Competition in Mission Planner

2.3 Communication and Data Link


Following the mission requirements analysis in Section 1.1, subsystem requirements were derived forthe communication and data link. Some of the main driving requirements are listed below.

5-1 The communication system shall interface with the ground station at a distance of up to 1.25 miles.5-2 The communication system shall transmit aircraft location, and attitude to the ground station.5-3 The communication system shall transmit flight commands to the aircraft.5-4 The communication system shall permit the safety pilot to assume manual override.5-5 The communication system shall interface with the third party SRIC system.5-6 The communication system shall transmit aerial imagery to the ground during the mission.5-7 The communication system shall transmit aerial images at a rate of at least 1 MB/s at 1.25 miles.

2.3.2 Data Links

Given the proven reliability of the telemetry communication link, most of the effort has been put intodesigning the high data rate transmission. Two years ago, UTAT used a high gain antenna and tracker forhigh rate data link. Unfortunately, due to the the required accuracy of the antenna and the limitations ofthe tracker, reliable data link was not possible. Using a tracking gimbal, the Nanostation M5 by Ubiquitoffers an impressive power output of 27 dBm with 16 dBi antenna gain. The built in antenna on theNanostation provides a beamwidth of 45 degrees azimuth and 15 degree elevation, which is much largerthan antennas previously used. On the aircraft, we have chosen a Rocket M5 with two 5 dBi omnidirectional



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antennas. The extra power of the Rocket as well as dual polarization will ensure a robust connection ofranges up to 3 km at maximum data rate and up to 50 km at the lowest data rate.

This year, UT-X will employ an additional data link on the 2.4 GHz band to attempt the Simulated

Remote Information Center (SRIC) task. This will be operated using a small WiFi module connectedto the onboard payload computer. The payload computer will be running the software to search for theconnection and execute the actions necessary to complete the SRIC tasks. Finally, given past experiencewith RF interference on the remote control (RC) data link at 433 MHz, a backup RC communication linkwill be brought to the competition. Both the RC links utilize spread spectrum technology. The link to beused will be chosen based on conditions at the competition site.

2.3.3 Frequency List

Link Information Freq. Max Tx

Power

Max

Range Equipment

TelemetryFlight commands,aircraft attitude,GPS, airspeed

900 MHz 1 W 64 km XTend RF Module

w/ Dipole antenna

RC Override Manual aircraft

control 433 MHz 600 mW 40 km

Immersion RCezUHF w/ Dipoleantenna

RC Backup Manual aircraft

control 2.4 GHz - 4 km

Futaba T7CFASST

Payloaddata

Payload control,aerial images

5.8 GHz 600 mW 2 km (at 24

Mbps)Ubiquiti (Rocket /NanoStation M5)

SRIC Messages, images,

instructions 2.4 GHz -

200 m(estimated)

RealTekRTL8188CUS

Table 4: Frequency Data Table

2.4 Payload


Following the mission requirements analysis in Section 1.1, subsystem requirements were derived forthe payload. Some of the main driving requirements are listed below.

2-1 The payload shall provide aerial imagery to the Command and Control Station.2-2 Acquired images shall have a resolution of no less than 2 in. from an altitude of 500 feet.2-3 The payload shall gimbal to acquire images directly below the aircraft to within 2 degrees2-4 The payload shall acquire images at a rate of at least 1 frame per second2-5 Acquired images shall have a GPS tag detailing the coordinates and altitude at which they were taken.

2.4.2 Camera

In the past years, the UT-X payload was the Imperx Gigabit Ethernet camera, which was chosen dueto its superior resolution of 30 MP. While the resolution is more than enough to identify targets on the



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field, it leads to long processing times and large image file sizes. This year, the UT-X will carry theTeledyne TSC-4096 Gigabit Ethernet camera with a Nikon Nikkor 50 mm lens, shown in Figure 4. Its 12MP resolution will provide sufficient detail while having faster frame processing and transmission. Theethernet camera is connected to an onboard Odroid-C1 ARM computer, which operates a custom-written

software to activate the camera shutter and save the imagery. The Odroid is connected to a small GPSunit through its USB port to associate acquired images to a set of coordinates. Finally, the Odroid isconnected to the high-rate payload data link which allows it to send imagery back to the ground stationduring flight.

Figure 4: Teledyne TSC-4096 Camera. Its minimal design means it is much ligher than retail DSLRcameras of the same quality

2.4.3 Stabilization Gimbal

The camera is pointed inertially downward and actively stabilized by a custom made gimbal, shown inFigure 5. The gimbal design is the result of the optimal combination of elements taken from its previousiterations. The focus of this design was removing unnecessary components from the camera stabilizationsystem and minimizing the number of variables affecting the cameras orientation in response to the UAV.One key design change includes driving the system with TGY-778 servo motors as opposed to brushless DCmotors. Servo motors can be controlled directly via the autopilot, eliminating the need for an additionagyroscope and control loop for the DC motors. The previous transmission system utilized a timing beltwhich had a tendency to become loose and cause errors in mechanical response. As a result, a gear basedtorque transmission system was introduced in this iteration.

2.5 Ground Control Station and Post Processing


Following the mission requirements analysis in Section 1.1, subsystem requirements were derived forthe ground station and post processing. Some of the main driving requirements are listed below.

6-1 The GCS shall transmit waypoint, altitude and airspeed commands to the vehicle.6-2 The GCS shall be capable of modifying mission parameters during flight.6-3 The GCS shall display vehicle position, attitude and airspeed real-time.



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Figure 5: 3D CAD render of the gimbal and payload

6-4 The GCS shall receive geo-tagged aerial imagery from the vision payload

6-5 The GCS shall allow payload operators to identify tarets in aerial images.6-6 The GCS shall be capable of autonomous identification of targets in aerial images.6-7 The GCS shall be capable of geolocating targets in aerial images to within 75 feet.6-8 The GCS shall be controlled by five operators: one for mission control, three for payload control, and

one in case of manual RC flight.

2.5.2 Mission Control

The Mission Control station allows for operator to monitor the UAV progress and assign additionalwaypoints during the area search. This is done using Mission Planner , which displays updates of vehiclehealth, speed, position, and altitude to the operator. This software also allows the operator to re-task theaircraft during a mission by sending waypoint commands or changing a search area boundary. A screenshot

of the software can be found in Section 2.2.

2.5.3 Data Post-Processing

The Image Analysis station operates and monitors the payload on UT-X using a custom developedsoftware. This software interfaces with the onboard computer to download and display images to thepayload operator. It is designed for the operator to efficiently extract details that are relevant to thecompetition goals. The software allows for point-and-click geolocation, whereby the operator cansimply click on a location of interest within an aerial image. The software then determines the locationof the target based on the latitude and longitude of the image, as well as the altitude at which the imagewas taken. In addition to human-in-the-loop location and classification, the post-processing subsystem has

the option of employing an computer vision algorithm to attempt the Autonomous Detection, Localizationand Classification (ALDC) task.

The algorithm is comprised of two main parts, the onboard component and the ground station com-ponent. The onboard component identifies limited areas of interest and the ground station componentperforms more computationally expensive automated image characterization tasks. These algorithmswere developed in-house, using the OpenCV library with prototyping done in MATLAB. Onboard imageprocessing is aimed at decreasing the amount of mission critical data that must be sent to the ground



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station. A key design motivation in the target characterization system is that it should operate with aminimal amount of downlink bandwidth. Hence, the onboard image processing component is analogous toa high specificity compression algorithm. Only feature-rich areas of interest are sent to the ground stationfor further processing.

The Sped-Up Robust Features (SURF) algorithm included in the OpenCV library was used for blob-detection, shown in Figure 7. HSV colour space was experimentally determined to result in the greatestfeature sensitivity. Using public domain image analysis software from the National Institutes of Healthtarget samples from past competitions were inspected and HSV was chosen based on qualitative measure-ments. Specifically, the hue component of HSV space gave the best results as shown in Figure 6. Thereis the possibility of the algorithm giving false negatives that is, eliminating interesting features andthe bandwidth-reducing design precludes easy correction for this type of error. Hence, the threshold forthe SURF algorithm was intentionally set low and a two-step process implemented. Keypoints from theinitial SURF run are passed through a fixed-distance near neighbour search to detect groups of closelypacked keypoints. This reduces the noise resulting from lowering the threshold. The density-based spatia

clustering of applications with noise (DBSCAN) algorithm was applied for this second step. The endresults are cropped regions of interest of the original JPEG compressed image that are then sent to theground station.

Figure 6: HSV analysis of target image from the 2013 AUVSI Competition. The color inspector showsthat hue component is most effective for distinguishing brightly colored objects on a grassy background.

On the ground station component, an additional HSV color analysis is performed on each potentialtarget image. Disregarding the value (V) component, a K-means clustering is applied to the pixel hue andsatuation values to identify groups of similar colors. Using this clustering, the image should be segmented

into three main regions - a letter, a shape, and the background. Any potential target not meeting thiscriteria is disregarded. A sobel edge method is applied to extract the boundary points and tangent angles othe shape and letters. For both sets of boundary points, a collection of shape contexts are computed. Theshape context is a rotation and scale invariant rich shape descriptor introduced for character recognitionby Belongie et al.2. The shape context computed is compared to a database of computed shape contextsfor polygons, numbers, and letters to identify the target characteristics. The target is geolocated using the

2S. Belongie, J. Malik, and J. Puzincha. “Shape matching and object recognition using shape contexts.”



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Figure 7: Target image from the 2013 AUVSI Competition. The cropped image (left) shows the target foundfrom the image. The SURF analysis image (right) shows the robust features detected by the algorithmcircled on the hue component of the image.

GPS tag on the image and its pixel location relative to the image center.

3 Test and Evaluation Results

Over the past year and a half of development, UT-X has undergone extensive testing and iteration toensure that the design meets all the requirements of the AUVSI mission. This section details some of thetesting results which have been accumulated through previous competitions as well as local testing.

3.1 Autopilot System Performance

3.1.1 Autonomous Flight Task

At last year’s 2014 AUVSI competition, UT-X demonstrated its ability to accomplish autonomousflight and capture the waypoints within the required accuracy. Afterwards, the aircraft was able to fly alawnmower search of the competition field. Figure 8 shows a telemetry log playback showing the aircraftspath (blue) tracking the waypoint path (yellow). In the figure, UT-X is conducting a search of thecompetition field and following the path from waypoint 11 to waypoint 16. The aircraft demonstratesthe maneuverability and control to execute several consecutive ninety degree turns and track the pathwell. While this year’s airframe is different from the senior telemaster used in 2014, the autopilot has beentuned to achieve the same level of performance as the previous year.

3.2 Payload System Performance

3.2.1 Search Area Task

At this year’s 2015 Unmanned Systems Canada student competition, UT-X was able to locate andidentify numerous targets of interest on the competition field. Figure 9 shows the aerial images, and Table5 shows the reported target locations, the actual target locations as specified by the competition organizers,and the error in the location for each. The small relatively small errors in the location demonstrate theteam’s ability to locate each target well within the 75 feet criteria required for the Search Area Task. Dueto motion blur, the QR code in Figure 9 could not be successfully read - this is an issue that the team isactively working to rectify.



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Figure 8: Excerpt from the UT-X flight path for the 2014 AUVSI competition.

Target Latitude

(estimated)Longitude(estimated)

Latitude(actual)

Longitude(actual)

Error

Green Tarp 48.514266 -71.640215 48.514225 -71.640186 16 feetYellow Tarp 48.514339 -71.637667 48.514399 -71.637660 21 feetQR Code 48.514812 -71.639300 48.514750 -71.639353 26 feet

Table 5: Target geolocation error from the 2015 USC Competition

4 Safety Considerations and Approach

4.1 Operational Safety

4.1.1 Pre-flight Check List

The cornerstone of the UT-X system safety plan is a pre-flight checklist, which has been developed andexpanded throughout flight testing to create a comprehensive set of checks. These include verification ofthe autopilot, sensors, communication links with the GCS, control surfaces, center of gravity, mechanicaland electrical connections, and weather conditions. A full throttle test is always performed to ensure the

aircraft can takeoff and climb successfully. This checklist is completed thoroughly before every flight toreudce the chance of any system failing unexpectedly during the flight. As a result, the team can ensurethat each flight is safe and productive.

4.1.2 Ground Crew Training

Before each flight, all flight crew members are briefed on the flight objectives, flight path, altitudestake-off and landing locations, and duration. For each flight location, several alternatve flight plans are



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Figure 9: Aerial images acquired from the 2015 USC Competition - Green tarp, yellow tarp, and the QRCode

created to ensure that the aircraft is always taking off and landing upwind. During take-off and landingthe GCS Operator calls out the airspeeds to the safety pilot to prevent stall. The mission control operatoris responsible for making the pilot aware of any obstacles on the ground. When the aircraft is within visuarange, the safety pilot has full discretion to take over control whenever the aircraft is not behaving asexpected. When the aircraft travels out of visual range the pilot will notify the mission control operatorwho will then begin to communicate the position and state of the aircraft to the pilot at regular intervals

4.2 Design Safety

4.2.1 Avionics Precautions

The UT-X system design includes several safety features. The avionics battery voltage is monitoredin real-time via the telemetry link, and the propulsion batteries have been chosen to provide twice thenecessary capacity for the maximum endurance. In addition, the static margin for pitch is designedto be well within the stable region and checked each time the aircraft is loaded for flight. Due to theamount of communication equipment inside, all radios are chosen to have large frequency separationServo connections in the empennage, wing, and nose gear are made with latching connectors to preventany in-flight disconnections. Finally, the propulsion battery compartment of the fuselage is designed for



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easy access in the event that an emergency disconnection is required.

4.2.2 Modular Airframe

One of the major airframe improvements made this year was the implementation of a modular design.The main wing, horizontal stabilizer, and both landing gears are fastened using nylon bolts. The nylonbolts are designed to shear apart in the event of a crash or rough landing, ensuring that various componentsof the airframe fall off harmlessly instead of withstanding large stresses. As a result, parts such as thecarbon fiber wing and main landing gear are much less likely to break and can be reused in the eventof an accident. More importantly, this reduces the environmental impact, as it diminishes the likelyhoodof electronics and carbon fiber fragments being littered in an accident. The rear fuselage is reinforcedto protect the main avionics equipment of UT-X and is designed to break apart from the front fuselageand the wing. The propulsion batteries are housed in the front and in the event that it separates, theconnectors will safely come apart to cut power to the engine.

4.2.3 Emergency Flight Termination

At any point during a flight, the safety-pilot can take over manual control of the aircraft usinga dedicated switch on the RC transmitter. This override function is implemented using a hardwaremultiplexer on the Pixhawk autopilot, so it is entirely independent from the autopilot software. TheRC transmitter has a programmable failsafe function that is triggered when the RC link is lost, and thishas been programmed to turn off the motor and put the aircraft in a spiral dive. An additional kill switchcan be activated can be activated from ground station in the event that the RC kill switch fails to work.

4.3 Risk Management and Mitigation

The team has identified the most prominent single-point failures in each of the subsystems and deter-

mined the appropriate response actions in each case. These single point failures along with other projectrisks have been classified in a risk matrix to make the team more aware of the known risks. The risk matrixfollows a 5 point grading scale for likelihood and consequence, with 5 in either category being a worst casescenario. These risks fall under one of three profiles based on their total score in the two categories, shownin Table 6. The risk matrix is presented in Table 7. The table shows that almost all the risks are in theacceptable range and those that are not will be monitored closely. All flight crew members have beenbriefed on this table.

Low likelihood, lowconsequence Score≤4

Accept, risk is accepted by the team and no further action isrequired.

Low likelihood, highconsequence or viceversa 47

Action required, some system change must be realized toreduce this risk.

Table 6: Single-point failure color coding



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Failure Mode Crew Response

Autopilot software/hardwarefailure

If within visual range, the safety pilot will assume control of theaircraft. Otherwise, terminate flight.

Loss of autopilotcommunication link

Return home. If connection is not regained in 2 minutes, and it

is within visual range, the safety pilot will take control. If link isregained the mission can resume. If the link is not regained andit is outside visual range, terminate flight.

Loss of manual RC controllink

The Kill Switch will trigger automatically when the RC link islost and terminate the flight.

Ground control stationfailure

If within visual range, the safety pilot will take control and landthe aircraft. Otherwise, terminate flight.

Propulsion system failure orpropulsion battery drained

If possible, the safety pilot will land the aircraft at the landingarea or a safe alternate site. Otherwise terminate flight with thekill switch

Control surface failure or

degradation

If possible, the safety pilot will land the aircraft at the landing

area or a safe alternate site. Otherwise, terminate flight.

Payload sensor failure

If within visual range, the safety pilot will take control andreturn the aircraft to within visual range. If outside of visualrange, the GCS Operator will issue a return-to-home command,and the safety pilot will take over when the aircraft is in visualrange. If the payload cannot be fixed using the remoteconnection in flight, the aircraft will land.

Loss of payloadcommunication link

An attempt will be made to re-establish the link. The missionwill resume as the payload will remain functional regardless of the link.

Severe weather The safety pilot will take control and land the aircraft at the

predetermined landing site or at a safe alternate site.

Complete loss of control of the aircraft

The Kill Switch will be triggered to terminate the flight. If theaircraft is not responsive to the Kill Switch, the GCS Operatorwill note the last known position and heading, and report to thecompetition organizers, local authorities, and air traffic control.

Table 7: Single point failure and risk classification. Item number color coding indicates risk profile.

5 Conclusion

UT-X is a unique system that aims to complete the mission tasks using a high level of autonomy in flight

operations. Drawing upon extensive experience in designing RC aircraft, UTAT has designed a robustmodular airframe from a combination of balsa, plywood, and composites. The airframe is outfitted withstate-of-the-art payload and communications hardware to enable the in-flight transmission of high qualityaerial images. Finally, the UAV is complimented by an open source mission planning software, as well as acustom designed payload software to analyze the imagery and extract information relevant to the AUVSIcompetition goals.



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A UT-X CAD Drawing

THIS PAGE IS INTENTIONALLY LEFT BLANK

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B Weight and Balance Table

The mass locations (X) are measured in distance downstream from the nose of the aircraft.

Figure 10: Side view showing mass location

Item X (cm) Mass (kg)

1 Payload 25 1.38

2 Nose gear 39 0.203 Batteries 53 2.824 Fuselage 58 1.495 Main gear 83 0.326 Avionics 80 0.117 Servos 76 0.098 Wing 68 1.259 Motor 114 0.72

10 Tail booms (2) 132 0.3111 Servos 182 0.1812 Stabilizers 186 0.53

Centre of Gravity 71 9.40

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C Project Schedule

Figure 11 shows the approximate timeline for the completion of UT-X for the 2015 Competition inJune.

Figure 11: UTAT UAV Project Timeline

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D Sponsorships

The team would like to thank the numerous sponsors, and alumni/industry advisors that made thisproject possible.

University of Toronto Aeronautics Team v

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