Creative interdisciplinary UAV design
David C. Macke, Jr., Steve E. Watkins, and Thomas Rehmeier
I
nterdisciplinary design is an important aspect of engineering work. Opportunities for collaboration between disciplines exist at the undergraduate level through engineering competitions and senior design courses. To be successful, the various groups must be aware of the needed synergy and must develop cross-disciplinary communication. This article describes the collaborative design process for an unmanned aerial vehicle (UAV) between an IEEE competition team and an aerospace engineering senior design team.
UAV challenge UAVs are possible through the integration of diverse technologies including aeronautics, robotics, electronics, systems, software, and sensors. Civilian and military implementations range from fully autonoDigital Object Identifier 10.1109/MPOT.2013.2255518 Date of publication: 7 January 2014
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mous to semi-autonomous operation and from large-scale aircraft to microrobots. While UAV technologies touch many IEEE fields, UAVs are particularly relevant to the interdisciplinary interests of the IEEE Aerospace and Electronic Systems Society (AESS). IEEE AESS Student Chapters are encouraged to become involved in UAV design through competitions such as the UAV Challenge–Outback Rescue. This international competition is held in Australia every year to promote the development of interdisciplinary UAV technologies. The searchand-rescue tasks of a competition UAV are to fly over a search area, identify a mannequin placed in the outback, and drop a rescue package to this stranded “hiker.” A flight time of at least 1 h and a payload of a water bottle are basic requirements. Beyond safety capabilities through remote radio control, all tasks must be accomplished autonomously. IEEE POTENTIALS
The power of collaboration A Student Chapter of the IEEE AESS was formed at the Missouri University of Science and Technology (Missouri S&T) to provide opportunities to explore UAV technologies. A team within the Chapter decided to pursue the UAV Challenge as an extracurricular design project. The team’s background, in electrical and computer engineering, provided expertise for the various electronic, power, and sensing systems. However, the aeronautic systems were beyond the team’s knowledge base. Without collaboration, the options for airframe and flight control would be limited to the modification of a ready-to-fly, radio-control (RC) kit. The senior design project in the Aerospace Engineering Department at Missouri S&T is a two-semester course in which teams of five to six students design, construct, and test fly a subscale radio-controlled aircraft. Project options include a variety of manually controlled approaches for acrobatic or high-endurance tasks. While autonomous operation is possible in a project, the design work and cost associated with both airframe construction and autonomous systems are prohibitive. Also, the course emphasis is on airframe customization and performance. The “Project Eagle-Eye” team sought to gain experience with UAV systems but lacked the expertise and time to design the needed electrical systems. The teams had complementary backgrounds and similar interests. Effective synergy could meet the needs of both teams—a win-win. The collaboration was formalized through 1) an agreement as to scope, shared costs, timeline, etc. and 2) definition of a process for codesign. The codesign process was critical since each design decision influenced or constrained other design decisions. For instance, the choice of each electronic system added to the total weight that the airframe must lift, and the choice of an airframe determined the flight stability and the associated complexity of the image capture system. The cross–disciplinary communication was a challenge. Each team had to continually educate the other team on discipline-specific vocabulary and concepts. The team leaders were assigned an additional role as official liaisons between the teams.
Technical timeline To satisfy the competition qualifications and the senior design course requirements, the UAV design targets were set as shown in Table 1. The senior
From the UAV competition rules, estimates were made for needed flight time, payload capacity, and flight performance, e.g., safety constraints, stability, and altitude. These estimates became the “customer” parameters for the senior design project.
design course requirements are satisfied by a manually controlled flight test with image capture, although the report will document how the design satisfies the UAV competition needs. The costs for the airframe, flight-control avionics, and associated jigs were the responsibility of the aerospace engineering (AE) team, while the costs for the engine/motor and UAV systems were the responsibility of the electrical and computer engineering (ECE) team. The UAV became the property of the IEEE AESS Chapter at the completion of the senior design project.
The GANTT chart for the collaboration is shown in Fig. 1. From the UAV competition rules, estimates were made for needed flight time, payload capacity, and flight performance, e.g., safety constraints, stability, and altitude. These estimates became the “customer” parameters for the senior design project. The selections of an airframe type, the engine/ motor, and the camera hardware proceeded in parallel with monthly joint progress meetings. The propulsion selection and the associated energy storage requirements were the first decision and allowed the weight estimates to be improved based on manufacturers’ specifications (the electric motor and batteries are described later). The weight estimates were further refined after purchasing the motor, batteries, and camera by weighing each component. The airframe design had to accommodate the internal space requirements, payload placement, and lift needs. The collaboration has currently completed stage one.
Airframe selection The airframe design concept is shown in Fig. 2. The airplane is a pusher-propeller configuration with a v-tail empennage and a semicylindrical fuselage. To optimize the
Table 1. Design targets, measures, and responsibilities. Time
Tasks
End Goal
Primary Responsibility
Preliminary
Design requirements
Customer list
Joint AE/ECE
Stage 1
Airframe design/analysis Propulsion selection
Airframe mock-up Power calculations
AE lead ECE lead
Electronics system Airframe construction
Full system runtime test Completed airframe
ECE lead AE lead
Stage 2 Stage 3
Systems integration
Ready-to-fly aircraft
Joint AE/ECE
Stage 4
Piloted flight test
Successful flight
AE lead
Stage 5
Autonomous flight test
Successful flight
ECE lead
Project Progression AUG 2011
SEP OCT NOV DEC 2011 2011 2011 2012 Design Requirements
Legend: AE Lead ECE Lead Joint AE/ECE
JAN 2012
FEB 2012
MAR 2012
APR 2012
MAY 2012
JUN 2012
Aircraft Design/Analysis Propulsion System Analysis Aricraft Construction Electronics Design Electronics Construction Systems Integration Piloted Flight Test Autonomous Flight Test
Fig. 1 A GANTT chart for the design collaboration.
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GPS Location Modem
Auto Pilot
Camera Servos
Motor
Batteries
Engine/motor selection
Fig. 2 The airframe design concept.
Motor
Servos
The forward section was designed to house the electronics and the camera. Space and accessibility were systems issues. The shape of the section was optimized through iterative simulations in XFLR5 to achieve optimum aerodynamic performance. The aft section houses the flightcontrol linkages. The complete airframe was modeled in AutoCAD and SolidWorks and a full scale mock-up was constructed.
Power Distribution
Autopilot with GPS
Flight Control
Onboard Computer Ground Link
Camera
Payload
Ground Station
Fig. 3 A block diagram of the UAV systems.
An electric motor option was selected to drive the propeller. The alternate choice was an engine option as is common on many RC airplanes. While an engine can deliver more than adequate thrust, engines generally are heavier than comparable electric motors and the consumption of fuel can change the weight and center of gravity. Despite the number, and associated weight, of battery packs for long duration flights, the stability afforded by an electric motor was preferable for the UAV search-and-rescue application. The placement, housing and access for the battery packs consequently became critically important fuselage design issues. To incorporate an electronic propulsion system, a motor system had to be selected with sufficient thrust to propel the airplane. The thrust requirement was dictated by the lift and drag performance calculations for the aircraft while the battery needs were dictated by the competition requirement for a 1-h endurance. A Great Planes Rimfire 1.20 50-65-450 Outrunner Brushless motor and six battery packs were selected. This motor requires a high voltage compared to what most RC airplanes use, consequently a custom battery assembly was designed. The result is a customized airplane quite different than off-the-shelf RC approaches.
UAV systems overview Fig. 4 The team logos.
design and analysis process of the fuselage, three modular sections were considered: forward, center, and aft. Each of these sections is 0.61-m (2 ft) long, making the total length of the fuselage 1.83 m (6 ft). The wing uses a NACA 4412 airfoil section and has a rectangular planform area with a chord length of 0.36 m (1.167 ft) and a span of 3.67 m (12 ft) and is attached to the center section of the fuselage. A key aspect of the structural design is the need for a two-year working life of the airplane, which is much longer than the typical senior design project. Compo14
nent access, repair, breakage handling, and crash damage compensation influenced the design. The center section was designed as the integration point for the structural components of the aircraft including the wing mount, landing gear, and payload. The center section also contains the batteries required to power the aircraft during flight and houses all of the servos used to control the vehicle. Battery access and wing removal for shipping were design issues. The bulkheads were skeletonized to minimize weight.
The UAV systems are shown in Fig. 3. The airplane was designed for autonomous operation, but is also capable of full ground control. The batteries provide electrical power for the propeller motor and the other avionic systems. The ground link affords communication for manual radio control as well as for general flight telemetry and image download. The autopilot with internal GPS capability provides waypoint navigation capabilities. These systems will be integrated and tuned for autonomous operation.
Summary of lessons learned The interdisciplinary design for the Missouri S&T UAV required high levels IEEE POTENTIALS
Read more about it • J. P. How, C. Fraser, K. C. Kulling, L. F. Bertucelli, O. Troupet, L. Brunet, A. Bachrach, and N. Roy, “Increasing autonomy of UAVs,” IEEE Robot. Autom. Mag., vol. 16, no. 2, pp. 43–51, June 2009. • R. Loh, Y. Bian, and T. Roe, “UAVs in civil airspace: Safety requirement,” IEEE Aerosp. Electron. Syst. Mag., vol. 24, no. 1, pp. 5–17, Jan. 2009. • Australian Research Centre for Aerospace Automation. (2011). UAV Challenge [Online]. Available: http:// www.uavoutbackchallenge.com.au
About the authors David C. Macke, Jr. (david.c.macke.
[email protected].) is a senior in electrical engineering and is president of the IEEE AESS Student Chapter at Missouri
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University of Science & Technology. He is also the student representative for IEEE Region 5. Steve E. Watkins (steve.e.watkins@ieee. org) is a professor of electrical and computer engineering at Missouri University of Science & Technology. He graduated with a Ph.D. from the University of Texas at Austin. He is the faculty advisor for the local IEEE AESS Chapter and is involved in IEEE Region 5. Thomas Rehmeier (thomas.rehmeier@ mail.mst.edu) is a senior in aerospace engineering and is chief engineer of the Project Eagle-Eye Design Team at Missouri University of Science & Technology. He is also the president of the Missouri S&T Chapter of the American Institute of Aeronautics and Astronautics.
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Digital Object Identifier 10.1109/MPOT.2013.2295160
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of interaction between the IEEE AESS team and the AE senior design team. Each team has had to understand the vocabulary, concepts, and trade-offs associated with the other. The collaboration, as defined through a formal initial agreement to scope, costs, timeline, etc. and a codesign decision-making process, has been effective. The result is a design package that is better than what either team could accomplish alone. While the collaboration was challenging, the teams gained experience in complex engineering communication and decision making. They will have a creative design portfolio to accompany their resumes and a competitive entry into UAV competitions. This synergy is a good model for how to organize an interdisciplinary design project. The team logos are shown in Fig. 4.