DOC

Problem

By Marie Stevens,2014-01-20 03:02
10 views 0
Problem

    Development of an Autonomous Parafoil Vehicle

    Uday Gurnani (uxg031000@utdallas.edu )

    Electrical Engineering Undergraduate, The University of Texas at Dallas

    Intern, Centre for Aerospace Systems Design & Engineering,

    Department of Aerospace Engineering

    Indian Institute of Technology Bombay, Mumbai, India

    Technology without borders The term globalization has taken a new meaning in today’s small world where collaborations have

    moved beyond the corporate sector and into the field of education. Universities and schools

    around the globe have formed associations and setup exchange programs that allow students and

    faculty with different backgrounds to come together to discuss and develop ground-breaking ideas.

    The linkages between schools of science and engineering have broadened the scope of what is

    known as “technology without borders.” It is this very idea that drew me from Dallas, Texas to the

    Indian Institute of Technology (IIT), Bombay this June to work with three other students on a

    summer project in the Department of Aerospace Engineering. The work was supported by IDeAS

    Laboratory (http://www.casde.iitb.ac.in/ideas), at IIT Bombay.

    The Team

    A true blue Mumbai-ite, I am currently pursuing my bachelor’s degree in electrical engineering at The University of Texas at Dallas. In addition to me, the project team consists of two student

    interns, Aurelien Blanchard (a_blanchard@ensil.unilim.fr) and Laurent Pigale

    (pigale@ensil.unilim.fr), both Mechatronix majors from the National Higher Engineering School

    of Limoges (ENSIL) in France. The fourth member of the group was Trupti Ranka

    (trupti_ranka@yahoo.com), a sophomore, instrumentation and control major, at the Pune Institute

    of Technology. Professor Hemendra Arya and Mr. Amitay Isaacs of the Department of Aerospace

    Engineering, IIT Bombay, Mumbai were our supervisors for the project.

    The Project Autonomous Parafoil Vehicle

    Parafoil or Ram Air Parachute based Precision Aerial Delivery Systems hold considerable

    interest today. These unmanned, autonomous systems can be dropped from an aircraft and then

    glide to remote, inaccessible locations to deliver useful payloads in excess of 500 kg of medicines,

    food, etc.

    The aim of the project is to develop an autonomous Mini Parafoil system. A scaled down

    version of the full system that can carry a three-wheeled gondola of size smaller than a baby

    tricycle. The parafoil was procured from a hobbyist, but the construction, instrumentation and

    testing of the integrated system was the objective of the project.

    Parafoil systems have been of great interest to scientists; from the development of crew return

    vehicles (CRV) at NASA to the investigation of such autonomous systems at the Institute of Flight

    Research in Germany. What makes these parafoil systems special is that they involve low costs,

    are small in size, lightweight, easily maneuverable due to low speeds, and can be used in a broad

    range of activities from remote and precision delivery of payloads to surveillance.

    Parafoils and the Principle of Flight

    Parafoils or ram air parachutes are flexible wings having two surfaces or rectangular shaped

    membranes that are attached and sewn together except at the parafoil’s leading edge. Parafoils are

collapsible airfoils and maintain their shape by trapping air

    between these membranes. When not in use they can be

    collapsed and carried in compact containers. Parafoils can

    perform a landing at practically nil impact.

    Forward motion is necessary to produce lift force for the

    parafoil and to allow the vehicle to fly. The glide ratio or the

    distance covered on ground while loosing a given height for a

    parafoil is in the ratio of 5:3, when not powered. If the parafoil

    is dropped from an aircraft flying at 5 km altitude, then the

    parafoil can reach a spot 25 km from where it was dropped.

    This gives a good standoff distance from the target. A motor

    and propeller, when added to the basic system, provides thrust

    and can increase the distance covered.

    Vehicle Development

    Fig 1 : Parafoil with Gondola The roadmap for the project has three phases. Phase-1 involvess the construction of the basic vehicle, which has been completed. Figure-1 is view of parafoil vehicle built by the team in flight. Phase two of the project will see the development and testing of instrumentation to measure various flight parameters. Phase three will deal with the autonomy of the vehicle.

    Phase 1 Basic Vehicle Construction

    The main vehicle design went through several iterations, starting from a configuration suggested

    by a hobbyist (http://www.seabreezeparachutes.com), before arriving at the final frozen configuration.

    The mainframe and axle of the vehicle consist of spring steel wires that were bent in their

    desired shapes to support the various components. Spring steel material was used since it is elastic yet strong, and would be ideal to support the weight of the vehicle and instrumentation and prevent any changes in the orientation of the vehicle on landing. A

    strip of 3 mm thick aluminum was used to construct the 14 cm

    diameter propeller guard. The fly-bar was made from a steel tube,

    and pivoted along a perpendicular axis on the gondola. Holes at

    equal intervals were made in the tube to attach the parafoil as well

    as the push rods from the servo that determines the direction the

    vehicle should turn. Ready-made wheels, one in the front and two

    at the ends of the axle, were used to allow for smooth landings and

    take-offs.

    The central main box or the “heart” of the gondola holds the various electronic components that run the vehicle. It also serves as

    a support for the octagonal motor frame. Therefore, even though

    plywood would add to the weight of the gondola, a parameter we

    aimed to minimize, we decided to use it to construct the main box

    as well as crucial support frames. Balsa wood was used to

    construct the box for the pressure and angle sensors. The

    instrumentation box was placed over the propeller guard such that

    Fig 2. Gondola showing motor, it would not be affected by the air flow due to the propeller.

    propeller, vanes, etc.

Most of the wooden parts and wires were joined together using glass fiber thread, cotton thread,

    and epoxy. The joints were very strong and could withstand the various flight tests. Yet, the joints

    could be easily removed when required, thus giving us the flexibility to make any modifications.

    The motor was fixed to a modular octagonal wooden panel, which was fixed onto the main box

    using screws and nuts. An Actro C-4 brushless motor was attached to a 12 cm propeller, which

    provided the thrust. A Lithium polymer battery was used as the power source. The instrumentation

    boxes were also made modular to enable use with other aerial vehicles.

Phase 2 Instrumentation and Testing

    To achieve our final goal of autonomy of the vehicle, we first need to design or acquire sensors

    that would be able to accurately measure various flight parameters. These would help the system

    to navigate and guide itself during an autonomous flight.

    1) Air Data Sensors

    a) Air speed (V): The speed of the air with respect to the parafoil

    system is essential to determine at what speed it is traveling with

    respect to the ground.

    Instrumentation: A pitot-static tube consisting of two co-axial

    tubes, one measuring static pressure, and the other stagnation

    pressure is used (schematics in Figure 3). The static is

    communicated to low-pressure port (p

    ) of a differential pressure A

    transducer, while total pressure is connected to port (p). (refer B

    http://content.honeywell.com/sensing/hss/pressure/pdf/ascx.pdf).

    The sensor measures the difference in pressure between B and A,

    and returns a voltage reading, which can be calibrated to indicate

    air speed.

    Fig 3. Schematic of air speed Calibration: Since the pressure sensor gives us a value in Volts, measurement we needed to calibrate it, i.e. determine a way to convert from

    voltage to air speed. Bernoulli equation relates air speed to the

    2(p?p)pressure difference and air density. ABV??The system was further calibrated in a wind tunnel

    b) Altitude (h): The height at which the parafoil system flies with respect to the ground forms an

    important flight parameter.

    Instrumentation: The static pressure, p

     as in air speed measurement is connected to an absolute A

    pressure transducer.

    Calibration: Standard Atmospheric tables quantify the relationship of altitude and static pressure (http://www.ae.su.oz.au/aero/atmos/atmos.html). The voltage signal from the pressure transducer

    can thus be calibrated to read altitude.

    c) Angle of attack (α): The angle between the reference line of the vehicle and the oncoming wind. The reference line is an imaginary line that runs from the leading edge to the trailing edge of

    the vehicle. The angle of attack affects the lift force that is generated on the parafoil, and thus

    determines the aerodynamic behavior of the vehicle.

Instrumentation: An aluminum wind vane attached to a 5 kΩ potentiometer (http:

    //www.uniautomation.com/prod01.htm#CONDUCTIVE%20PLASTIC%20RESISTANCE%20EL

    EMENT) is used to measure α. The vane always aligns itself to the direction of wind, and our aim is to measure the angle it deflects by, with respect to the reference line. Since the vane is

    connected to the potentiometer shaft, a deflection in the vane causes the potentiometer shaft to

    rotate producing a change in voltage across the output terminals of the potentiometer.

    Calibration: The system was calibrated in a wind tunnel, where the angle of attack was known.

    Variation of potentiometer output voltage Vs angle of attack was realised as a fairly linear

    calibration curve.

    d) Angle of sideslip (β): The horizontal angle between the reference line and the oncoming wind. Instrumentation: A similar potentiometer-wind vane setup was used to measure the angle of

    sideslip. However, this instrumentation would be mounted such that the potentiometer plane lies

    parallel to the horizontal.

    Calibration: The method for calibration for the sensor was identical to that for angle of attack.

2) Inertial Sensor: Microstrain’s gyro enhanced orientation sensor,

    3DM-GX1 (www.microstrain.com/3dm-gx1.aspx) is used to determine

    the orientation of the vehicle. Orientation in roll, pitch and yaw about

    three axes are defined by Euler angles - φ, θ, ψ.

    (http://mathworld.wolfram.com/EulerAngles.html). The 3DM-GX1 is

    able to return these Euler angles both directly in degree units and in the

    form of corresponding voltages. A highly integrated package, the sensor

    consists of three orthogonal DC accelerometers, three orthogonal

    magnetometers, a multiplexer, a 16 bit ADC, and an embedded microcontroller. 3DM-GX1

    3) Navigation Sensor

    Global Positioning System (GPS): A GPS receiver mounted on the gondola is used to determine the position (latitude, longitude and height) and velocity of the vehicle. These parameters are

    calculated by the receiver with the help of encoded signals from GPS satellites. The velocity

    recorded by this receiver can be integrated with that obtained from the pitot tube arrangement to

    obtain a more accurate velocity reading. 4) Datalogger: The datalogger used was the Onset Tattletale TFX-11. (http:

    //www.onsetcomp.com/Products/Product_Pages/Tattletale_pages/2363_TFX_11.html). Four of

    the available 11 analog channels are used to record 12-bit data obtained from the sensors. A wind

    tunnel test was carried out and some of the parameters were recorded on the datalogger and later

    transferred to a PC using a TFBASIC program for calibration the altitude, velocity and α, β vanes

    as explained above.

    Phase 3 Autonomy The final phase of the project is to make the parafoil vehicle autonomous i.e. it should be able to perform a defined set of flying tasks without communicating with any external device. The basic structure of an autonomous vehicle consists of a guidance, navigation and control systems (GNC). All the sensors discussed in the earlier section form the navigation system and provide crucial parameters that help the guidance and control systems. Microcontrollers, on-board computers and actuators will be used to complete the GNC system and make the vehicle autonomous.

    As we come towards the end of our term at IIT, the parafoil with its gondola and instrumentation could take to air (Figure 1). The next few steps towards realizing the final goal of an autonomous parafoil vehicle might be for another group of students to take up. Maybe they will come from different parts of the globe, each one adding a piece not only to the parafoil vehicle puzzle, but also a piece to a cultural mosaic that transcends national borders and boundaries.

    Acknowledgements

    This project has been a great learning experience for me and I have really enjoyed working with my colleagues and guides. I’m truly grateful to Professor Hemendra Arya for giving me the opportunity to work with him on this project and for his constant guidance and support; Mr Amitay Isaacs for sharing with us his expertise and for his encouragement; all the IIT staffers including Mr. Jadhav, Mr. Hadkar, Mr. Sarkate, Mr. Bhave, Mr. Rakesh, Mr. Amit Doshi and Mr. Rahul Phatak for their help in the workshop and the lab; and Professor K. Sudhakar for the opportunity to write this article.

Note by Professor K Sudhakar, Head Dept. of Aerospace Engineering, IIT, Mumbai

    Ms. Karishma Babu (karishmababu@yahoo.com) invited an article from me for their IEEE VESIT publication targeted at undergraduate students of engineering. The article was to highlight my current research interests. I felt it may be more interesting and educative for the students to learn about working together and that too in cross-cultural groups. This article authored by Mr. Uday Gurnani outlines what four undergraduates from far-flung areas of the world did, with tight constraints on time. An opportunity to work in such groups on projects such as this brings about a better understanding of synthesis in engineering as also of cultures.

Report this document

For any questions or suggestions please email
cust-service@docsford.com