An overview of two UAV projects developed within the INNOVATE program

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An overview of two UAV projects developed within the INNOVATE program

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application/pdf An overview of two UAV projects developed within the INNOVATE program S. Roggia, Hervé Morvan, Jason Atkin
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An overview of two UAV projects developed within the INNOVATE program

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An overview of two UAV projects developed within the INNOVATE program S. Roggia, H. Morvan, J. Atkin Institute for Aerospace Technology, University Of Nottingham, Triumph Road, NG1 2TU Nottingham. INNOVATE Team, sarah.roggia@nottingham.ac.uk Abstract An Unmanned Aerial Vehicle (UAV) is a completely automated aircraft with no pilot on board. UAVs can be remote controlled aircraft (e.g. flown from a ground control station) or can fly autonomously based on pre- programmed flight plans [1]. UAVs are currently used for a number of missions, including reconnaissance and attack roles. The development of such drones was one of the first collective projects for the INNOVATE Team, that operates within the Institute for Aerospace Technology of the University of Nottingham. Two prototypes were built with the objective of accomplishing a pre-set mission. Considering the high level of interest in the development of drones the UAVs are expected to have a significant impact in the outreach activities of the INNOVATE project. In this paper, the aim of the project and the final outline of the UAVs will be described. The project represents an example of a full autonomous electric system realized without the use of any fuel engine or even hybrid solution for the propulsion subsystem. Introduction Aircraft applications are demanding in terms of reliability, availability, and power density. These priorities should be satisfied trying to reduce aircraft weight, complexity of their systems, the fuel consumption, the operational costs, and the environmental impact. In order to meet these goals, the aircraft operators and the aerospace industry are expected to find solutions and continuous improvements in technologies while reducing costs, noise, and CO2 emissions. The highest achievement will be to build “All Electric Aircraft” (AEA), but this represent a big step to be undertaken by the aerospace industry. Moving toward this direction, stepwise goals have been addressed and they are currently named the “More Electric Aircraft” (MEA). The main goals of the MEA are using electricity for powering the aircraft systems and replacing the hydraulic and pneumatic actuator with electrical equivalences.[2-4] The Institute for Aerospace Technology (IAT) of the University of Nottingham (UoN) is heavily involved with the drive towards having more electric systems. In general, the mission statement of the IAT is to adopt a multi-disciplinary attitude to the field of aerospace engineering. In accordance with this and the more electric aircraft initiative mentioned above, the INNOVATE Team [5] has been involved with the development of two Unmanned Aerial Vehicles (UAV) capable of operating in an autonomous manner, travelling swiftly via pre-planned waypoints, and dropping - relief-items at required locations by autonomous identification of targets. Two types of UAVs have been developed, namely a multi-rotor prototype and a fixed wing aircraft such as shown in Fig.1 (Fig. 1). Fig. 1: UAVs pictures – Quadcopter on the top and fixed wing on the bottom. Aim of the Project The main aim of these UAVs projects is to emphasise the need for a multi-disciplinary approach to aerospace engineering, by having a team of researchers from different engineering backgrounds teaming up to produce controllable flight objects. . In addition, these projects are expected to act as case studies of aircraft engineering at a system level. This will serve to showcase the mission of INNOVATE and also help to improve the INNOVATE’s team outreach. Outreach plan includes, organising activities in schools and colleges, and online promotion of the project through Twitter and blogs. The UAVs have been exhibited at the Farnborough Air-show 2014, where the INNOVATE Team together with the IAT co-hosted a stand. A main aspect of the project was to maintain as low a budget as possible. With a £1,500 budget for each project, it was decided to use the same control feature, GPS, processing unit and camera for both of the UAV. Technical Features The UAV project goals and requirements have been defined by the Institution of Mechanical Engineers and are listed in Table 1. Particularly, the requirements are stated by the Institution of Mechanical Engineers in the “Discussion Event for Proposed University UAS Challenge” document [6]. No Requirements 1 Maximum Take-off Weight < 7 Kg 2 Cost of each project < 1500£ 3 Maximum UAS speed < 60 KIAS 4 Noise pressure level < 60 dB at 20 meters 5 Object recognition: the UAV shall be able to detect and recognise target object on the ground (2 dimension letters or numbers, with size given in [7] 6 Delivering up to 2 payloads of flour weighing 1 kg each (UAS may carry both payload in one flight or returning after the first delivery to reload the second) 7 Payload maximum size: 13 x 50 x 23 cm 8 Payload shall be delivered safely, without damages (either dropped after landing or with the help of a parachute) 9 Real time video feedback 10 Autonomous operation at all stages of flight 11 Real time measurements of altitude: 100 ft. < delivery altitude< 500 ft 290 ft.< cruise altitude < 310 ft 12 Stability during Take-off and Landing with crosswind < 5 knots. 13 Stability during Take-off and Landing with gusts < 8 knots. 14 GPS data logging for real-time or post-flight evaluation 15 Real time monitoring of flight parameters at the ground station 16 Satisfactory completion of the Basic Flight Operations stated in [8] 17 Time of flight > 15 min 18 Propulsive thrust shall satisfy point 10 19 Telecommunication, Remote control and FPV allowed frequencies as stated in [9] and in [10]:  433Mhz for remote control and telemetry  2.4GHz with maximum power of 100mW for remote control and telemetry  5.8GHz with maximum power of 25mW for FPV 20 The UAS specification will be governed by [9] and by Article 166 and Article 167 in [11] Table 1: UAVs’ Requirements Both UAVs used the following subsystems in order to accomplish the mission specified at point 8 of Table 1. A. Propulsion System The propulsion systems comprise electrical motors, with carbon fibre propellers attached on them, connected to a system of batteries. Motors, propellers and batteries have the following specifics.  For the quad-copter a system of four motors of 269.11 W of power and 580 Kv was used. The motors are rated at 6200 rpm and they are connected to a set of two batteries of 8000 mAh. Attached to each motor there is a propeller of 16 inches of diameter and 5 inches of pitch.  For the fixed wing configuration two motors of 630 W of power and 690 Kv were used; the motors can spin at 9040 rpm and they are connected to one battery of 12000 mAh. Attached to each motor there is a propeller of 13 inches of diameter and 6.5 inches of pitch. B. Flight Control System An autopilot has been used in order to let the UAV performing autonomous manoeuvres. The system is composed by the software and the hardware interface, as shown in Fig. 2. Fig. 2: Autopilot schematic. The autopilot allows the user to turn any fixed-wing aircraft or multi-copter into a fully autonomous vehicle. It is linked to APM Mission Planner, which includes mission planning, in-air parameter setting, on-board video display and full data logging with replay. In particular the mission planner is connected to Google Maps, and allows planning trajectories and select mission commands. The Inertial Navigation System (INS, accelerometer + gyroscope) is included in the Autopilot, which uses a 5 Hz GPS module. The following sensors are also included.  3-axis Accelerometer  Barometer  Magnetometer  3-axis Gyro. C. Telecommunication System A video transmission system and a telemetry system are used for communication between the UAS and the Ground station, as well as for the transmission of video data to the Ground station. The telecommunication system consists of the following components:  Video transmission sub-system: 25mW 5.8 GHz Transmitter, Diversity Receiver, Circular Antenna.  Telemetry system: 433 MHz telemetry system. D. Navigation System The navigation system combines a Global Navigation Satellite System (GNSS) receiver with an Inertial Navigation System (INS). The INS system is included in the Autopilot system. The GNSS receiver works at 5 Hz and it includes the compass sensor, which has a horizontal accuracy of 2- 2.5 m. Other sensors in combination with the GNSS receiver and the Autopilot were used, including  An External Air Speed Sensor as feedback for the data given by the GNSS and the INS;  Sonar, to have a better estimate of the UAV altitude during take-off and landing. E. Image Recognition System In autonomous mode, the UAV is required to identify the targets (numbers and letters), adjust course and position itself to drop the payload. The image recognition and control system is comprised of two control boards: 1. The Autopilot – used for flight control and described above. 2. The RaspberryPi – used for image recognition and mission planning. The reason for doing the image recognition on the RaspberryPi is that the autopilot does not have enough processing power. The image recognition part has been done by using the open source libraries from OpenCV that can be supported by the Linux operating system running on the RaspberryPi. Cascade classifier technique has been used. It involves two parts:  Training the classifier (using the opencv_traincascade function).  Detecting the targets in images. The RaspberryPi acquires images from the camera and processes them in order to detect the targets placed on an area of 200x200 square meters. The UAVs move on a predefined search pattern. Once the RaspberryPi detects a valid character and the UAV is close enough to the letter, the payload is released. An example of the possible pattern to follow is provided in Fig. 3. Fig. 3: Example of grid to cover the mission area. F. Payload Delivery System The approach adopted for the automated delivery of the payload shown in Fig. 4. The system includes a belt/band fixed at the bottom of the frame centre plate where the payload is held. One end of the band is fixed to the arm or frame centre plate with a ring screw, whereas the other end is hung on to a metal rod through a hook. One end of the rod is connected to the shaft of the servo motor through a servo-horn. Therefore, a clock-wise rotation (with respect to the reader) of the shaft prompts the displacement of the rod and the subsequent detachment of the band, which in turn causes the release of the payload. Fig. 4: Payload Delivery System Tests and Performances In the final paper, some design and implementation aspects of the UAVs will be presented. Several tests have been conducted on the UAV, mainly grouped into sets, named for convenience as “Ground tests” and “Flight tests”. These tests enabled the validation of necessary performance parameters such as for example the antenna range and the sensor sensitivity, and of course the overall performances of the UAVs. Special attention was given to acoustic sound tests in order to verify the effective sound generated by the UAVs. From these tests it was clear that results are over the limits imposed by [12]. As a general conclusion it is felt that these limits are too restrictive and not realistic. A formal suggestion was issued to the IMechE association in order to extend this limit to more approachable levels. The safety procedure imposed by [12] has also been tested, with the conclusion that the required flight time is somewhat a little long. While the prototyped UAVs managed to achieve this requirement, the Team still felt it important to suggest a reduction of the requested time ranges in order to have a better safety margin. . More detailed results will be listed in the final paper, although it can be said that with the exceptions of the sound level specification the main requirements were successfully achieved. In fact, the given mission was accomplished with both the UAVs having an endurance of more than 15 minutes and weighing less than 7kg. Conclusions The team was able to successfully satisfy the major requirements of the project, working within the guidelines laid down by the CAA[13], OFCOM [3] and BMFA [14]. The project was completed within 5 months from the starting date. Two fully autonomous air vehicles with aerial image recognition and subsequent payload discharge capability were constructed. Further improvements are expected to be done, especially for the image recognition system. Programing the image recognition and connecting the processing unit to the pilot was one of the most challenging parts of the project. In order to improve the accuracy of the delivery point of the payload and have higher search times, it is felt that more processing power is necessary. Instead of using a raspberry Pi, it would be ideal to utilise a more powerful processor, such as that of a PC or laptop. This would reduce computational time and increase accuracy. Thus correct letter recognition could be potentially done at even higher flight heights, while improving payload delivery accuracy and having a more robust system. Considering all the technical difficulties encountered during the course of this project, the development of the UAVs proved to be a very challenging, system level, aerospace engineering project. . It gave excellent insight into how a propulsive system can be entirely realized with electrical subsystems (this is the case of an AEA). It also provides the INNOVATE Team with a potential idea of what the final technology demonstrator (required from the team) will be and has resulted in a set of tools and frameworks necessary for its development. It is very interesting to note how all the knowledge owned by the different members of Team (coming from different background) can be gathered together in order to build an aerospace system. Acknowledgements This work is funded by the European Commission under the project titled INNOVATE, The systematic Integration of Novel Aerospace Technologies, FP7 project number 608322 which is part of the FP7- PEOPLE-2013-ITN call. References [1] (2014, August 2014). The UAV. Available: www.theuav.com [2] K. J. B. C. Gerada, "Integrated PM Machine Design for an Aircraft EMA," presented at the Industrial Electronics, IEEE Transactions on 2008. [3] M. G. C. Gerada, T. Raminosa, "Design Considerations for a Fault-Tolerant Flux- Switching Permanent-Magnet Machine," presented at the Industrial Electronics, IEEE Transactions on July 2011. [4] J. A. O. J.A. Rosero, E. Aldabas, L. Romeral, "Moving Towards a More Electric Aircraft," IEEE A&E SYSTEMS MAGAZINE, MARCH 2007. [5] (2014). INNOVATE. Available: http://www.nottingham.ac.uk/innovate/index. aspx [6] Discussion event for poroposed university UAS challenge, I. o. m. enigineering, 2013. [7] ICAO 9157 - Aerodrome Design Manual, U. Nations, 2004. [8] Ofcom, "IR 2030 - UK Interface Requirements 2030 Licence Exempt Short Range Devices," Ofcom, Ed., 1.6 ed, 2011. [9] CAP 722: Unmanned Aircraft System Operations in UK Airspace - Guidance, C. A. Authority, 2012. [10] IR 2030 - UK Interface Requirements - License Exempt Short Range Devices, Ofcom, 2011. [11] CAP 393: Air Navigation: The Order and the Regulations, C. A. Authority, 2009. [12] IMechE, "Annex B UAS Safety and Certification Requirements in Discussion event for proposed University UAS challange " 2013. [13] C. A. Authority, "CAP 722 Unmanned Aircraft System Operations in UK Airspace – Guidance," in www.caa.co.uk, C. A. Authority, Ed., 5th ed: TSO (The Stationery Office) on behalf of the UK Civil Aviation Authority, 2012. [14] B. M. F. Association, "Member’s Handbook 2010 Issue," in http://www.bmfa.org/Downloads/, BMFA, Ed., ed: British Model Flying Association (SMAE Ltd.), Leicester 2010.