Implementation of Multi-mini UAV Navigation Control System *

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1 Journal of Aeronautics, Astronautics and Aviation, Series A, Vol.43, No.2 pp (2011) 129 Implementation of Multi-mini UAV Navigation Control System * Chia-Sung Lee 1, Chun-Liang Lin **,1, Van-Tsai Liu 2, Cheng-Chi Chen 3 Wei-Shin Chen 3, and Huan-Jung Lin 3 1 Department of Electrical Engineering, National Chung Hsing University 250 Kuo Kuang Rd., Taichung 402, Taiwan R.O.C. 2 Department of Electrical Engineering, National Formosa University 3 Graduate Institute of Aviation and Electronic Technology, National Formosa University No.64, Wunhua Rd., Huwei Township, Yunlin County 632, Taiwan, R.O.C. ABSTRACT The use of unmanned aerial vehicles (UAVs) is growing fast in recent years from reconnaissance to attack missions. They are increasingly being used in a small but growing number of civil applications. With regard to control of UAV, it is quite often that a ground-based control center only navigates one UAV at a time, and UAV in flight cannot communicate with each other. In the current stage, simultaneous navigation of multiple UAVs is still a challenging task. This study implements a multi-mini UAV navigation system which combines power supply module, flight control module, video transmission module, video receiver module, video processor and GPS module, And designed the communication protocol to fulfill the multiple UAVs navigation and control. Subsequent to the hardware-in-the-loop simulating tests, the field tests have been conducted to verify the functions and performance of the flight control software and the collaborative mission planning. Preliminary results of real-world flight tests show success of this research. Keywords: UAV, Flight control, Multiple UAV navigation I. INTRODUCTION In the past, unmanned aerial vehicle s (UAV s) tasks are mostly single mission type, see Fig. 1. It only needs one ground control station (GCS) and a single-shelf UAV communication conducted in a manner prior to implementation. The development of multiple UAV navigation for GCS has attracted many researchers in recent decades. In the case of time limit, traditional GCS structures are no longer able to meet the task demand. For example, single loop process (SLP) is only suitable for use in single UAV systems. The SLP design is single threaded execution, which is unable to process the multiple UAV navigation. For the multiple UAV navigation design, the authors of [1, 2, 3] presented the network-centric operations for Figure 1 One GCS control multiple UAVs * Manuscript received, Oct. 26, 2010, final revision, Mar. 23, 2011 ** To whom correspondence should be addressed, chunlin@dragon.nchu.edu.tw

2 130 Chia-Sung Lee Chun-Liang Lin Van-Tsai Liu Cheng-Chi Chen Wei-Shin Chen Huan-Jung Lin multiple UAVs on a basic framework model. In [4, 5], the authors depicted the development of a simulator for multiple UAVs based on the simulator XPlane developed under Matlab environment. In [6], a ground control station (GCS) for multiple UAVs equipped with multimodal interfaces were considered. For the design of flight control system for mini-uav, a flight control system has been proposed for a small unmanned aircraft in [7] with tests performed to verify the design. In [8], an on-board flight computer for the small UAV with the radio control system and GPS module was presented. The PC/104 commercial on-board computer, inertial measurement unit (IMU) and communication modem of onboard control system were implemented in a blended wing vehicle with autonomous flight control system design. Stability analysis of the flight control system for a small UAV was conducted in [9, 10]. In [11], the authors have implemented a flight control computer using a microprocessor and FPGA. More flight control designs for various types of UAVs could be found, for example, in [12-14]. Among the published literatures, the research dealing with the issue of implementation of navigation and control systems for multiple UAVs are not very common. This paper represents a complete design of a multiple UAV navigation architecture shown as in Fig. 1. Implementation of this mission only needs a GCS to command the multiple UAVs simultaneously. Table 1 Physical parameters of the developed mini UAV II. PLATFORM ARCHITECTURE Figure 2 Internal structure of the mini UAV; module descriptions: (a) Brushless Motor; (b) Li-Poly Battery; (c) Color CCD; (d) Flight Control Computer; (e) Video Transmitter; (f) RF Antenna; (g) Control Surfaces Servomotor. Network of Multiple UAVs The major challenge of the multiple mini UAV navigation is that a GCS has to simultaneously control multiple objects at a time. The success of this mission relies heavily on a high efficient computational kernel and powerful hardware. To this aim, the following functions have been implemented. a. Using RF modem provided by the network topology technology.this avoids data confusion of UAV and GCS in the broadcast mode of communication. b. Development of a compact communication protocol for multiple UAV navigation. c. Using MLP structure and C++OOP (object-oriented programming) to realize GCSS (ground control station software). The GCS receives information sent from multiple UAVs and avoids possible data confusion at the same time. Configuration of UAV The UAV possesses a wingspan with 0.62 m. It is able to cruise at a speed of 15 m/s. The center of gravity (CG) approximates to 15% of the mean aerodynamic chord (MAC). Table 1 shows the physical parameters of the mini UAV. The fuselage contains several modules displayed as in Fig. 2. Navigation System The flight control computer (FCC) is displayed in Fig. 3 with its architecture shown in Fig. 6. Kernel of the FCC is a dual programmed micro control unit (MCU). Item Length Wingspan Weight Wing area Wing loading Max. Cruise time Working current Propeller Value 0.52 m 0.62 m 1.2 kg 0.21 m kg/m 2 50 min 4.5 A mm Figure 3 FCC module Functionally, the FCC consists of a flight controller (FC) and a navigation controller (NC). The FC deals with input signal processing including the signals measured from a three-axis accelerometer, three-axis gyroscopes, a pressure altimeter, an airspeed sensor, an electronic magnetic compass, a signal receiver and a RF modem, and two servo motor-driven wing surface. The NC is

3 Implementation of Multi-mini UAV Navigation Control System responsible for navigation and video data processing. The updated cycle of the FC is 33 ms, and 200 ms for the NC. Based on the information from UAV aerodynamics, analog sensing signals and position information provided by the GPS and electronic compass, the control system adjusts the actuators and corrects the UAV s pitch and roll angles. Both MCUs interact with each other via MSSP (master synchronous serial port) modules in I²C-based communications, as shown in Fig. 4. Table 2 characterizes the FCC. 131 decodes the PWM command sent from the RC, which is more reliable in the quality of flight control. However, its effectiveness is strictly limited by the length of the wire. The hardware architecture is shown as in Fig. 5. Figure 5 GSIB Architecture The complete GSIB module is shown in Fig. 6 which includes a GPS receiver, a pressure altimeter, a UAV RF port and a GCS RF port integrated in a single PCB. Figure 4 FCC system architecture Table 2 Descriptions of the FCC Item MCU Gyro Acc Compass Altitude Sensor Airspeed sensor GPS RF Modem Characterization 2 Microchip PIC 18F axis gyroscopes; Murata ENV-05G 75 /s 3-axis accelerometers; ANALOG DEVICES ADXL103 Honeywell HMR3300 Free scale MPX4101A Free scale MPXV5004 Holux GR-213 Aerocomm AC-4490 Ground Station Interface Box GSIB (ground station interface box) and FCC share the same dual MCUs. The GSIB simultaneously receives the remote control s (RC s) command and the GCS s command. This permits the external pilot (EP) using the RC to guide the UAV during take-off and landing. The commands are received by the GSIB and then sent to the FCC after processing. Even when the GCS s PC is off-lined, the GSIB can still control the on-flight UAV because an emergency function is provided. The GSIB provides two receiving modes, i.e. remote and direct control modes. Remote control mode uses a radio receiver to directly receive and decode the remote control commands. For direct control mode, there should be a wire to link the GSIB and RC. The GSIB receives and Figure 6 GSIB module III. SOFTWARE STRUCTURE Protocol The communication protocol is designed to fulfill the navigation and control of multiple UAVs, see Table 3. Table 3 Communication Protocol Byte byte 1 byte 2 byte 3 byte 4 byte 5 byte 6~N byte N+1 byte N+2 Name Start Code UAV ID Msg ID (~)Msg ID Datum Len Datum Check Sum Sentence End byte

4 132 Chia-Sung Lee Chun-Liang Lin Van-Tsai Liu Cheng-Chi Chen Wei-Shin Chen Huan-Jung Lin Msg ID packet defines the range of 0x00 ~ 0XFF. Odd numbers are uplink command, whereas even numbers are down-link data, as described by Table 4. This packet will decide the UAV flight mode and status. The current design manual, automatic pilots, hovering and retune home of the flight mode. ID# ID 0 ID 1~20 ID 21~50 ID 51~150 ID 151~254 ID 255 Table 4 Definition of Msg ID Data Direction, Input (Uplink) odd Output(Downlink) even UAV GSIB PC UAV GSIB GSIB PC UAV PC Reserve PC GSIB UAV acknowledge the GCS with a confirmation message. If GCS fails to connect the UAV, the system will give up this packet and proceed to Step 6. Step 4: Register a SLP to the system. Step 5: The MLP assigned the data to the SLP of UAV ID. The SLP will then be decoded and displayed. Step 6: Check the receiving statuses of all UAVs. If all UAVs are successfully linked, the process goes back to step 1 and proceeds to the succeeding steps. Otherwise, the system will sends a warning message of UAV lost to EP and commands EP to make a correct decision. Go back to Step 1. GSIB deals with all the information, such as UAV, GCS and PC, and it thus reduces the workload on the system chips. We adopt odd and even numbers to differentiate up-link and down-link, and use ID ranges as the data transmission target. Table 4 explains how it works. Example: differentiate up-link and down-link: if( ID & 0x01 ) Uplink else Downlink differentiate direct where if(id range 1~20) not pass to PC if(id range 21~50) not pass to UAV if(id range 51~150) not decode, direct to pass to PC or UAV Ground Control Station Software The proposed design allows the registration of new UAV and interruption of the new events. Planning of new object registration and decoding mechanism are illustrated in Fig. 7. There is a crucial step when actual UAV takes off, that is, the GCS shall acknowledge the new UAV registration while the registered UAV is disconnected. The programming steps of the GCS program can be summarized as follows: Step 1: The communication program receives and checks header and checksum of the data obtained from the radio frequency module. Step 2: Identify the data header of UAV ID registered and receive the message (refers to Table Ⅰ for the communication protocol of multiple UAVs). If successful, move on to Step 5. Step 3: GCS sends a verification message to each UAV to build up the connection. If successful, each UAV will Figure 7 Framework of the GCS operational software for multiple UAVs Human-Computer Interaction The HCI (human computer interaction) is displayed as in Fig. 8. Figure 8 Multiple UAV man-computer interface:

5 Implementation of Multi-mini UAV Navigation Control System a. Selection of the operation b. Current location c. Attitude, head and power system information d. Enter data up-link parameters e. Real-time flight trajectory f. Flight mode, airspeed, altitude and system status g. Flight attitude h. UAV heading The experiments showed that the developed GCS allows up to sixteen UAV flies and is capable of displaying an information window for each UAV and decoding signals simultaneously at 10Hz data down-link rate. IV. FIELD TEST Three stages were conducted for flight tests: a. Performed communication test on the ground. Three sets of RF modem EVM (evaluation motherboard) were used to establish GCS (as the server) with two UAVs (as clients) joining the test. b. GCS (see Fig. 9) and mini UAV (see Fig. 10) joined the communication test. Checked the functions of UAV up- and down-links and verify the correctness of command coding/decoding schemes. Figure 9 GCS System Figure 10 Two mini-uavs joining the files test 133 c. Conducted actual flight tests. UAV1 and UAV2 played as a target and chase UAV, respectively. Firstly, UAV1 took-off by the aid of a human operator and flew at an altitude of around 300 m. To keep the hovering flight, the GCS uplinked to the control commands. On the other hand, UAV2 took off next and was manually controlled to reach at the altitude of 200 m. The two UAVs then performed the chasing flight One of the real-time images is captured by UAV1 when the actual flight is displayed in Fig. 11. Download the video and OSD module integrated flight data which provides important information including altitude, airspeed and operational voltage. The real-time monitor of the flight statuses of the two UAVs is shown in Fig. 12. Flight trajectories, speed and altitude of the two UAVs are shown in Figs Figs. 13 and 14 show the flight trajectories of UAV1 and UAV2, respectively. Figs. 15 and 16 show speeds of the two UAVs during flight. The average speed for UAV1 is 30 knot and 33 knot for UAV2. Speed variations of both UAVs are controlled at 7 knot and 5 knot, respectively. The difference is that both UAVS possess different configuration and servo control mechanism. In addition, Figs. 17 and 18 display the flight altitudes. Figs. 19 and 20 plot flight trajectories and altitudes of the two UAVs respectively. Fig. 19 shows one UAV flighted autonomously at the fixed bank angle, and another UAV Figure 11 Real-time video captured by UAV Figure 12 Real-time monitoring UAV statuses

6 134 Chia-Sung Lee Chun-Liang Lin Van-Tsai Liu Cheng-Chi Chen Wei-Shin Chen Huan-Jung Lin Figure 13 Flight trajectory of UAV1 Figure 16 Speed of UAV2 Figure 14 Flight trajectory of UAV2 Figure 17 Altitude of UAV1 Figure 15 Speed of UAV1 flighted at the manually controlled mode. Fig. 20 shows one UAV hovered at the higher altitude, another UAV launched next and then hovered at the lower altitude. Both UAVs are commanded via a GCS. The control system operated with 10Hz downlink data rate is able to simultaneously control up to 16 sortie UAVs like Extra, shown as in Fig. 21. It consists of a Figure 18 Altitude of UAV2 notebook with the CPU worked at 1.8GHz and memory of 1GB, the CPU utility rate is 95%. It should finally be mentioned that capacity of the simultaneous control of multiple UAVs relies heavily on the RF module s bandwidth. Because of the finite RF bandwidth, longer communication ranges only allows

7 Implementation of Multi-mini UAV Navigation Control System 135 Figure 19 Flight trajectories of the two UAVs Figure 22 Multiple UAVs data assignment based on the unified modeling language (UML) Figure 20 Altitudes of the UAVs lower baud rate in data transmission accompanied with shorter data length. The research undergoing is to include an integrated network database system (INDS) to virtually expand the system performance. The ultimate objective is to simultaneously control up to 30 UAVs. To this aim, the INDS s capability of data sharing allows richer data interflows to avoid collision, with which control of multiple UAVS is via a master GCS to control several slave GCSs from which to individually control the affiliated UAVs. V. CONCLUSIONS AND FUTURE WORKS Figure 21 Multi-windows display the capability of multi-uav flight control of the GCS This paper describes the detail design of an avionic, mission control, and communication system developed for navigating multi-mini UAVs. The multi-mini UAV navigation system has integrated power supply module, flight control module, video transmission module, video receiver module, video processor and GPS module. Field tests for functions and performance of the whole system have been conducted. Successful results showed the stability and reliability of the proposed design and also the durability of the hardware. For multiple UAVs navigation software planning, in addition to adopt the MLP structure and the suitably planned protocol, expandability of the software were considered. The software here was designed based on the C++ object-oriented programming (OOP) and UML. An INDS is developed for enhancing management efficiency of the mission dispatch and improves effectiveness of the security services. We have also implemented a preliminary INDS which is able to automatically dispatch multiple missions to UAVs. In the past, ground operators can only, simply manipulate a single UAV mission at a time. It is increasing to have the need to manage more than one

8 136 Chia-Sung Lee Chun-Liang Lin Van-Tsai Liu Cheng-Chi Chen Wei-Shin Chen Huan-Jung Lin UAV mission in the air at the same time, see, for example, Fig. 23. The functions of dispatching multiple UAVs to fulfill specific missions autonomously [1] are currently being developed which is designed to fit the multiple dynamic human supervisory control tasks, see Table 5, the design. Table 5 Automation Level Automation Automation Description Level 1 The computer offers no assistance: human must take all decision and actions. 2 The computer offers a complete set of decision/action alternatives, or 3 narrows the selection down to a few, or 4 suggests one alternative, and 5 executes that suggestion if the human approves, or 6 allows the human a restricted time to veto before automatic execution, or 7 executes automatically, then necessarily informs humans, and 8 informs the human only if asked, or 9 informs the human only if it, the computer, decides to. 10 The computer decides everything and acts autonomously, ignoring the human. Figure 23 Multiple UAVs mission architecture ACKNOWLEDGEMENT This research was supported by Chung Shan Institute of Science and Technology and supported in part by Industrial Technology Research Institute, Taiwan under the grant REFERENCES [1] Mitchell, P. J., Cummings, M. L., and Sheridan, T. B., Management of multiple dynamic human supervisory control tasks, Proceedings of the International Command and Control Research and Technology Symposium, McLean, VA, June [2] Mitchell, P. J. and Cummings, M. L., Operator scheduling strategies in supervisory control of multiple UAVs, Aerospace Science Technology, November 2007, pp [3] Finn, A., Kabacinski, K. S., and Drake, P., Design Challenges for an Autonomous Cooperative of UAVs, Proceedings of the IEEE Information Decision and Control, June 2007, pp [4] Garcia, R. and Barnes, L., Multi-UAV simulator utilizing X-Plane. Springer Science, Journal of Intelligent and Robotic Systems, October 2009, pp [5] Goktogan, A. H., Nettleton, E., Ridley, M., and Sukkarieh, S., Real time multi-uav simulator, Proceedings of the IEEE International Conference on Robotics and Automation, September 2003, pp [6] Maza, I., Caballero, F., Molina, R., Pena, N., and Ollero, A., Multimodal interface technologies for UAV ground control stations, Journal of Intelligent and Robotic Systems, No. 57, 2010, pp [7] Ozimina, C. D., Tayman, S. K., and Chaplin, H. E., Flight control system design for a small unmanned aircraft, Proceedings of the IEEE American Control Conference, June 1995, pp [8] Hall, C. E., On board flight computers for flight testing small uninhabited aerial vehicles, Proceedings of the IEEE International Conference on Circuits and Systems, August 2002, pp [9] Lee, D. J., Min, B. M., Tahk, M. J., Bang, H., and Shim, D. H., Autonomous flight control system design for a blended wing body, Proceedings of the IEEE International Conference on Control Automation and Systems, October 2008, pp [10] Campbell, J. L. and Kresge, J. T., Brumby uninhabited aerial vehicle flight dynamics-instru, mentation and flight test results, Proceedings of the IEEE Digital Avionics Systems Conference, October 2003, pp. 8.A [11] Wigley, G. and Jasiunas M., A low cost, high performance reconfigurable computing based unmanned aerial vehicle, Proceedings of the IEEE Aerospace Conference, October 2006, pp [12] Chandler, G. D., Jackson, D. K., Groves, A. W., and Rawashdeh, O. A., A Low-Cost Control System for a High-Altitude UAV, Proceedings of the IEEE Aerospace Conference, March 2005, pp [13] Klenke, R. H., A UAV-Based Computer Engineering Capstone Senior Design Project, Proceedings of the IEEE International Conference on Microelectronic Systems Education, June 2005, pp [14] Escare no, J., S-Cruz, S., and Lozano, R., Embedded control of a four-rotor UAV, Proceedings of the IEEE American Control Conference, June 2006, pp