Autonomous Control of Tilt Tri-Rotor Unmanned Aerial Vehicle

Transcription

1 Indian Journal of Science and Technology, Vol 9(36), DOI: /ijst/2016/v9i36/102160, September 2016 ISSN (Print) : ISSN (Online) : Autonomous Control of Tilt Tri-Rotor Unmanned Aerial Vehicle Rashidah Funke Olanrewaju 1 *, Rafhanah Shazwani Binti Rosli 1 and Balogun Wasiu Adebayo 2 1 Faculty of Engineering, International Islamic University Malaysia, Jalan Gombak 53100, Kuala Lumpur, Malaysia; frashidah@iium.edu.my, xania92@gmail.com 2 Department of Mechatronics Engineering, Lagos State Polytechnic Ikorodu Nigeria; balogunwa1999@yahoo.com Abstract A control algorithm of tri-rotor aircraft using PID control and the effect of it in a tilt tri-rotor aircraft is proposed and observed in this paper.in the development of the control algorithm, a mathematical model consisting variables from three motors used and its tilting mechanism is obtained and referred to. A significant improvement is observed when the control algorithm is applied to the system in which the pitch overshoot is greatly reduced and approach to a constant zero.tilt Tri- Rotor Unmanned Aerial Vehicle (TRUAV) is an aircraft that has three motors and does not allow pilot intervention in the management of the flight. There exist situations where the surrounding environment is not appropriate or even dangerous to a human being. Examples of such case is a war zone area, steep terrains, explosive area, or even during armed attacks. Keywords: Autonomous, Control, Tilt, Tri-Rotor,UAV 1. Introduction Some tasks are also overly complex that the maneuverability become very complicated. However, these problems can be overcome by using a UAV which is unpiloted and is autonomously controlled. In addition, three rotor configuration is less-expensive with great agility and more flexibility. Compared to quad rotors, TRUAVs is ideal for deployment in various research projects and missions because TRUAVs are less costly, less complex, smaller in size, and have longer flight time due to the reduced number of motors. Comparing to two-rotors, TRUAVs provides more stability 1. Most autonomous control consists of a controller. There exists variety type of controller used in solution to many types of problems and application. The application of control in an industrial process has observed controllers like Proportional (P), Proportional- Integration (PI), Proportional-Integral-Derivative (PID) and Fuzzy Logic 2. The control algorithm focused in the autonomous control is using PID controller designed for tilt tri-rotor UAV that is operating in Vertical Take-Off and Landing (VTOL) mode. The mathematical model will only consist of the three motors used including the tilting mechanism. The algorithm for other UAV is not discussed in this paper. This paper focuses on the stability of the tilt TRUAV in each flight mission and not the navigation, tracking and communication system of the tilt TRUAV. The flight missions discussed in this paper are Take-Off, Hover, Transition, Forward Flight and Landing. The code developed for the arduino microcontroller will only take data variables from the feedback sensors integrated in the tilt TRUAV and do the calculations to generate the appropriate command in maintaining the stability of the tilt TRUAV. 2. Tilt Tri-rotor Unmanned Aerial Vehicle Conceptually, Tilt Tri-Rotor Unmanned Aerial Vehicle (TRUAV) is an aircraft that have three motors and does not allow pilot intervention in the management of the flight. Figure 1 shows an incomplete prototype model of UAV developed by IIUM Supernova Team, it can be used *Author for correspondence

2 Autonomous Control of Tilt Tri-Rotor Unmanned Aerial Vehicle Figure 1. Example of UAV design model. as an example on where the control algorithm could be applied on. UAV offers options to be controlled autonomously or to be remotely piloted. Such options bring advantages to diverse areas depending on its application. The application of UAV is very wide. It is used in remote sensing (refer Figure 2), commercial aerial surveillance, oil and gas exploration, commercial and motion picture filmmaking, sports, law enforcement-related, disaster relief and medical assistance, scientific research, search and rescue, maritime patrol, forest fire detection, archaeology and many other potentials in the future. 3. Autonomous Control Autonomous Control (AC) mentioned in this paper is in the context of the control and guidance of an UAV. Autonomous control simply means automatic control. AC consist of a combination of hardware and software, that can operate control functions as needed. Such control functions should not be intervened over a required period of time. The controller is able to handle task in an unexpected situation, evaluate a new task for control and errors. However, a high level decision making techniques for reasoning with the constraint of uncertainty and execute action have to be utilized. It is somehow similar to intelligent behavior of humans. Thus, utilizing high level decision making techniques, intelligent methods, in the autonomous controller is a step towards autonomy Research Methodology The tools used is MATLAB software and Arduino. MATLAB software is used to simulate the feedback control stability in a TRUAV based on the feedback control system applied. Arduino software is used to code the arduino microcontroller. Arduino serial monitor is used to analyze data from feedback sensors. Data is evaluated Figure 2. Application of UAV in remote sensing showing moss health and moss surface temperature from visible mosaic of Robison Ridge site in Antarctica 3. through Proportional-Integral-Derivative (PID) feedback control system which then calculate the control command to be sent to the aircraft dynamics. Aircraft dynamics consist of control surfaces and external control of the TRUAV. The control for each flight mission which are Take-Off, Altitude, Hover, Transition, Forward Flight and Landing is discussed separately. Figure 3 shows the flowchart used in this paper to apply AC in a TRUAV. 4.1 PID Feedback Control There are two types of control systems in general, open loop and closed loop control systems. An open loop control system consists of input acting on a plant which then generates an output signal. However, the open loop control system is not sufficient to be used in the proposed system. This is because, it does not meet the requirement where accuracy is highly important and the attitude of the TRUAV may change variously. Furthermore, an open loop control system does not have a way of compensating an error nor correcting them which is a huge disadvantage to be used in this proposed system. Thus, a solution to this is to use closed loop control system. In a closed loop system, a feedback control is applied by sensing the output of the plant and sending it back so the system can make adjustment accordingly. In a feedback system, there should be a reference signal which is the desired value or goal. The reference signal is then compared to the measured signal from the feedback. The comparison of the reference signal and measured signal will show the resulting error that shows the difference between the desired value and the current value of the plant. The error is fed to a controller and the controller 2 Vol 9 (36) September Indian Journal of Science and Technology

3 Rashidah Funke Olanrewaju, Rafhanah Shazwani Binti Rosli and Balogun Wasiu Adebayo Figure 4. controller. Closed loop control system with a PID Figure 3. Flowchart of AC system in a TRUAV. will convert it into command that is then sent to the plant. The controller should drive the error to zero as time progressed. The controller used in the design is PID controller. It is used because it is simple, efficient and effective in wide area of application. The flow diagram of a closed loop control system with a PID controller is shown in Figure Flight Dynamics Flight dynamics can be explained as the control of aircraft in three dimensions and its orientation. Angles of rotation in three dimensions about the aircraft s centre of mass is the three critical flight dynamics parameters. The aircraft may rotate freely in three axes known as pitch, roll and yaw. Pitch is the lateral axis from the tip of the aircraft s wings in which the rotation about this axis changes vertical pointing direction of the aircraft s nose. Roll is the longitudinal axis from the aircraft s nose to its tail in which rotation about this axis changes the wings orientation moving clockwise or anticlockwise. Yaw is the vertical axis that pass through aircraft s centre of gravity and the rotation about this axis changes the horizontal pointing direction of the aircraft s nose. Figure 5 shows the three axes that intersect in the centre of gravity of the aircraft and is perpendicular to each other. In a basic aircraft maneuvering, there are multiple components of control surfaces that control the aircraft s flight dynamics. Control surfaces can be categorized into several categories according to the type of aircraft. In the TRUAV of the proposed system, the category involved is main control surfaces, which consist of ailerons, elevator and rudder. Second category involved is secondary control surfaces, which consist of flaps. Ailerons is used to control rotation about roll axis by moving left and right aileron inversely. For example, if the aircraft is to be rolled clockwise, the left aileron will be lowered causing increase in lift and the right aileron will be raised causing reduce in lift. Elevator is used to control rotation about pitch axis by moving raising or lowering both elevator on left and right horizontal tail simultaneously. For example, if the aircraft s nose is to be pitched up, the elevator will be raised pushing the tail down. Rudder is used to control rotation about yaw axis by moving the rudder on the vertical tail to the left or right. For example, if the nose is to be yawed to the right, the rudder will be moved to the right causing the tail to be pushed to the left. In addition, flaps are used to control lift of the aircraft by deflecting it. If the flaps are lowered down, it will cause the aircraft to be lifted up. It is also used during transition from forward flight to hovering by increasing the drag when it is lowered down so the speed of the aircraft can be reduced. External control involved in this paper is rotational per minute (rpm) of motors. It exerts forces in many directions thus producing moments or rotational force in the aircraft s aerodynamic center thus creating a rotation around the flight dynamics. The rpm of motors is manipulated to change the altitude of aircraft during hovering Vol 9 (36) September Indian Journal of Science and Technology 3

4 Autonomous Control of Tilt Tri-Rotor Unmanned Aerial Vehicle tilting of nacelle change to the appropriate position, forward flight and landing. Through all flight missions, the stability of the aircraft needs to be maintained by maintaining the roll, pitch and yaw angle to be at zero angle. The model of aircraft s feedback control is shown in figure6. Aircraft dynamics consist of control surfaces (flap, ailerons, elevator and rudder) and rpm of motors used in the aircraft. Figure 5. Aircraft s axes of motion. and speed of aircraft during forward flight. Rpm of motors create thrust. For example, when the rpm is decreased, the thrust from the motors will decrease resulting in decreasing altitude or speed. The position of the motors used in this paper is at each tip of its wings and one at the nose. Right motor is located at the tip of the right wing, left motor located at the tip of the left wing and finally the front motor located at the nose. The right and left motor is used to control stability about roll axis. For example, the feedback value of roll angle will give either positive or negative feedback and the error from the comparison of desired and measured value will be fed to PID and PID generates a signal to be sent to both rpm of left motor and right motor on which one to be increased or decreased. The front motor is used to control stability about pitch axis. For example, if the aircraft s nose is to be pitched up, the front motor s rpm is to be increased. 4.3 Feedback Sensors The feedback sensor used in the proposed system is Inertial Measurement Unit (IMU). IMU is used to measure and give feedback on aircraft s angular orientation, velocity and gravitational forces. IMU consist of combination of accelerometers and gyroscopes that can sense motion and distinguish its rate, type and direction. In this proposed system, the TRUAV attitude is continuously measured and sent to the arduino microcontroller for calculation. The variable that is received by the arduino from the IMU is in the form of IMU s output voltage through pulse with modulation pin. 4.5 Take-Off Feedback Control Aircraft dynamics that is active during this mission is rpm of the three motors used. The motors generate thrust that will produce a lift to the aircraft since all the control surfaces is not active during this time. The feedback control during this mission can be explained using the model in figure 6. During take-off, the aircraft will increase in altitude to a determined altitude, h. The current value of altitude is fed through feedback and compared to the desired value of altitude, h. The PID calculates the rate that the motor rpm should operates at and the aircraft s rate of climb. Rate of climb (RoC) is the vertical speed of aircraft which is the altitude s rate of change. The rise time is made higher by increasing the Kd of the PID to apply delay in RoC in order to maintain the stability. dynamics is observed by maintaining the roll and pitch angles at zero. The current measured value of roll/pitch angle is fed through feedback and compared to the desired value of roll/pitch angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to be fed to the left or right motor for roll and front motor for pitch through arduino microcontroller. The arduino microcontroller acts as a medium of signal processing. 4.4 Feedback Control of Flight Missions The aircraft in this proposed system has a mission profile that includes take-off to a certain altitude, hover for a determined amount of time, transition on which the Figure 6. Model of aircraft s feedback control. 4 Vol 9 (36) September Indian Journal of Science and Technology

5 Rashidah Funke Olanrewaju, Rafhanah Shazwani Binti Rosli and Balogun Wasiu Adebayo 4.6 Hover Feedback Control Aircraft dynamics that is active during this mission is rpm of the three motors used. The feedback control during this mission can also be explained using the model in figure 6. During hover, when the aircraft reach the desired altitude, h, the aircraft have to maintain the Rate of Climb (RoC) to be zero. This is by continuously taking the feedback of the altitude and adjusting the rpm of motor to maintain the position of aircraft at h. When the appropriate rpm value is obtained to keep the value of RoC at zero and position of aircraft at h, the rpm value is made constant for a determined amount of time before the next mission. The PID calculates the rate that the motor rpm should operates at and sends the signal to the arduino microcontroller. dynamics is observed by maintaining the roll and pitch angles at zero. The current measured value of roll/pitch angle is fed through feedback and compared to the desired value of roll/pitch angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to be fed to the left or right motor for roll and front motor for pitch through arduino microcontroller. The arduino microcontroller acts as a medium of signal processing. 4.7 Transition Feedback Control Aircraft dynamics that are active during this mission are control surfaces and rpm of the three motors used. During transition, the nacelle of all three motors will gradually tilt to 90 degrees to prepare for the next flight mission which is forward flight. The aircraft may increase in a considerable altitude during transition. dynamics should be observed by maintaining the roll, pitch and yaw angles at zero. The current measured value of roll/pitch/yaw angle is fed through feedback and compared to the desired value of roll/pitch/yaw angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to the control surfaces through arduino microcontroller. The ailerons are used to adjust roll angle, elevators are to adjust the pitch angle, the flaps are to adjust the lift and the rudder is to adjust the yaw angle. The arduino microcontroller acts as a medium of signal processing. 4.8 Forward flight Feedback Control Aircraft dynamics that is active during this mission is control surfaces. During forward flight, the rpm of all three motors should be in the same rate. The aircraft is steered by the control surfaces. The feedback control during this mission can be explained using the model in Figure 7. For the aircraft to turn to the right or left, the ailerons and rudder will work together to achieve it. The lift of the aircraft is affected by the flaps. A change in the angle of the flaps will change the drag thus affecting the speed of aircraft. The aircraft is slowed down and stopped by deflecting the flaps that will cause an increase in drag and also by decreasing the rate of the rpm of motors. dynamics should be observed by maintaining the roll, pitch and yaw angles at zero. The current measured value of roll/pitch/yaw angle is fed through feedback and compared to the desired value of roll/pitch/yaw angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to the control surfaces through arduino microcontroller. The ailerons are used to adjust roll angle, elevators is to adjust the pitch angle, the flaps is to adjust the lift and the rudder is to adjust the yaw angle. The arduino microcontroller acts as a medium of signal processing. 4.9 Landing Feedback Control The fifth flight mission discussed is landing. Before the landing mission started, the aircraft will undergo transition mission on which the nacelle of all three motors gradually return to 0 degrees. Aircraft dynamics that is Figure 7. Angle vs time graph representing roll, pitch and yaw angles of uncontrolled hover system 5. Vol 9 (36) September Indian Journal of Science and Technology 5

6 Autonomous Control of Tilt Tri-Rotor Unmanned Aerial Vehicle active during this mission is rpm of the three motors used. The motors generate thrust that will produce a lift to the aircraft since all the control surfaces is not active during this time. Thus, by reducing the rpm of the motors, the lift is also reduced. The feedback control during this mission can be explained using the model in Figure 7. During landing, the aircraft s altitude is decreased to h=0. The current value of altitude is fed through feedback and compared to the desired value of altitude, h=0. The PID calculates the rate that the motor rpm should operates at and the aircraft s rate of descent. Rate of descent is the vertical speed of a descending aircraft. The rise time is made higher by increasing the Kd of the PID to apply delay in rate of descent in order to maintain the stability. dynamics is observed by maintaining the roll and pitch angles at zero. The current measured value of roll/pitch angle is fed through feedback and compared to the desired value of roll/pitch angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to be fed to the left or right motor for roll and front motor for pitch through arduino microcontroller. The arduino microcontroller acts as a medium of signal processing. 5. Results and Analysis A simulation is done by using MATLAB Simulink software. The mathematical model is represented through Simulink. The PID applied in the Simulink is auto tuned without having to determine the constants. Simulink calculates the best constants that should be used by the system. The graph of the simulation is graphed using MATLAB 5. The analysis for only one flight mission is observed for the time being, which is at hover. The graph of roll, pitch and yaw angles is analyzed in an uncontrolled and controlled system of hover to see the effect of the control on the system. The aircraft s solution of mathematical model for thrust generation is presented 5. F=Thrust, D=diameter of propeller Pitch=Axial distance cross by propeller for each revolution RPM=Revolution of engine per minute = Assume, Fxnet = Fznet = Drag = Lift = Using MATLAB Simulation, the equations are solved using the following input value 5 : Mass:13kg Number of engine:3 Tilting rate:0.04rad/s Propeller diameter:20inch Pitch:13inch Wing area: 0.728m2 Initial forward velocity:0ms-1 Initial vertical velocity:0ms-1 Results: Uncontrolled system at hover: Controlled system at hover: The result shows the control system of aircraft during hover flight mission. Figure 8 shows the graph of an uncontrolled hover system. The absence of PID control in the system has shown inconsiderable amount of overshoot to the pitch angle. The roll angle is constant. The yaw angle is not considered at this flight mission. The roll and pitch angle should achieve zero angle for the system to be stable. However, the pitch angle is inversely diverging to negative infinity. This graph shows the system is highly unstable and a controller is highly needed. When PID control is applied to the system, it fixed the problems of delay time, inverse response and overshoot from the ongoing process. Thus, a significant improvement is 6 Vol 9 (36) September Indian Journal of Science and Technology

7 Rashidah Funke Olanrewaju, Rafhanah Shazwani Binti Rosli and Balogun Wasiu Adebayo work. Due to some limitations, it became a great challenge to come up with an ideal control algorithm for the aircraft. Hence, the pursuit continues.there exist many types of control system method that can be implemented in a tilt tri-rotor UAV. Such control system may also be applied to improve the stability and efficiency of the control system method used in this paper. Thus, for future works, it is recommended to use a different control system method other than PID control, apply another control system method to the PID control to improve the efficiency and adapt the control algorithm to another type of UAV. Figure 8. Angle vs time graph representing roll, pitch and yaw angles of controlled hover system 5. observed from the graph in figure 8 in which the pitch angle and roll angle achieve zero after 40s. The pitch overshoot is greatly reduced and approach to a constant zero. The aircraft dynamics that is active during hover flight mission is rpm of the three motors used. The feedback control during this mission can be explained using the model in figure 7. The stability of the aircraft is achieved through the observation of the flight dynamics by adjusting the roll and pitch angles to achieve zero angle. The current measured value of roll/pitch angle is fed through feedback and compared to the desired value of roll/pitch angles which is zero. The error from this comparison is sent to PID for calculations. PID sends appropriate value of signal to be fed to the left and right motor for roll and front motor for pitch. 7. References 1. Kara MM, Lanzon A. Design and control of novel tri-rotor UAV. UKACC International Conference on Control Cardiff, UK, 2012 Sep Aslam F, Kaur G. Comparative analysis of conventional, P, PI, PID and fuzzy logic controllers for the efficient control of concentration in CSTR. International Journal of Computer Applications Mar; 17(6): Esther S, Barrado C, Pastor E. UAV flight experiments applied to the remote sensing of vegetated areas. Remote Sens. 2014; 6: DOI: /rs Antsaklis PJ, Passino KM, Wang SJ. An introduction to autonomous control systems. control systems, IEEE. 1991; 11(4). 5. Abdur M. Design and development of two-rotor tilting VTOL Aircraft. Final Year Project. International Islamic University Malaysia, Malaysia; Conclusion and Future Works In conclusion, to develop a control algorithm that is more effective needs an intensive study on how the aircraft itself Vol 9 (36) September Indian Journal of Science and Technology 7