Effectiveness of Fast Speed Yaw and Roll Control Switching Instead of Normal Roll Control for AR...

International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2763 Issue 07, Volume 3 (July 2016) www.ijirae.com

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Effectiveness of Fast Speed Yaw and Roll Control

Switching Instead of Normal Roll Control for AR Drone 4 rotor Helicopter

Hideki Toda* Syuichi Honda Hiroaki Takano University of Toyama University of Toyama University of Toyama

Abstract—In this paper, the effectiveness of new position control strategy - fast speed yaw and roll control switching method instead of the roll control only in Parrot AR Drone 4 rotor helicopter in horizontal plane for automatic fixed position flight was confirmed. General 4 rotor basic flight controller considers only simple floating control and does not concern the position control in the space, the AR Drone was also developed as realizing the floating control only and it is necessary to control the position by the user. Instead of a simple roll control, fast speed switching yaw and roll controls (plus pitch control) could realize stable automatic fixed position control comparing with the simple roll plus pitch controls in the horizontal plane. Proposed method reduced the AR Drone automatic fixed control within S.D. of x and y axis to 31.6% and 54.8% comparing with the normal roll plus pitch controls S.D. of x and y in 3.5 x 5 x 2.4 m room, and it will useful for hobby-class 4 rotor system's the aircraft position control in such a small room condition.

Keywords— Fast speed yaw and roll control switching, AR Drone, automatic fixed position control, degree of freedom of spin axis.

I. INTRODUCTION

In this paper, the effectiveness of new position control strategy - fast speed yaw and roll control switching method instead of the roll control only in Parrot AR Drone 4 rotor helicopter in horizontal plane for automatic fixed position flight was confirmed. In order to apply the 4 rotor system in real difficult wind flow environments (outdoor, tunnel, bridge site inspections and so on), there are large demands to improve a positional movement control performance of the 4 rotor system [1, 2]. The main object of this paper is to show the effectiveness of new position control strategy - (a) fast speed yaw and roll control switching method instead of (b) the roll control only (Fig.1). Automatic fixed position control experiments show that the fast speed yaw and roll control switching + pitch control method realizes a high performance of the fixed position control comparing with the normal roll + pitch control method. By just changing the roll control strategy, the improvement of the fixed position control performance was confirmed.

Fig. 1 (a) Fast speed yaw and roll control switching method of 4 rotor's roll movement method. (b) Normal 4 rotor

system roll movement control.

A. Previous study Attitude estimation [3-6] and autonomous flight control [4], [7-11] have been one of important topics for multi-rotor

system. General 4 rotor basic flight controller does not concern the position control in the space and the AR Drone was




also developed as realizing the floating control only and it is necessary to control the position by the user. In order to control the drone position in the space, InfraRed 3D positioning system have generally been used almost all the cases [5, 12] and it is the highest positional measurement technique so far. However, since it is necessary to setup many 3D cameras in the room, generally it could not use the technique in outside situation. To avoid the problem, there is another methods that the 3D position was measured by many normal (or high resolution) cameras. It was called as visual servo system [3], [13-18]. In proposed system, the horizontal plane position of the drone is measured by the small camera equipped in the front of the drone, and it is the same with visual servo controlling method except for the difference between internal / external camera.

After the positional measurement process in the space, it is necessary to develop the feedback controller of the position control. Mainly the drone's movement in the horizontal plane was controlled by the pitch (forward-backward) and the roll (left-right) control [11]. Since the system does not have actuators to move the roll direction directly (such as side propellers), the roll control is realized by tilting the drone right or left side, there is a some delay until the drone actually moves (it depends on the airframe design and the rotor power). This method considers as conventional method (Fig.1b). As a method to compare, fast speed yaw and roll control switching was newly measured in this paper when the drone performs the roll movement (Fig.1a). This method was used as substitute control strategy of the roll movement and it is a technique to mix the short time (~50 msec) yaw control while the roll control. Generally, the yaw movement of the drone is not directly related to the position movement control in the space and it is only used to control the direction of the camera or the drone body [4, 19]. Our previous studies have been discussed about the application [20-22].

B. Outline In section 2, the AR Drone hardware and algorithms of fast speed yaw and roll control switching method were

described. Section 3 and 4 show the experimental setup and the result of the normal roll control / fast speed yaw and roll control switching method. At last, discussed and concluded were denoted in section 5 and 6 respectively.

II. METHOD A. AR Drone

AR Drone version 1.0, 4 rotor hobby-class helicopter was used for automatic stop position control experiment and feedback positional information was acquired by using only the built-in camera in the front (QVGA 320 x 240 image with 30 Hz frame rate). In Fig.2, the aircraft is positioned at the center of the room (5 x 3.5 m square, room height is 2.4 m) and it flows automatically with the height of 80 cm from the ground by using ultrasound height sensor. In order to control the movement of the aircraft, AR Drone library for Processing named ARDroneForP5 was used as developed by Y. Shigeo [23] and it was connected to a PC1 with Wi-Fi network. The basic time period of movement command transmission between the aircraft and the PC1 was about 49.8 msec (8.99 msec standard deviation S.D.). It was mainly restricted by the camera frame rate and the ARDroneForP5 library architecture.

Fig. 2 Experimental setup of AR Drone helicopter movement control. PC1 controls the aircraft via Wi-Fi network and

PC2 is measuring the aircraft position from the camera on the ceiling.




B. Fast speed yaw and roll control switching method of AR Drone

Fig.3a shows fast speed yaw and roll control switching method of AR Drone's command output example. The main object of this paper is to show the effectiveness of new position control strategy - (a) fast speed yaw and roll control switching method instead of (b) the normal roll control. By the reason that AR Drone architecture is not possible to execute two commands at the same time, it was realized it by changing the roll and the yaw control with short time period (50 msec bin).

Fig. 3 Mechanism of fast speed yaw and roll control switching method of AR Drone when the drone perform the roll

movement. Normal roll control uses only the roll control.

C. Position estimation and the position controller by using the built-in camera

Since there is no sensor of the measurement of the absolute position of the AR Drone aircraft in the room, the QVGA (320 x 240) camera that is attached in the front of the aircraft was used for real time position information measurement and it performed the control by using the position and the area of the target object (red cylinder) on the camera image. When the center of the gravity of the red target object is (퐺 ,퐺 ) and the area is A, the drone's movement roll and pitch speed commands 푉 , 푉 are described as,

푉 = 훾 (160− 퐺 )

푉 = 훾 (퐴 − 퐴)

where the meaning of 훾 , 훾 are constant and 퐴 is initial target area when the drone take off. This method is same

with visual servo system. The concept of the visual servo is adopted in many controlling procedures of aircraft control including 4 rotor helicopter [3], [11], [13-19].

III. EXPERIMENT

Figure 2 showed the experimental setup in 5x 3.5 x 2.4 m room of performing the 30 sec automatic position stop in the center of the room. USB camera that was installed on a ceiling used to trace the drone position (there was a red board on the top of the drone) while the experiment by using PC2 (position discrimination was about 2 mm). The tracing drone position was evaluated by the center of the gravity and the standard deviation S.D. (휎 , 휎 ) of the trace positions. It is necessary to note that the tracing drone position is not used in PC1's the drone control.

IV. RESULT

A. Result of experiment 1

AR Drone implements the attitude control to keep maintaining the aircraft horizontally (just floating) as the initial function. Figure 4 shows the result of simple floating experiment and the trajectory goes away from the initial position. The drone was collided to the wall in about 11 sec after the take off. The result shows that there is no positional controller originally in the AR Drone system.

Figure 5 shows the result of the normal drone movement using the pitch and roll control. The oscillating motion of x and y axis was measured and the average position (red circle) was positioned between the target and the initial positions. The average position depends on the 퐴 that is initial target area when the drone take off. S.D. 휎 =34.4 cm and 휎 =24.6 cm were measured (the cross black bars mean the S.D.)

(a) Fast speed yaw and roll control switching method

Time

yaw yaw

roll roll

50msec 50msec

(b) Normal roll control (conventional)

Time

roll roll




Fig. 4 Result of simple floating experiment without the position control. Red square means the target marker position and green dot means the initial position of the drone. Black dots mean the drone trajectory measured by the camera on

the ceiling.

Fig. 5 30 sec automatic position stopping control of the normal drone movement using the pitch and roll control.

B. Result of experiment 2

Fig.6 shows the result of the movement trajectory in the condition of fast speed yaw and roll control switching method. It was basically did not move away from the red circle's average position (S.D. of the $30$ sec movement is 휎 =10.9, 휎 =13.5 cm) and the S.D. was clearly decreased from the S.D. of the experiment 1. It reduced S.D. of x and y to 31.6% and 54.8% respectively.

Fig. 6 30 sec automatic position stopping control of fast speed yaw and roll control switching method.




V. DISCUSSION In this paper, the effectiveness of the fast speed yaw and roll control switching method was evaluated by comparing

with normal roll control in simple automatic fixed position control. By changing the roll control strategy, the stability of the fixed position control was improved, however, the main reason of this effect is basically unknown. There is possibility that the effect may be related to the airplane's horizontal turn control. Horizontal turn is used to operate general airplane's turn direction in the air flow turbulence and unpredictable wind flow [24]. Basic mechanism is to suppress the vibration and the change of the airplane's nose direction induced by the external unpredictable wind flows by tilting the airplane's wing. The tilting airplane's wing changes the lift force to move the airplane body to go to the turn direction and it is effective in changing and maintaining the airplane's nose direction stably. In the case of the fast speed yaw and roll control switching method, there is almost no speed factor of forward direction when performing this control in the drone, however, since the drone's roll direction movement could be realized by the rotor airflow and the airflow could generate the lift force, if the drone's nose direction would be changed by the yaw control, it could also be considered to move the drone body to go to turn direction. But the above description would be one assumption at present and it would need more detailed verification.

VI. CONCLUSION

In this paper, the effectiveness of fast speed yaw and roll control switching method of AR Drone 4 rotor helicopter for automatic position stop was confirmed. General 4 rotor basic flight controller considers only simple floating control and does not concern the position control in the space, the AR Drone was also developed as realizing the floating control only and it is necessary to control the position by the user. Instead of a simple roll control, the fast speed switching yaw and roll controls (plus pitch control) could realize stable automatic fixed position control comparing with the simple roll plus pitch controls in the horizontal plane. Proposed method reduced the AR Drone automatic fixed control within S.D. of x and y axis to 31.6% and 54.8% comparing with the normal roll plus pitch controls S.D. of x and y in 3.5 x 5 x 2.4 m room, and it will useful for hobby-class 4 rotor system's the aircraft position control in such a small room condition.

ACKNOWLEDGMENT

This work was supported by JSPS KAKENHI Grant Number 15K12598.

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