Abstract — In this paper two new conceptual robotic system designs, called ‘aerial-retrieval’ and ‘aerial-rescue’ are presented and demonstrated by simulation results. The Unmanned air vehicles (UAV) used in this design are thrust vector controlled robotic systems. The ‘aerial-retrieval’ concept aims at entrapping and retrieving a (lost) floating object in the air. The second concept, ‘aerial-rescue’ aims at rescuing a free falling object (e.g. a person) in the air using a stretched net attached to the UAV’s. Position and angular control are applied in both systems. I. INTRODUCTION he objective in this paper is to introduce two airborne robotic systems composed of UAV‟s; 1) for aerial retrieval of uncontrollably floating objects such as meteorological sensing devices 2) for aerial rescue of free falling object by an aerial safety net UAV‟s are used in many search and rescue mission. They are used as means of collecting information from the disaster area [1], [3], human search and rescue, or in a larger scale they are used as an emergency management system [2]. In most of the cases the unmanned air vehicles are used as an aid for terrestrial rescue missions. In this paper, an air rescue robotic system is going to be discussed. Towards this objective two robotic coordination systems composed of three UAV‟s are designed (Figure 1). The first cooperation of UAV‟s is for encircling and capturing an object floating in the air by three UAV‟s forming a closed chain (Figure 2). The second airborne cooperation of UAV‟s is to expand and stretch a safety net while flying in the air and catching a falling object and slowing it down toward a controlled altogether landing (Figure 3). II. UAV CONFIGURATIONS The three flying robotic units that cooperate in aerial retrieval and aerial rescue are all identically designed. Here we provide aconceptually description of the UAV‟s. The proposed UAV is given in Figure 1. Z. Cakir, MSc student, Middle East Technical University, Department of Aerospace Engineering (e-mail: zcakir@ ae.metu.edu.tr). A. M. Erkmen, Faculty Member, Middle East Technical University, Department of Electrical Engineering, IEEE Senior Member No: 08925810 (e-mail: aydan@metu.edu.tr) I. Yavrucuk, Faculty Member, Middle East Technical University, Department of Aerospace Engineering (e-mail: yavrucuk@ metu.edu.tr). Figure 1 UAV body The central part of the UAV body resembles that of a wide missile body which carries the controller, miscellaneous electronics, rocket motor and solid rocket fuel. The robot has two arms each having two revolute joints and two links. The arm links move in the body y-z plane (Figure 1). There are three static grippers on the robot body located as shown in Figure 1 (colored gray) to hold the floating object when necessary during aerial retrieval of a free floating object. The propulsion system is similar to thrust vector control missile propulsion. The nozzles are located as shown in the figure (on top, bottom and on the sides). The thrust generated by rocket propulsion is directed to these nozzles that work in pair according to the desired motion. They are located so that the generated forces and moments are fully decoupled. For both aerial rescue formation and aerial retrieval formation, the flying robots are released from a helicopter with which the UAV‟s establish a communication at all times during their mission by wireless data links. Cooperation control of the three UAV‟s arranges them in a formation named after their mission. In aerial-retrieval mission, the floating object is detected by the helicopter. The inertial position of the object is calculated from the inertial position of the helicopter and the relative distance of the object with respect to the helicopter. This relative distance is measured by a laser range-finder located at the helicopter. Knowing the inertial position of the object, the robots are released from the helicopter at locations nearby the corners of an equilateral triangle having the object located at its geometric center. The second coordination control system is called „aerial- rescue‟. In the aerial-rescue mission, the three flying UAV‟s have an unfolded net attached to each of them and are released from the helicopter close to each other. After being released, the robots move quickly to an altitude below the falling object such that they will have enough time to stretch the net before the object reaches that altitude. The free Cooperation Control of Three UAV’s for Aerial Rescue and Aerial Retrieval Zeynep Cakir, Aydan M. Erkmen, and Ilkay Yavrucuk T