## 3 Hardware System Design  
Multirotor aerial vehicles can outperform fixed-wing UAVs in terms of hovering capabilities and their ability to move slowly in air. This feature makes them very useful in applications from aerial photography [24] to aerial manipulation [25]. The quadrotor, with its relatively simple mechanical structure, is the most proven and widely used UAV among them, especially the commercial ones sold for recreational purposes. Another popular type of multirotor is a hexarotor [26] with six rotors mounted on an airframe. Its propulsion system provides the hexarotor with increased robustness over the quadrotor, allowing it to improve its actuator fault detection and isolation capabilities [27]. When a malfunction is detected immediately, the control law can be adjusted to meet the closed-loop criteria or to statically hover [28] or safely return the aerial vehicle to the ground if continued flight is no longer possible [29]. Usually performing aerial manipulation requires the UAV to carry additional hardware or manipulators on-board. Therefore, to safely carry this additional hardware on-board, several studies on aerial manipulation such as in [30; 31; 32; 33] use hexarotor as their aerial platform for its higher thrust and stability. The manipulators can be mounted on different region of the airframe depending on the task. Therefore, the literature in [34] classifies various manipulator system mounted on the UAV based on the configuration of the workspace and function. In addition, the evolution and current trends in aerial robotic manipulation can be analyzed by the work in [35]. Previously, with TAMS [12], we considered the workspace such that the manipulator tips can reach the regions around, below and above the airframe. This is achieved by passing the three manipulators through the gaps in between the arms of the airframe, which are mounting the motors and rotors. In this study, light-weight manipulators are designed and constructed using a parallel link mechanism as shown in Figure 3. The links of the arms are made of thin aluminum pipes of 10 [mm] radius. 3D-printed PLA parts are used to attach the links together with the actuator motors. For the actuation of the joints, Dynamixel AX12-A and MX-28 AT motors are used. Figure 2: General-purpose manipulator and parallel link manipulator design comparison for different tasks. Especially noteworthy is that for each task only one of the joints needs to be actuated (Figure 2). Additionally, when landing, the weight of the robot is strategically distributed on the manipulator's structure, without putting too much strain on the joint actuators. Although the motors could generate enough torque to hold the weight of the UAV easily, when moving the manipulator after being landed, a torque ceiling might be reached, were there not a strategic weight distribution. To assure proper torque and ability to move the frame even in extreme landing situations, a motor with higher torque (MX-28 AT) is used for the last link. In addition, two extension springs are attached on each manipulator to provide some force to easily stretch the manipulator outwards. For simplicity of the design, active grippers are not attached as end-effectors. Various parameters of the developed hardware system are listed in Table 1.  
The kinematics of this manipulator are calculated using Equation (1), where \(s_{i}\) and \(c_{i}\) are \(\sin\theta_{i}\) and \(\cos\theta_{i}\) for \(i\)th joint respectively and \(L_{1}\) to \(L_{5}\) are the link lengths as marked in Figure 4.