## 3 Design and Implementation of the ATD
### Components of the System  
The proposed system (shown in Figure 1a) consists of a multirotor UAV with ATD. The multirotor platform is constructed using DJI F550 frame (the diameters of the body and propellers are 550 and 238 mm, respectively) and DJI N3 flight controller. High level control for the multirotor navigation is achieved by the communication link between the flight controller and the on-board CPU. The pictures of ATD with multirotor system is shown Figure 3. The coordination is defined as the same as in Figure 2. RealSense T265 is used for estimating velocity of the UAV.  
Through the communication between flight controller of the multirotor and the on-board CPU, we constructed the system, as shown in Figure 4, based on ROS(Robot Operating System). In the figure, the processes inside the CPU board block shows ROS nodes what we mainly developed and data flow shows the topics being published and subscribed in each nodes. Constructing the system using ROS improves the reusability of the system, and additional devices can be easily integrated into the system. To verify positioning accuracy of ATD with multirotor, a motion capture system is used for estimating the position. In the system, the state estimator summarizes converted sensor feedback and transmits necessary values to UAV and ATD controller. The I2C interface receives control input of three ducted fans and converts it to desired PWM signal using Python library of PCA9685. The UAV controller includes roll and pitch angle, yaw angle rate, throttle (vertical velocity/thrust), and enable/disable brake-like motion as control inputs. The brake-like motion of the multirotor will effect the flight, if it is enabled with the ATD control. Thus, we designed three different control modes, namely position control mode, manual ATD control mode, and manual UAV control mode, by making a switch based on CH5 position on the remote controller (RC) (shown in Figures 3 (side view) and 4). These control modes are described as follows.  
* Position control mode allows the multirotor to translate automatically by keeping body frame horizontal. In the UAV controller, control inputs of roll and pitch angle are set to 0, yaw angle rate is controlled automatically, throttle is controlled manually, and break-like motion is disabled. In the ATD controller, the ducted fans are controlled automatically.  
Manual ATD control mode allows the operator to control the multirotor manually and translate it with fixed attitude of the airframe. In the UAV controller, the control inputs are set the same as in position control mode. The ATD controller is designed based on CH1\(\sim\)2 input values on the RC for operating the multirotor translating in horizontal, and a brake-like motion is designed for stopping the multirotor immediately after the operation.
* Manual UAV control mode allows the operator to control the multirotor manually which is same as typical operation. The UAV's roll and pitch angle, yaw rate, and throttle are set based on RC input of CH1\(\sim\)4 and brake-like motion is enabled. The ducted fans in the ATD controller are disabled.  
Through our designed system with three different control modes, the system allows the operator to easily switch desired control mode depending on the task. In the position control mode, the horizontal position and heading direction of multirotor are controlled automatically, and the operator only needs to adjust its height. It makes some inspection tasks much easier than when controlling the multirotor normally, such as the cases shown in Figure 1d. It can be realized by adding sensors such as LIDAR or RGB-D camera to our system for localization. On the other hand, it can be useful for performing some aerial manipulation tasks by switching to manual ATD control mode from UAV control mode. It allows an aerial manipulator to reach smoothly to the manipulated target.  
Figure 4: Block diagram of the ATD with multirotor system.  
Figure 3: Pictures of ATD with multirotor system.