# Cartesian Aerial Manipulator with Compliant Arm
## 2 System Description
### Mechanical Design  
The Cartesian aerial manipulator shown in Figure 1 consists of two systems. The aerial platform is built from a Banggood S550 hexa-rotor (similar to the DJI F550) that integrates the DJI 2312E brushless motors with 9 \(\times\) 4.5 inch propellers, and DJI 430 LITE electronic speed controllers (ESC). The onboard controller comprises a Pixhawk autopilot and a Raspberry Pi model 3B+ that implements the software architecture described in the next subsection. The Cartesian manipulator is divided into the five parts identified in Figure 2: X-axis linear guide (base), Y-axis linear guide, servo actuator, compliant arm and battery counterweight mechanism. The mechanical specifications of the manipulator are indicated in Table 1, representing in Table 2 the mass and inertia parameters obtained from the 3D model. Figure 2: Components of the Cartesian manipulator, indicating the center of mass of each structure (XYZ axes). The 2-DOF Cartesian base is built from the igus(r) NS-01-17-600 (X-axis) and NS-01-17-300 (Y-axis) linear guides, using three NW-02-17 carriages to support the mobile parts. Two 22 mm \(\mathcal{O}\) timing pulleys are placed at the tip of both linear guides to transmit the motion of the Pololu micro metal gear motors (10 g weight, 250:1 reduction ratio, 2.7 kg-cm stall torque) to the timing belts, measuring the rotation angle with a Murata SV01A potentiometer and with the magnetic encoder of the micro-motors. The linear displacement of the Cartesian base relative to an initial position is obtained from the rotation angle and the number of turns given by the encoder (6 pulses per revolution at the micro motor shaft, 1500 pulses per turn at the output shaft of the gearbox). Figure 3 illustrates the timing pulley-belt actuator in the X and Y linear guides. The battery counterweight is supported by a C-shaped aluminum frame that can slide along the X-axis linear guide and move in synchronization with the Y-axis structure, but in the opposite direction when it is attached to the X-axis timing belt (see Section 5.2). The integration of the Cartesian manipulator in the hexa-rotor platform and the battery counter-weight mechanism are shown in Figure 4. The X-axis linear guide is supported by the carbon fiber tubes attached to the multirotor base through the two U-shaped aluminum frames identified in Figure 2. As can be seen in the front view of Figure 4, the legs of the landing gear should be separated to avoid collision of the Y-axis linear guide. However, this additional separation is not needed if the battery counter-weight mechanism is enabled. As depicted in Figure 4, this mechanism consists of a C-shaped aluminum frame that supports the 2S LiPo battery and is actuated by the X-axis timing pulley, but in the opposite direction to the Y-axis linear guide. Since both structures share the same linear guide, the effective range is reduced by half. The counterweight mechanism can be set to a fixed position by simply removing the zip tie that connects the timing belt with the linear carriage. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Cartesian Manipulator** & \multicolumn{2}{c}{**Compliant Joint Arm**} \\ \hline \multirow{2}{*}{Actuator features} & Stall torque: 0.3 Nm & \multirow{2}{*}{Actuator features} & Stall torque: 1.17 Nm \\  & Mass: 10 g, 120 RPM & & Stiffness: 1.4 Nm/rad \\ \hline \multirow{2}{*}{Linear range} & X-axis: 500 mm & Rotation range & \(\pm\)120\({}^{\circ}\) \\ \cline{2-4}  & Y-axis: 250 mm & Joint deflection & 30\({}^{\circ}\) \\ \hline Max. speed & 100 mm/s & Link length & 250 mm \\ \hline Total mass & 0.85 kg (including battery–2S LiPo, 1500 mAh) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of the Cartesian manipulator and the compliant joint arm.