**2.2 Flight command unit and related software**

The PixHawk Cube FCU was selected [13] featuring triple redundant dampened Inertial Measurement Units (IMUs), with a modular design and industrial standard I/O connectors. Additional telemetry and R/C circuits are deployed to enable monitoring and intervention and comply with flying regulations.

The *Here* + Global Navigation Satellite System (GNSS) [14] with Real-time kinematic (RTK) capabilities was selected for outdoor navigation and placed on top of a carbon fiber pole at a height of 35 cm from the main frame's top plane. For immunity to electromagnetic interference, the primary magnetometer of the flight controller is selected to be the build-in magnetometer module of the GNSS receiver.

A high processing power 8th generation Intel NUC i7-computing unit with 32 GB RAM and 1 TB SSD, shown in **Figure 3**, was mounted symmetrically to

#### **Figure 2.**

*Landing gear detail (left) and payload assembly with battery holder (right).*

**Figure 3.** *Enhanced power distribution board (left) and i7-minicomputer (right).*

the buck converter on the underside of the main frame. This 90 W computing unit allows for online computations on demanding tasks such as the visual object tracking methods of Section 4, as well as the easy development of autonomous flying applications.

On the software side, the ArduCopter flight stack [15] was selected to run on the FCU. The pose estimation is carried through a sophisticated Extended Kalman Filter (EKF) at 400 Hz. The Intel NUC companion computer is serially connected to the FCU at a baud rate of 1 Mbps and the communication packages are following the MAVlink protocol. The NUC's operating system was Ubuntu Linux 16.04 and all applications are developed through the Robot Operating System (ROS) and MAVROS [16] middleware with a 50 Hz refresh rate.

**43**

**Figure 5.**

*Development of a Versatile Modular Platform for Aerial Manipulators*

The RTK enhancement feature of GPS is used for outdoor localization purposes. This is due to the more precise positioning [17] because the of the GPS satellite measurements' correction using feedback from an additional stationary GPS module. The disadvantage of such systems is that their use is bounded to a significant pre-flight setup time which is inversely proportional to the achieved

Although the internal loop of the flight controller operates at 400 Hz, the GPS receiver streams data at a lower rate of 5 Hz. In popular flight software such as ArduPilot, the aforementioned rate needs to be taken into consideration by the underlying EKFs running by the FCU. A typical comparison of the achieved

The drone was flown in a hovering position with the RTK GPS module injecting measurements to the flight controller and the output of the FCU's EKF was compared with and without the presence of the injected RTK measurements. The red line represents the EKF's output based solely on the GPS signal, whilst the blue line indicates the same output when RTK correction (using a 30 min warmup period) is

The standard deviation was computed equal to 0.74 m, 0.47 m and 0.27 m for *X* , *Y* and *Z* respectively when no RTK correction was applied. Contrary to this, the same values with RTK injection were computed to equal 0.05 m, 0.02 m and 0.23 m respectively. It should be noted that there is no significant improvement in the *Z* -direction, indicating the need to use either a barometer or a laser sensor for ground clearance

During indoor navigation: a) the lack of GPS guidance, b) pressure changes affecting the barometric sensor, and c) power lines affecting compass accuracy can severely affect the output of a FCU. With only the accelerometers and gyroscopes being unaffected, the injection of an external feedback source to the FCU is considered essential. Such feedback is usually based on visual techniques, such as those

*Drone's EKF 3D-position output with (red) and without (blue) RTK correction.*

accuracy using a drone in a hovering state can be seen in **Figure 5**.

*DOI: http://dx.doi.org/10.5772/intechopen.94027*

**3.1 Drone outdoor localization using RTK GNSS**

**3. Drone localization**

accuracy (cm range).

injected on the FCU.

measurements.

presented in [18, 19].

**3.2 Drone indoor localization**

The developed drone without any payload can be visualized in **Figure 4**.
