# Improvement of Hexacopter UAVs Attitude Parameters Employing Control and Decision Support Systems
## 4 Laboratory and In Situ Measurement Results and Discussion
### Hover Flight Tests  
After the completion of the ground experiment, the hexacopter was tested in stationary flight. The tests were carried out in a plain area without obstacles around, within a radius of 5 km, in order to avoid the occurrence of unpleasant events such as drone crash, property destruction or person injuries. Regarding the wind speed at the test site, days with low wind speed of 1-2 m/s were chosen, measured with an anemometer (Figure 23).  
In this manoeuvre, after the operator has given the command to increase the engine speed, the speed stick is kept in the 50-75% rpm range (for the hexacopter configuration),  
Figure 23: Wind speed measurement with anemometer.  
Figure 21: Drone-mounted GoPro camera footage, on the ground and in flight.  
Figure 22: Mission planner interface. Images acquired by GoPro camera mounted on the hexacopter.  
and the lift force required to lift the drone off the ground and keep it stationary is obtained. The lift force is created by the rotation of the six rotors, which revolve at the same rpm during the vertical climb, while the hexacopter tries to stabilize its attitude. During the vertical lift, until the altitude set by the operator is reached and in respect to the command given by the operator, the hexacopter attitude PIDs apply corrections to maintain the position of the drone within the values of the commanded parameters. When stabilizing the hexacopter at a given altitude, the operator keeps the speed stick in the appropriate speed range, and the PID altitude controller applies the necessary corrections to the thrust of the engines to maintain the drone at the desired altitude.  
The general architecture of the closed-loop PID controller is depicted in Figure 24.  
In the case of the physically designed hexacopter equipped with a three-axis gimbal and a photo/video camera, the drone must be able to maintain its position at a fixed point in order to carry out surveillance, reconnaissance and photography missions. For this purpose, when using the manual radio control by the ground operator, it is recommended to operate it in the following modes: stabilize, in which the PID controllers automatically adjust pitch and roll; alt hold, in which the PID controllers automatically adjust pitch and roll and maintain drone altitude; and RTL (return to land) for emergency cases. Loiter can also be employed (semiautonomous flight--the PID controllers automatically adjust the drone's altitude and position; the hexacopter uses GPS for movement), PosHold (similar to loiter mode, but when the roll and pitch sticks are not centred, the operator controls the two movements) and land (the hexacopter descends and lands directly, without returning to the take-off point). Auto mode is utilized for autonomous movement along a predefined flight path. For PID controller tuning procedures, AUTOTUNE mode is employed after sensor calibration procedures (accelerometers, gyroscopes, magnetometers) and initial tuning.  
In the case of fixed-point tests, take-off was performed in stabilize mode, which was then switched to alt hold mode and subsequently to RTL mode.