# Improvement of Hexacopter UAVs Attitude Parameters Employing Control and Decision Support Systems
## 4 Laboratory and In Situ Measurement Results and Discussion
### Laboratory Tests  
To ensure that all the components were correctly chosen and the hexacopter will perform as expected, preliminary laboratory tests were conducted using dedicated built test stands and testing equipment. Aside from the mentioned sensors, the electronic speed controller (ESC) sensor must be considered due to its major importance when discussing motors functionality. The basic function of an ESC is to control the motor speed based on the PWM (pulse width modulation) signal that the AP sends to the motor, which is too weak to drive the brushless DC motor directly (Figure 10). This is achieved by the pilot operating the speed stick in the range 0-100%, and the ESC will send the power commanded by the pilot to the motor. In addition, some ESCs also perform other functions: dynamic braking, battery short-circuit protection, motor start protection and power supply (battery disposal circuit) for the radio receiver or servo motors. Unlike a general ESC, the ESC for brushless motors can act as an inverter, converting the direct current received from the battery into three-phase alternating current (AC), which is then applied to the motor. The ESC also determines the direction of rotation of the motor. The simplified diagram of ESC, depicted in Figure 10b, employs real-time operation. The main features and parameters of the ESC mounted on the hexacopter are as follows: it is equipped with specially optimized firmware for disc-type motors and a special core program for rapid throttle response, and the refresh rate of the throttle signal supported is up to 621 Hz, making the ESC perfectly compatible with various flight controllers (if the refresh rate is higher than 500 Hz, then the ESC control signal is the nonstandard throttle signal); it is equipped with driving efficiency technology (DEO), which effectively reduces the ESC operating temperature by about 20%, improves the flight time and brings a better throttle linearity and good stability--thus the operating efficiency improves by maximum 10%. In addition, its MOSFETs have extra-low resistance, offering high performance and great current endurance, with a continuous output current of 40 A and a burst of 60 A up to 10 s.  
Figure 10: The ESC architecture and simplified diagram of ESC operation. (**a**) ESC general architecture; (**b**) Simplified diagram of ESC operation. The most important components of the ESC, as presented in Figure 11, are the microcontroller, the driver for the gateway between the autopilot (AP) and the MOSFETs and the MOSFETs, respectively. As illustrated previously, the hexacopter is equipped with six Hobbywing XRotor 40A Opto ESCs sensors, each of these being connected to each of the six BLDC motors. To determine the thrust force, and therefore the efficiency of the propulsion system, laboratory tests were carried out using the Mayatech MT10 PRO 10 KG test stand. A Turnigy LiPo battery, 20,000 mAh capacity, 4 cells in 4S1P configuration, voltage 14.8 V, was employed to power the ESC-motor-propeller assembly. The Tx-Rx chain was provided by a 2.4 GHz radio remote control, model RadioLink AT10 II, and a 12-channel receiver, model RadioLink R12 DS. The test configuration is shown in Figure 12.  
Using a tachometer, in the same test configuration, the maximum speed of the rotor assembly was determined, obtaining a maximum value of 13418 RPM (Figure 13). The thrust force, current consumption, battery voltage and mechanical power were measured using the test stand (Figure 12), and the rotational speed using the tachometer (Figure 13). The results are plot in the graphs presented in Figure 14.  
Therefore, the results obtained were as follows:  
* The maximum thrust force produced by the rotor assembly, measured on the stand, was approximately 1.718 Kgf \(\approx\) 16.84 N.
* Maximum speed measured by the tachometer--13418 rpm. * The efficiency of the propulsion system decreases with increasing rpm. In the idling zone, at 30-40% rpm, the efficiency reaches a value of 13-14 g/W (\(\geq\)6 g/W--high-efficiency drone).