# Balance Control of Brushless Direct Current Motor Driven Two-Rotor UAV
## 5 Results and Discussion  
In the Co-Simulation studies, the system was controlled with the classical PID, 2-DOF PID, and AF 2-DOF PID controller. In order to analyse the controller performances, the system was tested with varying loads and reference values. In the first scenario, the reference balance angle is given as 10 degrees. In this case, the balance angle changes for all controllers given in Figure 20. Table 8 gives the performance criteria of the controllers for this scenario. As seen in Figure 20 and Table 8, all of the controllers caught the reference value in a short time and followed the reference steadily. However, although the 2-DOF PID controller achieved the reference earlier, the AF 2-DOF PID controller showed a finer performance than other controllers due to its lower overshoot value and less ripple value in steady state.  
reached the settled reference in a shorter time than the other controllers while the system went to the 30 degree reference balance angle. However, as the reference balance angle goes from 30 degrees to \(-30\) degrees, it is seen that the AF 2-DOF PID controller proposed in this study has a shorter settling time than other controllers with the effect of adaptivity, and its overshoot and steady-state error are less.  
Figure 23 shows the speed change of both motors in the case with AF 2-DOF PID controller for the second scenario. When these motor speed changes are examined, it is seen that the speed of the BLDCM-1 increases and the speed of the BLDCM-2 decreases to ensure the 30 degree reference balance angle at the start. When the reference position is reached, it is seen that both motors operate stably at 2000 rpm, which is the equilibrium speed. When the reference balance angle is reduced to \(-30\) degrees, the speed of the BLDCM-1 decreases while the speed of the BLDCM-2 increases. Then, after the speed of both motors fluctuates for a short time, when the reference balance angle is reached, the motors operate stably at the balance speed.  
Figure 21: Changes in motor speeds for 10 degrees balance angle reference.  
Figure 23: Changes in motor speeds for 30 to \(-\)30 degrees balance angle reference.  
Figure 22: Changes in balance angle for 30 to \(-\)30 reference.  
In order to examine the effect of the load on the controller performances in the 2R-UAV Balance System, in the third scenario, the reference balance angle was given as 10 degrees and after the first second, 250 g of load was added to the arm where the BLDCM-1 is located in the system, 15 cm away from the center. In this case, the change of balance angle for all controllers is given in Figure 24. When Figure 24 is examined, all controllers achieved the 10 degree reference balance angle in a short time, as given in the first scenario, and continued to operate stably. When the load was added in the first second, there was a short-term decrease in the balance angle for all controllers and then the reference balance angle was regained. However, it was observed that the AF 2-DOF PID controller proposed in this study achieved the reference balance angle with a much smaller decrease than other controllers.  
Figure 25 shows both motor speeds for the third scenario with the AF 2-DOF PID controller. When these speed changes are examined, it is seen that there is no significant change in motor speeds when a load is added and both motors operate stably at 2000 rpm balance speed.  
When the results obtained for all three scenarios are examined, it is seen that all the controllers used for balance angle and motor speed control in the BLDCM driven 2R-UAV balance system in this study successfully control the balance angle and motor speeds. However, we observed that the AF 2-DOF PID controller proposed in this study is more successful, especially under variable operating conditions, due to its adaptive feature.  
Figure 24: Changes of balance angle when condition of adding load.