No drone can fly properly without a PID controller. In short, the PID loop ensures that the angle commands from your transmitter are followed by the drone as accurately as possible:

• P (Proportional) – reacts quickly to reach the desired angle
• I (Integral) – corrects steady-state errors over time
• D (Derivative) – smooths the movement and prevents overshooting

The amount the drone tilts or rotates in response to stick movement depends on the rates you’ve set.