Reinforcement Learning-Based PD Controller Gains Prediction for Quadrotor UAVs

This paper presents a reinforcement learning (RL)-based methodology for the online fine-tuning of PD controller gains, with the goal of bridging the gap between simulation-trained controllers and real-world quadrotor applications. As a first step toward real-world implementation, the proposed approach applies a Deep Deterministic Policy Gradient (DDPG) algorithm—an off-policy actor–critic method—to adjust the gains of a quadrotor attitude PD controller during flight. The RL agent was initially trained offline in a simulated environment, using MATLAB/Simulink 2024a and the UAV Toolbox Support Package for PX4 Autopilots v1.14.0. The trained controller was then validated through both simulation and experimental flight tests. Comparative performance analyses were conducted between the hand-tuned and RL-tuned controllers. Our results demonstrate that the RL-based tuning method successfully adapts the controller gains in real time, leading to improved attitude tracking and reduced steady-state error. This study constitutes the first stage of a broader research effort investigating RL-based PID, LQR, MRAC, and Koopman-integrated RL-based PID controllers for real-time quadrotor control.