Design of 2-DOF PID Control for Wall-Climbing Quadrotors under Surface Variability

This paper addresses set point tracking control for a wall–climbing quadrotor operating over surfaces of varying inclination and contact properties. We formulate the problem as reference tracking along the climbing axis under changing effective gravity projection and surface interaction, and we evaluate a two–degree–of–freedom (2-DOF) PID controller with set–point weighting and a command prefilter against a classical (1-DOF) PID baseline. Numerical simulations across multiple surface scenarios (e.g., changes in inclination/friction and step commands) indicate that the 2-DOF PID consistently improves transient performance and control economy: overshoot is reduced, settling is faster, and peak/average control effort is lower, while maintaining zero steady–state error. These results suggest that simple structural modifications to PID without resorting to complex nonlinear designs can yield meaningful performance gains for contact–constrained aerial locomotion. The study is simulation–only, but the observed trends are robust across tested operating conditions, otivating future hardware validation and surface–aware gain scheduling.