  This paper studies the performance of a model-free LQR based PID (i-LQR-PID)
controller designed for tracking control problem of a 2-DoF laboratory
helicopter. The control problem addressed in 2-DoF helicopter system aims to
track the desired pitch and yaw axes trajectories despite disturbed operating
conditions. In addition to the unpredictable variations, the 2-DoF helicopter
dynamic is highly nonlinear with having strong cross-couplings in their models
as well as being open loop unstable system. Thus, we propose a model-free LQR
based PID control strategy in order to achieve better trajectory tracking
control objectives. Robustness tests are performed experimentally to show the
effectiveness of the model-free control.
