Multi-Timescale Nonlinear Robust Control for a Miniature Helicopter

A new nonlinear control approach, which is applied to a miniature aerobatic helicopter through a multi-timescale structure, is proposed. Because of the highly nonlinear, unstable, and underactuated nature of a miniature helicopter, it is a challenge to design an autonomous flight control system that is capable of operating in the full flight envelope. To deal with unstable internal dynamics, the translational, rotational, and flapping dynamics of the helicopter (eleven degrees of freedom) are organized into a three-timescale, nonlinear model. The concepts of dynamic inversion and sliding manifold are combined together such that 1) the controller proposed is robust with respect to functional and parametric uncertainties, and 2) the settling time in faster modes is guaranteed to be less than the fixed step size of slower modes. A time-varying feedback gain, derived according to global stability and sliding manifold variations, is proved to be uniquely solvable based on the Perron-Frobenius Theorem. Partial uncertainties are explicitly taken into account in the nonlinear robust control design, and Monte Carlo simulations are used for validations under other sensor noises, model uncertainties, and a Federal Aviation Administration suggested gust condition.