Altitude Control of an Unmanned Air-Water Hybrid Vehicle in the Media Transition

This work deals with the closed-loop altitude control of a hybrid unmanned aerial-underwater vehicle (HUAUV) during media transition. Researches about HUAUVs are important for hard-to-reach operations. There are already several studies developed for unmanned vehicles, either in air or underwater. However, research on HUAUVs is a recent topic. There is a significant complexity in adapting of vehicles to navigate in both environments, and design a controller for hybrid vehicles is not a trivial task, mainly due to the transition region. This paper presents the analysis of the altitude control of a hybrid vehicle in the media transition region between the air and water. The main objective is the development of an altitude controller suitable for the challenge of media transition and able to deal with the abrupt changing characteristics ineherent to this region. Moreover, physical limitations are also estimated for the rotational speed of the motors to improve the mathematical model of HUAUV, and a smooth reference trajectory is generated for better environment transitions. A classical proportional-integral-derivative (PID) controller and a nonlinear controller are proposed for the altitude control. Finally, simulation results present the main characteristics of the altitude controllers on media transition, corroborating its feasibility for control of this complex system.