Aerial-underwater systems, a new paradigm in unmanned vehicles

Singularity-free modeling and control of Unmanned Aerial-Underwater Vehicles (UAUVs) are covered in this work. UAUVs are a new kind of unmanned vehicles capable of performing equally well in different mediums, and seamlessly transitioning between them. In particular, this work covers the modeling and attitude control of a special class of air-underwater vehicles with full torque actuation and a single thrust force. A quaternion based representation is used to avoid singularities. A nonlinear quaternion feedback and a Proportional-Integral-Derivative (PID) with compensation of the restoring forces are used to control the quaternion and altitude errors, respectively, while gain scheduling handles the abrupt change in the medium density. The use of quaternions allows for the vehicle to follow any desired angular reference, which is critical when underwater in order to efficiently overcome the vehicle's buoyancy and drag. Numerical simulations are presented to validate the proposed control scheme.