This chapter discusses the design and modelling of a spherical flying robot. The main objective is to control its hovering and omnidirectional mobility by controlling the air mass differential pressure between two asynchronous coaxial rotors that are aligned collinearly. The spherical robot design has embedded a gyroscopic mechanism of three rings that allow the rotors' under-actuated mobility with 3DOF. The main objective of this study is to maintain the thrust force with nearly vertical direction. The change in pressure between rotors allows to vary the rotors' tilt and pitch. The system uses special design propellers to improve the laminar air mass flux. A nonlinear fitting model automatically calibrates the rotors' angular speed as a function of digital values. This model is the functional form that represents the reference input to control the rotors' speed, validated by three types controllers: P, PI, and PID. The robot's thrust and induced forces and flight mechanics are proposed and analysed. The simulation results show the feasibility of the approach.