2. Quadrotor system

A quadrotor UAV (refer Figure 1) has four motors that independently provide thrust (as indicated by F1, F2, F<sup>3</sup> and F4) and based on these thrusts the UAV can change its attitude (roll f, pitch θ and yaw ψ) and altitude (z). This chapter will focus on the inner loop control of the attitude and altitude variables and is based on the work of Bakshi and Ramachandran [1].

Figure 1. Quadrotor coordinate system [2].

The horizontal coordinates of the UAV (x, y) can be controlled using an outer loop on this inner loop but that is not covered here, we shall assume that the environment of the quadrotor is boundless in all directions except the datum in z, i.e. the ground.

The quadrotor model that has been used is based on work done by Bouabdallah et al. [2]. Following Bouabdallah, the earth-fixed frame E and the body-fixed frame B are as seen in Figure 1. The aerodynamic forces and moments considered in the model are based on the work of Gary Fay as in Ref. [3].

A dynamic model for the quadrotor is used for the purpose of simulation in this chapter so that the control strategy that has been presented here can be thoroughly evaluated.
