This paper proposes a simple solution regarding the stabilization of a quadcopter unmanned aerial vehicle endowed with a manipulator arm. The manipulator robot is attached below the rotors plane and this one induces torques producing stability issues. The present study deals with the stabilization of the full system (quadcopter and arm) by means of a set of nonlinear control techniques. First, a mathematical model is proposed for the system. Then, an attitude control, consisting on a bounded quaternion-based feedback allows the quadcopter attitude stabilization while compensating adverse torques from manipulator's motion. A simple-to-implement strategy is proposed to estimate the actual torque for compensation purposes. Then, the formulation of a nonlinear control, which drives the aerial vehicle to a desired position is presented. Both controls consist on saturation functions. Simulation results validate the proposed control strategy and compare the results with different manipulator torque estimations.