How to design control of quadcoptor model in simscape multibody

Hello. I have made a quadcopter model in simcpae multibody, it's a simple model with no battery and motor model yet....I want to design a controller for the quadcopter but i don't know how to begin because the model is non-linear and i don't know much about simscape physical model linearization. Also i am having difficulty in tunning the cascaded PID controllers....i can only control the qaudcopter in vertical direction. but cannot develop a controller for roll, pitch and yaw including position control....can anyone help me and guide me in right direction....this is my first time designing an controller.