Angle errors in IMU (using Accl & Gyro)
(This question has been posted more than a year ago)

You need these angles in order to apply a control, a PID for example, to stabilize the quadcopter in hovering mode. Your control is supposed to be active when you are not remote controlling your drone and you want it to be perfectly horizontal. This means that the theta(x axis) and phi(y axis) angles will be close to zero and will reach the desired reference value ( =0 ) thanks to the control. 

I have a question for you: Have you recorded these values while the motors were spinning? I've noticed an important increase in noise amplitude caused by vibrations on the chassis.