I am trying to simulate a custom modeled quadcopter in Gazebo-7 using ROS kinetic. I tried using the px4 flight stack and the plugins available with Iris model. The quadcopter arms normally but as i give the takeoff command it becomes unstable and crashes.Here is my SDF file C:\fakepath\iris.sdf.

I would like to know how can i make the takeoff stable. What change do i have to make in the SDF file. And are there any other plugins that i can look into.