I conduct an experiment on the Quanser Aero device using Simulink/MATLAB, which is a twin-rotor MIMO system with two degrees of freedom; pitch and yaw angles. I want to obtain the pitch angular acceleration, so I put a double continuous derivative after the pitch angular position (rad) obtained from the USB interface but when I put a display to check the value of the angular acceleration, it gives me zero, any suggestion to obtain a value for the pitch angular acceleration?