title_body: What are controllers of Parrot AR drone 2? I have a few questions about Parrot AR drone 2. Here is the official website
  Q1:What are the controllers for the AR drone 2? Is there a position controller (GPS), velocity controller (accelerometer), attitude controller, heading controller (compass), and/or altitude controller (barometer) in the microchip of AR drone 2?
  Q2:If there are some of the controllers that I mentioned above, and these controllers may need the current states for feedback control purpose, do the current states form the estimation based on IMU data?
  To be more specific, if there is a PID position controller, we need the desired position and current position information for feedback controlling. Is the current position from the estimation algorithm (like EKF) based on IMU sensor data?
  Q3:Is there any way that I can control the motor speed for AR drone 2 directly and use my own controllers?
  any suggestions and comments would be helpful! Thanks in advance!
upvoted_answer: After reading relevant materials, i think I have find the answers for this question.
  Q1:Since AR drone2 is a proprietary system,  this company didn't publish any documentation about the internal structure.
  Q2:According to my understanding and guess, the controllers will use the estimated states of AR drone2 and the estimated states may from EKF(I am not 100% sure)
  Q3:Since AR drone2 is a proprietary system, it seems there is no way you can control the motors directly by using your own controllers. But there is an alternative way:
  using Simulink and Optitrack to control AR Drone
  using Simulink and Vicon to control AR Drone