Using Ardupilot to answer the needs

Questions I am working on : 

* How do I change from a flight mode to another in ardupilot mega, if I plan on sending commands from my PC on the ground ?

* How do I define which channel is used for auto stabilization of tilt & roll ?

* How do I specify what kind of movement is required on the servo to stabilize my camera gimball ?

* How do I setup headlock and how do I define servo movement associated to Z axis ? (must support continuous rotation)

According to this article : http://code.google.com/p/arducopter/wiki/AC2_Camera, if I load a arducopter firmware,

By default, quad and hex mutlicopters have stabilization turned on. APM's Out 5 and Out 6 pins will drive tilt/roll servos to auto-stabilize a camera. Out 5 is pitch and Out 6 is roll.

The default is that you can also control the pitch of your camera (but not the roll) with your RC transmitter. 

You can reverse the direction of either servo in the Mission Planner by changing the MAVLink parameters for that channel  

According to the description of the arducopter main page (arducopter.com), it seems that all needed is available under the arducopter firmware :

ArduCopter Platform Feature List

• 6 Degree of Freedom IMU stabilized control

• Gyro stabilized flight mode enabling acrobatics (loops and barrel rolls)

• GPS for position hold

• Magnetometer for heading determination

• What is a sketch file ? what is a PDE file ?
  
• A sketch is the name that Arduino uses for a program. It's the unit of code that is uploaded to and run on an Arduino board.
• pde is the extension of a sketch file

• How do I modify the behavior of arducopter ?
  
• According to this tutorial, I have to modify the arducopteur.pde  file.

My first test :

I want to move my APM around the Z axis clockwise, and have a unique servo go counterclockwise, at the same angular speed.