[...]
> I was looking at your driver docs and noticed a bit of nonstandard 
> coordinate frames going on. First, see 
> http://www.ros.org/reps/rep-0103.html for an overview of how 
> coordinate systems are defined in ROS. Body frames are generally 
> defined as +X forward, +Y left and +Z up. In that case, what you do 
> with the Twist is a bit non-standard; linear.x should be forward/back, 
> linear.y would be left/right and linear.z would be up/down, with 
> angular.z as yaw if the AR.Drone's body frame was following the 
> standard ROS convention for coordinate systems. Any reason why you 
> went with the Twist interpretation as documented on the wiki at 
> http://www.ros.org/wiki/ardrone_driver as opposed to a more standard 
> interpretation?
>

Hi,

Actually, the standard coordinate frame for flying system is with Z down 
(it allows standard compass angle to be coherent with the X,Y motion). 
For this reason,
I'm voting in favour of a Z down coordinate system for the AR-Drone.

However, I agree that I would be suprised without  x forward, y 
sideways, and yaw around z....

As soon as we have velocity control on the CoaX helicopter, our control 
will definitely be like that.

Best regards

-- 
Dr. Cedric Pradalier
http://www.asl.ethz.ch/people/cedricp