[Paparazzi-devel] New auto_pitch mode

[Pascal]

Hi,

A new longitudinal mode have been added in the autopilot; its aim is to 
control the vertical climb only using the pitch, with a constant 
throttle command. This mode is compatible with the "alt" (the default),
"climb" and "glide" vertical mode's.

Syntax in a flight plan: set the "pitch" value to "auto" along with a 
"gaz"  value (required).
For example:

    <go pitch="auto" gaz="0.75" wp="1"/>

or, if you want to crash ASAP (roll=30°, vertical speed=-2 m/s, full 
throttle)

    <attitude roll="30" vmode="climb" climb="-2" pitch="auto" gaz="1.0" 
until="FALSE"/>

New parameters are needed in the airframe description to handle this mode:
In the PID section, some limits on the desired pitch:

   <define name="MAX_PITCH" value="0.25"/>
   <define name="MIN_PITCH" value="-0.35"/>

and in the ALT section, two gains for the new controller. Unit of PGAIN 
is rad/(m/s) .

   <define name="PITCH_PGAIN" value="-0.1"/>
   <define name="PITCH_IGAIN" value="1.0"/>


Some details: The source code has been patched in pid.c:climb_pid_run() 
: The "auto_pitch" boolean flag is used to select the standard 
controller (FALSE, desired_gaz computed from desired_climb, 
desired_pitch almost constant) or the new one (TRUE, desired_gaz 
constant, desired_pitch computed from desired_climb).

Warning:  the single test on this new code has been done with gcc: We 
cannot simulate it with the current simulator. So be ready to switch 
back to auto1 mode ...

Comments are welcome.

--Pascal