[Paparazzi-devel] Reply to "How to adjust surface travel and throttle? (Edixon Giraldo)"

[Chris]

I always hand launch in auto2 without a single failure until now.
What i simply do is in the early stages of tuning to fly manual first 
and engage AUTO1 high
enough in order to see if the plane turns as expected.
In the airframe file there is a section that defines the maximum bank 
angles in AUTO1
<section name="AUTO1" prefix="AUTO1_">
<define name="MAX_ROLL" value="RadOfDeg(45)"/>
<define name="MAX_PITCH" value="RadOfDeg(45)"/>
</section>
and i always make sure that i can achieve those during AUTO1 flight.

If i can't then the PFD is not showing the actual pitch and roll angles 
because the
<define name="HORIZ_SENSOR_TILTED" value="1"/>
<define name="LATERAL_CORRECTION" value="1.0"/>
<define name="LONGITUDINAL_CORRECTION" value="1.0"/>
<define name="VERTICAL_CORRECTION" value="1.5"/>
need to be adjusted.

You can also adjust each side alone using those definitions:
<define name="CORRECTION_UP" value="1."/>
<define name="CORRECTION_DOWN" value="1."/>
<define name="CORRECTION_LEFT" value="1."/>
<define name="CORRECTION_RIGHT" value="1."/>

Then after i achieve correct roll and pitch indications i increase the 
roll and pitch gains until
the oscillations just begin.
Finally i decrease the gain 500 units from where the oscilations begin.
For example if the oscillations start at a gain of -7500 then i set the 
gain at -7000.
Those gains mainly affect the servo movement when you roll and/or pitch 
the aircraft
as the calculate the servo movement from the angle error.
For example if the wind has forced the plane to roll -10 degrees (to the 
left, positive is to the right)
then the autopilot will calculate that it needs to change the aileron 
servo pulse width from 1500 to 1600 with a gain of -5000 and to 1700 if 
the gain is set to -10000!!!
I hope i made that clear.
This of course will only work if the -10 degrees the autopilot sees are 
indeed -10 degrees and not -20
because your PFD indications are in error.
To make things worst if you use slow servos you will find that the 
minimum needed gain induces oscillation where if you have used fast 
servos (0.1ms or lower) you could increase the gain even more.
A slow servo will take more time to get to the desired angle and until 
it reaches it's position
the autopilot sees that the plane is not responding well and commands 
more servo travel.
When the servo finally reaches the commanded angle the plane has started 
to roll to the opposite side
due to over correction and the autopilot commands an opposite servo 
movement only to overshoot again and the oscillation start.
Chris