Re: [Paparazzi-devel] Incorrect Proportional Pitch Deflection, Correct Derivative Pitch Deflection

[Chris Wozny]

All,

After tirelessly analyzing the data from some "flights" today, I've
determined that some (if not all) of the issue I'm having is coming
from gimbal lock. At such a high angle of attack, I'm seeing phi and
psi values rolling over from positive 180 to -180 degrees and vice
versa very rapidly. My understanding was that complementary
quaternions "solved" the gimbal lock problem. From the commit logs, it
looks like Felix and Christophe both put a lot of work into this and
wanted to see if either of you saw gimbal locks at all? I know Felix
mentioned that any quaternion method taking Euler angles as input can
run into these singularities, but I just wanted to double check since
the almighty wikipedia says the quaternions are an alternate to Euler
angle solutions and are not intertwined. At this point, I have a
feeling that the only solution to this problem would be to mount the
Lisa board (with IMU on it) in a perpendicular fashion to the
fixed-wing VTOL aircrafts' chord line.

Best,
Chris

On Fri, Feb 17, 2012 at 5:42 PM, Chris Wozny <address@hidden> wrote:
> All,
>
> I've run into a peculiar situation with my PD gains for pitch on my
> elevons in AUTO1. I'm using Lisa/M 1.0 on the dev branch. The
> deflection I'm receiving to counteract the motion of the aircraft in
> pitch is correct (i.e. PITCH_DGAIN is correct.) However, the
> proportional gain is the opposite of what it should be doing i.e. when
> I'm pitched lower than my set point, the elevons pitch further down
> instead of trying to pitch the aircraft back up. The obvious
> correction to me would be to flip the sign on the PITCH_PGAIN, but the
> range on the numbers is only negative and zero, so I don't know how
> that would work. Does anyone know how to flip the effect of the
> PITCH_PGAIN? The pitch and roll commands in MANUAL work properly so I
> don't think it could be a reversal of the servos that would fix it
> (especially since the PITCH_DGAIN works properly.) Finally, the servos
> do not hold their commanded position in AUTO1 and overshoot when going
> from the commanded pitch/roll back to neutral. I've included the logs
> of the flights, the airframe configuration, and even the video of the
> (attempted) flight which the logs correspond to. Has anyone seen this
> type of behavior from their aircraft?
>
> Video of (Attempted) Flight
> http://www.youtube.com/watch?v=i9y_Nh8QQYY
>
> Video of Commanded Input in AUTO1
> http://www.youtube.com/watch?v=uDeERiqehjU
>
> Airframe Configuration
> http://ece.arizona.edu/~cwozny/mini_vertigo_az_high_aoa.xml
>
> Flight Data/Log
> http://ece.arizona.edu/~cwozny/flight_03_filmed.data
> http://ece.arizona.edu/~cwozny/flight_03_filmed.log
>
> I hope everyone has a good weekend!
>
> Cheers,
> Chris