Re: [Paparazzi-devel] BODY_TO_IMU Rotation for Hovering VTOL Fixed-wing

[Felix Ruess]

Hi Chris,

I'm not sure what you expect by telling the aircraft it is horizontal while it actually is pitched up at 80deg. You can do that, but what exactly do you hope to achieve by that?

The fixedwing firmware really won't work properly with that (without modifications that is), as the guidance/stabilization there assumes a CTOL without hover capability. Also stuff like roll basically becomes yaw when you suddenly hover, etc.

If you have an aircraft capable of both, VTOL/hover and transition to normal flight, you probably want to base that on the rotorcraft firmware (just like the quadshot, but which is arguably much more like a quadrotor in hover) or maybe even make a new firmware taking from the others what you need... 

What we call a firmware is "just" a main.c with a collection of appropriate peripherals and subsystems listed in a bunch of makefiles.

Ok, maybe that is a bit simplified, but basically that's it ;-)

Regarding the singularities (of the euler angle representations):

Even if your estimation does not have any (e.g. ahrs int_cmpl_quat), if the control is using euler angles, you can of course still run into singularities there... basically anything that takes euler angles as inputs is potentially prone to problems around the singularities.

Cheers, Felix

On Fri, Feb 17, 2012 at 8:31 PM, Roman Krashanitsa <address@hidden> wrote:

Chris,

 

Most possibly, yes. Also this is easy to check - just make modifications and look at the telemetry values, it should show 0 deg pitch at aircraft hovering orientation.

 

Roman

2012/2/17 Chris Wozny <address@hidden>

All,

If I have a fixed-wing aircraft capable of hovering at high angle of attack (80-90 degrees), would it be possible for me to just change the BODY_TO_IMU rotation for theta to that angle of attack so that it could hover at that angle? I'm sure I'd have to adjust some PID gains for it to function properly. Also, if this is possible, would I have to worry about singularities at that angle even though I'm using complementary quaternions on the dev branch?

Best,
Chris

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