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

[Roman Krashanitsa]

Chris, it was not very much hovering but flying at 80-85 pitch. Moving very slowly.

But then it can transition to essentially 7 deg pitch horizontal flight.

 

Yes, it works totally fine in auto2.

 

Roman

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

Felix,

I know in the past when we used IR sensors instead of an IMU, we just
mounted the IR sensors on this aircraft such that it thought it was
level when flying at high angles of attack. This is why I believe such
a pitch offset will allow the aircraft to fly horizontally with high
AoA's (especially since Roman has worked with essentially a prior
version of the same aircraft.) I understand what you're saying about
the mechanics being different when hovering vs. horizontal flight.
However, this aircraft will just fly around horizontally with a very
high AoA and is capable of hovering in AUTO1 (my memory is foggy about
it hovering in AUTO2.) I hope that my explanation is a little clearer
than mud :)

- Chris

On Fri, Feb 17, 2012 at 1:00 PM, Felix Ruess <address@hidden> wrote:
> 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
>>> _______________________________________________
>>> Paparazzi-devel mailing list
>>> address@hidden
>>> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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