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

[Chris Wozny]

Does anyone at TU Delft know the status of this project? I'm looking
at it and it looks quite robust. I'd be curious to try it with our
Mini-Vertigo. Are there any limits to the control laws for this branch
like trying to fly a fixed-wing at 90 degrees? The quadshot would see
similar issues from autonomous control and singularities as ours does
and this does look like the right direction for our project. Thank you
for pointing me this out to me Bart and Roman!

- Chris

On Tue, Feb 21, 2012 at 4:22 PM, Roman Krashanitsa
<address@hidden> wrote:
> I looked at the
> https://github.com/tudelft-atmos/paparazzi/tree/quadshot/sw/airborne/firmwares/rotorcraft/stabilization
> branch and the changes look very solid. I think this is the way to go.
>
> Roman
>
>
> 2012/2/21 Bart Remes <address@hidden>
>>
>> chris,
>>
>> look at the https://github.com/tudelft-atmos/paparazzi/network
>>
>> they are making the quatshot autonomous.
>>
>> It will do basically the same as the vertigo but with
>> other controls organs.
>>
>> Bart Remes
>>
>>
>> On Friday, February 17, 2012, Roman Krashanitsa wrote:
>>>
>>> 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
>>>> >>> _______________________________________________
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>>>> >>> address@hidden
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