Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.

[Stephen Dwyer]

Hello Mitchell,

Any chance you can post somewhere your raw .data and .log files from
the flight, and also your airframe configuration file? I think it may
help to have access to all the data.

Thanks,
-Stephen Dwyer

On Sat, Sep 15, 2012 at 9:24 AM, Mitchell SLOWER
<address@hidden> wrote:
> Dear all,
>
> First of all, I'm sorry to put that topic on the forefront, but this strange
> behaviour seems to be still unexplained for many of us.
>
> To resume what's happening: after MANUAL launch, then switch au AUTO2 plane
> goes into a violent dive of about 40m, then go back into a normal flight,
> and from here everything is okay until the end of the flight. So that's a
> severe, but temporary problem.
>
> I linked graphs of the situation here (real flights):
> 1/ Desired altitude / estimated altitude (z):
> http://cjoint.com/12sp/BIjvSa0IgAX.htm
> 2/ Desired climb / Estimated climbrate (zdot) are plotted:
> http://cjoint.com/12sp/BIjvQBPg2o3.htm
> 3/ Desired pitch / attitude (theta) are plotted:
> http://cjoint.com/12sp/BIjvRwfJAxP.htm
> 4/ Airspeed / Airspeed setpoint: http://cjoint.com/12sp/BIjvPfdZ16D.htm
>
> Gauthier suggested to have a look at this link:
> http://lists.gnu.org/archive/html/paparazzi-devel/2012-06/msg00107.html
> It looks a bit similar, but as pitch is controlled by the vertical speed
> error, I don't understand why the plane pitches down when switching to
> AUTO2, as altitude setpoint is > than altitude, and cruise setpoint is never
> negative. Look here:  http://cjoint.com/12sp/BIjvQBPg2o3.htm
>
> I'm pretty sure it's airspeed control laws related (forther details are
> available in the last messages), but I really don't understand what's
> happening.
>
> It would be really great if anyone could pinpoint where we should have a
> look in order to understand and correct what's wrong.
>
> Thanks,
> Mitchell
>
>
>
> 2012/9/9 Mitchell SLOWER <address@hidden>
>>
>> Dear all,
>>
>> I did a flight this morning, it was very similar to Jefferson's flight
>> (holding 15° pitch and 100% throttle after bungee launch, then engaging
>> standby), to see if I can reproduce the behavior Jefferson decribed.
>>
>> What happened was exactly what Jefferson wrote: the plane hold really well
>> the first part, quickly gaining altitude after bungee lauch, then when it
>> switched to the standby block, plane went into a violent dive of about 40m,
>> then went back in a normal flight.
>>
>> I had a look at the logs, and linked some screenshots below.
>>
>>
>> Note about these log screenshots:
>> - At 320s: bungee launch
>> - At 343s: switch to standby block
>> - At 390s: standard flight (from here, everything is ok,  problem does not
>> happen anymore).
>>
>>
>> Logs screenshots:
>>
>> 1/ Desired altitude / estimated altitude (z):
>> http://cjoint.com/12sp/BIjvSa0IgAX.htm
>>
>> Comment: this graph  shows the altitude increase right after bungee, then
>> the dive when switching to standby, and the altitude that decrease at a
>> lower rate then stabilizes and went up again.
>>
>> 2/ Desired climb / Estimated climbrate (zdot) are plotted:
>> http://cjoint.com/12sp/BIjvQBPg2o3.htm
>>
>> Comment: climbrate goes from 6m/s (setpoint) to 0m/s when standby block
>> engages. It's interesting how the climbrate increases over time, slowly
>> getting back to the setpoint. There might something here to look at.
>>
>>
>> 3/ Desired pitch / attitude (theta) are plotted:
>> http://cjoint.com/12sp/BIjvRwfJAxP.htm
>>
>> Comment: to Felix: you were right, attitude:theta went up to 40 degrees
>> during bungee takeoff. That's another subject, but interesting to mention
>> here. Otherwise, we clearly see that the control loops are asking for a
>> pitch down when switching to standby block. This is not normal, as altitude
>> setpoint > current altitude and airspeed > airspeed setpoint.
>>
>> 4/ Airspeed / Airspeed setpoint: http://cjoint.com/12sp/BIjvPfdZ16D.htm
>>
>> As mentioned before: when switching to standby block, airspeed is over the
>> airspeed setpoint, so the plane does not need to pitch down in order to gain
>> airspeed.
>>
>>
>> To summarize:
>>
>> - Problem can be reproduced, on different planes. Both planes were
>> launched using a bungee / catapult.
>>
>> - It seems not to be AHRS related as plane can hold a steady pitch
>> attitude right after bungee launch.
>>
>> - It seems to be airspeed specific control loops related, because these
>> are not used when flying at a fixed pitch/throttle (vmode=throttle) but used
>> in the standby block, and we see on the graphs that control loops are asking
>> for a pitch down instead of a pitch up right after bungee launch.
>>
>> - Can anyone explain the desired climbrate step down (from 6 m/s to 0m/s
>> at 324s), then gradually increase here:
>> http://cjoint.com/12sp/BIjvQBPg2o3.htm ?
>>
>> Regards,
>> Mitchell
>>
>> Le 9 sept. 2012 03:38, "Romney, Jefferson S" <address@hidden> a écrit
>> :
>>
>>> I have had a similar problem that I think is the same cause. I take off
>>> in Auto2 with a catapult and it holds 15 degrees pitch until it gets to
>>> altitude. (that means it must not be the AHRS) then as soon as speed control
>>> kicks in when it moves to the standby block, it dives very violently it
>>> recovers after losing about 10-30 meters altitude, then flies normally. It
>>> must be in the airspeed or altitude loops because those are the only ones
>>> not active on takeoff when it works just fine. I haven't been able to figure
>>> this one out all year so if anyone can, it would be great.
>>>
>>> -Jefferson Romney
>>> ________________________________
>>> From: address@hidden
>>> address@hidden on behalf of
>>> Gautier Hattenberger address@hidden
>>> Sent: Saturday, September 08, 2012 3:16 PM
>>> To: address@hidden
>>> Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging
>>> AUTO2, only after launch.
>>>
>>> Hi,
>>>
>>> Maybe you can look at this
>>> http://lists.gnu.org/archive/html/paparazzi-devel/2012-06/msg00107.html
>>> It looks very similar.
>>>
>>> Gautier
>>>
>>> Le 08/09/2012 23:10, Mitchell SLOWER a écrit :
>>>
>>> I think you are right Eduardo.
>>> The attitude estimation when taking off with bungee might be not perfect,
>>> we should try the int_cmpl_quat_gravity_heuristic written by Felix.
>>>
>>> As I said before, I thought it was some I-term winding up, so I tried to
>>> decrease, even set to zero the two I-terms used in the control loops:
>>> v_ctl_auto_pitch_igain and v_ctl_auto_airspeed_igain. No improvement.
>>>
>>> Improvement happened when I commented out in the config file the auto
>>> pitch inner loop parameters: V_CTL_AUTO_PITCH_PGAIN et
>>> V_CTL_AUTO_PITCH_IGAIN. The plane was not diving dangerously anymore, but
>>> not getting altitude, just gliding on its track.
>>>
>>> Regards,
>>>
>>>
>>>
>>>
>>>
>>>
>>> 2012/9/8 Eduardo lavratti <address@hidden>
>>>>
>>>> Felix, the behavior that mitchel say is completely different than the
>>>> takeoff with bungee.
>>>>
>>>> BTW, some week ago i tested the auto takeoff using bungee and this
>>>> behavior not occur.
>>>> because of this i think its a integrator problem.
>>>>
>>>> i see int the code that some integrator are reset when manual are
>>>> engaged.
>>>> I not remember if it is a throttle or climb integrator.
>>>>
>>>> ________________________________
>>>> Date: Sat, 8 Sep 2012 22:47:53 +0200
>>>> From: address@hidden
>>>>
>>>> To: address@hidden
>>>> Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when
>>>> engaging AUTO2, only after launch.
>>>>
>>>> I'm pretty sure that the AHRS_GRAVITY_UPDATE_NORM_HEURISTIC in 4.0.1 has
>>>> almost no effect compared to not having it defined.
>>>> Whereas the improvements in my int_cmpl_quat_gravity_heuristic clearly
>>>> should help a lot (if the acceleration of the bungee takeoff is indeed the
>>>> problem).
>>>> At least in simulation I see a large (temporary) pitch error of up to
>>>> ~20deg before the improvements (of course depends on duration and
>>>> acceleration in bungee takeoff) before the improvements.
>>>>
>>>> On Sat, Sep 8, 2012 at 10:42 PM, Mitchell SLOWER
>>>> <address@hidden> wrote:
>>>>
>>>> Felix,
>>>>
>>>> I did a bungee test in AUTO1 with AHRS_GRAVITY_UPDATE_NORM_HEURISTIC
>>>> (4.0.1). It worked.
>>>>
>>>>
>>>> 2012/9/8 Felix Ruess <address@hidden>
>>>>
>>>> Hi,
>>>>
>>>> the pitching down after a bungee takeoff is definitely noticable,
>>>> however from what you describe I'm not sure if that is the only effect you
>>>> are seeing.
>>>>
>>>> But please note that AHRS_GRAVITY_UPDATE_NORM_HEURISTIC in v4.0 does not
>>>> really have a big effect.
>>>> As already mentioned previously in
>>>> http://lists.gnu.org/archive/html/paparazzi-devel/2012-08/msg00053.html
>>>> you can test the improved gravity norm heuristic from my
>>>> int_cmpl_quat_gravity_heuristic branch which is up-to-date with v4.0
>>>> otherwise.
>>>>
>>>> Would be great to get some feedback on this as I can't test this with a
>>>> real bungee takeoff myself.
>>>>
>>>> Cheers, Felix
>>>>
>>>>
>>>> On Sat, Sep 8, 2012 at 10:19 PM, Eduardo lavratti
>>>> <address@hidden> wrote:
>>>>
>>>> I have the same behavior.
>>>> i am using float_dcm and bungee but i think this is not due bungee.
>>>>
>>>> this behavior occur if i engage auto2 when pitching up.
>>>> If i pitch up, stabilize altitude and engage auto2 this behavior not
>>>> occur.
>>>> this seem that some I term are working but i not have time to search the
>>>> cause.
>>>>
>>>> i have to make this test.
>>>> takeoff in manual then engage auto2.
>>>> this will reset the integrator.
>>>>
>>>> regards
>>>>
>>>>
>>>> ________________________________
>>>> Date: Sat, 8 Sep 2012 21:57:52 +0200
>>>> From: address@hidden
>>>> To: address@hidden
>>>> Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when
>>>> engaging AUTO2, only after launch.
>>>>
>>>>
>>>> Marc, Christophe: initially, I thought it could be an AHRS related
>>>> problem, but I'm think it's something else.
>>>> (I'm using int_cmpl_quat and the  AHRS_GRAVITY_UPDATE_NORM_HEURISTIC
>>>> flag).
>>>>
>>>> I think it's not related to AHRS because:
>>>> - I had a look at the estimator (theta), and pitch seems to be correct.
>>>> - If I lauch with the capatult, fly some time in manual, and engage
>>>> AUTO2, diving also happens.
>>>> - When I disable the airspeed from the airframe config file, everything
>>>> seems to work (I say "seems" because I did only one try that was
>>>> successful).
>>>>
>>>> Regards,
>>>> Mitchell
>>>>
>>>>
>>>> 2012/9/8 Christophe De Wagter <address@hidden>
>>>>
>>>> We have implemented the acceleration feedback in
>>>>
>>>>
>>>> https://github.com/tudelft/paparazzi/blob/tudelft4.0/sw/airborne/subsystems/ahrs/ahrs_float_dcm.c
>>>>
>>>> It has flown several times, including catapult launches but with the
>>>> complexity of all aspects involved (e.g. gps latency etc.) that is not a
>>>> guarantee. If you would be so kind to help test it it would be highly
>>>> appreciated.
>>>>
>>>> copy the file to your repo, add USE_AHRS_GPS_ACCELERATIONS to your
>>>> airframe (should pop a message during compile)
>>>>
>>>> -Christophe
>>>>
>>>>
>>>>
>>>> On Sat, Sep 8, 2012 at 8:58 PM, Marc Schwarzbach
>>>> <address@hidden> wrote:
>>>>
>>>> Hi Mitchell,
>>>>
>>>> your problem seems to be an AHRS calculation thing related with the high
>>>> acceleration at bungee take-off.
>>>> See the conversation one month ago: Subject: Re: [Paparazzi-devel]
>>>> int_cmpl_quat and bungee takeoff
>>>>
>>>> As a short note, I had a similar, but very light behaviour when hand
>>>> throwing my Easystar also with Lisa/M. It does a little pitch down before
>>>> starting to climb after the throw...
>>>>
>>>> Probably we should look into the ACC signals for fixed wing..
>>>>
>>>> Cheers
>>>>
>>>> Marc
>>>>
>>>>
>>>>
>>>> -------- Original-Nachricht --------
>>>> > Datum: Sat, 8 Sep 2012 20:37:18 +0200
>>>> > Von: Mitchell SLOWER <address@hidden>
>>>> > An: address@hidden
>>>> > Betreff: [Paparazzi-devel] Strange behavior: pitch down when engaging
>>>> > AUTO2,  only after launch.
>>>>
>>>>
>>>> > Dear all,
>>>> >
>>>> > I encounter a really strange behavior on a fixedwing.
>>>> > I had a look at the logs, made a lot of flights in order to find out
>>>> > what's
>>>> > wrong, but I really don't understand what's happening.
>>>> > So here is the situation:
>>>> >
>>>> > First, the setup:
>>>> > Lisa/M 2.0, PPZ Version: 4.0.1. I'm using an airspeed sensor,
>>>> > I'm launching the plane with a bungee, in manual mode.
>>>> > Before launch, current clock is set to circle over home, 150m AGL.
>>>> >
>>>> > What's happening:
>>>> > After launch, when I change to AUTO2 , the plane does not pitch up
>>>> > with
>>>> > motor on as expected in order to reach the desired altitude, but
>>>> > pitches
>>>> > down, gaining airspeed and loosing altitude (I checked that airspeed
>>>> > is
>>>> > near or over desired airspeed when I switch mode).
>>>> >
>>>> > As things get dangerous, I switch to MANUAL, get some altitude, engage
>>>> > AUTO2, and the same behavior occurs.
>>>> > Then, after a few tries like this, everything works ! And it works
>>>> > really
>>>> > fine, as I have a very good airspeed control and climb rate.
>>>> > After that, I can switch from MANUAL to AUTO2, and the plane behaves
>>>> > normally (get some altitude at the right airspeed and climbrate).
>>>> >
>>>> > I did a lot of tests (I initially thought of a I-term winding up), all
>>>> > were
>>>> > unsuccessful.
>>>> > The only clue I found: this problem might be related to the airspeed
>>>> > specific control loops, because when I disable the airspeed sensor
>>>> > from
>>>> > the
>>>> > airframe config file the plane seems to behave correctly (no pitch
>>>> > down
>>>> > when engaging auto2).
>>>> >
>>>> > Did anyone encounter the same behavior ?
>>>> > Do you have any idea about what could be happening ?
>>>> >
>>>> > Of course, I can provide further details, setup and logs.
>>>> >
>>>> > Regards,
>>>> > Mitchell
>>>>
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