Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2,
From:
Eduardo lavratti
Subject:
Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Date:
Sun, 16 Sep 2012 03:49:16 +0000
Gautier, if you read my past messages you see that i say tha same. Every time i launch and stabilize the plane then engage AUTO2 the behavior not occurs. Sorry for my bad english.
Well, i think this problem need to be solved. Last year i do the same with my ARDUP.... and this behavior not occur.
Date: Sat, 15 Sep 2012 23:34:46 +0200 From: address@hidden To: address@hidden Subject: Re: [Paparazzi-devel] Strange behavior: pitch down when engaging AUTO2, only after launch.
Hello,
As you said, pitch is control by vertical speed error. When you
enter AUTO2 (just after 340s), the vertical speed is +15m/s while
the desired climb speed is 0 and rising slowly because of a rate
limiter. So the result is pretty obvious: your climb speed is too
high and thus the control commands to pitch down, overshoot and then
slowly recover.
And simple way to avoid this is probably to stabilize your plane in
level flight in manual before switching to AUTO2, or at least with a
climb rate and airspeed close to the desired value for navigation.
Gautier
Le 15/09/2012 17:24, Mitchell SLOWER a
écrit :
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):
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.
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).
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:
paparazzi-devel-bounces+romneyj=address@hidden
[paparazzi-devel-bounces+romneyj=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.
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.
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.
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.
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).
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