Has anyone put together a list of advantages / disadvantages of each
IMU yet?
On 09/02/2011 04:03 AM, Prof. Dr.Ing. Heinrich Warmers wrote:
Hello Christophe,
after Martin has corrected the error in BMP85 driver we use
only the
pressure for altitude estimation.
I have implemented a average over 10 samples in the driver so
that the
noise is fixed in the 0.5m range.
This is compared with the altitude error of the GPS (in the range
8..30m) a real improvement.
Automatic landing is now possible without problems.
Last week we have flown circles with a radius of 37m with a TAS up
to
27m/s.
I found a consideration in a application note (from Freescale)
that a
low pass filter will give better results than calculating the
average.
Has someone the application note from Bosch of noise reduction?
Knows someone the part of the software were the altitude of the
GPS is
used to manipulate all altitudes of the way points when a GPS fix
occurs?
In the Version 1.7 of the DCM used for the adreino quadcopter the
following changes are made:
low pass filter for the acceleration signals.
correcting the centrifugal force with the horizontal ground speed
vector.
using a magnetometer (but this part has to bee improved to get
exact
results)
Regards
Heinrich
Christophe De Wagter schrieb:
Hear
Hector,
the DCM_float implementation in paparazzi indeed only
estimates attitude (called AHRS in paparazzi) but it
does use GPS
velocity to compensate centripetal forces and to estimate
heading
(magnetometer could be used)
however:
assumes all velocity is in body X direction (= aircraft
model)
does not compensate longitudinal acceleration (change is
velocity)
does not improve GPS measurements using accelerometers
(called
INS in paparazzi)
On Thursday, September 1, 2011, Hector Garcia de Marina wrote:
Hello
professor,
I have writen about the DCM algorithm (mahony papers) only
estimates
the attitude, not the 3D position as it does not take into
account any
position observation, as GPS, vision, or whatever :P. But of
course,
the DCM algorithm estimates the attitude, althougt as it
only relies in
accelerometer for measuring the gravity, the algotihm can
not estimate
the yaw angle.
Cheers.
On Tue, Aug 9, 2011 at 11:17 AM, Prof. Dr.Ing.
Heinrich
Warmers <address@hidden>
wrote:
Hector,
you're are right that in the current implementation
only compensate
the centrifugal force for circles around the z
axis.
It it not a problem to solve vector f = vector
omega (vector
multiplication ) vector V.
By adding this simple equation also to the AHS of
paparazzi it would
be possible to fly acrobatic with normal planes for a
long time period.
I think you're are wrong, that the current
implementation oft the
DCM do not estimate the 3D attitude.
We have flown circles for 20 minutes (angel up to 70°
radius down to
70m).
We have also flown in clouds and circles up to to
1700m ground level
without problems.
The paparazzi estimator (estimator.c) calculate
position and speed and
fill the gap between the 250ms until the next gps
information.
It would be a nice work to implement acrobatic flight
components like
F3A in Paparazzi.
Heinrich
Hector Garcia de Marina schrieb:
Hello
Todd,
as the DCM algorithm does not estimate the 3D
position/velocity,
it can not compensante the centripetal
acceleration. You can still
using the DCM algorithm but with poor
performance, specially when you
have mid/large wz (gyro in z axis) for instance
in a turn, even at low
velocities.
Note that even if you have a GPS, the ground
speed will have a delay
(depending on your GPS could be even more than 1
sec). So if you do not
take account this, for nonstationary flight
(under
linearaccelerations) the performance of the DCM
algorithm stills poor.
As always, the quality performance depends on
your mission requirements.
Héctor
On Tue, Aug 9, 2011 at 2:30 AM, Todd
Sandercock <address@hidden>
wrote:
From just my reading into the
Paparazzi's DCM
code, it
also does centripetal acceleration
compensation via GPS... as long as
"USE_GPS" is defined.
Todd
From:
Prof. Dr.Ing. Heinrich Warmers
<address@hidden>
To: address@hidden
Sent:
Tuesday,
9
August 2011 1:31 AM
Subject: Re:
[Paparazzidevel] IMU's
Hi Oli,
I think the rating of the
IMU`s depend of there
vibration resistance
and the bias of the rate
sensors.
I think there is the following
rating:
1. Bosch (SMG074)
2. Analog device
(ADXRS620..) 3.Melexsis 4.
Invensense 5. ST
electronic
The Bosch and the Analoag
device are made for
automotive applications
and therefore they deliver a
maximum of vibration
tolerance.
For normal planes the best
algorithm in my opinion is
the dydrohnes
DCM, since this can correct
the attitude given by
integration of the
rates
even when continuos circles
are flown.
You have to consider the
centripetal forces. Every IMU
without
measuring the speed over
ground can't do this.
If you want to test the Analog
device types you can fit
sparkefun
modules ( http://www.watterott.com/de/ADXRS620Breakout
ADXRS613Breakout )
to a box (total cost < 80
Euro). This is software
compatible to the
paparazzi DCM implementation.
You can find them in the
repository of
Christian Niemann.
I think this will also solve
you problem with ICmotors.
Regards
Heinrich

Christophe
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