Hello,
The sensors used by Booz and HB-Autopilot (ADXRS610) have higher
vibration resistance and lower drifts.
You can also use Spakfun PCBs with the adxRS610 and glue them together
to a cube . But this is expensive about 180 Euros.
The first sensors LISY300AL used by the diydrohnes project had poor
vibrations resistance.
The Razor IMU has new sensors with better performance. Also the new
IMUSENSE sensors have good performances to fly quadcopters and
normal planes. If you want to fly with MEMS you must look that you
have fully balanced the drive train (propellers).
Sometimes it is necessary to damp vibrations by the use of rubber
mounts or foam.
The advertange of the DCM algorithm introduced by William Premerlani
and Paul Bizard is that they also take the centrifugal forces into
account in
correcting the gyro drift and to correct the orthogonallity of the
DCM. Both are scientists and no hobbyist and wrote easy to understand
documents and take matlab simulations before going to the C code. Also
a EKF was implemented.
If very closer circles are flown with high speed the range of the
acceleration sensors has to be extended.
Booz and HB-Autopilot can measure up to 5g. The new HB autopilot can
measure up to 6g. The RazzorIMU can measure up to 3g.
There is no limitation on the speed.
The diydrohens project works first as paparazzi wiht IR-Sensors and
AVR processors. The community is very active:
normal planes, quadrocopters and helicopters.
Most of the hardware is sealed by Sparkfun.
You can by a IMU with processor for 99$ with the same algorithms.
http://www.sparkfun.com/commerce/product_info.php?products_id=9956
In the actual version 1.7 also pressure measurement and magnetometer
signals are taken into account.
It is also possible to use this system with the paparazzi Towg. There
is a comment in the paparazzi wiki..
Regards
Heinrich
David Conger schrieb:
Hello,
One of their users flies a FunJet > 100mph, not in a straight
line only, quite well with the DCM code. How is this possible from a
project so new by someone with no experience with UAV before?
It should be noted that the code for the DIY is a simpler
version of the orig. code from the UAV Devboard so maybe better results
would come from code more like the UAV Devboard and not the DIY IMU.
I want to help, try out code, fly, ask programmers I work with
to take a look... but I don't want to use DIY code and still use IR to
fly fixed wing. I also can not afford a 2000.00 IMU. To me Booz is fine
because anyone can assemble one or have one assembled from available
plans or it can be purchased for about the same price as a VT100. I do
not get the feeling having a 100.00 IMU will make all the difference.
It's the lack of actually being able to do it or that it's not widely
done with any IMU that seems to get the complaints from people I
interact with. They simply point to the UAV Devboard and DIY for the
examples.
-David
On Sep 1, 2010, at 11:34 PM, Christophe De Wagter wrote:
Hello,
The AHRS works fine as long as there are no long-lasting
kinematic accelerations. An airplane however does accelerate very often
for a long time: for instance when making something as simple as a
turn. This is a big problem for "Inertial/Magnetic-Only" AHRS. For
quadrotors, as long as you hover or move slowly and always keep your
nose in the same direction, these sensors are sufficient. For aircraft
you NEED to compensate for kinematic accelerations. This is why either
airspeed of GPS is required in order to make the filter stay within the
+/-10 degree error range like thermopiles.
The code in the HW branch uses this type of filter as was
written by diydrones.
If the Raisor IMU can be converted to accept GPS data, it
could do the full computation. Once reliable attitude data is
available, like you say: "it can simply be copied to the estimator
variables"
If you run for instance the XSens Mti-G Module (with internal
GPS and barometer for kinematic conpensations), that is exactly what
happens.
-Christophe
On Thu, Sep 2, 2010 at 8:16 AM, David
Conger <address@hidden>
wrote:
Hello,
I took a look at the HW branch code today. Am I correct when
I think the HW code in razor_imu is bypassing the DCM code on the Razor
and just using the ADC outputs and then calculating the Euler Angles in
the Autopilot. Then feeding them to estimator.
Since the Razor is an AHRS already can't the outputs from
the AHRS just be fed to estimator directly? Just over SPI feel the
Euler Angles output into:
From estimator.c
/* attitude in radian */
float estimator_phi;
float estimator_psi;
float estimator_theta;
I also see the wiring diagram in the HR branch shows IR
sensors are still used alongside the Razor IMU. Is this because it's
difficult to remove the IR code?
-David
Germar,
Have a look at the post by Prof. Dr.-Ing. Heinrich Warmers on 23 July
2010.
He
has tested a low cost Sparkfun IMU ( RAZZOR IMU 6DOF Razor - Ultra-Thin
IMU) with the paparazzi hardware.
Contact
hwarm or check out his branch in svn. I believe they have this IMU
working with the autopilot already.
Buzz
On 09/01/2010 09:31 AM, Germar Walter wrote:
Hi,
We are building a fixedwing Aircraft with tiny board.
We want to replace the Thermopiles with a AHRS System. We have
purchased the Sparkfun9DOF Razor IMU. On the IMU we are directly
calculating eulerian angles via the code provided by http://code.google.com/p/sf9domahrs/source/list.
We have activated the SPI interface on the board to communicate with
the paparazzi.
Has anybody done something similar or knows how to use the angles for
roll and pitch for stbilization? The code from the gyro.c only takes
analogue measurements, but since We have a digital interface we don't
want to convert to analogue just to convert back on the paparazzi.
cheers
Germar
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