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Re: [Paparazzi-devel] IMU's

From: Prof. Dr.-Ing. Heinrich Warmers
Subject: Re: [Paparazzi-devel] IMU's
Date: Tue, 09 Aug 2011 11:17:53 +0200
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; de-DE; rv:1.4) Gecko/20030619 Netscape/7.1 (ax)

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.


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 non-stationary flight (under linear-accelerations) the performance of the DCM algorithm stills poor. As always, the quality performance depends on your mission requirements.


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.


From: Prof. Dr.-Ing. Heinrich Warmers <address@hidden>
To: address@hidden
Sent: Tuesday, 9 August 2011 1:31 AM
Subject: Re: [Paparazzi-devel] 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 (  ADXRS613-Breakout  )

 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 IC-motors.


Ensslin Oliver (enso) schrieb:
Hi All
I beleive the ArduIMU+ V2 has been discontinued. As we fly our UMARS (with Tiny 2.11) with this IMU and several “student planes” I am thinking of changing to another IMU.
What would be your recommendation?
How do the other IMU’s compare with the ArduIMU? (for fixed wing)
Would the Aspirin IMU be appropriate for the replacement?
How is the vibration tolerance for Aspirin?
I would be thankful if you would tell me your experience.

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