
From:  Christophe De Wagter 
Subject:  Re: [Paparazzidevel] IMU's 
Date:  Thu, 1 Sep 2011 20:17:55 +0200 
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
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