[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Paparazzi-devel] IMU's

From: Chad Koehnen
Subject: Re: [Paparazzi-devel] IMU's
Date: Tue, 06 Sep 2011 13:38:07 -0400
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20110831 Thunderbird/3.1.13

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 BMP-85 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)



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)


-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.


On Tue, Aug 9, 2011 at 11:17 AM, Prof. Dr.-Ing. Heinrich Warmers <address@hidden> wrote:
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.



_______________________________________________ Paparazzi-devel mailing list address@hidden
_______________________________________________ Paparazzi-devel mailing list address@hidden



Chad Koehnen
Embedded Engineer

IEM Corporation
850 River Street, Troy, New York 12180-1239
T: (518) 268-1636 ext:27 | F: (518) 268-1639
Confidential Information: This communication is for the use of the intended recipient only to the benefit of the sender. It may contain information that is privileged and confidential. If you are not the intended recipient of this communication,any disclosure, copying, further distribution or use thereof is prohibited. If you have received this communication in error, please advise me by return e-mail or by telephone and delete/destroy it.

Attachment: ckoehnen.vcf
Description: Vcard

reply via email to

[Prev in Thread] Current Thread [Next in Thread]