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Re: [Paparazzi-devel] Using Thermopiles for AHRS on Lisa/M instead of IM

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Using Thermopiles for AHRS on Lisa/M instead of IMU
Date: Tue, 3 Apr 2012 09:05:54 +0200


The default assignment of adc should be written in conf/board/lisa-m.makefile

There might still be the issue that ADC_1 is called 0
USE_0 instead of USE_ADC_1

For the gyros: the value of the gyro is only distorted a few percent. So for simple stabilization like a roll damper the aspirin is good 3noug even with vibrations. The problems start when you start integrating, which is not needed for damping but required for attitude. Then all errors accumulate. And a gyro error of 1% (sounds like a small error) on a 2000 degree/sec gyro gives 20 degree of additional attitude error PER SECOND. This is corrected with accelerometers. However the accelerometers also measure vibrations. These can be several times bigger than gravity. This means that at times the accelerometer even could measure that the earth is up. And low pass filtering them too much gives latency. And that again gives correction errors:  e.g. if you suddenly roll 90 degrees, but the accelerometer follows with a delay, initially the filtered accelerometer will measure a huge error and estimate this is due to the gyro bias.

Did you try to mount the lisa on 4 corners of 3x3x10mm pieces of tempur foam and use very thin flexible cables?

On Apr 3, 2012 5:06 AM, "Chris Wozny" <address@hidden> wrote:

For reasons outside of my power (trying to dampen vibrations in tiny,
tiny aircraft leads to massive hair loss and frustration) I've got to
resort to using IR for the AHRS on our aircraft instead of Aspirin
v1.0. We're using Lisa/M and I was wondering: are there any default
assignments for which ports to use for thermopiles like with Tiny? The
wiki says there should be, but I have a feeling Lisa was designed
without thermopiles in mind since an IMU would work much better.

Also, why do analog gyros (more specifically Futaba Mini Piezo gyros)
work great for stabilizing the same plane with the same vibrations
that cripple the use of Aspirin v1.0 for AHRS?


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