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

From: Chris Wozny
Subject: Re: [Paparazzi-devel] Using Thermopiles for AHRS on Lisa/M instead of IMU
Date: Thu, 5 Apr 2012 13:35:07 -0700


Something you said made me curious. Is it possible to use the Aspirin
IMU solely for gyro stabilization if thermopiles are being used for
attitude estimation? I know we've used 3-axis gyros in the past with
Tiny v0.99 for roll/pitch/yaw dampening while using IR, but I don't
know if this is any different since the gyros are on the Aspirin IMU.


On Tue, Apr 3, 2012 at 12:05 AM, Christophe De Wagter
<address@hidden> wrote:
> Hi,
> 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:
>> All,
>> 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?
>> Best,
>> Chris
>> _______________________________________________
>> Paparazzi-devel mailing list
>> address@hidden

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