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

From: Felix Ruess
Subject: Re: [Paparazzi-devel] Using Thermopiles for AHRS on Lisa/M instead of IMU
Date: Thu, 5 Apr 2012 22:46:00 +0200

Hi Chris,

something similar is currently implemented... If you use ahrs type="infrared" and have analog gyros defined then you get something like that (without gyro bias estimation).
You could pimp sw/airborne/subsystems/ahrs/ahrs_infrared.c to do that...

To use it with aspirin (and without gyro bias estimation) you would only have to remove the #ifdef ADC_CHANNEL_GYRO_P, etc.
But we would have to replace that with a nicer way of which gyros are available (if you don't have an IMU with full 3-axis gyros, but just separate ones, maybe only roll, like in the old days...)

You could also estimate the gyro bias using the infrared sensors as absolute reference... you could even combine it with accels and use IR if they are too bad and vice versa.
I just didn't think it was worth the effort as you are not likely to use both...

Cheers, Felix

On Thu, Apr 5, 2012 at 10:35 PM, Chris Wozny <address@hidden> wrote:

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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