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Re: [Paparazzi-devel] re: razor imu


From: Oliver Riesener
Subject: Re: [Paparazzi-devel] re: razor imu
Date: Wed, 19 Jan 2011 11:02:11 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.13) Gecko/20101208 Thunderbird/3.1.7

Hi Ana, Hi Felix, Hi Heinrich,

the SENS values in hb_tiny_razor.xml airframe file (4096 = 12 Bit) are only set 
to reverse the BFP
formating what ist done for rates in RATES_FLOAT_OF_BFP(gyro_float, imu.gyro); 
in ahrs_propagate();

/* convert bfp imu data to floating point */
RATES_FLOAT_OF_BFP(gyro_float, imu.gyro); // olri div by (1<<12)

/* unbias rate measurement */
RATES_DIFF(ahrs_float.imu_rate, gyro_float, ahrs_impl.gyro_bias);

The trick to get it work is to scale the values from deg/s to RAD/s,
see the lines below from my ahrs_propagate();.

// scale gyro adc raw to [rad/s] FIXME // olri
ahrs_float.imu_rate.p /= 61.35f;
ahrs_float.imu_rate.q /= 57.96f;
ahrs_float.imu_rate.r /= 60.10f;

The result of the that *must* give closest-by 0.0... rate on silence!

It's at the moment *impossible* to combine these 2 factors,
becourse the bias is substracted between these to steps.

I worked hard for finding out that ;-), but i didn't see the
jumping point to solve it better, i am not fimiliar with BFP.

Regards
Oliver


On 19.01.2011 09:00, Prof. Dr.-Ing. Heinrich Warmers wrote:
Hi Ana,
please make a output of the rate sensor and accelerator values.
I fond that an value of 2-3 LSB results in rolling PFD.
This is also given if , wire has broken.
Sometimes the accelerators values have an error up to 20%. when measuring g.
Regards
Heinrich


GARCIA ALVAREZ, ANA schrieb:

Hi Felix,

As Oliver said, after waiting 3minutes, the ATTITUDE message and PFD works…but 
still not well.

I haven’t the right sens parameters up to now. I looked into Oliver’s ones, but 
they don’t work for me(too much sensibility according to the PFD, and I have an 
offset(I think) which rolls the PFD continuously). I’m trying changing the 
values but I’m afraid it’s a really empiric method and don’t know if some day 
it’ll work.

Are these values(sens and neutrals) the only parameters I’m supposed to touch?

I am also looking for Christoph’s values, but I haven’t found them-I think they 
aren’t in an airframe file but in another one-.

Ana

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