[Space] draft blog post

Christoph Maier cm.hardware.software.elsewhere at gmail.com
Tue Feb 9 02:36:47 PST 2010


On Tue, 2010-02-09 at 00:48 -0800, Michael O wrote:
> The orientation sensor is supposedly showing pitch,roll,yaw angles as
> derived from the magnetometer.
> 
> The accelerometer is supposedly showing meters/second^2 acceleration
> per X,Y,Z axis. So it should show 9.8m/s^2 on the ground.
> I seriously mis-trust the accelerometer data. It's showing
> acceleration values that are way too high or too low at different
> parts of the flight.
> 
> The GPS data is also mildly strange. It looks like the GPS is low-pass
> filtering altitude, and it's unable to cope with the high ascent and
> decent rates. That's my best guess for why it steps altitude by up to
> 500 meters on occasion. The lat/long data looks fine; it's just the
> altitude.
> 
> I'm yet to go and take a close look at the acceleration directions (I
> just did the magnitude) so it may be that the payload really was
> swinging that wildly...

I'll put my attempts to make sense of the data at
http://pony.noisebridge.net/~cmaier/EpicBalloonWin/
until shown a better place. 

I agree that the GPS seems to limit ascent and descent rates to
something like 5 meters/second. Latitude and longitude _does_ seem to be
affected somewhat, but this is less apparent than in the altitue
dimension. 

The data from the accelerometers and magnetometers drifts substantially
while on the ground, which makes me doubt the accuracy of the readings. 

In the air, _all_ the readings oscillate wildly ... so far, I haven't
zoomed in on a region to verify that the oscillations are consistent
between sensor outputs, but it looks like the swinging was real. The
pictures and movies support this assumption, too. 



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