[Paparazzi-devel] Airspeed Sensor

[Tobias]

Hey guys,

I spend some time with the eagle tree to get it working....

so I can confirm that there is a big problem with the offset at startup, thats 
why we have the calculation and no fixed values - however if you wane check 
your sensor at an pressure difference (maybe the equivalent for 15m/s for 
example) you will notice that the drift and noise are well in an acceptable 
range, just seems to be an issue with offset at startup...

just an idea for the calibration - some years ago I also started with 
calibrating my sensors on a car, but there are two things you should have in 
mind 
1 you will probably stay inside the boundary layer of the car which will effect 
you measurement (hard to overcome when your not at the very front of it...)
2. even if you are able to calibrate it perfectly you will get IAS when mounted 
to your plane...  

sounds good, but its not since you will have to correct this for the mounting 
error to get CAS (which is actually named as IAS in PPZ)

so what I do, is just checking the GS compared to IAS(ppz) in a constant circle 
at constant altitude. 
IAS should be exactly in the middle between GSmax and GSmin 
if it is, you probably calibrated it perfectly and therefor already corrected 
for any mounting error (you got CAS!)
if not adjust the scaling factor 
thats an quick and easy way and is working just fine

just a tip, I changed to this sensor which has a temperature sensor and i2c, 
the code is already in v5 - looks very promising 
http://www.amsys.de/products/ams5812.htm


hope that helps ;-)

Tobi