Re: [Paparazzi-devel] Fwd: ETS airspeed sensor data.

[Felix Ruess]

Hi Helge,

To try and get a better airspeed reading from the EagleTree v3 airspeed sensor in default mode, I now read pressure and temperature from my BMP085 baro into airspeed_ets.c via air_data.c. Air density is taken into account using the pitot formula http://en.wikipedia.org/wiki/Pitot_tube . I have not tried this in flight yet, but calculations I have done predict some, but not big, improvements.

you did see the newer functions in the air_data module to calculate equivalent/true airspeed, etc. (introduced with #853), right?
http://docs.paparazziuav.org/latest/air__data_8h.html

But then there is the offset drift. At low airspeeds (15m/s) this is a rather big problem. Not knowing the spesification of the raw data from the sensor it is difficult, if at all possible, to compensate for it.

I read somewhere about making a differential pressure unit consisting of two ms5611 barometers. I don't know if this will give the desired results, as these will also have drift, but I may give it a try. Then I would want to connect the two baros physically close together. I have a Twog and a Lisa/M, and for this I would like to use the Twog.

I am not sure about the best method of configuring two standalone ms5611's into Paparazzi, one of them using the alternate I2C address. Is there a straightforward way to do this?

There are basically two options:
- write a wrapper that reads two ms5611 peripherals
- write another module wrapper like sw/airborne/modules/sensors/baro_ms5611_i2c.c but with different variable/function names so you can both modules at the same time.

 

It seems that the calculation of airspeed is supposed to be done in air_data.c. Is this correct?

If you have a "standard" pitot sensor and want to calculate airspeed from dynamic/differential pressure, then yes (no need to duplicate this in every driver).

Cheers, Felix