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From: | alonso acuña |
Subject: | Re: [Paparazzi-devel] Fwd: ETS airspeed sensor data. |
Date: | Tue, 20 Jan 2015 07:06:58 -0600 |
Hi Helge, did you consider changing the ETS sensor to third party mode which supposedly would then give the actual airspeed value with no further calculations needed? I am planning on working on that this week so if there is any reason it won't work it would be useful to know.
Thanks Felix,This should be enough to get started.On first thought I would like to handle both barometers in one module.Helge.2015-01-18 15:26 GMT+01:00 Felix Ruess <address@hidden>: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.htmlBut 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
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