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Re: [Paparazzi-devel] Re: Interfacing to the EagleTree airspeed sensor

From: Vassilis V .
Subject: Re: [Paparazzi-devel] Re: Interfacing to the EagleTree airspeed sensor
Date: Thu, 10 Sep 2009 22:56:15 -0400

I got a reply from Bill of EagleTree that they will be adding an option to configure the sensors for standalone mode. In that mode they will output actual measurements, that will remove some of the assumptions I had to make in my current implementation (since I only had the raw values to work with). I have been pretty busy at work this week, I will let you know once I have a chance to test it.


On Sep 8, 2009, at 10:27 PM, Vassilis V. wrote:


I was thinking about this, but my concern is that I am not sure how much confidence I should have on the GPS data. The speed should be relatively accurate but it is ground speed so any wind gusts or changes in the attitude will introduce an error related to the airspeed. I never had too much confidence on the GPS reported altitude. I can upload the CSV files from my test flights if you would like to have a look at the raw data. Keep in mind that at this point I had to reverse engineer the I2C protocol and conversion of the raw values to altitude and airspeed so I can not be certain on the calculations done by the sensor itself. 

A few days ago I finally got a response from Bill Parry of EagleTree and he offered to give me some information. I will let you know when I get more details. 

A few emails from those of you interested may give Bill him an extra intensive to be more forthcoming ( billpa_at_eagletreesystems_dot_com)



On Sep 8, 2009, at 4:40 PM, Roman Krashanitsa wrote:

Hi Vassilis,
Good job on the airspeed sensor. Did you do any finer analysis on error estimates for the sensor? From the plot, I can see that your GPS measurements were not very stable and/or airspeed measurements are very inertial. Is it true?
What was the mean and deviation of the difference between GPS and airspeed readings in a stable portion of the flight?

2009/9/7 Vassilis V. <address@hidden>
I got both the airspeed and altimeter sensors from EagleTree working. The source code and some data can be found at:

At this point I am simply passing the airspeed and altitude through the telemetry down to the ground station. The next step is to work on fw_v_ctl.c to allow the airspeed to be used for  controlling the throttle (i.e. maintain constant airspeed). This will take me a bit longer, I will let you know when I have something working.


On Sep 6, 2009, at 9:59 AM, Vassilis V. wrote:


I had a successful flight with the EagleTree airspeed module ( ) connected to my TWOG. I did not have to do any hardware modifications, the sensor has an I2C interface that I connected directly to the TWOG I2C port. I was able to figure out the slave address and decode the raw output of the sensor. The results are quite good, the module is low cost ($43) and comes with a very good pitot tube that includes static and dynamic ports. For now I am simply sending the airspeed through the telemetry, the next step would be to modify the autopilot code to regulate the throttle in order to keep the airspeed constant (and a minimum ground speed). I will do the same with the altimeter sensor.

See for more information, I will publish the code as soon as I have the altimeter tested (probably in a week or so). Is there any interest on getting this released code released into CVS?


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