From 16e49c447d788c73535a6dd36474673cbf9b8e4f Mon Sep 17 00:00:00 2001 From: Lorenz Meier Date: Wed, 9 Jan 2013 16:37:45 +0100 Subject: Added support for battery voltage and differential pressure to logging and plot script --- apps/systemlib/airspeed.c | 79 ++++++++++++++++++++++++++++++++++++++++ apps/systemlib/airspeed.h | 86 ++++++++++++++++++++++++++++++++++++++++++++ apps/systemlib/conversions.c | 9 +++++ apps/systemlib/conversions.h | 5 +++ 4 files changed, 179 insertions(+) create mode 100644 apps/systemlib/airspeed.c create mode 100644 apps/systemlib/airspeed.h (limited to 'apps/systemlib') diff --git a/apps/systemlib/airspeed.c b/apps/systemlib/airspeed.c new file mode 100644 index 000000000..e213b66c2 --- /dev/null +++ b/apps/systemlib/airspeed.c @@ -0,0 +1,79 @@ +/**************************************************************************** + * + * Copyright (C) 2012-2013 PX4 Development Team. All rights reserved. + * Author: Lorenz Meier + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name PX4 nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/** + * @file airspeed.c + * Airspeed estimation + * + * @author Lorenz Meier + * + */ + +#include "math.h" + + +float calc_indicated_airspeed(float pressure_front, float pressure_ambient, float temperature) +{ + return sqrtf((2.0f*(pressure_front - pressure_ambient)) / air_density_sea_level); +} + +/** + * Calculate true airspeed from indicated airspeed. + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param speed current indicated airspeed + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature air temperature in degrees celcius + * @return true airspeed in m/s + */ +float calc_true_airspeed_from_indicated(float speed, float pressure_ambient, float temperature) +{ + return speed * sqrtf(air_density_sea_level / get_air_density(pressure_ambient, temperature)); +} + +/** + * Directly calculate true airspeed + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param pressure_front pressure inside the pitot/prandl tube + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature air temperature in degrees celcius + * @return true airspeed in m/s + */ +float calc_true_airspeed(float pressure_front, float pressure_ambient, float temperature) +{ + return sqrtf((2.0f*(pressure_front - pressure_ambient)) / get_air_density(pressure_ambient, temperature)); +} \ No newline at end of file diff --git a/apps/systemlib/airspeed.h b/apps/systemlib/airspeed.h new file mode 100644 index 000000000..62acfe2b0 --- /dev/null +++ b/apps/systemlib/airspeed.h @@ -0,0 +1,86 @@ +/**************************************************************************** + * + * Copyright (C) 2012-2013 PX4 Development Team. All rights reserved. + * Author: Lorenz Meier + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name PX4 nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/** + * @file airspeed.c + * Airspeed estimation + * + * @author Lorenz Meier + * + */ + +#include "math.h" +#include "conversions.h" + + __BEGIN_DECLS + +/** + * Calculate indicated airspeed. + * + * Note that the indicated airspeed is not the true airspeed because it + * lacks the air density compensation. Use the calc_true_airspeed functions to get + * the true airspeed. + * + * @param pressure_front pressure inside the pitot/prandl tube + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature air temperature in degrees celcius + * @return indicated airspeed in m/s + */ +__EXPORT float calc_indicated_airspeed(float pressure_front, float pressure_ambient, float temperature); + +/** + * Calculate true airspeed from indicated airspeed. + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param speed current indicated airspeed + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature air temperature in degrees celcius + * @return true airspeed in m/s + */ +__EXPORT float calc_true_airspeed_from_indicated(float speed, float pressure_ambient, float temperature); + +/** + * Directly calculate true airspeed + * + * Note that the true airspeed is NOT the groundspeed, because of the effects of wind + * + * @param pressure_front pressure inside the pitot/prandl tube + * @param pressure_ambient pressure at the side of the tube/airplane + * @param temperature air temperature in degrees celcius + * @return true airspeed in m/s + */ +__EXPORT float calc_true_airspeed(float pressure_front, float pressure_ambient, float temperature); + +__END_DECLS \ No newline at end of file diff --git a/apps/systemlib/conversions.c b/apps/systemlib/conversions.c index 9105d83cb..78e89f951 100644 --- a/apps/systemlib/conversions.c +++ b/apps/systemlib/conversions.c @@ -42,6 +42,10 @@ #include "conversions.h" +#define air_gas_constant 8.31432f +#define air_density_sea_level 1.225f +#define absolute_null_kelvin 273.15f + int16_t int16_t_from_bytes(uint8_t bytes[]) { @@ -55,3 +59,8 @@ int16_t_from_bytes(uint8_t bytes[]) return u.w; } + +float get_air_density(float static_pressure, float temperature_celsius) +{ + return static_pressure/(air_gas_constant * (temperature_celsius + absolute_null_kelvin)); +} diff --git a/apps/systemlib/conversions.h b/apps/systemlib/conversions.h index dc383e770..33c21f8f9 100644 --- a/apps/systemlib/conversions.h +++ b/apps/systemlib/conversions.h @@ -56,6 +56,11 @@ __BEGIN_DECLS */ __EXPORT int16_t int16_t_from_bytes(uint8_t bytes[]); +/** + * Calculates air density. + */ +__EXPORT float get_air_density(float static_pressure, float temperature_celsius); + __END_DECLS #endif /* CONVERSIONS_H_ */ -- cgit v1.2.3