ardupilot/libraries/AP_Soaring/Variometer.cpp

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/* Variometer class by Samuel Tabor
Manages the estimation of aircraft total energy, drag and vertical air velocity.
*/
#include "Variometer.h"
#include <AP_Logger/AP_Logger.h>
Variometer::Variometer(const AP_Vehicle::FixedWing &parms) :
_aparm(parms)
{
}
void Variometer::update(const float thermal_bank, const float polar_K, const float polar_Cd0, const float polar_B)
{
const AP_AHRS &_ahrs = AP::ahrs();
_ahrs.get_relative_position_D_home(alt);
alt = -alt;
float aspd = 0;
if (!_ahrs.airspeed_estimate(aspd)) {
aspd = _aparm.airspeed_cruise_cm / 100.0f;
}
float aspd_filt = _sp_filter.apply(aspd);
// Constrained airspeed.
const float minV = sqrtf(polar_K/1.5);
_aspd_filt_constrained = aspd_filt>minV ? aspd_filt : minV;
tau = calculate_circling_time_constant(radians(thermal_bank));
float dt = (float)(AP_HAL::micros64() - _prev_update_time)/1e6;
// Logic borrowed from AP_TECS.cpp
// Update and average speed rate of change
// Get DCM
const Matrix3f &rotMat = _ahrs.get_rotation_body_to_ned();
// Calculate speed rate of change
float temp = rotMat.c.x * GRAVITY_MSS + AP::ins().get_accel().x;
// take 5 point moving average
float dsp = _vdot_filter.apply(temp);
// Now we need to high-pass this signal to remove bias.
_vdotbias_filter.set_cutoff_frequency(1/(20*tau));
float dsp_bias = _vdotbias_filter.apply(temp, dt);
float dsp_cor = dsp - dsp_bias;
Vector3f velned;
float raw_climb_rate = 0.0f;
if (_ahrs.get_velocity_NED(velned)) {
// if possible use the EKF vertical velocity
raw_climb_rate = -velned.z;
}
_climb_filter.set_cutoff_frequency(1/(3*tau));
float smoothed_climb_rate = _climb_filter.apply(raw_climb_rate, dt);
// Compute still-air sinkrate
float roll = _ahrs.roll;
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float sinkrate = calculate_aircraft_sinkrate(roll, polar_K, polar_Cd0, polar_B);
reading = raw_climb_rate + dsp_cor*_aspd_filt_constrained/GRAVITY_MSS + sinkrate;
float filtered_reading = _trigger_filter.apply(reading, dt); // Apply low pass timeconst filter for noise
_audio_filter.apply(reading, dt); // Apply low pass timeconst filter for noise
_prev_update_time = AP_HAL::micros64();
_expected_thermalling_sink = calculate_aircraft_sinkrate(radians(thermal_bank), polar_K, polar_Cd0, polar_B);
// @LoggerMessage: VAR
// @Vehicles: Plane
// @Description: Variometer data
// @Field: TimeUS: Time since system startup
// @Field: aspd_raw: always zero
// @Field: aspd_filt: filtered and constrained airspeed
// @Field: alt: AHRS altitude
// @Field: roll: AHRS roll
// @Field: raw: estimated air vertical speed
// @Field: filt: low-pass filtered air vertical speed
// @Field: cl: raw climb rate
// @Field: fc: filtered climb rate
// @Field: exs: expected sink rate relative to air in thermalling turn
// @Field: dsp: average acceleration along X axis
// @Field: dspb: detected bias in average acceleration along X axis
AP::logger().WriteStreaming("VAR", "TimeUS,aspd_raw,aspd_filt,alt,roll,raw,filt,cl,fc,exs,dsp,dspb", "Qfffffffffff",
AP_HAL::micros64(),
(double)0.0,
(double)_aspd_filt_constrained,
(double)alt,
(double)roll,
(double)reading,
(double)filtered_reading,
(double)_raw_climb_rate,
(double)smoothed_climb_rate,
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(double)_expected_thermalling_sink,
(double)dsp,
(double)dsp_bias);
}
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float Variometer::calculate_aircraft_sinkrate(float phi,
const float polar_K,
const float polar_CD0,
const float polar_B) const
{
// Remove aircraft sink rate
float CL0; // CL0 = 2*W/(rho*S*V^2)
float C1; // C1 = CD0/CL0
float C2; // C2 = CDi0/CL0 = B*CL0
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CL0 = polar_K / (_aspd_filt_constrained * _aspd_filt_constrained);
C1 = polar_CD0 / CL0; // constant describing expected angle to overcome zero-lift drag
C2 = polar_B * CL0; // constant describing expected angle to overcome lift induced drag at zero bank
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float cosphi = (1 - phi * phi / 2); // first two terms of mclaurin series for cos(phi)
return _aspd_filt_constrained * (C1 + C2 / (cosphi * cosphi));
}
float Variometer::calculate_circling_time_constant(float thermal_bank)
{
// Calculate a time constant to use to filter quantities over a full thermal orbit.
// This is used for rejecting variation in e.g. climb rate, or estimated climb rate
// potential, as the aircraft orbits the thermal.
// Use the time to circle - variations at the circling frequency then have a gain of 25%
// and the response to a step input will reach 64% of final value in three orbits.
return 2*M_PI*_aspd_filt_constrained/(GRAVITY_MSS*tanf(thermal_bank));
}