1
0
mirror of https://bitbucket.org/librepilot/librepilot.git synced 2024-12-11 19:24:10 +01:00
LibrePilot/flight/modules/PathFollower/fixedwingflycontroller.cpp
2016-04-25 18:45:35 +02:00

675 lines
27 KiB
C++

/*
******************************************************************************
*
* @file FixedWingFlyController.cpp
* @author The LibrePilot Project, http://www.librepilot.org Copyright (C) 2016.
* The OpenPilot Team, http://www.openpilot.org Copyright (C) 2015.
* @brief Fixed wing fly controller implementation
* @see The GNU Public License (GPL) Version 3
*
* @addtogroup LibrePilot LibrePilotModules Modules PathFollower Navigation
*
*****************************************************************************/
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
extern "C" {
#include <openpilot.h>
#include <pid.h>
#include <sin_lookup.h>
#include <pathdesired.h>
#include <paths.h>
#include <fixedwingpathfollowersettings.h>
#include <fixedwingpathfollowerstatus.h>
#include <flightstatus.h>
#include <pathstatus.h>
#include <positionstate.h>
#include <velocitystate.h>
#include <velocitydesired.h>
#include <stabilizationdesired.h>
#include <airspeedstate.h>
#include <attitudestate.h>
#include <systemsettings.h>
}
// C++ includes
#include "fixedwingflycontroller.h"
// Private constants
// pointer to a singleton instance
FixedWingFlyController *FixedWingFlyController::p_inst = 0;
FixedWingFlyController::FixedWingFlyController()
: fixedWingSettings(NULL), mActive(false), mMode(0), indicatedAirspeedStateBias(0.0f)
{}
// Called when mode first engaged
void FixedWingFlyController::Activate(void)
{
if (!mActive) {
mActive = true;
SettingsUpdated();
resetGlobals();
mMode = pathDesired->Mode;
lastAirspeedUpdate = 0;
}
}
uint8_t FixedWingFlyController::IsActive(void)
{
return mActive;
}
uint8_t FixedWingFlyController::Mode(void)
{
return mMode;
}
// Objective updated in pathdesired
void FixedWingFlyController::ObjectiveUpdated(void)
{}
void FixedWingFlyController::Deactivate(void)
{
if (mActive) {
mActive = false;
resetGlobals();
}
}
void FixedWingFlyController::SettingsUpdated(void)
{
// fixed wing PID only
pid_configure(&PIDposH[0], fixedWingSettings->HorizontalPosP, 0.0f, 0.0f, 0.0f);
pid_configure(&PIDposH[1], fixedWingSettings->HorizontalPosP, 0.0f, 0.0f, 0.0f);
pid_configure(&PIDposV, fixedWingSettings->VerticalPosP, 0.0f, 0.0f, 0.0f);
pid_configure(&PIDcourse, fixedWingSettings->CoursePI.Kp, fixedWingSettings->CoursePI.Ki, 0.0f, fixedWingSettings->CoursePI.ILimit);
pid_configure(&PIDspeed, fixedWingSettings->SpeedPI.Kp, fixedWingSettings->SpeedPI.Ki, 0.0f, fixedWingSettings->SpeedPI.ILimit);
pid_configure(&PIDpower, fixedWingSettings->PowerPI.Kp, fixedWingSettings->PowerPI.Ki, 0.0f, fixedWingSettings->PowerPI.ILimit);
}
/**
* Initialise the module, called on startup
* \returns 0 on success or -1 if initialisation failed
*/
int32_t FixedWingFlyController::Initialize(FixedWingPathFollowerSettingsData *ptr_fixedWingSettings)
{
PIOS_Assert(ptr_fixedWingSettings);
fixedWingSettings = ptr_fixedWingSettings;
resetGlobals();
return 0;
}
/**
* reset integrals
*/
void FixedWingFlyController::resetGlobals()
{
pid_zero(&PIDposH[0]);
pid_zero(&PIDposH[1]);
pid_zero(&PIDposV);
pid_zero(&PIDcourse);
pid_zero(&PIDspeed);
pid_zero(&PIDpower);
pathStatus->path_time = 0.0f;
}
void FixedWingFlyController::UpdateAutoPilot()
{
uint8_t result = updateAutoPilotFixedWing();
if (result) {
AlarmsSet(SYSTEMALARMS_ALARM_GUIDANCE, SYSTEMALARMS_ALARM_OK);
} else {
pathStatus->Status = PATHSTATUS_STATUS_CRITICAL;
AlarmsSet(SYSTEMALARMS_ALARM_GUIDANCE, SYSTEMALARMS_ALARM_WARNING);
}
PathStatusSet(pathStatus);
}
/**
* fixed wing autopilot:
* straight forward:
* 1. update path velocity for limited motion crafts
* 2. update attitude according to default fixed wing pathfollower algorithm
*/
uint8_t FixedWingFlyController::updateAutoPilotFixedWing()
{
updatePathVelocity(fixedWingSettings->CourseFeedForward, true);
return updateFixedDesiredAttitude();
}
/**
* Compute desired velocity from the current position and path
*/
void FixedWingFlyController::updatePathVelocity(float kFF, bool limited)
{
PositionStateData positionState;
PositionStateGet(&positionState);
VelocityStateData velocityState;
VelocityStateGet(&velocityState);
VelocityDesiredData velocityDesired;
const float dT = fixedWingSettings->UpdatePeriod / 1000.0f;
// look ahead kFF seconds
float cur[3] = { positionState.North + (velocityState.North * kFF),
positionState.East + (velocityState.East * kFF),
positionState.Down + (velocityState.Down * kFF) };
struct path_status progress;
path_progress(pathDesired, cur, &progress, true);
// calculate velocity - can be zero if waypoints are too close
velocityDesired.North = progress.path_vector[0];
velocityDesired.East = progress.path_vector[1];
velocityDesired.Down = progress.path_vector[2];
if (limited &&
// if a plane is crossing its desired flightpath facing the wrong way (away from flight direction)
// it would turn towards the flightpath to get on its desired course. This however would reverse the correction vector
// once it crosses the flightpath again, which would make it again turn towards the flightpath (but away from its desired heading)
// leading to an S-shape snake course the wrong way
// this only happens especially if HorizontalPosP is too high, as otherwise the angle between velocity desired and path_direction won't
// turn steep unless there is enough space complete the turn before crossing the flightpath
// in this case the plane effectively needs to be turned around
// indicators:
// difference between correction_direction and velocitystate >90 degrees and
// difference between path_direction and velocitystate >90 degrees ( 4th sector, facing away from everything )
// fix: ignore correction, steer in path direction until the situation has become better (condition doesn't apply anymore)
// calculating angles < 90 degrees through dot products
(vector_lengthf(progress.path_vector, 2) > 1e-6f) &&
((progress.path_vector[0] * velocityState.North + progress.path_vector[1] * velocityState.East) < 0.0f) &&
((progress.correction_vector[0] * velocityState.North + progress.correction_vector[1] * velocityState.East) < 0.0f)) {
;
} else {
// calculate correction
velocityDesired.North += pid_apply(&PIDposH[0], progress.correction_vector[0], dT);
velocityDesired.East += pid_apply(&PIDposH[1], progress.correction_vector[1], dT);
}
velocityDesired.Down += pid_apply(&PIDposV, progress.correction_vector[2], dT);
// update pathstatus
pathStatus->error = progress.error;
pathStatus->fractional_progress = progress.fractional_progress;
pathStatus->path_direction_north = progress.path_vector[0];
pathStatus->path_direction_east = progress.path_vector[1];
pathStatus->path_direction_down = progress.path_vector[2];
pathStatus->correction_direction_north = progress.correction_vector[0];
pathStatus->correction_direction_east = progress.correction_vector[1];
pathStatus->correction_direction_down = progress.correction_vector[2];
VelocityDesiredSet(&velocityDesired);
}
/**
* Compute desired attitude from the desired velocity for fixed wing craft
*/
uint8_t FixedWingFlyController::updateFixedDesiredAttitude()
{
uint8_t result = 1;
bool cutThrust = false;
bool hasAirspeed = true;
const float dT = fixedWingSettings->UpdatePeriod / 1000.0f;
VelocityDesiredData velocityDesired;
VelocityStateData velocityState;
StabilizationDesiredData stabDesired;
AttitudeStateData attitudeState;
FixedWingPathFollowerStatusData fixedWingPathFollowerStatus;
AirspeedStateData airspeedState;
SystemSettingsData systemSettings;
float groundspeedProjection;
float indicatedAirspeedState;
float indicatedAirspeedDesired;
float airspeedError = 0.0f;
float pitchCommand;
float descentspeedDesired;
float descentspeedError;
float powerCommand;
float airspeedVector[2];
float fluidMovement[2];
float courseComponent[2];
float courseError;
float courseCommand;
FixedWingPathFollowerStatusGet(&fixedWingPathFollowerStatus);
VelocityStateGet(&velocityState);
StabilizationDesiredGet(&stabDesired);
VelocityDesiredGet(&velocityDesired);
AttitudeStateGet(&attitudeState);
AirspeedStateGet(&airspeedState);
SystemSettingsGet(&systemSettings);
/**
* Compute speed error and course
*/
// check for airspeed sensor
fixedWingPathFollowerStatus.Errors.AirspeedSensor = 0;
if (fixedWingSettings->UseAirspeedSensor == FIXEDWINGPATHFOLLOWERSETTINGS_USEAIRSPEEDSENSOR_FALSE) {
// fallback algo triggered voluntarily
hasAirspeed = false;
fixedWingPathFollowerStatus.Errors.AirspeedSensor = 1;
} else if (PIOS_DELAY_GetuSSince(lastAirspeedUpdate) > 1000000) {
// no airspeed update in one second, assume airspeed sensor failure
hasAirspeed = false;
result = 0;
fixedWingPathFollowerStatus.Errors.AirspeedSensor = 1;
}
if (hasAirspeed) {
// missing sensors for airspeed-direction we have to assume within
// reasonable error that measured airspeed is actually the airspeed
// component in forward pointing direction
// airspeedVector is normalized
airspeedVector[0] = cos_lookup_deg(attitudeState.Yaw);
airspeedVector[1] = sin_lookup_deg(attitudeState.Yaw);
// current ground speed projected in forward direction
groundspeedProjection = velocityState.North * airspeedVector[0] + velocityState.East * airspeedVector[1];
// note that airspeedStateBias is ( calibratedAirspeed - groundspeedProjection ) at the time of measurement,
// but thanks to accelerometers, groundspeedProjection reacts faster to changes in direction
// than airspeed and gps sensors alone
indicatedAirspeedState = groundspeedProjection + indicatedAirspeedStateBias;
// fluidMovement is a vector describing the aproximate movement vector of
// the surrounding fluid in 2d space (aka wind vector)
fluidMovement[0] = velocityState.North - (indicatedAirspeedState * airspeedVector[0]);
fluidMovement[1] = velocityState.East - (indicatedAirspeedState * airspeedVector[1]);
// calculate the movement vector we need to fly to reach velocityDesired -
// taking fluidMovement into account
courseComponent[0] = velocityDesired.North - fluidMovement[0];
courseComponent[1] = velocityDesired.East - fluidMovement[1];
indicatedAirspeedDesired = boundf(sqrtf(courseComponent[0] * courseComponent[0] + courseComponent[1] * courseComponent[1]),
fixedWingSettings->HorizontalVelMin,
fixedWingSettings->HorizontalVelMax);
// if we could fly at arbitrary speeds, we'd just have to move towards the
// courseComponent vector as previously calculated and we'd be fine
// unfortunately however we are bound by min and max air speed limits, so
// we need to recalculate the correct course to meet at least the
// velocityDesired vector direction at our current speed
// this overwrites courseComponent
bool valid = correctCourse(courseComponent, (float *)&velocityDesired.North, fluidMovement, indicatedAirspeedDesired);
// Error condition: wind speed too high, we can't go where we want anymore
fixedWingPathFollowerStatus.Errors.Wind = 0;
if ((!valid) &&
fixedWingSettings->Safetymargins.Wind > 0.5f) { // alarm switched on
fixedWingPathFollowerStatus.Errors.Wind = 1;
result = 0;
}
// Airspeed error
airspeedError = indicatedAirspeedDesired - indicatedAirspeedState;
// Error condition: plane too slow or too fast
fixedWingPathFollowerStatus.Errors.Highspeed = 0;
fixedWingPathFollowerStatus.Errors.Lowspeed = 0;
if (indicatedAirspeedState > systemSettings.AirSpeedMax * fixedWingSettings->Safetymargins.Overspeed) {
fixedWingPathFollowerStatus.Errors.Overspeed = 1;
result = 0;
}
if (indicatedAirspeedState > fixedWingSettings->HorizontalVelMax * fixedWingSettings->Safetymargins.Highspeed) {
fixedWingPathFollowerStatus.Errors.Highspeed = 1;
result = 0;
cutThrust = true;
}
if (indicatedAirspeedState < fixedWingSettings->HorizontalVelMin * fixedWingSettings->Safetymargins.Lowspeed) {
fixedWingPathFollowerStatus.Errors.Lowspeed = 1;
result = 0;
}
if (indicatedAirspeedState < systemSettings.AirSpeedMin * fixedWingSettings->Safetymargins.Stallspeed) {
fixedWingPathFollowerStatus.Errors.Stallspeed = 1;
result = 0;
}
if (indicatedAirspeedState < fixedWingSettings->HorizontalVelMin * fixedWingSettings->Safetymargins.Lowspeed - fixedWingSettings->SafetyCutoffLimits.MaxDecelerationDeltaMPS) {
cutThrust = true;
result = 0;
}
}
// Vertical speed error
descentspeedDesired = boundf(
velocityDesired.Down,
-fixedWingSettings->VerticalVelMax,
fixedWingSettings->VerticalVelMax);
descentspeedError = descentspeedDesired - velocityState.Down;
/**
* Compute desired thrust command
*/
// Compute the cross feed from vertical speed to pitch, with saturation
float speedErrorToPowerCommandComponent = 0.0f;
if (hasAirspeed) {
speedErrorToPowerCommandComponent = boundf(
(airspeedError / fixedWingSettings->HorizontalVelMin) * fixedWingSettings->AirspeedToPowerCrossFeed.Kp,
-fixedWingSettings->AirspeedToPowerCrossFeed.Max,
fixedWingSettings->AirspeedToPowerCrossFeed.Max
);
}
// Compute final thrust response
powerCommand = pid_apply(&PIDpower, -descentspeedError, dT) +
speedErrorToPowerCommandComponent;
// Output internal state to telemetry
fixedWingPathFollowerStatus.Error.Power = descentspeedError;
fixedWingPathFollowerStatus.ErrorInt.Power = PIDpower.iAccumulator;
fixedWingPathFollowerStatus.Command.Power = powerCommand;
// set thrust
stabDesired.Thrust = boundf(fixedWingSettings->ThrustLimit.Neutral + powerCommand,
fixedWingSettings->ThrustLimit.Min,
fixedWingSettings->ThrustLimit.Max);
// Error condition: plane cannot hold altitude at current speed.
fixedWingPathFollowerStatus.Errors.Lowpower = 0;
if (fixedWingSettings->ThrustLimit.Neutral + powerCommand >= fixedWingSettings->ThrustLimit.Max && // thrust at maximum
velocityState.Down > 0.0f && // we ARE going down
descentspeedDesired < 0.0f && // we WANT to go up
airspeedError > 0.0f) { // we are too slow already
fixedWingPathFollowerStatus.Errors.Lowpower = 1;
if (fixedWingSettings->Safetymargins.Lowpower > 0.5f) { // alarm switched on
result = 0;
}
}
// Error condition: plane keeps climbing despite minimum thrust (opposite of above)
fixedWingPathFollowerStatus.Errors.Highpower = 0;
if (fixedWingSettings->ThrustLimit.Neutral + powerCommand <= fixedWingSettings->ThrustLimit.Min && // thrust at minimum
velocityState.Down < 0.0f && // we ARE going up
descentspeedDesired > 0.0f && // we WANT to go down
airspeedError < 0.0f) { // we are too fast already
// this alarm is often switched off because of false positives, however we still want to cut throttle if it happens
cutThrust = true;
fixedWingPathFollowerStatus.Errors.Highpower = 1;
if (fixedWingSettings->Safetymargins.Highpower > 0.5f) { // alarm switched on
result = 0;
}
}
/**
* Compute desired pitch command
*/
if (hasAirspeed) {
// Compute the cross feed from vertical speed to pitch, with saturation
float verticalSpeedToPitchCommandComponent = boundf(-descentspeedError * fixedWingSettings->VerticalToPitchCrossFeed.Kp,
-fixedWingSettings->VerticalToPitchCrossFeed.Max,
fixedWingSettings->VerticalToPitchCrossFeed.Max
);
// Compute the pitch command as err*Kp + errInt*Ki + X_feed.
pitchCommand = -pid_apply(&PIDspeed, airspeedError, dT) + verticalSpeedToPitchCommandComponent;
fixedWingPathFollowerStatus.Error.Speed = airspeedError;
fixedWingPathFollowerStatus.ErrorInt.Speed = PIDspeed.iAccumulator;
fixedWingPathFollowerStatus.Command.Speed = pitchCommand;
stabDesired.Pitch = boundf(fixedWingSettings->PitchLimit.Neutral + pitchCommand,
fixedWingSettings->PitchLimit.Min,
fixedWingSettings->PitchLimit.Max);
// Error condition: high speed dive
fixedWingPathFollowerStatus.Errors.Pitchcontrol = 0;
if (fixedWingSettings->PitchLimit.Neutral + pitchCommand >= fixedWingSettings->PitchLimit.Max && // pitch demand is full up
velocityState.Down > 0.0f && // we ARE going down
descentspeedDesired < 0.0f && // we WANT to go up
airspeedError < 0.0f && // we are too fast already
fixedWingSettings->Safetymargins.Pitchcontrol > 0.5f) { // alarm switched on
fixedWingPathFollowerStatus.Errors.Pitchcontrol = 1;
result = 0;
cutThrust = true;
}
} else {
// no airspeed sensor means we fly with constant pitch, like for landing pathfollower
stabDesired.Pitch = fixedWingSettings->LandingPitch;
}
// Error condition: pitch way out of wack
if (fixedWingSettings->Safetymargins.Pitchcontrol > 0.5f &&
(attitudeState.Pitch < fixedWingSettings->PitchLimit.Min - fixedWingSettings->SafetyCutoffLimits.PitchDeg ||
attitudeState.Pitch > fixedWingSettings->PitchLimit.Max + fixedWingSettings->SafetyCutoffLimits.PitchDeg)) {
fixedWingPathFollowerStatus.Errors.Pitchcontrol = 1;
result = 0;
cutThrust = true;
}
/**
* Compute desired roll command
*/
if (hasAirspeed) {
courseError = RAD2DEG(atan2f(courseComponent[1], courseComponent[0])) - attitudeState.Yaw;
} else {
// fallback based on effective movement direction when in fallback mode, hope that airspeed > wind velocity, or we will never get home
courseError = RAD2DEG(atan2f(velocityDesired.East, velocityDesired.North)) - RAD2DEG(atan2f(velocityState.East, velocityState.North));
}
if (courseError < -180.0f) {
courseError += 360.0f;
}
if (courseError > 180.0f) {
courseError -= 360.0f;
}
// overlap calculation. Theres a dead zone behind the craft where the
// counter-yawing of some craft while rolling could render a desired right
// turn into a desired left turn. Making the turn direction based on
// current roll angle keeps the plane committed to a direction once chosen
if (courseError < -180.0f + (fixedWingSettings->ReverseCourseOverlap * 0.5f)
&& attitudeState.Roll > 0.0f) {
courseError += 360.0f;
}
if (courseError > 180.0f - (fixedWingSettings->ReverseCourseOverlap * 0.5f)
&& attitudeState.Roll < 0.0f) {
courseError -= 360.0f;
}
courseCommand = pid_apply(&PIDcourse, courseError, dT);
fixedWingPathFollowerStatus.Error.Course = courseError;
fixedWingPathFollowerStatus.ErrorInt.Course = PIDcourse.iAccumulator;
fixedWingPathFollowerStatus.Command.Course = courseCommand;
stabDesired.Roll = boundf(fixedWingSettings->RollLimit.Neutral +
courseCommand,
fixedWingSettings->RollLimit.Min,
fixedWingSettings->RollLimit.Max);
// Error condition: roll way out of wack
fixedWingPathFollowerStatus.Errors.Rollcontrol = 0;
if (fixedWingSettings->Safetymargins.Rollcontrol > 0.5f &&
(attitudeState.Roll < fixedWingSettings->RollLimit.Min - fixedWingSettings->SafetyCutoffLimits.RollDeg ||
attitudeState.Roll > fixedWingSettings->RollLimit.Max + fixedWingSettings->SafetyCutoffLimits.RollDeg)) {
fixedWingPathFollowerStatus.Errors.Rollcontrol = 1;
result = 0;
cutThrust = true;
}
/**
* Compute desired yaw command
*/
// TODO implement raw control mode for yaw and base on Accels.Y
stabDesired.Yaw = 0.0f;
// safety cutoff condition
if (cutThrust) {
stabDesired.Thrust = 0.0f;
}
stabDesired.StabilizationMode.Roll = STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE;
stabDesired.StabilizationMode.Pitch = STABILIZATIONDESIRED_STABILIZATIONMODE_ATTITUDE;
stabDesired.StabilizationMode.Yaw = STABILIZATIONDESIRED_STABILIZATIONMODE_MANUAL;
stabDesired.StabilizationMode.Thrust = STABILIZATIONDESIRED_STABILIZATIONMODE_MANUAL;
StabilizationDesiredSet(&stabDesired);
FixedWingPathFollowerStatusSet(&fixedWingPathFollowerStatus);
return result;
}
/**
* Function to calculate course vector C based on airspeed s, fluid movement F
* and desired movement vector V
* parameters in: V,F,s
* parameters out: C
* returns true if a valid solution could be found for V,F,s, false if not
* C will be set to a best effort attempt either way
*/
bool FixedWingFlyController::correctCourse(float *C, float *V, float *F, float s)
{
// Approach:
// Let Sc be a circle around origin marking possible movement vectors
// of the craft with airspeed s (all possible options for C)
// Let Vl be a line through the origin along movement vector V where fr any
// point v on line Vl v = k * (V / |V|) = k' * V
// Let Wl be a line parallel to Vl where for any point v on line Vl exists
// a point w on WL with w = v - F
// Then any intersection between circle Sc and line Wl represents course
// vector which would result in a movement vector
// V' = k * ( V / |V|) = k' * V
// If there is no intersection point, S is insufficient to compensate
// for F and we can only try to fly in direction of V (thus having wind drift
// but at least making progress orthogonal to wind)
s = fabsf(s);
float f = vector_lengthf(F, 2);
// normalize Cn=V/|V|, |V| must be >0
float v = vector_lengthf(V, 2);
if (v < 1e-6f) {
// if |V|=0, we aren't supposed to move, turn into the wind
// (this allows hovering)
C[0] = -F[0];
C[1] = -F[1];
// if desired airspeed matches fluidmovement a hover is actually
// intended so return true
return fabsf(f - s) < 1e-3f;
}
float Vn[2] = { V[0] / v, V[1] / v };
// project F on V
float fp = F[0] * Vn[0] + F[1] * Vn[1];
// find component Fo of F that is orthogonal to V
// (which is exactly the distance between Vl and Wl)
float Fo[2] = { F[0] - (fp * Vn[0]), F[1] - (fp * Vn[1]) };
float fo2 = Fo[0] * Fo[0] + Fo[1] * Fo[1];
// find k where k * Vn = C - Fo
// |C|=s is the hypothenuse in any rectangular triangle formed by k * Vn and Fo
// so k^2 + fo^2 = s^2 (since |Vn|=1)
float k2 = s * s - fo2;
if (k2 <= -1e-3f) {
// there is no solution, we will be drifted off either way
// fallback: fly stupidly in direction of V and hope for the best
C[0] = V[0];
C[1] = V[1];
return false;
} else if (k2 <= 1e-3f) {
// there is exactly one solution: -Fo
C[0] = -Fo[0];
C[1] = -Fo[1];
return true;
}
// we have two possible solutions k positive and k negative as there are
// two intersection points between Wl and Sc
// which one is better? two criteria:
// 1. we MUST move in the right direction, if any k leads to -v its invalid
// 2. we should minimize the speed error
float k = sqrt(k2);
float C1[2] = { -k * Vn[0] - Fo[0], -k * Vn[1] - Fo[1] };
float C2[2] = { k *Vn[0] - Fo[0], k * Vn[1] - Fo[1] };
// project C+F on Vn to find signed resulting movement vector length
float vp1 = (C1[0] + F[0]) * Vn[0] + (C1[1] + F[1]) * Vn[1];
float vp2 = (C2[0] + F[0]) * Vn[0] + (C2[1] + F[1]) * Vn[1];
if (vp1 >= 0.0f && fabsf(v - vp1) < fabsf(v - vp2)) {
// in this case the angle between course and resulting movement vector
// is greater than 90 degrees - so we actually fly backwards
C[0] = C1[0];
C[1] = C1[1];
return true;
}
C[0] = C2[0];
C[1] = C2[1];
if (vp2 >= 0.0f) {
// in this case the angle between course and movement vector is less than
// 90 degrees, but we do move in the right direction
return true;
} else {
// in this case we actually get driven in the opposite direction of V
// with both solutions for C
// this might be reached in headwind stronger than maximum allowed
// airspeed.
return false;
}
}
void FixedWingFlyController::AirspeedStateUpdatedCb(__attribute__((unused)) UAVObjEvent *ev)
{
AirspeedStateData airspeedState;
VelocityStateData velocityState;
AirspeedStateGet(&airspeedState);
VelocityStateGet(&velocityState);
float airspeedVector[2];
float yaw;
AttitudeStateYawGet(&yaw);
airspeedVector[0] = cos_lookup_deg(yaw);
airspeedVector[1] = sin_lookup_deg(yaw);
// vector projection of groundspeed on airspeed vector to handle both forward and backwards movement
float groundspeedProjection = velocityState.North * airspeedVector[0] + velocityState.East * airspeedVector[1];
indicatedAirspeedStateBias = airspeedState.CalibratedAirspeed - groundspeedProjection;
// note - we do fly by Indicated Airspeed (== calibrated airspeed) however
// since airspeed is updated less often than groundspeed, we use sudden
// changes to groundspeed to offset the airspeed by the same measurement.
// This has a side effect that in the absence of any airspeed updates, the
// pathfollower will fly using groundspeed.
lastAirspeedUpdate = PIOS_DELAY_GetuS();
}