ardupilot/libraries/AC_WPNav/AC_Loiter.cpp

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#include <AP_HAL/AP_HAL.h>
#include "AC_Loiter.h"
extern const AP_HAL::HAL& hal;
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#define LOITER_SPEED_DEFAULT 1250.0f // default loiter speed in cm/s
#define LOITER_SPEED_MIN 20.0f // minimum loiter speed in cm/s
#define LOITER_ACCEL_MAX_DEFAULT 500.0f // default acceleration in loiter mode
#define LOITER_BRAKE_ACCEL_DEFAULT 250.0f // minimum acceleration in loiter mode
#define LOITER_BRAKE_JERK_DEFAULT 500.0f // maximum jerk in cm/s/s/s in loiter mode
#define LOITER_BRAKE_START_DELAY_DEFAULT 1.0f // delay (in seconds) before loiter braking begins after sticks are released
#define LOITER_VEL_CORRECTION_MAX 200.0f // max speed used to correct position errors in loiter
#define LOITER_POS_CORRECTION_MAX 200.0f // max position error in loiter
#define LOITER_ACTIVE_TIMEOUT_MS 200 // loiter controller is considered active if it has been called within the past 200ms (0.2 seconds)
const AP_Param::GroupInfo AC_Loiter::var_info[] = {
// @Param: ANG_MAX
// @DisplayName: Loiter Angle Max
// @Description: Loiter maximum lean angle. Set to zero for 2/3 of PSC_ANGLE_MAX or ANGLE_MAX
// @Units: deg
// @Range: 0 45
// @Increment: 1
// @User: Advanced
AP_GROUPINFO("ANG_MAX", 1, AC_Loiter, _angle_max, 0.0f),
// @Param: SPEED
// @DisplayName: Loiter Horizontal Maximum Speed
// @Description: Defines the maximum speed in cm/s which the aircraft will travel horizontally while in loiter mode
// @Units: cm/s
// @Range: 20 3500
// @Increment: 50
// @User: Standard
AP_GROUPINFO("SPEED", 2, AC_Loiter, _speed_cms, LOITER_SPEED_DEFAULT),
// @Param: ACC_MAX
// @DisplayName: Loiter maximum correction acceleration
// @Description: Loiter maximum correction acceleration in cm/s/s. Higher values cause the copter to correct position errors more aggressively.
// @Units: cm/s/s
// @Range: 100 981
// @Increment: 1
// @User: Advanced
AP_GROUPINFO("ACC_MAX", 3, AC_Loiter, _accel_cmss, LOITER_ACCEL_MAX_DEFAULT),
// @Param: BRK_ACCEL
// @DisplayName: Loiter braking acceleration
// @Description: Loiter braking acceleration in cm/s/s. Higher values stop the copter more quickly when the stick is centered.
// @Units: cm/s/s
// @Range: 25 250
// @Increment: 1
// @User: Advanced
AP_GROUPINFO("BRK_ACCEL", 4, AC_Loiter, _brake_accel_cmss, LOITER_BRAKE_ACCEL_DEFAULT),
// @Param: BRK_JERK
// @DisplayName: Loiter braking jerk
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// @Description: Loiter braking jerk in cm/s/s/s. Higher values will remove braking faster if the pilot moves the sticks during a braking maneuver.
// @Units: cm/s/s/s
// @Range: 500 5000
// @Increment: 1
// @User: Advanced
AP_GROUPINFO("BRK_JERK", 5, AC_Loiter, _brake_jerk_max_cmsss, LOITER_BRAKE_JERK_DEFAULT),
// @Param: BRK_DELAY
// @DisplayName: Loiter brake start delay (in seconds)
// @Description: Loiter brake start delay (in seconds)
// @Units: s
// @Range: 0 2
// @Increment: 0.1
// @User: Advanced
AP_GROUPINFO("BRK_DELAY", 6, AC_Loiter, _brake_delay, LOITER_BRAKE_START_DELAY_DEFAULT),
AP_GROUPEND
};
// Default constructor.
// Note that the Vector/Matrix constructors already implicitly zero
// their values.
//
AC_Loiter::AC_Loiter(const AP_InertialNav& inav, const AP_AHRS_View& ahrs, AC_PosControl& pos_control, const AC_AttitudeControl& attitude_control) :
_inav(inav),
_ahrs(ahrs),
_pos_control(pos_control),
_attitude_control(attitude_control)
{
AP_Param::setup_object_defaults(this, var_info);
}
/// init_target to a position in cm from ekf origin
void AC_Loiter::init_target(const Vector3f& position)
{
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sanity_check_params();
// initialise pos controller speed, acceleration
_pos_control.set_max_speed_accel_xy(LOITER_VEL_CORRECTION_MAX, _accel_cmss);
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// initialise position controller
_pos_control.init_xy_controller_stopping_point();
// initialise desired acceleration and angles to zero to remain on station
_predicted_accel.zero();
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_desired_accel.zero();
_predicted_euler_angle.zero();
_brake_accel = 0.0f;
// set target position
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_pos_control.set_pos_target_xy_cm(position.x, position.y);
}
/// initialize's position and feed-forward velocity from current pos and velocity
void AC_Loiter::init_target()
{
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sanity_check_params();
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// initialise position controller speed and acceleration
_pos_control.set_max_speed_accel_xy(LOITER_VEL_CORRECTION_MAX, _accel_cmss);
// initialise position controller
_pos_control.init_xy_controller();
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_pos_control.set_pos_error_max_xy_cm(LOITER_POS_CORRECTION_MAX);
// initialise predicted acceleration and angles from the position controller
_predicted_accel.x = _pos_control.get_accel_target_cmss().x;
_predicted_accel.y = _pos_control.get_accel_target_cmss().y;
_predicted_euler_angle.x = radians(_pos_control.get_roll_cd()*0.01f);
_predicted_euler_angle.y = radians(_pos_control.get_pitch_cd()*0.01f);
_brake_accel = 0.0f;
}
/// reduce response for landing
void AC_Loiter::soften_for_landing()
{
const Vector3f& curr_pos = _inav.get_position();
// set target position to current position
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_pos_control.set_pos_target_xy_cm(curr_pos.x, curr_pos.y);
// also prevent I term build up in xy velocity controller. Note
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// that this flag is reset on each loop, in update_xy_controller()
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_pos_control.set_externally_limited_xy();
}
/// set pilot desired acceleration in centi-degrees
// dt should be the time (in seconds) since the last call to this function
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void AC_Loiter::set_pilot_desired_acceleration(float euler_roll_angle_cd, float euler_pitch_angle_cd)
{
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const float dt = _pos_control.get_dt();
// Convert from centidegrees on public interface to radians
const float euler_roll_angle = radians(euler_roll_angle_cd*0.01f);
const float euler_pitch_angle = radians(euler_pitch_angle_cd*0.01f);
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// convert our desired attitude to an acceleration vector assuming we are not accelerating vertically
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const Vector3f desired_euler {euler_roll_angle, euler_pitch_angle, _ahrs.yaw};
const Vector3f desired_accel = _pos_control.lean_angles_to_accel(desired_euler);
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_desired_accel.x = desired_accel.x;
_desired_accel.y = desired_accel.y;
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// difference between where we think we should be and where we want to be
Vector2f angle_error(wrap_PI(euler_roll_angle - _predicted_euler_angle.x), wrap_PI(euler_pitch_angle - _predicted_euler_angle.y));
// calculate the angular velocity that we would expect given our desired and predicted attitude
_attitude_control.input_shaping_rate_predictor(angle_error, _predicted_euler_rate, dt);
// update our predicted attitude based on our predicted angular velocity
_predicted_euler_angle += _predicted_euler_rate * dt;
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// convert our predicted attitude to an acceleration vector assuming we are not accelerating vertically
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const Vector3f predicted_euler {_predicted_euler_angle.x, _predicted_euler_angle.y, _ahrs.yaw};
const Vector3f predicted_accel = _pos_control.lean_angles_to_accel(predicted_euler);
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_predicted_accel.x = predicted_accel.x;
_predicted_accel.y = predicted_accel.y;
}
/// get vector to stopping point based on a horizontal position and velocity
void AC_Loiter::get_stopping_point_xy(Vector3f& stopping_point) const
{
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_pos_control.get_stopping_point_xy_cm(stopping_point);
}
/// get maximum lean angle when using loiter
float AC_Loiter::get_angle_max_cd() const
{
if (is_zero(_angle_max)) {
return MIN(_attitude_control.lean_angle_max(), _pos_control.get_lean_angle_max_cd()) * (2.0f/3.0f);
}
return MIN(_angle_max*100.0f, _pos_control.get_lean_angle_max_cd());
}
/// run the loiter controller
void AC_Loiter::update(bool avoidance_on)
{
// initialise pos controller speed and acceleration
_pos_control.set_max_speed_accel_xy(LOITER_VEL_CORRECTION_MAX, _accel_cmss);
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calc_desired_velocity(_pos_control.get_dt(), avoidance_on);
_pos_control.update_xy_controller();
}
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// sanity check parameters
void AC_Loiter::sanity_check_params()
{
_speed_cms = MAX(_speed_cms, LOITER_SPEED_MIN);
_accel_cmss = MIN(_accel_cmss, GRAVITY_MSS * 100.0f * tanf(ToRad(_attitude_control.lean_angle_max() * 0.01f)));
}
/// calc_desired_velocity - updates desired velocity (i.e. feed forward) with pilot requested acceleration and fake wind resistance
/// updated velocity sent directly to position controller
void AC_Loiter::calc_desired_velocity(float nav_dt, bool avoidance_on)
{
float ekfGndSpdLimit, ekfNavVelGainScaler;
AP::ahrs_navekf().getEkfControlLimits(ekfGndSpdLimit, ekfNavVelGainScaler);
// calculate a loiter speed limit which is the minimum of the value set by the LOITER_SPEED
// parameter and the value set by the EKF to observe optical flow limits
float gnd_speed_limit_cms = MIN(_speed_cms, ekfGndSpdLimit*100.0f);
gnd_speed_limit_cms = MAX(gnd_speed_limit_cms, LOITER_SPEED_MIN);
float pilot_acceleration_max = GRAVITY_MSS*100.0f * tanf(radians(get_angle_max_cd()*0.01f));
// range check nav_dt
if (nav_dt < 0) {
return;
}
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// initialise pos controller speed, acceleration
_pos_control.set_max_speed_accel_xy(LOITER_VEL_CORRECTION_MAX, _accel_cmss);
// get loiters desired velocity from the position controller where it is being stored.
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const Vector3f &desired_vel_3d = _pos_control.get_vel_desired_cms();
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Vector2f desired_vel{desired_vel_3d.x,desired_vel_3d.y};
// update the desired velocity using our predicted acceleration
desired_vel.x += _predicted_accel.x * nav_dt;
desired_vel.y += _predicted_accel.y * nav_dt;
Vector2f loiter_accel_brake;
float desired_speed = desired_vel.length();
if (!is_zero(desired_speed)) {
Vector2f desired_vel_norm = desired_vel/desired_speed;
// TODO: consider using a velocity squared relationship like
// pilot_acceleration_max*(desired_speed/gnd_speed_limit_cms)^2;
// the drag characteristic of a multirotor should be examined to generate a curve
// we could add a expo function here to fine tune it
// calculate a drag acceleration based on the desired speed.
float drag_decel = pilot_acceleration_max*desired_speed/gnd_speed_limit_cms;
// calculate a braking acceleration if sticks are at zero
float loiter_brake_accel = 0.0f;
if (_desired_accel.is_zero()) {
if ((AP_HAL::millis()-_brake_timer) > _brake_delay * 1000.0f) {
float brake_gain = _pos_control.get_vel_xy_pid().kP() * 0.5f;
loiter_brake_accel = constrain_float(sqrt_controller(desired_speed, brake_gain, _brake_jerk_max_cmsss, nav_dt), 0.0f, _brake_accel_cmss);
}
} else {
loiter_brake_accel = 0.0f;
_brake_timer = AP_HAL::millis();
}
_brake_accel += constrain_float(loiter_brake_accel-_brake_accel, -_brake_jerk_max_cmsss*nav_dt, _brake_jerk_max_cmsss*nav_dt);
loiter_accel_brake = desired_vel_norm*_brake_accel;
// update the desired velocity using the drag and braking accelerations
desired_speed = MAX(desired_speed-(drag_decel+_brake_accel)*nav_dt,0.0f);
desired_vel = desired_vel_norm*desired_speed;
}
// add braking to the desired acceleration
_desired_accel -= loiter_accel_brake;
// Apply EKF limit to desired velocity - this limit is calculated by the EKF and adjusted as required to ensure certain sensor limits are respected (eg optical flow sensing)
float horizSpdDem = desired_vel.length();
if (horizSpdDem > gnd_speed_limit_cms) {
desired_vel.x = desired_vel.x * gnd_speed_limit_cms / horizSpdDem;
desired_vel.y = desired_vel.y * gnd_speed_limit_cms / horizSpdDem;
}
if (avoidance_on) {
// Limit the velocity to prevent fence violations
// TODO: We need to also limit the _desired_accel
AC_Avoid *_avoid = AP::ac_avoid();
if (_avoid != nullptr) {
Vector3f avoidance_vel_3d{desired_vel.x, desired_vel.y, 0.0f};
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_avoid->adjust_velocity(avoidance_vel_3d, _pos_control.get_pos_xy_p().kP(), _accel_cmss, _pos_control.get_pos_z_p().kP(), _pos_control.get_max_accel_z_cmss(), nav_dt);
desired_vel = Vector2f{avoidance_vel_3d.x, avoidance_vel_3d.y};
}
}
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// get loiters desired velocity from the position controller where it is being stored.
const Vector3f &target_pos_3d = _pos_control.get_pos_target_cm();
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Vector2f target_pos{target_pos_3d.x, target_pos_3d.y};
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// update the target position using our predicted velocity
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target_pos += desired_vel * nav_dt;
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// send adjusted feed forward acceleration and velocity back to the Position Controller
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_pos_control.set_pos_vel_accel_xy(target_pos, desired_vel, _desired_accel);
}