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ardupilot/libraries/AC_AttitudeControl/AC_PosControl.cpp

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/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
#include <AP_HAL.h>
#include <AC_PosControl.h>
extern const AP_HAL::HAL& hal;
const AP_Param::GroupInfo AC_PosControl::var_info[] PROGMEM = {
// @Param: THR_HOVER
// @DisplayName: Throttle Hover
// @Description: The autopilot's estimate of the throttle required to maintain a level hover. Calculated automatically from the pilot's throttle input while in stabilize mode
// @Range: 0 1000
// @Units: Percent*10
// @User: Advanced
AP_GROUPINFO("THR_HOVER", 0, AC_PosControl, _throttle_hover, POSCONTROL_THROTTLE_HOVER),
AP_GROUPEND
};
// Default constructor.
// Note that the Vector/Matrix constructors already implicitly zero
// their values.
//
AC_PosControl::AC_PosControl(const AP_AHRS& ahrs, const AP_InertialNav& inav,
const AP_Motors& motors, AC_AttitudeControl& attitude_control,
AC_P& p_alt_pos, AC_P& p_alt_rate, AC_PID& pid_alt_accel,
AC_P& p_pos_xy, AC_PID& pid_rate_lat, AC_PID& pid_rate_lon) :
_ahrs(ahrs),
_inav(inav),
_motors(motors),
_attitude_control(attitude_control),
_p_alt_pos(p_alt_pos),
_p_alt_rate(p_alt_rate),
_pid_alt_accel(pid_alt_accel),
_p_pos_xy(p_pos_xy),
_pid_rate_lat(pid_rate_lat),
_pid_rate_lon(pid_rate_lon),
_dt(POSCONTROL_DT_10HZ),
_dt_xy(POSCONTROL_DT_50HZ),
_last_update_xy_ms(0),
_last_update_z_ms(0),
_speed_down_cms(POSCONTROL_SPEED_DOWN),
_speed_up_cms(POSCONTROL_SPEED_UP),
_speed_cms(POSCONTROL_SPEED),
_accel_z_cms(POSCONTROL_ACCEL_Z),
_accel_cms(POSCONTROL_ACCEL_XY),
_leash(POSCONTROL_LEASH_LENGTH_MIN),
_leash_down_z(POSCONTROL_LEASH_LENGTH_MIN),
_leash_up_z(POSCONTROL_LEASH_LENGTH_MIN),
_roll_target(0.0f),
_pitch_target(0.0f),
_alt_max(0.0f),
_distance_to_target(0.0f)
{
AP_Param::setup_object_defaults(this, var_info);
// initialise flags
#if HAL_CPU_CLASS >= HAL_CPU_CLASS_150
_flags.slow_cpu = false;
#else
_flags.slow_cpu = true;
#endif
_flags.recalc_leash_xy = true;
_flags.recalc_leash_z = true;
_flags.reset_desired_vel_to_pos = true;
_flags.reset_rate_to_accel_xy = true;
_flags.reset_rate_to_accel_z = true;
_flags.reset_accel_to_throttle = true;
}
///
/// z-axis position controller
///
/// set_dt - sets time delta in seconds for all controllers (i.e. 100hz = 0.01, 400hz = 0.0025)
void AC_PosControl::set_dt(float delta_sec)
{
_dt = delta_sec;
// update rate controller's d filter
_pid_alt_accel.set_d_lpf_alpha(POSCONTROL_ACCEL_Z_DTERM_FILTER, _dt);
// update rate z-axis velocity error and accel error filters
_vel_error_filter.set_cutoff_frequency(_dt,POSCONTROL_VEL_ERROR_CUTOFF_FREQ);
_accel_error_filter.set_cutoff_frequency(_dt,POSCONTROL_ACCEL_ERROR_CUTOFF_FREQ);
}
/// set_speed_z - sets maximum climb and descent rates
/// To-Do: call this in the main code as part of flight mode initialisation
/// calc_leash_length_z should be called afterwards
/// speed_down should be a negative number
void AC_PosControl::set_speed_z(float speed_down, float speed_up)
{
// ensure speed_down is always negative
speed_down = (float)-fabs(speed_down);
if (((float)fabs(_speed_down_cms-speed_down) > 1.0f) || ((float)fabs(_speed_up_cms-speed_up) > 1.0f)) {
_speed_down_cms = speed_down;
_speed_up_cms = speed_up;
_flags.recalc_leash_z = true;
}
}
/// set_accel_z - set vertical acceleration in cm/s/s
void AC_PosControl::set_accel_z(float accel_cmss)
{
if ((float)fabs(_accel_z_cms-accel_cmss) > 1.0f) {
_accel_z_cms = accel_cmss;
_flags.recalc_leash_z = true;
}
}
/// set_alt_target_with_slew - adjusts target towards a final altitude target
/// should be called continuously (with dt set to be the expected time between calls)
/// actual position target will be moved no faster than the speed_down and speed_up
/// target will also be stopped if the motors hit their limits or leash length is exceeded
void AC_PosControl::set_alt_target_with_slew(float alt_cm, float dt)
{
float alt_change = alt_cm-_pos_target.z;
_vel_desired.z = constrain_float(alt_change * dt, _speed_down_cms, _speed_up_cms);
// adjust desired alt if motors have not hit their limits
if ((alt_change<0 && !_motors.limit.throttle_lower) || (alt_change>0 && !_motors.limit.throttle_upper)) {
_pos_target.z += constrain_float(alt_change, _speed_down_cms*dt, _speed_up_cms*dt);
}
// do not let target get too far from current altitude
float curr_alt = _inav.get_altitude();
_pos_target.z = constrain_float(_pos_target.z,curr_alt-_leash_down_z,curr_alt+_leash_up_z);
}
/// set_alt_target_from_climb_rate - adjusts target up or down using a climb rate in cm/s
/// should be called continuously (with dt set to be the expected time between calls)
/// actual position target will be moved no faster than the speed_down and speed_up
/// target will also be stopped if the motors hit their limits or leash length is exceeded
void AC_PosControl::set_alt_target_from_climb_rate(float climb_rate_cms, float dt, bool force_descend)
{
// adjust desired alt if motors have not hit their limits
// To-Do: add check of _limit.pos_up and _limit.pos_down?
if ((climb_rate_cms<0 && (!_motors.limit.throttle_lower || force_descend)) || (climb_rate_cms>0 && !_motors.limit.throttle_upper)) {
_pos_target.z += climb_rate_cms * dt;
}
_vel_desired.z = climb_rate_cms;
}
// get_alt_error - returns altitude error in cm
float AC_PosControl::get_alt_error() const
{
return (_pos_target.z - _inav.get_altitude());
}
/// set_target_to_stopping_point_z - returns reasonable stopping altitude in cm above home
void AC_PosControl::set_target_to_stopping_point_z()
{
// check if z leash needs to be recalculated
calc_leash_length_z();
get_stopping_point_z(_pos_target);
}
/// get_stopping_point_z - sets stopping_point.z to a reasonable stopping altitude in cm above home
void AC_PosControl::get_stopping_point_z(Vector3f& stopping_point) const
{
const float curr_pos_z = _inav.get_altitude();
float curr_vel_z = _inav.get_velocity_z();
float linear_distance; // half the distance we swap between linear and sqrt and the distance we offset sqrt
float linear_velocity; // the velocity we swap between linear and sqrt
// if position controller is active add current velocity error to avoid sudden jump in acceleration
if (is_active_z()) {
curr_vel_z += _vel_error.z;
}
// calculate the velocity at which we switch from calculating the stopping point using a linear function to a sqrt function
linear_velocity = _accel_z_cms/_p_alt_pos.kP();
if ((float)fabs(curr_vel_z) < linear_velocity) {
// if our current velocity is below the cross-over point we use a linear function
stopping_point.z = curr_pos_z + curr_vel_z/_p_alt_pos.kP();
} else {
linear_distance = _accel_z_cms/(2.0f*_p_alt_pos.kP()*_p_alt_pos.kP());
if (curr_vel_z > 0){
stopping_point.z = curr_pos_z + (linear_distance + curr_vel_z*curr_vel_z/(2.0f*_accel_z_cms));
} else {
stopping_point.z = curr_pos_z - (linear_distance + curr_vel_z*curr_vel_z/(2.0f*_accel_z_cms));
}
}
stopping_point.z = constrain_float(stopping_point.z, curr_pos_z - POSCONTROL_STOPPING_DIST_Z_MAX, curr_pos_z + POSCONTROL_STOPPING_DIST_Z_MAX);
}
/// init_takeoff - initialises target altitude if we are taking off
void AC_PosControl::init_takeoff()
{
const Vector3f& curr_pos = _inav.get_position();
_pos_target.z = curr_pos.z + POSCONTROL_TAKEOFF_JUMP_CM;
// freeze feedforward to avoid jump
freeze_ff_z();
// shift difference between last motor out and hover throttle into accelerometer I
_pid_alt_accel.set_integrator(_motors.get_throttle_out()-_throttle_hover);
}
// is_active_z - returns true if the z-axis position controller has been run very recently
bool AC_PosControl::is_active_z() const
{
return ((hal.scheduler->millis() - _last_update_z_ms) <= POSCONTROL_ACTIVE_TIMEOUT_MS);
}
/// update_z_controller - fly to altitude in cm above home
void AC_PosControl::update_z_controller()
{
// check time since last cast
uint32_t now = hal.scheduler->millis();
if (now - _last_update_z_ms > POSCONTROL_ACTIVE_TIMEOUT_MS) {
_flags.reset_rate_to_accel_z = true;
_flags.reset_accel_to_throttle = true;
}
_last_update_z_ms = now;
// check if leash lengths need to be recalculated
calc_leash_length_z();
// call position controller
pos_to_rate_z();
}
/// calc_leash_length - calculates the vertical leash lengths from maximum speed, acceleration
/// called by pos_to_rate_z if z-axis speed or accelerations are changed
void AC_PosControl::calc_leash_length_z()
{
if (_flags.recalc_leash_z) {
_leash_up_z = calc_leash_length(_speed_up_cms, _accel_z_cms, _p_alt_pos.kP());
_leash_down_z = calc_leash_length(-_speed_down_cms, _accel_z_cms, _p_alt_pos.kP());
_flags.recalc_leash_z = false;
}
}
// pos_to_rate_z - position to rate controller for Z axis
// calculates desired rate in earth-frame z axis and passes to rate controller
// vel_up_max, vel_down_max should have already been set before calling this method
void AC_PosControl::pos_to_rate_z()
{
float curr_alt = _inav.get_altitude();
// clear position limit flags
_limit.pos_up = false;
_limit.pos_down = false;
// do not let target alt get above limit
if (_alt_max > 0 && _pos_target.z > _alt_max) {
_pos_target.z = _alt_max;
_limit.pos_up = true;
}
// calculate altitude error
_pos_error.z = _pos_target.z - curr_alt;
// do not let target altitude get too far from current altitude
if (_pos_error.z > _leash_up_z) {
_pos_target.z = curr_alt + _leash_up_z;
_pos_error.z = _leash_up_z;
_limit.pos_up = true;
}
if (_pos_error.z < -_leash_down_z) {
_pos_target.z = curr_alt - _leash_down_z;
_pos_error.z = -_leash_down_z;
_limit.pos_down = true;
}
// calculate _vel_target.z using from _pos_error.z using sqrt controller
_vel_target.z = AC_AttitudeControl::sqrt_controller(_pos_error.z, _p_alt_pos.kP(), _accel_z_cms);
// call rate based throttle controller which will update accel based throttle controller targets
rate_to_accel_z();
}
// rate_to_accel_z - calculates desired accel required to achieve the velocity target
// calculates desired acceleration and calls accel throttle controller
void AC_PosControl::rate_to_accel_z()
{
const Vector3f& curr_vel = _inav.get_velocity();
float p; // used to capture pid values for logging
float desired_accel; // the target acceleration if the accel based throttle is enabled, otherwise the output to be sent to the motors
// check speed limits
// To-Do: check these speed limits here or in the pos->rate controller
_limit.vel_up = false;
_limit.vel_down = false;
if (_vel_target.z < _speed_down_cms) {
_vel_target.z = _speed_down_cms;
_limit.vel_down = true;
}
if (_vel_target.z > _speed_up_cms) {
_vel_target.z = _speed_up_cms;
_limit.vel_up = true;
}
// reset last velocity target to current target
if (_flags.reset_rate_to_accel_z) {
_vel_last.z = _vel_target.z;
}
// feed forward desired acceleration calculation
if (_dt > 0.0f) {
if (!_flags.freeze_ff_z) {
_accel_feedforward.z = (_vel_target.z - _vel_last.z)/_dt;
} else {
// stop the feed forward being calculated during a known discontinuity
_flags.freeze_ff_z = false;
}
} else {
_accel_feedforward.z = 0.0f;
}
// store this iteration's velocities for the next iteration
_vel_last.z = _vel_target.z;
// reset velocity error and filter if this controller has just been engaged
if (_flags.reset_rate_to_accel_z) {
// Reset Filter
_vel_error.z = 0;
_vel_error_filter.reset(0);
_flags.reset_rate_to_accel_z = false;
} else {
// calculate rate error and filter with cut off frequency of 2 Hz
_vel_error.z = _vel_error_filter.apply(_vel_target.z - curr_vel.z);
}
// calculate p
p = _p_alt_rate.kP() * _vel_error.z;
// consolidate and constrain target acceleration
desired_accel = _accel_feedforward.z + p;
desired_accel = constrain_int32(desired_accel, -32000, 32000);
// set target for accel based throttle controller
accel_to_throttle(desired_accel);
}
// accel_to_throttle - alt hold's acceleration controller
// calculates a desired throttle which is sent directly to the motors
void AC_PosControl::accel_to_throttle(float accel_target_z)
{
float z_accel_meas; // actual acceleration
int32_t p,i,d; // used to capture pid values for logging
// Calculate Earth Frame Z acceleration
z_accel_meas = -(_ahrs.get_accel_ef_blended().z + GRAVITY_MSS) * 100.0f;
// reset target altitude if this controller has just been engaged
if (_flags.reset_accel_to_throttle) {
// Reset Filter
_accel_error.z = 0;
_accel_error_filter.reset(0);
_flags.reset_accel_to_throttle = false;
} else {
// calculate accel error and Filter with fc = 2 Hz
_accel_error.z = _accel_error_filter.apply(constrain_float(accel_target_z - z_accel_meas, -32000, 32000));
}
// separately calculate p, i, d values for logging
p = _pid_alt_accel.get_p(_accel_error.z);
// get i term
i = _pid_alt_accel.get_integrator();
// update i term as long as we haven't breached the limits or the I term will certainly reduce
// To-Do: should this be replaced with limits check from attitude_controller?
if ((!_motors.limit.throttle_lower && !_motors.limit.throttle_upper) || (i>0&&_accel_error.z<0) || (i<0&&_accel_error.z>0)) {
i = _pid_alt_accel.get_i(_accel_error.z, _dt);
}
// get d term
d = _pid_alt_accel.get_d(_accel_error.z, _dt);
// send throttle to attitude controller with angle boost
_attitude_control.set_throttle_out((int16_t)p+i+d+_throttle_hover, true);
}
///
/// position controller
///
/// set_accel_xy - set horizontal acceleration in cm/s/s
/// calc_leash_length_xy should be called afterwards
void AC_PosControl::set_accel_xy(float accel_cmss)
{
if ((float)fabs(_accel_cms-accel_cmss) > 1.0f) {
_accel_cms = accel_cmss;
_flags.recalc_leash_xy = true;
}
}
/// set_speed_xy - set horizontal speed maximum in cm/s
/// calc_leash_length_xy should be called afterwards
void AC_PosControl::set_speed_xy(float speed_cms)
{
if ((float)fabs(_speed_cms-speed_cms) > 1.0f) {
_speed_cms = speed_cms;
_flags.recalc_leash_xy = true;
}
}
/// set_pos_target in cm from home
void AC_PosControl::set_pos_target(const Vector3f& position)
{
_pos_target = position;
// initialise roll and pitch to current roll and pitch. This avoids a twitch between when the target is set and the pos controller is first run
// To-Do: this initialisation of roll and pitch targets needs to go somewhere between when pos-control is initialised and when it completes it's first cycle
//_roll_target = constrain_int32(_ahrs.roll_sensor,-_attitude_control.lean_angle_max(),_attitude_control.lean_angle_max());
//_pitch_target = constrain_int32(_ahrs.pitch_sensor,-_attitude_control.lean_angle_max(),_attitude_control.lean_angle_max());
}
/// set_xy_target in cm from home
void AC_PosControl::set_xy_target(float x, float y)
{
_pos_target.x = x;
_pos_target.y = y;
}
/// set_target_to_stopping_point_xy - sets horizontal target to reasonable stopping position in cm from home
void AC_PosControl::set_target_to_stopping_point_xy()
{
// check if xy leash needs to be recalculated
calc_leash_length_xy();
get_stopping_point_xy(_pos_target);
}
/// get_stopping_point_xy - calculates stopping point based on current position, velocity, vehicle acceleration
/// distance_max allows limiting distance to stopping point
/// results placed in stopping_position vector
/// set_accel_xy() should be called before this method to set vehicle acceleration
/// set_leash_length() should have been called before this method
void AC_PosControl::get_stopping_point_xy(Vector3f &stopping_point) const
{
const Vector3f curr_pos = _inav.get_position();
Vector3f curr_vel = _inav.get_velocity();
float linear_distance; // the distance at which we swap from a linear to sqrt response
float linear_velocity; // the velocity above which we swap from a linear to sqrt response
float stopping_dist; // the distance within the vehicle can stop
float kP = _p_pos_xy.kP();
// add velocity error to current velocity
if (is_active_xy()) {
curr_vel.x += _vel_error.x;
curr_vel.y += _vel_error.y;
}
// calculate current velocity
float vel_total = pythagorous2(curr_vel.x, curr_vel.y);
// avoid divide by zero by using current position if the velocity is below 10cm/s, kP is very low or acceleration is zero
if (kP <= 0.0f || _accel_cms <= 0.0f || vel_total == 0.0f) {
stopping_point.x = curr_pos.x;
stopping_point.y = curr_pos.y;
return;
}
// calculate point at which velocity switches from linear to sqrt
linear_velocity = _accel_cms/kP;
// calculate distance within which we can stop
if (vel_total < linear_velocity) {
stopping_dist = vel_total/kP;
} else {
linear_distance = _accel_cms/(2.0f*kP*kP);
stopping_dist = linear_distance + (vel_total*vel_total)/(2.0f*_accel_cms);
}
// constrain stopping distance
stopping_dist = constrain_float(stopping_dist, 0, _leash);
// convert the stopping distance into a stopping point using velocity vector
stopping_point.x = curr_pos.x + (stopping_dist * curr_vel.x / vel_total);
stopping_point.y = curr_pos.y + (stopping_dist * curr_vel.y / vel_total);
}
/// get_distance_to_target - get horizontal distance to loiter target in cm
float AC_PosControl::get_distance_to_target() const
{
return _distance_to_target;
}
// is_active_xy - returns true if the xy position controller has been run very recently
bool AC_PosControl::is_active_xy() const
{
return ((hal.scheduler->millis() - _last_update_xy_ms) <= POSCONTROL_ACTIVE_TIMEOUT_MS);
}
/// init_xy_controller - initialise the xy controller
/// sets target roll angle, pitch angle and I terms based on vehicle current lean angles
/// should be called once whenever significant changes to the position target are made
/// this does not update the xy target
void AC_PosControl::init_xy_controller(bool reset_I)
{
// set roll, pitch lean angle targets to current attitude
_roll_target = _ahrs.roll_sensor;
_pitch_target = _ahrs.pitch_sensor;
// initialise I terms from lean angles
if (reset_I) {
// reset last velocity if this controller has just been engaged or dt is zero
lean_angles_to_accel(_accel_target.x, _accel_target.y);
_pid_rate_lat.set_integrator(_accel_target.x);
_pid_rate_lon.set_integrator(_accel_target.y);
}
// flag reset required in rate to accel step
_flags.reset_desired_vel_to_pos = true;
_flags.reset_rate_to_accel_xy = true;
}
/// update_xy_controller - run the horizontal position controller - should be called at 100hz or higher
void AC_PosControl::update_xy_controller(bool use_desired_velocity, float ekfNavVelGainScaler)
{
// compute dt
uint32_t now = hal.scheduler->millis();
float dt = (now - _last_update_xy_ms) / 1000.0f;
_last_update_xy_ms = now;
// sanity check dt - expect to be called faster than ~5hz
if (dt > POSCONTROL_ACTIVE_TIMEOUT_MS) {
dt = 0.0f;
}
// check if xy leash needs to be recalculated
calc_leash_length_xy();
// translate any adjustments from pilot to loiter target
desired_vel_to_pos(dt);
// run position controller's position error to desired velocity step
pos_to_rate_xy(use_desired_velocity, dt, ekfNavVelGainScaler);
// run position controller's velocity to acceleration step
rate_to_accel_xy(dt, ekfNavVelGainScaler);
// run position controller's acceleration to lean angle step
accel_to_lean_angles(dt, ekfNavVelGainScaler);
}
float AC_PosControl::time_since_last_xy_update() const
{
uint32_t now = hal.scheduler->millis();
return (now - _last_update_xy_ms)*0.001f;
}
/// init_vel_controller_xyz - initialise the velocity controller - should be called once before the caller attempts to use the controller
void AC_PosControl::init_vel_controller_xyz()
{
// set roll, pitch lean angle targets to current attitude
_roll_target = _ahrs.roll_sensor;
_pitch_target = _ahrs.pitch_sensor;
// reset last velocity if this controller has just been engaged or dt is zero
lean_angles_to_accel(_accel_target.x, _accel_target.y);
_pid_rate_lat.set_integrator(_accel_target.x);
_pid_rate_lon.set_integrator(_accel_target.y);
// flag reset required in rate to accel step
_flags.reset_desired_vel_to_pos = true;
_flags.reset_rate_to_accel_xy = true;
// set target position in xy axis
const Vector3f& curr_pos = _inav.get_position();
set_xy_target(curr_pos.x, curr_pos.y);
// move current vehicle velocity into feed forward velocity
const Vector3f& curr_vel = _inav.get_velocity();
set_desired_velocity_xy(curr_vel.x, curr_vel.y);
}
/// update_velocity_controller_xyz - run the velocity controller - should be called at 100hz or higher
/// velocity targets should we set using set_desired_velocity_xyz() method
/// callers should use get_roll() and get_pitch() methods and sent to the attitude controller
/// throttle targets will be sent directly to the motors
void AC_PosControl::update_vel_controller_xyz(float ekfNavVelGainScaler)
{
// capture time since last iteration
uint32_t now = hal.scheduler->millis();
float dt = (now - _last_update_xy_ms) / 1000.0f;
// sanity check dt - expect to be called faster than ~5hz
if (dt >= POSCONTROL_ACTIVE_TIMEOUT_MS) {
dt = 0.0f;
}
// check if xy leash needs to be recalculated
calc_leash_length_xy();
// apply desired velocity request to position target
desired_vel_to_pos(dt);
// run position controller's position error to desired velocity step
pos_to_rate_xy(true, dt, ekfNavVelGainScaler);
// run velocity to acceleration step
rate_to_accel_xy(dt, ekfNavVelGainScaler);
// run acceleration to lean angle step
accel_to_lean_angles(dt, ekfNavVelGainScaler);
// update altitude target
set_alt_target_from_climb_rate(_vel_desired.z, dt);
// run z-axis position controller
update_z_controller();
// record update time
_last_update_xy_ms = now;
}
///
/// private methods
///
/// calc_leash_length - calculates the horizontal leash length given a maximum speed, acceleration
/// should be called whenever the speed, acceleration or position kP is modified
void AC_PosControl::calc_leash_length_xy()
{
if (_flags.recalc_leash_xy) {
_leash = calc_leash_length(_speed_cms, _accel_cms, _p_pos_xy.kP());
_flags.recalc_leash_xy = false;
}
}
/// desired_vel_to_pos - move position target using desired velocities
void AC_PosControl::desired_vel_to_pos(float nav_dt)
{
// range check nav_dt
if( nav_dt < 0 ) {
return;
}
// update target position
if (_flags.reset_desired_vel_to_pos) {
_flags.reset_desired_vel_to_pos = false;
} else {
_pos_target.x += _vel_desired.x * nav_dt;
_pos_target.y += _vel_desired.y * nav_dt;
}
}
/// pos_to_rate_xy - horizontal position error to velocity controller
/// converts position (_pos_target) to target velocity (_vel_target)
/// when use_desired_rate is set to true:
/// desired velocity (_vel_desired) is combined into final target velocity and
/// velocity due to position error is reduce to a maximum of 1m/s
void AC_PosControl::pos_to_rate_xy(bool use_desired_rate, float dt, float ekfNavVelGainScaler)
{
Vector3f curr_pos = _inav.get_position();
float linear_distance; // the distance we swap between linear and sqrt velocity response
float kP = ekfNavVelGainScaler * _p_pos_xy.kP(); // scale gains to compensate for noisy optical flow measurement in the EKF
// avoid divide by zero
if (kP <= 0.0f) {
_vel_target.x = 0.0f;
_vel_target.y = 0.0f;
}else{
// calculate distance error
_pos_error.x = _pos_target.x - curr_pos.x;
_pos_error.y = _pos_target.y - curr_pos.y;
// constrain target position to within reasonable distance of current location
_distance_to_target = pythagorous2(_pos_error.x, _pos_error.y);
if (_distance_to_target > _leash && _distance_to_target > 0.0f) {
_pos_target.x = curr_pos.x + _leash * _pos_error.x/_distance_to_target;
_pos_target.y = curr_pos.y + _leash * _pos_error.y/_distance_to_target;
// re-calculate distance error
_pos_error.x = _pos_target.x - curr_pos.x;
_pos_error.y = _pos_target.y - curr_pos.y;
_distance_to_target = _leash;
}
// calculate the distance at which we swap between linear and sqrt velocity response
linear_distance = _accel_cms/(2.0f*kP*kP);
if (_distance_to_target > 2.0f*linear_distance) {
// velocity response grows with the square root of the distance
float vel_sqrt = safe_sqrt(2.0f*_accel_cms*(_distance_to_target-linear_distance));
_vel_target.x = vel_sqrt * _pos_error.x/_distance_to_target;
_vel_target.y = vel_sqrt * _pos_error.y/_distance_to_target;
}else{
// velocity response grows linearly with the distance
_vel_target.x = _p_pos_xy.kP() * _pos_error.x;
_vel_target.y = _p_pos_xy.kP() * _pos_error.y;
}
// decide velocity limit due to position error
float vel_max_from_pos_error;
if (use_desired_rate) {
// if desired velocity (i.e. velocity feed forward) is being used we limit the maximum velocity correction due to position error to 2m/s
vel_max_from_pos_error = POSCONTROL_VEL_XY_MAX_FROM_POS_ERR;
}else{
// if desired velocity is not used, we allow position error to increase speed up to maximum speed
vel_max_from_pos_error = _speed_cms;
}
// scale velocity to stays within limits
float vel_total = pythagorous2(_vel_target.x, _vel_target.y);
if (vel_total > vel_max_from_pos_error) {
_vel_target.x = vel_max_from_pos_error * _vel_target.x/vel_total;
_vel_target.y = vel_max_from_pos_error * _vel_target.y/vel_total;
}
// add desired velocity (i.e. feed forward).
if (use_desired_rate) {
_vel_target.x += _vel_desired.x;
_vel_target.y += _vel_desired.y;
}
}
}
/// rate_to_accel_xy - horizontal desired rate to desired acceleration
/// converts desired velocities in lat/lon directions to accelerations in lat/lon frame
void AC_PosControl::rate_to_accel_xy(float dt, float ekfNavVelGainScaler)
{
const Vector3f &vel_curr = _inav.get_velocity(); // current velocity in cm/s
float accel_total; // total acceleration in cm/s/s
float lat_i, lon_i;
// reset last velocity target to current target
if (_flags.reset_rate_to_accel_xy) {
_vel_last.x = _vel_target.x;
_vel_last.y = _vel_target.y;
_flags.reset_rate_to_accel_xy = false;
}
// feed forward desired acceleration calculation
if (dt > 0.0f) {
if (!_flags.freeze_ff_xy) {
_accel_feedforward.x = (_vel_target.x - _vel_last.x)/dt;
_accel_feedforward.y = (_vel_target.y - _vel_last.y)/dt;
} else {
// stop the feed forward being calculated during a known discontinuity
_flags.freeze_ff_xy = false;
}
} else {
_accel_feedforward.x = 0.0f;
_accel_feedforward.y = 0.0f;
}
// store this iteration's velocities for the next iteration
_vel_last.x = _vel_target.x;
_vel_last.y = _vel_target.y;
// calculate velocity error
_vel_error.x = _vel_target.x - vel_curr.x;
_vel_error.y = _vel_target.y - vel_curr.y;
// get current i term
lat_i = _pid_rate_lat.get_integrator();
lon_i = _pid_rate_lon.get_integrator();
// update i term if we have not hit the accel or throttle limits OR the i term will reduce
if ((!_limit.accel_xy && !_motors.limit.throttle_upper) || ((lat_i>0&&_vel_error.x<0)||(lat_i<0&&_vel_error.x>0))) {
lat_i = _pid_rate_lat.get_i(_vel_error.x, dt);
}
if ((!_limit.accel_xy && !_motors.limit.throttle_upper) || ((lon_i>0&&_vel_error.y<0)||(lon_i<0&&_vel_error.y>0))) {
lon_i = _pid_rate_lon.get_i(_vel_error.y, dt);
}
// combine feed forward accel with PID output from velocity error and scale PID output to compensate for optical flow measurement induced EKF noise
_accel_target.x = _accel_feedforward.x + (_pid_rate_lat.get_p(_vel_error.x) + lat_i + _pid_rate_lat.get_d(_vel_error.x, dt)) * ekfNavVelGainScaler;
_accel_target.y = _accel_feedforward.y + (_pid_rate_lon.get_p(_vel_error.y) + lon_i + _pid_rate_lon.get_d(_vel_error.y, dt)) * ekfNavVelGainScaler;
// scale desired acceleration if it's beyond acceptable limit
// To-Do: move this check down to the accel_to_lean_angle method?
accel_total = pythagorous2(_accel_target.x, _accel_target.y);
if (accel_total > POSCONTROL_ACCEL_XY_MAX && accel_total > 0.0f) {
_accel_target.x = POSCONTROL_ACCEL_XY_MAX * _accel_target.x/accel_total;
_accel_target.y = POSCONTROL_ACCEL_XY_MAX * _accel_target.y/accel_total;
_limit.accel_xy = true; // unused
} else {
// reset accel limit flag
_limit.accel_xy = false;
}
}
/// accel_to_lean_angles - horizontal desired acceleration to lean angles
/// converts desired accelerations provided in lat/lon frame to roll/pitch angles
void AC_PosControl::accel_to_lean_angles(float dt, float ekfNavVelGainScaler)
{
float accel_right, accel_forward;
float lean_angle_max = _attitude_control.lean_angle_max();
// To-Do: add 1hz filter to accel_lat, accel_lon
// rotate accelerations into body forward-right frame
accel_forward = _accel_target.x*_ahrs.cos_yaw() + _accel_target.y*_ahrs.sin_yaw();
accel_right = -_accel_target.x*_ahrs.sin_yaw() + _accel_target.y*_ahrs.cos_yaw();
// update angle targets that will be passed to stabilize controller
_roll_target = constrain_float(fast_atan(accel_right*_ahrs.cos_pitch()/(GRAVITY_MSS * 100))*(18000/M_PI), -lean_angle_max, lean_angle_max);
_pitch_target = constrain_float(fast_atan(-accel_forward/(GRAVITY_MSS * 100))*(18000/M_PI),-lean_angle_max, lean_angle_max);
// apply a rate limit of 100 deg/sec - required due to optical flow sensor saturation and impulse noise effects
static float lastRollDem = 0.0f;
static float lastPitchDem = 0.0f;
float maxDeltaAngle = dt * 10000.0f;
if (_roll_target - lastRollDem > maxDeltaAngle) {
_roll_target = lastRollDem + maxDeltaAngle;
} else if (_roll_target - lastRollDem < -maxDeltaAngle) {
_roll_target = lastRollDem - maxDeltaAngle;
}
lastRollDem = _roll_target;
if (_pitch_target - lastPitchDem > maxDeltaAngle) {
_pitch_target = lastPitchDem + maxDeltaAngle;
} else if (_pitch_target - lastPitchDem < -maxDeltaAngle) {
_pitch_target = lastPitchDem - maxDeltaAngle;
}
lastPitchDem = _pitch_target;
// 5Hz lowpass filter on angles - required due to optical flow noise
float freq_cut = 5.0f * ekfNavVelGainScaler;
float alpha = constrain_float(dt/(dt + 1.0f/(2.0f*(float)M_PI*freq_cut)),0.0f,1.0f);
static float roll_target_filtered = 0.0f;
static float pitch_target_filtered = 0.0f;
roll_target_filtered += alpha * ( _roll_target - roll_target_filtered);
pitch_target_filtered += alpha * (_pitch_target - pitch_target_filtered);
_roll_target = roll_target_filtered;
_pitch_target = pitch_target_filtered;
}
// get_lean_angles_to_accel - convert roll, pitch lean angles to lat/lon frame accelerations in cm/s/s
void AC_PosControl::lean_angles_to_accel(float& accel_x_cmss, float& accel_y_cmss) const
{
// rotate our roll, pitch angles into lat/lon frame
accel_x_cmss = (GRAVITY_MSS * 100) * (-(_ahrs.cos_yaw() * _ahrs.sin_pitch() / max(_ahrs.cos_pitch(),0.5f)) - _ahrs.sin_yaw() * _ahrs.sin_roll() / max(_ahrs.cos_roll(),0.5f));
accel_y_cmss = (GRAVITY_MSS * 100) * (-(_ahrs.sin_yaw() * _ahrs.sin_pitch() / max(_ahrs.cos_pitch(),0.5f)) + _ahrs.cos_yaw() * _ahrs.sin_roll() / max(_ahrs.cos_roll(),0.5f));
}
/// calc_leash_length - calculates the horizontal leash length given a maximum speed, acceleration and position kP gain
float AC_PosControl::calc_leash_length(float speed_cms, float accel_cms, float kP) const
{
float leash_length;
// sanity check acceleration and avoid divide by zero
if (accel_cms <= 0.0f) {
accel_cms = POSCONTROL_ACCELERATION_MIN;
}
// avoid divide by zero
if (kP <= 0.0f) {
return POSCONTROL_LEASH_LENGTH_MIN;
}
// calculate leash length
if(speed_cms <= accel_cms / kP) {
// linear leash length based on speed close in
leash_length = speed_cms / kP;
}else{
// leash length grows at sqrt of speed further out
leash_length = (accel_cms / (2.0f*kP*kP)) + (speed_cms*speed_cms / (2.0f*accel_cms));
}
// ensure leash is at least 1m long
if( leash_length < POSCONTROL_LEASH_LENGTH_MIN ) {
leash_length = POSCONTROL_LEASH_LENGTH_MIN;
}
return leash_length;
}
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