/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*- #include #include 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), _last_update_xy_ms(0), _last_update_z_ms(0), _last_update_vel_xyz_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), _roll_target(0.0), _pitch_target(0.0), _alt_max(0), _distance_to_target(0), _xy_step(0), _dt_xy(0), _vel_xyz_step(0) { AP_Param::setup_object_defaults(this, var_info); // initialise flags _flags.force_recalc_xy = false; #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.keep_xy_I_terms = false; _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); } /// 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 = -fabs(speed_down); if ((fabs(_speed_down_cms-speed_down) > 1.0f) || (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 (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; // 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) { // 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) || (climb_rate_cms>0 && !_motors.limit.throttle_upper)) { _pos_target.z += climb_rate_cms * _dt; } } // 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 (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; // clear i term from acceleration controller if (_pid_alt_accel.get_integrator() < 0) { _pid_alt_accel.reset_I(); } } // 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(); float linear_distance; // half the distance we swap between linear and sqrt and the distance we offset sqrt. // clear position limit flags _limit.pos_up = false; _limit.pos_down = false; // 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; } // 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; } // check kP to avoid division by zero if (_p_alt_pos.kP() != 0) { linear_distance = _accel_z_cms/(2.0f*_p_alt_pos.kP()*_p_alt_pos.kP()); if (_pos_error.z > 2*linear_distance ) { _vel_target.z = safe_sqrt(2.0f*_accel_z_cms*(_pos_error.z-linear_distance)); }else if (_pos_error.z < -2.0f*linear_distance) { _vel_target.z = -safe_sqrt(2.0f*_accel_z_cms*(-_pos_error.z-linear_distance)); }else{ _vel_target.z = _p_alt_pos.get_p(_pos_error.z); } }else{ _vel_target.z = 0; } // 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; _flags.reset_rate_to_accel_z = false; } // 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; desired_accel = 0; _flags.reset_rate_to_accel_z = false; } else { _vel_error.z = (_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().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; _flags.reset_accel_to_throttle = false; } else { // calculate accel error and Filter with fc = 2 Hz // To-Do: replace constant below with one that is adjusted for update rate _accel_error.z = _accel_error.z + 0.11164f * (constrain_float(accel_target_z - z_accel_meas, -32000, 32000) - _accel_error.z); } // 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); // To-Do: pull min/max throttle from motors // To-Do: we had a contraint here but it's now removed, is this ok? with the motors library handle it ok? _attitude_control.set_throttle_out((int16_t)p+i+d+_throttle_hover, true); // to-do add back in PID logging? } /// /// 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 (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 (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) { 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() { // reset xy controller to first step _xy_step = 0; // 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 (!_flags.keep_xy_I_terms) { // 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); } else { // reset keep_xy_I_term flag in case it has been set _flags.keep_xy_I_terms = false; } // flag reset required in rate to accel step _flags.reset_desired_vel_to_pos = true; _flags.reset_rate_to_accel_xy = true; // update update time _last_update_xy_ms = hal.scheduler->millis(); } /// 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) { // catch if we've just been started uint32_t now = hal.scheduler->millis(); if ((now - _last_update_xy_ms) >= POSCONTROL_ACTIVE_TIMEOUT_MS) { init_xy_controller(); } // check if xy leash needs to be recalculated calc_leash_length_xy(); // reset step back to 0 if loiter or waypoint parents have triggered an update and we completed the last full cycle if (_flags.force_recalc_xy && _xy_step > 3) { _flags.force_recalc_xy = false; _xy_step = 0; } // run loiter steps switch (_xy_step) { case 0: // capture time since last iteration _dt_xy = (now - _last_update_xy_ms) / 1000.0f; _last_update_xy_ms = now; // translate any adjustments from pilot to loiter target desired_vel_to_pos(_dt_xy); _xy_step++; break; case 1: // run position controller's position error to desired velocity step pos_to_rate_xy(use_desired_velocity,_dt_xy); _xy_step++; break; case 2: // run position controller's velocity to acceleration step rate_to_accel_xy(_dt_xy); _xy_step++; break; case 3: // run position controller's acceleration to lean angle step accel_to_lean_angles(); _xy_step++; break; } } /// 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() { // force the xy velocity controller to run immediately _vel_xyz_step = 3; // 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); // record update time _last_update_vel_xyz_ms = hal.scheduler->millis(); } /// 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() { // capture time since last iteration uint32_t now = hal.scheduler->millis(); float dt_xy = (now - _last_update_vel_xyz_ms) / 1000.0f; // check if xy leash needs to be recalculated calc_leash_length_xy(); // we will run the horizontal component every 4th iteration (i.e. 50hz on Pixhawk, 20hz on APM) if (dt_xy >= POSCONTROL_VEL_UPDATE_TIME) { // record update time _last_update_vel_xyz_ms = now; // sanity check dt if (dt_xy >= POSCONTROL_ACTIVE_TIMEOUT_MS) { dt_xy = 0.0f; } // apply desired velocity request to position target desired_vel_to_pos(dt_xy); // run position controller's position error to desired velocity step pos_to_rate_xy(true, dt_xy); // run velocity to acceleration step rate_to_accel_xy(dt_xy); // run acceleration to lean angle step accel_to_lean_angles(); } // update altitude target set_alt_target_from_climb_rate(_vel_desired.z, _dt); // run z-axis position controller update_z_controller(); } /// /// 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) { Vector3f curr_pos = _inav.get_position(); float linear_distance; // the distance we swap between linear and sqrt velocity response float kP = _p_pos_xy.kP(); // avoid divide by zero if (kP <= 0.0f) { _vel_target.x = 0.0; _vel_target.y = 0.0; }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) { 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 _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); _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); // 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 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); } // 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(),0.5)) - _ahrs.sin_yaw() * _ahrs.sin_roll() / max(_ahrs.cos_roll(),0.5)); accel_y_cmss = (GRAVITY_MSS * 100) * (-(_ahrs.sin_yaw() * _ahrs.sin_pitch() / max(_ahrs.cos_pitch(),0.5)) + _ahrs.cos_yaw() * _ahrs.sin_roll() / max(_ahrs.cos_roll(),0.5)); } /// 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; }