void TECS::_update_speed_states(float airspeed_setpoint, float indicated_airspeed, float EAS2TAS)
{
// Calculate the time in seconds since the last update and use the default time step value if out of bounds
uint64_t now = ecl_absolute_time();
const float dt = constrain((now - _speed_update_timestamp) * 1.0e-6f, DT_MIN, DT_MAX);
// Convert equivalent airspeed quantities to true airspeed
_EAS_setpoint = airspeed_setpoint;
_TAS_setpoint = _EAS_setpoint * EAS2TAS;
_TAS_max = _indicated_airspeed_max * EAS2TAS;
_TAS_min = _indicated_airspeed_min * EAS2TAS;
// If airspeed measurements are not being used, fix the airspeed estimate to halfway between
// min and max limits
if (!ISFINITE(indicated_airspeed) || !airspeed_sensor_enabled()) {
_EAS = 0.5f * (_indicated_airspeed_min + _indicated_airspeed_max);
} else {
_EAS = indicated_airspeed;
}
// If first time through or not flying, reset airspeed states
if (_speed_update_timestamp == 0 || !_in_air) {
_tas_rate_state = 0.0f;
_tas_state = (_EAS * EAS2TAS);
}
// Obtain a smoothed airspeed estimate using a second order complementary filter
// Update TAS rate state
float tas_error = (_EAS * EAS2TAS) - _tas_state;
float tas_rate_state_input = tas_error * _tas_estimate_freq * _tas_estimate_freq;
// limit integrator input to prevent windup
if (_tas_state < 3.1f) {
tas_rate_state_input = max(tas_rate_state_input, 0.0f);
}
// Update TAS state
_tas_rate_state = _tas_rate_state + tas_rate_state_input * dt;
float tas_state_input = _tas_rate_state + _speed_derivative + tas_error * _tas_estimate_freq * 1.4142f;
_tas_state = _tas_state + tas_state_input * dt;
// Limit the airspeed state to a minimum of 3 m/s
_tas_state = max(_tas_state, 3.0f);
_speed_update_timestamp = now;
}
void
RTL::set_rtl_item()
{
_navigator->set_can_loiter_at_sp(false);
const home_position_s &home = *_navigator->get_home_position();
const vehicle_global_position_s &gpos = *_navigator->get_global_position();
position_setpoint_triplet_s *pos_sp_triplet = _navigator->get_position_setpoint_triplet();
switch (_rtl_state) {
case RTL_STATE_CLIMB: {
// check if we are pretty close to home already
const float home_dist = get_distance_to_next_waypoint(home.lat, home.lon, gpos.lat, gpos.lon);
// if we are close to home we do not climb as high, otherwise we climb to return alt
float climb_alt = home.alt + _param_return_alt.get();
// we are close to home, limit climb to min
if (home_dist < _param_rtl_min_dist.get()) {
climb_alt = home.alt + _param_descend_alt.get();
}
_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
_mission_item.lat = gpos.lat;
_mission_item.lon = gpos.lon;
_mission_item.altitude = climb_alt;
_mission_item.altitude_is_relative = false;
_mission_item.yaw = NAN;
_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
_mission_item.time_inside = 0.0f;
_mission_item.autocontinue = true;
_mission_item.origin = ORIGIN_ONBOARD;
mavlink_and_console_log_info(_navigator->get_mavlink_log_pub(), "RTL: climb to %d m (%d m above home)",
(int)(climb_alt), (int)(climb_alt - _navigator->get_home_position()->alt));
break;
}
case RTL_STATE_RETURN: {
// don't change altitude
_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
_mission_item.lat = home.lat;
_mission_item.lon = home.lon;
_mission_item.altitude = gpos.alt;
_mission_item.altitude_is_relative = false;
// use home yaw if close to home
/* check if we are pretty close to home already */
const float home_dist = get_distance_to_next_waypoint(home.lat, home.lon, gpos.lat, gpos.lon);
if (home_dist < _param_rtl_min_dist.get()) {
_mission_item.yaw = home.yaw;
} else {
// use current heading to home
_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, home.lat, home.lon);
}
_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
_mission_item.time_inside = 0.0f;
_mission_item.autocontinue = true;
_mission_item.origin = ORIGIN_ONBOARD;
mavlink_and_console_log_info(_navigator->get_mavlink_log_pub(), "RTL: return at %d m (%d m above home)",
(int)(_mission_item.altitude), (int)(_mission_item.altitude - home.alt));
break;
}
case RTL_STATE_TRANSITION_TO_MC: {
_mission_item.nav_cmd = NAV_CMD_DO_VTOL_TRANSITION;
_mission_item.params[0] = vtol_vehicle_status_s::VEHICLE_VTOL_STATE_MC;
break;
}
case RTL_STATE_DESCEND: {
_mission_item.nav_cmd = NAV_CMD_WAYPOINT;
_mission_item.lat = home.lat;
_mission_item.lon = home.lon;
_mission_item.altitude = min(home.alt + _param_descend_alt.get(), gpos.alt);
_mission_item.altitude_is_relative = false;
// except for vtol which might be still off here and should point towards this location
const float d_current = get_distance_to_next_waypoint(gpos.lat, gpos.lon, _mission_item.lat, _mission_item.lon);
if (_navigator->get_vstatus()->is_vtol && (d_current > _navigator->get_acceptance_radius())) {
_mission_item.yaw = get_bearing_to_next_waypoint(gpos.lat, gpos.lon, _mission_item.lat, _mission_item.lon);
} else {
_mission_item.yaw = home.yaw;
}
_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
_mission_item.time_inside = 0.0f;
_mission_item.autocontinue = true;
_mission_item.origin = ORIGIN_ONBOARD;
/* disable previous setpoint to prevent drift */
pos_sp_triplet->previous.valid = false;
mavlink_and_console_log_info(_navigator->get_mavlink_log_pub(), "RTL: descend to %d m (%d m above home)",
(int)(_mission_item.altitude), (int)(_mission_item.altitude - home.alt));
break;
}
case RTL_STATE_LOITER: {
const bool autoland = (_param_land_delay.get() > FLT_EPSILON);
// don't change altitude
_mission_item.lat = home.lat;
_mission_item.lon = home.lon;
_mission_item.altitude = gpos.alt;
_mission_item.altitude_is_relative = false;
_mission_item.yaw = home.yaw;
_mission_item.loiter_radius = _navigator->get_loiter_radius();
_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
_mission_item.time_inside = max(_param_land_delay.get(), 0.0f);
_mission_item.autocontinue = autoland;
_mission_item.origin = ORIGIN_ONBOARD;
_navigator->set_can_loiter_at_sp(true);
if (autoland && (get_time_inside(_mission_item) > FLT_EPSILON)) {
_mission_item.nav_cmd = NAV_CMD_LOITER_TIME_LIMIT;
mavlink_and_console_log_info(_navigator->get_mavlink_log_pub(), "RTL: loiter %.1fs",
(double)get_time_inside(_mission_item));
} else {
_mission_item.nav_cmd = NAV_CMD_LOITER_UNLIMITED;
mavlink_and_console_log_info(_navigator->get_mavlink_log_pub(), "RTL: completed, loitering");
}
break;
}
case RTL_STATE_LAND: {
// land at home position
_mission_item.nav_cmd = NAV_CMD_LAND;
_mission_item.lat = home.lat;
_mission_item.lon = home.lon;
_mission_item.yaw = home.yaw;
_mission_item.altitude = home.alt;
_mission_item.altitude_is_relative = false;
_mission_item.acceptance_radius = _navigator->get_acceptance_radius();
_mission_item.time_inside = 0.0f;
_mission_item.autocontinue = true;
_mission_item.origin = ORIGIN_ONBOARD;
mavlink_log_critical(_navigator->get_mavlink_log_pub(), "RTL: land at home");
break;
}
case RTL_STATE_LANDED: {
set_idle_item(&_mission_item);
set_return_alt_min(false);
break;
}
default:
break;
}
reset_mission_item_reached();
/* execute command if set. This is required for commands like VTOL transition */
if (!item_contains_position(_mission_item)) {
issue_command(_mission_item);
}
/* convert mission item to current position setpoint and make it valid */
mission_apply_limitation(_mission_item);
if (mission_item_to_position_setpoint(_mission_item, &pos_sp_triplet->current)) {
_navigator->set_position_setpoint_triplet_updated();
}
}
void TECS::_update_pitch_setpoint()
{
/*
* The SKE_weighting variable controls how speed and height control are prioritised by the pitch demand calculation.
* A weighting of 1 givea equal speed and height priority
* A weighting of 0 gives 100% priority to height control and must be used when no airspeed measurement is available.
* A weighting of 2 provides 100% priority to speed control and is used when:
* a) an underspeed condition is detected.
* b) during climbout where a minimum pitch angle has been set to ensure height is gained. If the airspeed
* rises above the demanded value, the pitch angle demand is increased by the TECS controller to prevent the vehicle overspeeding.
* The weighting can be adjusted between 0 and 2 depending on speed and height accuracy requirements.
*/
// Calculate the weighting applied to control of specific kinetic energy error
float SKE_weighting = constrain(_pitch_speed_weight, 0.0f, 2.0f);
if ((_underspeed_detected || _climbout_mode_active) && airspeed_sensor_enabled()) {
SKE_weighting = 2.0f;
} else if (!airspeed_sensor_enabled()) {
SKE_weighting = 0.0f;
}
// Calculate the weighting applied to control of specific potential energy error
float SPE_weighting = 2.0f - SKE_weighting;
// Calculate the specific energy balance demand which specifies how the available total
// energy should be allocated to speed (kinetic energy) and height (potential energy)
float SEB_setpoint = _SPE_setpoint * SPE_weighting - _SKE_setpoint * SKE_weighting;
// Calculate the specific energy balance rate demand
float SEB_rate_setpoint = _SPE_rate_setpoint * SPE_weighting - _SKE_rate_setpoint * SKE_weighting;
// Calculate the specific energy balance and balance rate error
_SEB_error = SEB_setpoint - (_SPE_estimate * SPE_weighting - _SKE_estimate * SKE_weighting);
_SEB_rate_error = SEB_rate_setpoint - (_SPE_rate * SPE_weighting - _SKE_rate * SKE_weighting);
// Calculate derivative from change in climb angle to rate of change of specific energy balance
float climb_angle_to_SEB_rate = _tas_state * _pitch_time_constant * CONSTANTS_ONE_G;
// Calculate pitch integrator input term
float pitch_integ_input = _SEB_error * _integrator_gain;
// Prevent the integrator changing in a direction that will increase pitch demand saturation
// Decay the integrator at the control loop time constant if the pitch demand from the previous time step is saturated
if (_pitch_setpoint_unc > _pitch_setpoint_max) {
pitch_integ_input = min(pitch_integ_input,
min((_pitch_setpoint_max - _pitch_setpoint_unc) * climb_angle_to_SEB_rate / _pitch_time_constant, 0.0f));
} else if (_pitch_setpoint_unc < _pitch_setpoint_min) {
pitch_integ_input = max(pitch_integ_input,
max((_pitch_setpoint_min - _pitch_setpoint_unc) * climb_angle_to_SEB_rate / _pitch_time_constant, 0.0f));
}
// Update the pitch integrator state
_pitch_integ_state = _pitch_integ_state + pitch_integ_input * _dt;
// Calculate a specific energy correction that doesn't include the integrator contribution
float SEB_correction = _SEB_error + _SEB_rate_error * _pitch_damping_gain + SEB_rate_setpoint * _pitch_time_constant;
// During climbout, bias the demanded pitch angle so that a zero speed error produces a pitch angle
// demand equal to the minimum pitch angle set by the mission plan. This prevents the integrator
// having to catch up before the nose can be raised to reduce excess speed during climbout.
if (_climbout_mode_active) {
SEB_correction += _pitch_setpoint_min * climb_angle_to_SEB_rate;
}
// Sum the correction terms and convert to a pitch angle demand. This calculation assumes:
// a) The climb angle follows pitch angle with a lag that is small enough not to destabilise the control loop.
// b) The offset between climb angle and pitch angle (angle of attack) is constant, excluding the effect of
// pitch transients due to control action or turbulence.
_pitch_setpoint_unc = (SEB_correction + _pitch_integ_state) / climb_angle_to_SEB_rate;
_pitch_setpoint = constrain(_pitch_setpoint_unc, _pitch_setpoint_min, _pitch_setpoint_max);
// Comply with the specified vertical acceleration limit by applying a pitch rate limit
float ptchRateIncr = _dt * _vert_accel_limit / _tas_state;
if ((_pitch_setpoint - _last_pitch_setpoint) > ptchRateIncr) {
_pitch_setpoint = _last_pitch_setpoint + ptchRateIncr;
} else if ((_pitch_setpoint - _last_pitch_setpoint) < -ptchRateIncr) {
_pitch_setpoint = _last_pitch_setpoint - ptchRateIncr;
}
_last_pitch_setpoint = _pitch_setpoint;
}