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ardupilot/libraries/AP_Landing/AP_Landing_Deepstall.cpp

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/*
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, see <http://www.gnu.org/licenses/>.
*/
/*
* AP_Landing_Deepstall.cpp - Landing logic handler for ArduPlane for deepstall landings
*/
#include "AP_Landing.h"
#include <GCS_MAVLink/GCS.h>
#include <AP_HAL/AP_HAL.h>
#include <SRV_Channel/SRV_Channel.h>
// table of user settable parameters for deepstall
const AP_Param::GroupInfo AP_Landing_Deepstall::var_info[] = {
// @Param: V_FWD
// @DisplayName: Deepstall forward velocity
// @Description: The forward velocity of the aircraft while stalled
// @Range: 0 20
// @Units: m/s
// @User: Advanced
AP_GROUPINFO("V_FWD", 1, AP_Landing_Deepstall, forward_speed, 1),
// @Param: SLOPE_A
// @DisplayName: Deepstall slope a
// @Description: The a component of distance = a*wind + b
// @User: Advanced
AP_GROUPINFO("SLOPE_A", 2, AP_Landing_Deepstall, slope_a, 1),
// @Param: SLOPE_B
// @DisplayName: Deepstall slope b
// @Description: The a component of distance = a*wind + b
// @User: Advanced
AP_GROUPINFO("SLOPE_B", 3, AP_Landing_Deepstall, slope_b, 1),
// @Param: APP_EXT
// @DisplayName: Deepstall approach extension
// @Description: The forward velocity of the aircraft while stalled
// @Range: 10 200
// @Units: m
// @User: Advanced
AP_GROUPINFO("APP_EXT", 4, AP_Landing_Deepstall, approach_extension, 50),
// @Param: V_DWN
// @DisplayName: Deepstall veloicty down
// @Description: The downward velocity of the aircraft while stalled
// @Range: 0 20
// @Units: m/s
// @User: Advanced
AP_GROUPINFO("V_DWN", 5, AP_Landing_Deepstall, down_speed, 2),
// @Param: SLEW_SPD
// @DisplayName: Deepstall slew speed
// @Description: The speed at which the elevator slews to deepstall
// @Range: 0 2
// @Units: s
// @User: Advanced
AP_GROUPINFO("SLEW_SPD", 6, AP_Landing_Deepstall, slew_speed, 0.5),
// @Param: ELEV_PWM
// @DisplayName: Deepstall elevator PWM
// @Description: The PWM value for the elevator at full deflection in deepstall
// @Range: 900 2100
// @Units: PWM
// @User: Advanced
AP_GROUPINFO("ELEV_PWM", 7, AP_Landing_Deepstall, elevator_pwm, 1500),
// @Param: ARSP_MAX
// @DisplayName: Deepstall enabled airspeed
// @Description: The maximum aispeed where the deepstall steering controller is allowed to have control
// @Range: 5 20
// @Units: m/s
// @User: Advanced
AP_GROUPINFO("ARSP_MAX", 8, AP_Landing_Deepstall, handoff_airspeed, 15.0),
// @Param: ARSP_MIN
// @DisplayName: Deepstall minimum derating airspeed
// @Description: Deepstall lowest airspeed where the deepstall controller isn't allowed full control
// @Range: 5 20
// @Units: m/s
// @User: Advanced
AP_GROUPINFO("ARSP_MIN", 9, AP_Landing_Deepstall, handoff_lower_limit_airspeed, 10.0),
// @Param: L1
// @DisplayName: Deepstall L1 period
// @Description: Deepstall L1 navigational controller period
// @Range: 5 50
// @Units: m
// @User: Advanced
AP_GROUPINFO("L1", 10, AP_Landing_Deepstall, L1_period, 30.0),
// @Param: L1_I
// @DisplayName: Deepstall L1 I gain
// @Description: Deepstall L1 integratior gain
// @Range: 0 1
// @User: Advanced
AP_GROUPINFO("L1_I", 11, AP_Landing_Deepstall, L1_i, 0),
// @Param: YAW_LIM
// @DisplayName: Deepstall yaw rate limit
// @Description: The yaw rate limit while navigating in deepstall
// @Range: 0 90
// @Units degrees per second
// @User: Advanced
AP_GROUPINFO("YAW_LIM", 12, AP_Landing_Deepstall, yaw_rate_limit, 10),
// @Param: L1_TCON
// @DisplayName: Deepstall L1 time constant
// @Description: Time constant for deepstall L1 control
// @Range: 0 1
// @Units seconds
// @User: Advanced
AP_GROUPINFO("L1_TCON", 13, AP_Landing_Deepstall, time_constant, 0.4),
// @Group: DS_
// @Path: ../PID/PID.cpp
AP_SUBGROUPINFO(ds_PID, "", 13, AP_Landing_Deepstall, PID),
AP_GROUPEND
};
// if DEBUG_PRINTS is defined statustexts will be sent to the GCS for debug purposes
//#define DEBUG_PRINTS
void AP_Landing_Deepstall::do_land(const AP_Mission::Mission_Command& cmd, const float relative_altitude)
{
stage = DEEPSTALL_STAGE_FLY_TO_LANDING;
ds_PID.reset_I();
// load the landing point in, the rest of path building is deferred for a better wind estimate
memcpy(&landing_point, &cmd.content.location, sizeof(Location));
}
// currently identical to the slope aborts
void AP_Landing_Deepstall::verify_abort_landing(const Location &prev_WP_loc, Location &next_WP_loc, bool &throttle_suppressed)
{
// when aborting a landing, mimic the verify_takeoff with steering hold. Once
// the altitude has been reached, restart the landing sequence
throttle_suppressed = false;
landing.nav_controller->update_heading_hold(get_bearing_cd(prev_WP_loc, next_WP_loc));
}
/*
update navigation for landing
*/
bool AP_Landing_Deepstall::verify_land(const Location &prev_WP_loc, Location &next_WP_loc, const Location &current_loc,
const float height, const float sink_rate, const float wp_proportion, const uint32_t last_flying_ms,
const bool is_armed, const bool is_flying, const bool rangefinder_state_in_range)
{
switch (stage) {
case DEEPSTALL_STAGE_FLY_TO_LANDING:
if (get_distance(current_loc, landing_point) > 2 * landing.aparm.loiter_radius) {
landing.nav_controller->update_waypoint(current_loc, landing_point);
return false;
}
stage = DEEPSTALL_STAGE_ESTIMATE_WIND;
loiter_sum_cd = 0; // reset the loiter counter
// no break
case DEEPSTALL_STAGE_ESTIMATE_WIND:
{
landing.nav_controller->update_loiter(landing_point, landing.aparm.loiter_radius, 1);
if (!landing.nav_controller->reached_loiter_target() || (fabsf(height) > DEEPSTALL_LOITER_ALT_TOLERANCE)) {
// wait until the altitude is correct before considering a breakout
return false;
}
// only count loiter progress when within the target altitude
int32_t target_bearing = landing.nav_controller->target_bearing_cd();
int32_t delta = wrap_180_cd(target_bearing - last_target_bearing);
if (delta > 0) { // only accumulate turns in the correct direction
loiter_sum_cd += delta;
}
last_target_bearing = target_bearing;
if (loiter_sum_cd < 36000) {
// wait until we've done at least one complete loiter at the correct altitude
landing.nav_controller->update_loiter(landing_point, landing.aparm.loiter_radius, 1);
return false;
}
stage = DEEPSTALL_STAGE_WAIT_FOR_BREAKOUT;
loiter_sum_cd = 0; // reset the loiter counter
// no break
}
case DEEPSTALL_STAGE_WAIT_FOR_BREAKOUT:
// rebuild the approach path if we have done less then a full circle to allow it to be
// more into the wind as the estimator continues to refine itself, and allow better
// compensation on windy days. This is limited to a single full circle though, as on
// a no wind day you could be in this loop forever otherwise.
if (loiter_sum_cd < 36000) {
build_approach_path();
}
if (!verify_breakout(current_loc, arc_entry, height)) {
int32_t target_bearing = landing.nav_controller->target_bearing_cd();
int32_t delta = wrap_180_cd(target_bearing - last_target_bearing);
if (delta > 0) { // only accumulate turns in the correct direction
loiter_sum_cd += delta;
}
last_target_bearing = target_bearing;
landing.nav_controller->update_loiter(landing_point, landing.aparm.loiter_radius, 1);
return false;
}
stage = DEEPSTALL_STAGE_FLY_TO_ARC;
memcpy(&breakout_location, &current_loc, sizeof(Location));
// no break
case DEEPSTALL_STAGE_FLY_TO_ARC:
if (get_distance(current_loc, arc_entry) > 2 * landing.aparm.loiter_radius) {
landing.nav_controller->update_waypoint(breakout_location, arc_entry);
return false;
}
stage = DEEPSTALL_STAGE_ARC;
// no break
case DEEPSTALL_STAGE_ARC:
{
Vector2f groundspeed = landing.ahrs.groundspeed_vector();
if (!landing.nav_controller->reached_loiter_target() ||
(fabsf(wrap_180(target_heading_deg -
degrees(atan2f(-groundspeed.y, -groundspeed.x) + M_PI))) >= 10.0f)) {
landing.nav_controller->update_loiter(arc, landing.aparm.loiter_radius, 1);
return false;
}
stage = DEEPSTALL_STAGE_APPROACH;
}
// no break
case DEEPSTALL_STAGE_APPROACH:
{
Location entry_point;
landing.nav_controller->update_waypoint(arc_exit, extended_approach);
float relative_alt_D;
landing.ahrs.get_relative_position_D_home(relative_alt_D);
const float travel_distance = predict_travel_distance(landing.ahrs.wind_estimate(), -relative_alt_D);
memcpy(&entry_point, &landing_point, sizeof(Location));
location_update(entry_point, target_heading_deg + 180.0, travel_distance);
if (!location_passed_point(current_loc, arc_exit, entry_point)) {
if (location_passed_point(current_loc, arc_exit, extended_approach)) {
// this should never happen, but prevent against an indefinite fly away
stage = DEEPSTALL_STAGE_FLY_TO_LANDING;
}
return false;
}
stage = DEEPSTALL_STAGE_LAND;
stall_entry_time = AP_HAL::millis();
const SRV_Channel* elevator = SRV_Channels::get_channel_for(SRV_Channel::k_elevator);
if (elevator != nullptr) {
// take the last used elevator angle as the starting deflection
// don't worry about bailing here if the elevator channel can't be found
// that will be handled within override_servos
initial_elevator_pwm = elevator->get_output_pwm();
}
L1_xtrack_i = 0; // reset the integrators
}
// no break
case DEEPSTALL_STAGE_LAND:
// while in deepstall the only thing verify needs to keep the extended approach point sufficently far away
landing.nav_controller->update_waypoint(current_loc, extended_approach);
return false;
default:
return true;
}
}
bool AP_Landing_Deepstall::override_servos(void)
{
if (!(stage == DEEPSTALL_STAGE_LAND)) {
return false;
}
SRV_Channel* elevator = SRV_Channels::get_channel_for(SRV_Channel::k_elevator);
if (elevator == nullptr) {
// deepstalls are impossible without these channels, abort the process
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_CRITICAL,
"Deepstall: Unable to find the elevator channels");
request_go_around();
return false;
}
// calculate the progress on slewing the elevator
float slew_progress = 1.0f;
if (slew_speed > 0) {
slew_progress = (AP_HAL::millis() - stall_entry_time) / (100.0f * slew_speed);
slew_progress = constrain_float (slew_progress, 0.0f, 1.0f);
}
// mix the elevator to the correct value
elevator->set_output_pwm(linear_interpolate(initial_elevator_pwm, elevator_pwm,
slew_progress, 0.0f, 1.0f));
// use the current airspeed to dictate the travel limits
float airspeed;
landing.ahrs.airspeed_estimate(&airspeed);
// only allow the deepstall steering controller to run below the handoff airspeed
if (slew_progress >= 1.0f || airspeed <= handoff_airspeed) {
// run the steering conntroller
float pid = update_steering();
float travel_limit = constrain_float((handoff_airspeed - airspeed) /
(handoff_airspeed - handoff_lower_limit_airspeed) *
0.5f + 0.5f,
0.5f, 1.0f);
float output = constrain_float(pid, -travel_limit, travel_limit);
SRV_Channels::set_output_scaled(SRV_Channel::k_aileron, output*4500);
SRV_Channels::set_output_scaled(SRV_Channel::k_aileron_with_input, output*4500);
SRV_Channels::set_output_scaled(SRV_Channel::k_rudder, output*4500);
} else {
// allow the normal servo control of the channel
SRV_Channels::set_output_scaled(SRV_Channel::k_aileron_with_input,
SRV_Channels::get_output_scaled(SRV_Channel::k_aileron));
}
// hand off rudder control to deepstall controlled
return true;
}
bool AP_Landing_Deepstall::request_go_around(void)
{
landing.flags.commanded_go_around = true;
return true;
}
bool AP_Landing_Deepstall::is_throttle_suppressed(void) const
{
return stage == DEEPSTALL_STAGE_LAND;
}
bool AP_Landing_Deepstall::is_flying_forward(void) const
{
return stage != DEEPSTALL_STAGE_LAND;
}
bool AP_Landing_Deepstall::get_target_altitude_location(Location &location)
{
memcpy(&location, &landing_point, sizeof(Location));
return true;
}
int32_t AP_Landing_Deepstall::get_target_airspeed_cm(void) const
{
if (stage == DEEPSTALL_STAGE_APPROACH ||
stage == DEEPSTALL_STAGE_LAND) {
return landing.pre_flare_airspeed * 100;
} else {
return landing.aparm.airspeed_cruise_cm;
}
}
const DataFlash_Class::PID_Info& AP_Landing_Deepstall::get_pid_info(void) const
{
return ds_PID.get_pid_info();
}
void AP_Landing_Deepstall::build_approach_path(void)
{
float loiter_radius = landing.nav_controller->loiter_radius(landing.aparm.loiter_radius);
Vector3f wind = landing.ahrs.wind_estimate();
// TODO: Support a user defined approach heading
target_heading_deg = (degrees(atan2f(-wind.y, -wind.x)));
memcpy(&extended_approach, &landing_point, sizeof(Location));
memcpy(&arc_exit, &landing_point, sizeof(Location));
//extend the approach point to 1km away so that there is always a navigational target
location_update(extended_approach, target_heading_deg, 1000.0);
float expected_travel_distance = predict_travel_distance(wind, landing_point.alt / 100);
float approach_extension_m = expected_travel_distance + approach_extension;
// an approach extensions must be at least half the loiter radius, or the aircraft has a
// decent chance to be misaligned on final approach
approach_extension_m = MAX(approach_extension_m, loiter_radius * 0.5f);
location_update(arc_exit, target_heading_deg + 180, approach_extension_m);
memcpy(&arc, &arc_exit, sizeof(Location));
memcpy(&arc_entry, &arc_exit, sizeof(Location));
// TODO: Support loitering on either side of the approach path
location_update(arc, target_heading_deg + 90.0, loiter_radius);
location_update(arc_entry, target_heading_deg + 90.0, loiter_radius * 2);
#ifdef DEBUG_PRINTS
// TODO: Send this information via a MAVLink packet
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Arc: %3.8f %3.8f",
(double)(arc.lat / 1e7),(double)( arc.lng / 1e7));
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Loiter en: %3.8f %3.8f",
(double)(arc_entry.lat / 1e7), (double)(arc_entry.lng / 1e7));
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Loiter ex: %3.8f %3.8f",
(double)(arc_exit.lat / 1e7), (double)(arc_exit.lng / 1e7));
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Extended: %3.8f %3.8f",
(double)(extended_approach.lat / 1e7), (double)(extended_approach.lng / 1e7));
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Extended by: %f (%f)", (double)approach_extension_m,
(double)expected_travel_distance);
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Target Heading: %3.1f", (double)target_heading_deg);
#endif // DEBUG_PRINTS
}
float AP_Landing_Deepstall::predict_travel_distance(const Vector3f wind, const float height) const
{
bool reverse = false;
float course = radians(target_heading_deg);
// a forward speed of 0 will result in a divide by 0
float forward_speed_ms = MAX(forward_speed, 0.1f);
Vector2f wind_vec(wind.x, wind.y); // work with the 2D component of wind
float wind_length = MAX(wind_vec.length(), 0.05f); // always assume a slight wind to avoid divide by 0
Vector2f course_vec(cosf(course), sinf(course));
float offset = course + atan2f(-wind.y, -wind.x) + M_PI;
// estimator for how far the aircraft will travel while entering the stall
float stall_distance = slope_a * wind_length * cosf(offset) + slope_b;
float theta = acosf(constrain_float((wind_vec * course_vec) / wind_length, -1.0f, 1.0f));
if ((course_vec % wind_vec) > 0) {
reverse = true;
theta *= -1;
}
float cross_component = sinf(theta) * wind_length;
float estimated_crab_angle = asinf(constrain_float(cross_component / forward_speed_ms, -1.0f, 1.0f));
if (reverse) {
estimated_crab_angle *= -1;
}
float estimated_forward = cosf(estimated_crab_angle) * forward_speed_ms + cosf(theta) * wind_length;
#ifdef DEBUG_PRINTS
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "Predict: %f %f", stall_distance, estimated_forward * height / down_speed + stall_distance);
#endif // DEBUG_PRINTS
return estimated_forward * height / down_speed + stall_distance;
}
bool AP_Landing_Deepstall::verify_breakout(const Location &current_loc, const Location &target_loc,
const float height_error) const
{
Vector2f location_delta = location_diff(current_loc, target_loc);
const float heading_error = degrees(landing.ahrs.groundspeed_vector().angle(location_delta));
// Check to see if the the plane is heading toward the land waypoint. We use 20 degrees (+/-10 deg)
// of margin so that the altitude to be within 5 meters of desired
if (heading_error <= 10.0 && fabsf(height_error) < DEEPSTALL_LOITER_ALT_TOLERANCE) {
// Want to head in a straight line from _here_ to the next waypoint instead of center of loiter wp
return true;
}
return false;
}
float AP_Landing_Deepstall::update_steering()
{
Location current_loc;
if (!landing.ahrs.get_position(current_loc)) {
// panic if no position source is available
// continue the but target just holding the wings held level as deepstall should be a minimal energy
// configuration on the aircraft, and if a position isn't available aborting would be worse
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_CRITICAL, "Deepstall: No position available. Attempting to hold level");
memcpy(&current_loc, &landing_point, sizeof(Location));
}
uint32_t time = AP_HAL::millis();
float dt = constrain_float(time - last_time, (uint32_t)10UL, (uint32_t)200UL) / 1000.0;
last_time = time;
Vector2f ab = location_diff(arc_exit, extended_approach);
ab.normalize();
Vector2f a_air = location_diff(arc_exit, current_loc);
float crosstrack_error = a_air % ab;
float sine_nu1 = constrain_float(crosstrack_error / MAX(L1_period, 0.1f), -0.7071f, 0.7107f);
float nu1 = asinf(sine_nu1);
if (L1_i > 0) {
L1_xtrack_i += nu1 * L1_i / dt;
L1_xtrack_i = constrain_float(L1_xtrack_i, -0.5f, 0.5f);
nu1 += L1_xtrack_i;
}
float desired_change = wrap_PI(radians(target_heading_deg) + nu1 - landing.ahrs.yaw);
float yaw_rate = landing.ahrs.get_gyro().z;
float yaw_rate_limit_rps = radians(yaw_rate_limit);
float error = wrap_PI(constrain_float(desired_change / time_constant,
-yaw_rate_limit_rps, yaw_rate_limit_rps) - yaw_rate);
#ifdef DEBUG_PRINTS
GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_INFO, "x: %f e: %f r: %f d: %f",
(double)crosstrack_error,
(double)error,
(double)degrees(yaw_rate),
(double)location_diff(current_loc, landing_point).length());
#endif // DEBUG_PRINTS
return ds_PID.get_pid(error);
}
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