ardupilot/APMrover2/mode.cpp

#include "mode.h"
#include "Rover.h"

#define MODE_AHRS_GPS_ERROR_MAX    10      // accept up to 10m difference between AHRS and GPS

Mode::Mode() :
    ahrs(rover.ahrs),
    g(rover.g),
    g2(rover.g2),
    channel_steer(rover.channel_steer),
    channel_throttle(rover.channel_throttle),
    mission(rover.mission),
    attitude_control(rover.g2.attitude_control)
{ }

void Mode::exit()
{
    // call sub-classes exit
    _exit();

    _desired_lat_accel = 0.0f;
}

// these are basically the same checks as in AP_Arming:
bool Mode::enter_gps_checks() const
{
    const AP_GPS &gps = AP::gps();

    if (gps.status() < AP_GPS::GPS_OK_FIX_3D) {
        gcs().send_text(MAV_SEVERITY_CRITICAL, "Bad GPS Position");
        return false;
    }
    //GPS update rate acceptable
    if (!gps.is_healthy()) {
        gcs().send_text(MAV_SEVERITY_CRITICAL, "GPS is not healthy");
    }

    // check GPSs are within 50m of each other and that blending is healthy
    float distance_m;
    if (!gps.all_consistent(distance_m)) {
        gcs().send_text(MAV_SEVERITY_CRITICAL,
                        "GPS positions differ by %4.1fm",
                        (double)distance_m);
        return false;
    }
    if (!gps.blend_health_check()) {
        gcs().send_text(MAV_SEVERITY_CRITICAL, "GPS blending unhealthy");
        return false;
    }

    // check AHRS and GPS are within 10m of each other
    const Location gps_loc = gps.location();
    Location ahrs_loc;
    if (ahrs.get_position(ahrs_loc)) {
        float distance = location_3d_diff_NED(gps_loc, ahrs_loc).length();
        if (distance > MODE_AHRS_GPS_ERROR_MAX) {
            gcs().send_text(MAV_SEVERITY_CRITICAL, "GPS and AHRS differ by %4.1fm", (double)distance);
            return false;
        }
    }

    return true;
}

bool Mode::enter()
{
    const bool ignore_checks = !hal.util->get_soft_armed();   // allow switching to any mode if disarmed.  We rely on the arming check to perform
    if (!ignore_checks) {
        if (requires_gps() && !enter_gps_checks()) {
            return false;
        }
    }

    return _enter();
}

void Mode::get_pilot_desired_steering_and_throttle(float &steering_out, float &throttle_out)
{
    // no RC input means no throttle and centered steering
    if (rover.failsafe.bits & FAILSAFE_EVENT_THROTTLE) {
        steering_out = 0;
        throttle_out = 0;
        return;
    }

    // apply RC skid steer mixing
    switch ((enum pilot_steer_type_t)rover.g.pilot_steer_type.get())
    {
        case PILOT_STEER_TYPE_DEFAULT:
        default: {
            // by default regular and skid-steering vehicles reverse their rotation direction when backing up
            // (this is the same as PILOT_STEER_TYPE_DIR_REVERSED_WHEN_REVERSING below)
            throttle_out = rover.channel_throttle->get_control_in();
            steering_out = rover.channel_steer->get_control_in();
            break;
        }

        case PILOT_STEER_TYPE_TWO_PADDLES: {
            // convert the two radio_in values from skid steering values
            // left paddle from steering input channel, right paddle from throttle input channel
            // steering = left-paddle - right-paddle
            // throttle = average(left-paddle, right-paddle)
            const float left_paddle = rover.channel_steer->norm_input();
            const float right_paddle = rover.channel_throttle->norm_input();

            throttle_out = 0.5f * (left_paddle + right_paddle) * 100.0f;

            const float steering_dir = is_negative(throttle_out) ? -1 : 1;
            steering_out = steering_dir * (left_paddle - right_paddle) * 4500.0f;
            break;
        }

        case PILOT_STEER_TYPE_DIR_REVERSED_WHEN_REVERSING:
            throttle_out = rover.channel_throttle->get_control_in();
            steering_out = rover.channel_steer->get_control_in();
            break;

        case PILOT_STEER_TYPE_DIR_UNCHANGED_WHEN_REVERSING: {
            throttle_out = rover.channel_throttle->get_control_in();
            const float steering_dir = is_negative(throttle_out) ? -1 : 1;
            steering_out = steering_dir * rover.channel_steer->get_control_in();
            break;
        }
    }
}

// set desired location
void Mode::set_desired_location(const struct Location& destination, float next_leg_bearing_cd)
{
    // record targets
    _origin = rover.current_loc;
    _destination = destination;

    // initialise distance
    _distance_to_destination = get_distance(_origin, _destination);
    _reached_destination = false;

    // set final desired speed
    _desired_speed_final = 0.0f;
    if (!is_equal(next_leg_bearing_cd, MODE_NEXT_HEADING_UNKNOWN)) {
        // if not turning can continue at full speed
        if (is_zero(next_leg_bearing_cd)) {
            _desired_speed_final = _desired_speed;
        } else {
            // calculate maximum speed that keeps overshoot within bounds
            const float curr_leg_bearing_cd = get_bearing_cd(_origin, _destination);
            const float turn_angle_cd = wrap_180_cd(next_leg_bearing_cd - curr_leg_bearing_cd);
            const float radius_m = fabsf(g.waypoint_overshoot / (cosf(radians(turn_angle_cd * 0.01f)) - 1.0f));
            _desired_speed_final = MIN(_desired_speed, safe_sqrt(g.turn_max_g * GRAVITY_MSS * radius_m));
        }
    }
}

// set desired location as an offset from the EKF origin in NED frame
bool Mode::set_desired_location_NED(const Vector3f& destination, float next_leg_bearing_cd)
{
    Location destination_ned;
    // initialise destination to ekf origin
    if (!ahrs.get_origin(destination_ned)) {
        return false;
    }
    // apply offset
    location_offset(destination_ned, destination.x, destination.y);
    set_desired_location(destination_ned, next_leg_bearing_cd);
    return true;
}

// set desired heading and speed
void Mode::set_desired_heading_and_speed(float yaw_angle_cd, float target_speed)
{
    // handle initialisation
    _reached_destination = false;

    // record targets
    _desired_yaw_cd = yaw_angle_cd;
    _desired_speed = target_speed;
}

// get default speed for this mode (held in (CRUISE_SPEED, WP_SPEED or RTL_SPEED)
float Mode::get_speed_default(bool rtl) const
{
    if (rtl && is_positive(g2.rtl_speed)) {
        return g2.rtl_speed;
    } else if (is_positive(g2.wp_speed)) {
        return g2.wp_speed;
    } else {
        return g.speed_cruise;
    }
}

// restore desired speed to default from parameter values (CRUISE_SPEED or WP_SPEED)
void Mode::set_desired_speed_to_default(bool rtl)
{
    _desired_speed = get_speed_default(rtl);
}

void Mode::calc_throttle(float target_speed, bool nudge_allowed)
{
    // add in speed nudging
    if (nudge_allowed) {
        target_speed = calc_speed_nudge(target_speed, g.speed_cruise, g.throttle_cruise * 0.01f);
    }

    // call throttle controller and convert output to -100 to +100 range
    float throttle_out = 100.0f * attitude_control.get_throttle_out_speed(target_speed, g2.motors.limit.throttle_lower, g2.motors.limit.throttle_upper, g.speed_cruise, g.throttle_cruise * 0.01f);

    // send to motor
    g2.motors.set_throttle(throttle_out);
}

// performs a controlled stop with steering centered
bool Mode::stop_vehicle()
{
    // call throttle controller and convert output to -100 to +100 range
    bool stopped = false;
    float throttle_out = 100.0f * attitude_control.get_throttle_out_stop(g2.motors.limit.throttle_lower, g2.motors.limit.throttle_upper, g.speed_cruise, g.throttle_cruise * 0.01f, stopped);

    // send to motor
    g2.motors.set_throttle(throttle_out);

    // do not attempt to steer
    g2.motors.set_steering(0.0f);

    // return true once stopped
    return stopped;
}

// estimate maximum vehicle speed (in m/s)
float Mode::calc_speed_max(float cruise_speed, float cruise_throttle)
{
    float speed_max;

    // sanity checks
    if (cruise_throttle > 1.0f || cruise_throttle < 0.05f) {
        speed_max = cruise_speed;
    } else {
        // project vehicle's maximum speed
        speed_max = (1.0f / cruise_throttle) * cruise_speed;
    }

    // constrain to 30m/s (108km/h) and return
    return constrain_float(speed_max, 0.0f, 30.0f);
}

// calculate pilot input to nudge speed up or down
//  target_speed should be in meters/sec
//  cruise_speed is vehicle's cruising speed, cruise_throttle is the throttle (from -1 to +1) that achieves the cruising speed
//  return value is a new speed (in m/s) which up to the projected maximum speed based on the cruise speed and cruise throttle
float Mode::calc_speed_nudge(float target_speed, float cruise_speed, float cruise_throttle)
{
    // return immediately if pilot is not attempting to nudge speed
    // pilot can nudge up speed if throttle (in range -100 to +100) is above 50% of center in direction of travel
    const int16_t pilot_throttle = constrain_int16(rover.channel_throttle->get_control_in(), -100, 100);
    if (((pilot_throttle <= 50) && (target_speed >= 0.0f)) ||
        ((pilot_throttle >= -50) && (target_speed <= 0.0f))) {
        return target_speed;
    }

    // sanity checks
    if (cruise_throttle > 1.0f || cruise_throttle < 0.05f) {
        return target_speed;
    }

    // project vehicle's maximum speed
    const float vehicle_speed_max = calc_speed_max(cruise_speed, cruise_throttle);

    // return unadjusted target if already over vehicle's projected maximum speed
    if (target_speed >= vehicle_speed_max) {
        return target_speed;
    }

    const float speed_increase_max = vehicle_speed_max - fabsf(target_speed);
    float speed_nudge = ((static_cast<float>(abs(pilot_throttle)) - 50.0f) * 0.02f) * speed_increase_max;
    if (pilot_throttle < 0) {
        speed_nudge = -speed_nudge;
    }

    return target_speed + speed_nudge;
}

// calculated a reduced speed(in m/s) based on yaw error and lateral acceleration and/or distance to a waypoint
// should be called after calc_lateral_acceleration and before calc_throttle
// relies on these internal members being updated: lateral_acceleration, _yaw_error_cd, _distance_to_destination
float Mode::calc_reduced_speed_for_turn_or_distance(float desired_speed)
{
    // this method makes use the following internal variables
    const float yaw_error_cd = _yaw_error_cd;
    const float target_lateral_accel_G = _desired_lat_accel;
    const float distance_to_waypoint = _distance_to_destination;

    // calculate the yaw_error_ratio which is the error (capped at 90degrees) expressed as a ratio (from 0 ~ 1)
    float yaw_error_ratio = constrain_float(fabsf(yaw_error_cd / 9000.0f), 0.0f, 1.0f);

    // apply speed_turn_gain parameter (expressed as a percentage) to yaw_error_ratio
    yaw_error_ratio *= (100 - g.speed_turn_gain) * 0.01f;

    // calculate absolute lateral acceleration expressed as a ratio (from 0 ~ 1) of the vehicle's maximum lateral acceleration
    const float lateral_accel_ratio = constrain_float(fabsf(target_lateral_accel_G / (g.turn_max_g * GRAVITY_MSS)), 0.0f, 1.0f);

    // calculate a lateral acceleration based speed scaling
    const float lateral_accel_speed_scaling = 1.0f - lateral_accel_ratio * yaw_error_ratio;

    // calculate a pivot steering based speed scaling (default to no reduction)
    float pivot_speed_scaling = 1.0f;
    if (rover.use_pivot_steering(yaw_error_cd)) {
        pivot_speed_scaling = 0.0f;
    }

    // scaled speed
    float speed_scaled = desired_speed * MIN(lateral_accel_speed_scaling, pivot_speed_scaling);

    // limit speed based on distance to waypoint and max acceleration/deceleration
    if (is_positive(distance_to_waypoint) && is_positive(attitude_control.get_accel_max())) {
        const float speed_max = safe_sqrt(2.0f * distance_to_waypoint * attitude_control.get_accel_max() + sq(_desired_speed_final));
        speed_scaled = constrain_float(speed_scaled, -speed_max, speed_max);
    }

    // return minimum speed
    return speed_scaled;
}

// calculate the lateral acceleration target to cause the vehicle to drive along the path from origin to destination
// this function update lateral_acceleration and _yaw_error_cd members
void Mode::calc_steering_to_waypoint(const struct Location &origin, const struct Location &destination, bool reversed)
{
    // Calculate the required turn of the wheels
    // negative error = left turn
    // positive error = right turn
    rover.nav_controller->set_reverse(reversed);
    rover.nav_controller->update_waypoint(origin, destination);
    _desired_lat_accel = rover.nav_controller->lateral_acceleration();
    if (reversed) {
        _yaw_error_cd = wrap_180_cd(rover.nav_controller->target_bearing_cd() - ahrs.yaw_sensor + 18000);
    } else {
        _yaw_error_cd = wrap_180_cd(rover.nav_controller->target_bearing_cd() - ahrs.yaw_sensor);
    }
    if (rover.use_pivot_steering(_yaw_error_cd)) {
        if (_yaw_error_cd >= 0.0f) {
            _desired_lat_accel = g.turn_max_g * GRAVITY_MSS;
        } else {
            _desired_lat_accel = -g.turn_max_g * GRAVITY_MSS;
        }
    }

    // call lateral acceleration to steering controller
    calc_steering_from_lateral_acceleration(reversed);
}

/*
    calculate steering output given lateral_acceleration
*/
void Mode::calc_steering_from_lateral_acceleration(bool reversed)
{
    // add obstacle avoidance response to lateral acceleration target
    if (!reversed) {
        _desired_lat_accel += (rover.obstacle.turn_angle / 45.0f) * g.turn_max_g;
    }

    // constrain to max G force
    _desired_lat_accel = constrain_float(_desired_lat_accel, -g.turn_max_g * GRAVITY_MSS, g.turn_max_g * GRAVITY_MSS);

    // send final steering command to motor library
    float steering_out = attitude_control.get_steering_out_lat_accel(_desired_lat_accel, g2.motors.have_skid_steering(), g2.motors.limit.steer_left, g2.motors.limit.steer_right, reversed);
    g2.motors.set_steering(steering_out * 4500.0f);
}