VTOL_Assist.cpp

#include "Plane.h"

#if HAL_QUADPLANE_ENABLED

// Assistance hysteresis helpers

// Reset state
void VTOL_Assist::Assist_Hysteresis::reset()
{
    start_ms = 0;
    last_ms = 0;
    active = false;
}

// Update state, return true when first triggered
bool VTOL_Assist::Assist_Hysteresis::update(const bool trigger, const uint32_t &now_ms, const uint32_t &trigger_delay_ms, const uint32_t &clear_delay_ms)
{
    bool ret = false;

    if (trigger) {
        last_ms = now_ms;
        if (start_ms == 0) {
            start_ms = now_ms;
        }
        if ((now_ms - start_ms) > trigger_delay_ms) {
            // trigger delay has elapsed
            if (!active) {
                // return true on first trigger
                ret = true;
            }
            active = true;
        }

    } else if (active) {
        if ((last_ms == 0) || ((now_ms - last_ms) > clear_delay_ms)) {
            // Clear delay passed
            reset();
        }

    } else {
        reset();
    }

    return ret;
}

// Assistance not needed, reset any state
void VTOL_Assist::reset()
{
    force_assist = false;
    speed_assist = false;
    angle_error.reset();
    alt_error.reset();
}

/*
  return true if the quadplane should provide stability assistance
 */
bool VTOL_Assist::should_assist(float aspeed, bool have_airspeed)
{
    if (!plane.arming.is_armed_and_safety_off() || (state == STATE::ASSIST_DISABLED) || quadplane.tailsitter.is_control_surface_tailsitter()) {
        // disarmed or disabled by aux switch or because a control surface tailsitter
        reset();
        return false;
    }

    if (!quadplane.tailsitter.enabled() && !( (plane.control_mode->does_auto_throttle() && !plane.throttle_suppressed)
                                                                      || is_positive(plane.get_throttle_input()) 
                                                                      || plane.is_flying() ) ) {
        // not in a flight mode and condition where it would be safe to turn on vertical lift motors
        // skip this check for tailsitters because the forward and vertical motors are the same and are controlled directly by throttle input unlike other quadplanes
        reset();
        return false;
    }

    if (plane.flare_mode != Plane::FlareMode::FLARE_DISABLED) {
        // Never active in fixed wing flare
        reset();
        return false;
    }

    force_assist = state == STATE::FORCE_ENABLED;

    if (speed <= 0) {
        // all checks disabled via speed threshold, still allow force enabled
        speed_assist = false;
        alt_error.reset();
        angle_error.reset();
        return force_assist;
    }

    // assistance due to Q_ASSIST_SPEED
    // if option bit is enabled only allow assist with real airspeed sensor
    speed_assist = (have_airspeed && aspeed < speed) && 
       (!quadplane.option_is_set(QuadPlane::Option::DISABLE_SYNTHETIC_AIRSPEED_ASSIST) || plane.ahrs.using_airspeed_sensor());

    const uint32_t now_ms = AP_HAL::millis();
    const uint32_t tigger_delay_ms = delay * 1000;
    const uint32_t clear_delay_ms = tigger_delay_ms * 2;

    /*
      optional assistance when altitude is too close to the ground
     */
    if (alt <= 0) {
        // Alt assist disabled
        alt_error.reset();

    } else {
        const float height_above_ground = plane.relative_ground_altitude(RangeFinderUse::ASSIST);
        if (alt_error.update(height_above_ground < alt, now_ms, tigger_delay_ms, clear_delay_ms)) {
            gcs().send_text(MAV_SEVERITY_WARNING, "Alt assist %.1fm", height_above_ground);
        }
    }

    if (angle <= 0) {
        // Angle assist disabled
        angle_error.reset();

    } else {

        /*
        now check if we should provide assistance due to attitude error
        */
        const auto ahrs_roll_deg = plane.ahrs.get_roll_deg();
        const auto ahrs_pitch_deg = plane.ahrs.get_pitch_deg();
        constexpr float allowed_envelope_error_deg = 5.0;
        const bool inside_envelope =
            (fabsf(ahrs_roll_deg) <= (plane.aparm.roll_limit + allowed_envelope_error_deg)) &&
            (ahrs_pitch_deg < (plane.aparm.pitch_limit_max + allowed_envelope_error_deg)) &&
            (ahrs_pitch_deg > (plane.aparm.pitch_limit_min - allowed_envelope_error_deg));

        const bool inside_angle_error =
            (fabsf(ahrs_roll_deg - plane.nav_roll_cd*0.01) < angle) &&
            (fabsf(ahrs_pitch_deg - plane.nav_pitch_cd*0.01) < angle);

        if (angle_error.update(!inside_envelope && !inside_angle_error, now_ms, tigger_delay_ms, clear_delay_ms)) {
            gcs().send_text(MAV_SEVERITY_WARNING, "Angle assist r=%d p=%d",
                            (int)ahrs_roll_deg,
                            (int)ahrs_pitch_deg);
        }
    }

    return force_assist || speed_assist || alt_error.is_active() || angle_error.is_active();
}

/*
  check if we are in VTOL recovery
*/
bool VTOL_Assist::check_VTOL_recovery(void)
{
    const bool allow_fw_recovery =
        !option_is_set(OPTION::FW_FORCE_DISABLED) &&
        !quadplane.tailsitter.enabled() &&
        plane.control_mode != &plane.mode_qacro;
    if (!allow_fw_recovery) {
        quadplane.force_fw_control_recovery = false;
        quadplane.in_spin_recovery = false;
        return false;
    }

    // see if the attitude is outside twice the Q_A_ANGLE_MAX
    const auto &ahrs = plane.ahrs;
    const float angle_max_cd = quadplane.attitude_control->lean_angle_max_cd();
    const float abs_angle_cd = fabsf(Vector2f{float(ahrs.roll_sensor), float(ahrs.pitch_sensor)}.length());

    if (abs_angle_cd > 2*angle_max_cd) {
        // we are 2x the angle limits, trigger fw recovery
        quadplane.force_fw_control_recovery = true;
    }

    if (quadplane.force_fw_control_recovery) {
        // stop fixed wing recovery if inside Q_A_ANGLE_MAX
        if (abs_angle_cd <= angle_max_cd) {
            quadplane.force_fw_control_recovery = false;
            quadplane.attitude_control->reset_target_and_rate(false);

            if (ahrs.groundspeed() > quadplane.wp_nav->get_default_speed_NE_ms()) {
                /* if moving at high speed also reset position
                   controller and height controller

                   this avoids an issue where the position
                   controller may limit pitch after a strong
                   acceleration event
                */
                quadplane.pos_control->D_init_controller();
                quadplane.pos_control->NE_init_controller();
            }
        }
    }

    if (!option_is_set(OPTION::SPIN_DISABLED) &&
        quadplane.force_fw_control_recovery) {
        // additionally check for needing spin recovery
        const auto &gyro = plane.ahrs.get_gyro();
        quadplane.in_spin_recovery =
            fabsf(gyro.z) > radians(10) &&
            fabsf(gyro.x) > radians(30) &&
            fabsf(gyro.y) > radians(30) &&
            gyro.x * gyro.z < 0 &&
            plane.ahrs.get_pitch_deg() < -45;
    } else {
        quadplane.in_spin_recovery = false;
    }
    
    return quadplane.force_fw_control_recovery;
}


/* if we are in a spin then counter with rudder and elevator

   if roll rate and yaw rate are opposite and yaw rate is
   significant then put in full rudder to counter the yaw rate
   for spin recovery
*/
void VTOL_Assist::output_spin_recovery(void)
{
    if (!quadplane.in_spin_recovery) {
        return;
    }
    if (quadplane.motors->get_desired_spool_state() !=
        AP_Motors::DesiredSpoolState::THROTTLE_UNLIMITED) {
        // if we and no longer running the VTOL motors we need to
        // clear the spin flag
        quadplane.in_spin_recovery = false;
        return;
    }
    const Vector3f &gyro = plane.ahrs.get_gyro();

    // put in opposite rudder to counter yaw, and neutral
    // elevator until we're out of the spin
    SRV_Channels::set_output_scaled(SRV_Channel::k_rudder, gyro.z > 0 ? -SERVO_MAX : SERVO_MAX);
    SRV_Channels::set_output_scaled(SRV_Channel::k_elevator, 0);
}


#endif  // HAL_QUADPLANE_ENABLED