ardupilot/ArduSub/Attitude.cpp

#include "Sub.h"

// get_smoothing_gain - returns smoothing gain to be passed into attitude_control.input_euler_angle_roll_pitch_euler_rate_yaw
//      result is a number from 2 to 12 with 2 being very sluggish and 12 being very crisp
float Sub::get_smoothing_gain()
{
    return (2.0f + (float)g.rc_feel_rp/10.0f);
}

// get_pilot_desired_angle - transform pilot's roll or pitch input into a desired lean angle
// returns desired angle in centi-degrees
void Sub::get_pilot_desired_lean_angles(float roll_in, float pitch_in, float &roll_out, float &pitch_out, float angle_max)
{
    // sanity check angle max parameter
    aparm.angle_max = constrain_int16(aparm.angle_max,1000,8000);

    // limit max lean angle
    angle_max = constrain_float(angle_max, 1000, aparm.angle_max);

    // scale roll_in, pitch_in to ANGLE_MAX parameter range
    float scaler = aparm.angle_max/(float)ROLL_PITCH_INPUT_MAX;
    roll_in *= scaler;
    pitch_in *= scaler;

    // do circular limit
    float total_in = norm(pitch_in, roll_in);
    if (total_in > angle_max) {
        float ratio = angle_max / total_in;
        roll_in *= ratio;
        pitch_in *= ratio;
    }

    // do lateral tilt to euler roll conversion
    roll_in = (18000/M_PI) * atanf(cosf(pitch_in*(M_PI/18000))*tanf(roll_in*(M_PI/18000)));

    // return
    roll_out = roll_in;
    pitch_out = pitch_in;
}

// get_pilot_desired_heading - transform pilot's yaw input into a
// desired yaw rate
// returns desired yaw rate in centi-degrees per second
float Sub::get_pilot_desired_yaw_rate(int16_t stick_angle)
{
    // convert pilot input to the desired yaw rate
    return stick_angle * g.acro_yaw_p;
}

// check for ekf yaw reset and adjust target heading
void Sub::check_ekf_yaw_reset()
{
    float yaw_angle_change_rad = 0.0f;
    uint32_t new_ekfYawReset_ms = ahrs.getLastYawResetAngle(yaw_angle_change_rad);
    if (new_ekfYawReset_ms != ekfYawReset_ms) {
        attitude_control.shift_ef_yaw_target(ToDeg(yaw_angle_change_rad) * 100.0f);
        ekfYawReset_ms = new_ekfYawReset_ms;
    }
}

/*************************************************************
 * yaw controllers
 *************************************************************/

// get_roi_yaw - returns heading towards location held in roi_WP
// should be called at 100hz
float Sub::get_roi_yaw()
{
    static uint8_t roi_yaw_counter = 0;     // used to reduce update rate to 100hz

    roi_yaw_counter++;
    if (roi_yaw_counter >= 4) {
        roi_yaw_counter = 0;
        yaw_look_at_WP_bearing = pv_get_bearing_cd(inertial_nav.get_position(), roi_WP);
    }

    return yaw_look_at_WP_bearing;
}

float Sub::get_look_ahead_yaw()
{
    const Vector3f& vel = inertial_nav.get_velocity();
    float speed = norm(vel.x,vel.y);
    // Commanded Yaw to automatically look ahead.
    if (position_ok() && (speed > YAW_LOOK_AHEAD_MIN_SPEED)) {
        yaw_look_ahead_bearing = degrees(atan2f(vel.y,vel.x))*100.0f;
    }
    return yaw_look_ahead_bearing;
}

/*************************************************************
 *  throttle control
 ****************************************************************/

// get_pilot_desired_climb_rate - transform pilot's throttle input to climb rate in cm/s
// without any deadzone at the bottom
float Sub::get_pilot_desired_climb_rate(float throttle_control)
{
    // throttle failsafe check
    if (failsafe.pilot_input) {
        return 0.0f;
    }

    float desired_rate = 0.0f;
    float mid_stick = channel_throttle->get_control_mid();
    float deadband_top = mid_stick + g.throttle_deadzone;
    float deadband_bottom = mid_stick - g.throttle_deadzone;

    // ensure a reasonable throttle value
    throttle_control = constrain_float(throttle_control,0.0f,1000.0f);

    // ensure a reasonable deadzone
    g.throttle_deadzone = constrain_int16(g.throttle_deadzone, 0, 400);

    // check throttle is above, below or in the deadband
    if (throttle_control < deadband_bottom) {
        // below the deadband
        desired_rate = g.pilot_velocity_z_max * (throttle_control-deadband_bottom) / deadband_bottom;
    } else if (throttle_control > deadband_top) {
        // above the deadband
        desired_rate = g.pilot_velocity_z_max * (throttle_control-deadband_top) / (1000.0f-deadband_top);
    } else {
        // must be in the deadband
        desired_rate = 0.0f;
    }

    // desired climb rate for logging
    desired_climb_rate = desired_rate;

    return desired_rate;
}

// get_surface_tracking_climb_rate - hold vehicle at the desired distance above the ground
//      returns climb rate (in cm/s) which should be passed to the position controller
float Sub::get_surface_tracking_climb_rate(int16_t target_rate, float current_alt_target, float dt)
{
#if RANGEFINDER_ENABLED == ENABLED
    static uint32_t last_call_ms = 0;
    float distance_error;
    float velocity_correction;
    float current_alt = inertial_nav.get_altitude();

    uint32_t now = millis();

    // reset target altitude if this controller has just been engaged
    if (now - last_call_ms > RANGEFINDER_TIMEOUT_MS) {
        target_rangefinder_alt = rangefinder_state.alt_cm + current_alt_target - current_alt;
    }
    last_call_ms = now;

    // adjust rangefinder target alt if motors have not hit their limits
    if ((target_rate<0 && !motors.limit.throttle_lower) || (target_rate>0 && !motors.limit.throttle_upper)) {
        target_rangefinder_alt += target_rate * dt;
    }

    // do not let target altitude get too far from current altitude above ground
    // Note: the 750cm limit is perhaps too wide but is consistent with the regular althold limits and helps ensure a smooth transition
    target_rangefinder_alt = constrain_float(target_rangefinder_alt,rangefinder_state.alt_cm-pos_control.get_leash_down_z(),rangefinder_state.alt_cm+pos_control.get_leash_up_z());

    // calc desired velocity correction from target rangefinder alt vs actual rangefinder alt (remove the error already passed to Altitude controller to avoid oscillations)
    distance_error = (target_rangefinder_alt - rangefinder_state.alt_cm) - (current_alt_target - current_alt);
    velocity_correction = distance_error * g.rangefinder_gain;
    velocity_correction = constrain_float(velocity_correction, -THR_SURFACE_TRACKING_VELZ_MAX, THR_SURFACE_TRACKING_VELZ_MAX);

    // return combined pilot climb rate + rate to correct rangefinder alt error
    return (target_rate + velocity_correction);
#else
    return (float)target_rate;
#endif
}

// updates position controller's maximum altitude using fence and EKF limits
void Sub::update_poscon_alt_max()
{
    // minimum altitude, ie. maximum depth
    // interpreted as no limit if left as zero
    float min_alt_cm = 0.0;

    // no limit if greater than 100, a limit is necessary,
    // or the vehicle will try to fly out of the water
    float max_alt_cm = g.surface_depth; // minimum depth

#if AC_FENCE == ENABLED
    // set fence altitude limit in position controller
    if ((fence.get_enabled_fences() & AC_FENCE_TYPE_ALT_MAX) != 0) {
        min_alt_cm = fence.get_safe_alt_min()*100.0f;
        max_alt_cm = fence.get_safe_alt_max()*100.0f;
    }
#endif
    // pass limit to pos controller
    pos_control.set_alt_min(min_alt_cm);
    pos_control.set_alt_max(max_alt_cm);
}

// rotate vector from vehicle's perspective to North-East frame
void Sub::rotate_body_frame_to_NE(float &x, float &y)
{
    float ne_x = x*ahrs.cos_yaw() - y*ahrs.sin_yaw();
    float ne_y = x*ahrs.sin_yaw() + y*ahrs.cos_yaw();
    x = ne_x;
    y = ne_y;
}