ardupilot/ArduCopter/Attitude.pde

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-

// get_smoothing_gain - returns smoothing gain to be passed into attitude_control.angle_ef_roll_pitch_rate_ef_yaw_smooth
//      result is a number from 2 to 12 with 2 being very sluggish and 12 being very crisp
float 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
static void get_pilot_desired_lean_angles(float roll_in, float pitch_in, float &roll_out, float &pitch_out)
{
    float angle_max = constrain_float(aparm.angle_max,1000,8000);
    float scaler = (float)angle_max/(float)ROLL_PITCH_INPUT_MAX;

    // scale roll_in, pitch_in to correct units
    roll_in *= scaler;
    pitch_in *= scaler;

    // do circular limit
    float total_in = pythagorous2((float)pitch_in, (float)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_F) * atanf(cosf(pitch_in*(M_PI_F/18000))*tanf(roll_in*(M_PI_F/18000)));

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

// get_pilot_desired_heading - transform pilot's yaw input into a desired heading
// returns desired angle in centi-degrees
// To-Do: return heading as a float?
static float get_pilot_desired_yaw_rate(int16_t stick_angle)
{
    // convert pilot input to the desired yaw rate
    return stick_angle * g.acro_yaw_p;
}

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

// get_roi_yaw - returns heading towards location held in roi_WP
// should be called at 100hz
static float 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;
}

static float get_look_ahead_yaw()
{
    // Commanded Yaw to automatically look ahead.
    if (gps.status() >= AP_GPS::GPS_OK_FIX_2D && gps.ground_speed_cm() > YAW_LOOK_AHEAD_MIN_SPEED) {
        yaw_look_ahead_bearing = gps.ground_course_cd();
    }
    return yaw_look_ahead_bearing;
}

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

// update_thr_average - update estimated throttle required to hover (if necessary)
//  should be called at 100hz
static void update_thr_average()
{
    // ensure throttle_average has been initialised
    if( throttle_average == 0 ) {
        throttle_average = g.throttle_mid;
        // update position controller
        pos_control.set_throttle_hover(throttle_average);
    }

    // if not armed or landed exit
    if (!motors.armed() || ap.land_complete) {
        return;
    }

    // get throttle output
    int16_t throttle = g.rc_3.servo_out;

    // calc average throttle if we are in a level hover
    if (throttle > g.throttle_min && abs(climb_rate) < 60 && labs(ahrs.roll_sensor) < 500 && labs(ahrs.pitch_sensor) < 500) {
        throttle_average = throttle_average * 0.99f + (float)throttle * 0.01f;
        // update position controller
        pos_control.set_throttle_hover(throttle_average);
    }
}

// set_throttle_takeoff - allows parents to tell throttle controller we are taking off so I terms can be cleared
static void
set_throttle_takeoff()
{
    // tell position controller to reset alt target and reset I terms
    pos_control.init_takeoff();

    // tell motors to do a slow start
    motors.slow_start(true);
}

// get_pilot_desired_throttle - transform pilot's throttle input to make cruise throttle mid stick
// used only for manual throttle modes
// returns throttle output 0 to 1000
static int16_t get_pilot_desired_throttle(int16_t throttle_control)
{
    int16_t throttle_out;

    int16_t mid_stick = g.rc_3.get_control_mid();

    // ensure reasonable throttle values
    throttle_control = constrain_int16(throttle_control,0,1000);
    g.throttle_mid = constrain_int16(g.throttle_mid,300,700);

    // check throttle is above, below or in the deadband
    if (throttle_control < mid_stick) {
        // below the deadband
        throttle_out = g.throttle_min + ((float)(throttle_control-g.throttle_min))*((float)(g.throttle_mid - g.throttle_min))/((float)(mid_stick-g.throttle_min));
    }else if(throttle_control > mid_stick) {
        // above the deadband
        throttle_out = g.throttle_mid + ((float)(throttle_control-mid_stick)) * (float)(1000-g.throttle_mid) / (float)(1000-mid_stick);
    }else{
        // must be in the deadband
        throttle_out = g.throttle_mid;
    }

    return throttle_out;
}

// get_pilot_desired_climb_rate - transform pilot's throttle input to
// climb rate in cm/s.  we use radio_in instead of control_in to get the full range
// without any deadzone at the bottom
static int16_t get_pilot_desired_climb_rate(int16_t throttle_control)
{
    int16_t desired_rate = 0;

    // throttle failsafe check
    if( failsafe.radio ) {
        return 0;
    }

    int16_t mid_stick = g.rc_3.get_control_mid();
    int16_t deadband_top = mid_stick + g.throttle_deadzone;
    int16_t deadband_bottom = mid_stick - g.throttle_deadzone;

    // ensure a reasonable throttle value
    throttle_control = constrain_int16(throttle_control,g.throttle_min,1000);

    // 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 = (int32_t)g.pilot_velocity_z_max * (throttle_control-deadband_bottom) / (deadband_bottom-g.throttle_min);
    }else if (throttle_control > deadband_top) {
        // above the deadband
        desired_rate = (int32_t)g.pilot_velocity_z_max * (throttle_control-deadband_top) / (1000-deadband_top);
    }else{
        // must be in the deadband
        desired_rate = 0;
    }

    // desired climb rate for logging
    desired_climb_rate = desired_rate;

    return desired_rate;
}

// get_non_takeoff_throttle - a throttle somewhere between min and mid throttle which should not lead to a takeoff
static int16_t get_non_takeoff_throttle()
{
    return (g.throttle_mid / 2.0f);
}

// get_throttle_pre_takeoff - convert pilot's input throttle to a throttle output before take-off
// used only for althold, loiter, hybrid flight modes
// returns throttle output 0 to 1000
static int16_t get_throttle_pre_takeoff(int16_t throttle_control)
{
    int16_t throttle_out;

    // exit immediately if throttle_control is zero
    if (throttle_control <= 0) {
        return 0;
    }

    // calculate mid stick and deadband
    int16_t mid_stick = g.rc_3.get_control_mid();
    int16_t deadband_top = mid_stick + g.throttle_deadzone;

    // sanity check throttle input
    throttle_control = constrain_int16(throttle_control,0,1000);

    // sanity check throttle_mid
    g.throttle_mid = constrain_int16(g.throttle_mid,300,700);

    // sanity check throttle_min vs throttle_mid
    if (g.throttle_min > get_non_takeoff_throttle()) {
        return g.throttle_min;
    }

    // check throttle is below top of deadband
    if (throttle_control < deadband_top) {
        throttle_out = g.throttle_min + ((float)(throttle_control-g.throttle_min))*((float)(get_non_takeoff_throttle() - g.throttle_min))/((float)(deadband_top-g.throttle_min));
    }else{
        // must be in the deadband
        throttle_out = get_non_takeoff_throttle();
    }

    return throttle_out;
}

// get_throttle_surface_tracking - hold copter at the desired distance above the ground
//      returns climb rate (in cm/s) which should be passed to the position controller
static float get_throttle_surface_tracking(int16_t target_rate, float current_alt_target, float dt)
{
    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 > SONAR_TIMEOUT_MS) {
        target_sonar_alt = sonar_alt + current_alt_target - current_alt;
    }
    last_call_ms = now;

    // adjust sonar 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_sonar_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_sonar_alt = constrain_float(target_sonar_alt,sonar_alt-pos_control.get_leash_down_z(),sonar_alt+pos_control.get_leash_up_z());

    // calc desired velocity correction from target sonar alt vs actual sonar alt (remove the error already passed to Altitude controller to avoid oscillations)
    distance_error = (target_sonar_alt - sonar_alt) - (current_alt_target - current_alt);
    velocity_correction = distance_error * g.sonar_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 sonar alt error
    return (target_rate + velocity_correction);
}

// set_accel_throttle_I_from_pilot_throttle - smoothes transition from pilot controlled throttle to autopilot throttle
static void set_accel_throttle_I_from_pilot_throttle(int16_t pilot_throttle)
{
    // shift difference between pilot's throttle and hover throttle into accelerometer I
    g.pid_accel_z.set_integrator(pilot_throttle-throttle_average);
}