ardupilot/ArduCopter/Attitude.cpp

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

#include "Copter.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 Copter::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 Copter::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 Copter::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
float Copter::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 Copter::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
 ****************************************************************/

// update estimated throttle required to hover (if necessary)
//  called at 100hz
void Copter::update_throttle_hover()
{
#if FRAME_CONFIG != HELI_FRAME
    // if not armed or landed exit
    if (!motors.armed() || ap.land_complete) {
        return;
    }

    // do not update in manual throttle modes or Drift
    if (mode_has_manual_throttle(control_mode) || (control_mode == DRIFT)) {
        return;
    }

    // do not update while climbing or descending
    if (!is_zero(pos_control.get_desired_velocity().z)) {
        return;
    }

    // get throttle output
    float throttle = motors.get_throttle();

    // calc average throttle if we are in a level hover
    if (throttle > 0.0f && abs(climb_rate) < 60 && labs(ahrs.roll_sensor) < 500 && labs(ahrs.pitch_sensor) < 500) {
        // Can we set the time constant automatically
        motors.update_throttle_hover(0.01f);
    }
#endif
}

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

// transform pilot's manual throttle input to make hover throttle mid stick
// used only for manual throttle modes
// thr_mid should be in the range 0 to 1
// returns throttle output 0 to 1
float Copter::get_pilot_desired_throttle(int16_t throttle_control, float thr_mid)
{
    if (thr_mid <= 0.0f) {
        thr_mid = motors.get_throttle_hover();
    }

    int16_t mid_stick = channel_throttle->get_control_mid();
    // protect against unlikely divide by zero
    if (mid_stick <= 0) {
        mid_stick = 500;
    }

    // ensure reasonable throttle values
    throttle_control = constrain_int16(throttle_control,0,1000);

    // calculate normalised throttle input
    float throttle_in;
    if (throttle_control < mid_stick) {
        // below the deadband
        throttle_in = ((float)throttle_control)*0.5f/(float)mid_stick;
    }else if(throttle_control > mid_stick) {
        // above the deadband
        throttle_in = 0.5f + ((float)(throttle_control-mid_stick)) * 0.5f / (float)(1000-mid_stick);
    }else{
        // must be in the deadband
        throttle_in = 0.5f;
    }

    float expo = constrain_float(-(thr_mid-0.5)/0.375, -0.5f, 1.0f);
    // calculate the output throttle using the given expo function
    float throttle_out = throttle_in*(1.0f-expo) + expo*throttle_in*throttle_in*throttle_in;
    return throttle_out;
}

// get_pilot_desired_climb_rate - transform pilot's throttle input to climb rate in cm/s
// without any deadzone at the bottom
float Copter::get_pilot_desired_climb_rate(float throttle_control)
{
    // throttle failsafe check
    if( failsafe.radio ) {
        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_non_takeoff_throttle - a throttle somewhere between min and mid throttle which should not lead to a takeoff
float Copter::get_non_takeoff_throttle()
{
    return MAX(0,motors.get_throttle_hover()/2.0f);
}

// get_surface_tracking_climb_rate - hold copter at the desired distance above the ground
//      returns climb rate (in cm/s) which should be passed to the position controller
float Copter::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
}

// set_accel_throttle_I_from_pilot_throttle - smoothes transition from pilot controlled throttle to autopilot throttle
void Copter::set_accel_throttle_I_from_pilot_throttle()
{
    // get last throttle input sent to attitude controller
    float pilot_throttle = constrain_float(attitude_control.get_throttle_in(), 0.0f, 1.0f);
    // shift difference between pilot's throttle and hover throttle into accelerometer I
    g.pid_accel_z.set_integrator((pilot_throttle-motors.get_throttle_hover()) * 1000.0f);
}

// updates position controller's maximum altitude using fence and EKF limits
void Copter::update_poscon_alt_max()
{
    float alt_limit_cm = 0.0f;  // interpreted as no limit if left as zero

#if AC_FENCE == ENABLED
    // set fence altitude limit in position controller
    if ((fence.get_enabled_fences() & AC_FENCE_TYPE_ALT_MAX) != 0) {
        alt_limit_cm = pv_alt_above_origin(fence.get_safe_alt()*100.0f);
    }
#endif

    // get alt limit from EKF (limited during optical flow flight)
    float ekf_limit_cm = 0.0f;
    if (inertial_nav.get_hgt_ctrl_limit(ekf_limit_cm)) {
        if ((alt_limit_cm <= 0.0f) || (ekf_limit_cm < alt_limit_cm)) {
            alt_limit_cm = ekf_limit_cm;
        }
    }

    // pass limit to pos controller
    pos_control.set_alt_max(alt_limit_cm);
}

// rotate vector from vehicle's perspective to North-East frame
void Copter::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;
}