ardupilot/ArduSub/control_poshold.cpp

// ArduSub position hold flight mode
// GPS required
// Jacob Walser August 2016

#include "Sub.h"

#if POSHOLD_ENABLED == ENABLED

// poshold_init - initialise PosHold controller
bool Sub::poshold_init()
{
    // fail to initialise PosHold mode if no GPS lock
    if (!position_ok()) {
        return false;
    }
    pos_control.init_vel_controller_xyz();
    pos_control.set_desired_velocity_xy(0, 0);
    pos_control.set_target_to_stopping_point_xy();

    // initialize vertical speeds and acceleration
    pos_control.set_max_speed_z(-get_pilot_speed_dn(), g.pilot_speed_up);
    pos_control.set_max_accel_z(g.pilot_accel_z);

    // initialise position and desired velocity
    pos_control.set_alt_target(inertial_nav.get_altitude());
    pos_control.set_desired_velocity_z(inertial_nav.get_velocity_z());

    // Stop all thrusters
    attitude_control.set_throttle_out(0.5f ,true, g.throttle_filt);
    attitude_control.relax_attitude_controllers();
    pos_control.relax_alt_hold_controllers();

    last_pilot_heading = ahrs.yaw_sensor;

    return true;
}

// poshold_run - runs the PosHold controller
// should be called at 100hz or more
void Sub::poshold_run()
{
    uint32_t tnow = AP_HAL::millis();
    // When unarmed, disable motors and stabilization
    if (!motors.armed()) {
        motors.set_desired_spool_state(AP_Motors::DesiredSpoolState::GROUND_IDLE);
        // Sub vehicles do not stabilize roll/pitch/yaw when not auto-armed (i.e. on the ground, pilot has never raised throttle)
        attitude_control.set_throttle_out(0.5f ,true, g.throttle_filt);
        attitude_control.relax_attitude_controllers();
        pos_control.set_target_to_stopping_point_xy();
        pos_control.relax_alt_hold_controllers();
        last_pilot_heading = ahrs.yaw_sensor;
        return;
    }

    // set motors to full range
    motors.set_desired_spool_state(AP_Motors::DesiredSpoolState::THROTTLE_UNLIMITED);

    ///////////////////////
    // update xy outputs //
    float pilot_lateral = channel_lateral->norm_input();
    float pilot_forward = channel_forward->norm_input();

    float lateral_out = 0;
    float forward_out = 0;

    pos_control.set_desired_velocity_xy(0,0);

    if (position_ok()) {
        // Allow pilot to reposition the sub
        if (fabsf(pilot_lateral) > 0.1 || fabsf(pilot_forward) > 0.1) {
            pos_control.set_target_to_stopping_point_xy();
        }
        translate_pos_control_rp(lateral_out, forward_out);
        pos_control.update_xy_controller();
    } else {
        pos_control.init_vel_controller_xyz();
        pos_control.set_desired_velocity_xy(0, 0);
        pos_control.set_target_to_stopping_point_xy();
    }
    motors.set_forward(forward_out + pilot_forward);
    motors.set_lateral(lateral_out + pilot_lateral);
    /////////////////////
    // Update attitude //

    // get pilot's desired yaw rate
    float target_yaw_rate = get_pilot_desired_yaw_rate(channel_yaw->get_control_in());

    // convert pilot input to lean angles
    // To-Do: convert get_pilot_desired_lean_angles to return angles as floats
    float target_roll, target_pitch;
    get_pilot_desired_lean_angles(channel_roll->get_control_in(), channel_pitch->get_control_in(), target_roll, target_pitch, aparm.angle_max);

    // update attitude controller targets
    if (!is_zero(target_yaw_rate)) { // call attitude controller with rate yaw determined by pilot input
        attitude_control.input_euler_angle_roll_pitch_euler_rate_yaw(target_roll, target_pitch, target_yaw_rate);
        last_pilot_heading = ahrs.yaw_sensor;
        last_pilot_yaw_input_ms = tnow; // time when pilot last changed heading

    } else { // hold current heading

        // this check is required to prevent bounce back after very fast yaw maneuvers
        // the inertia of the vehicle causes the heading to move slightly past the point when pilot input actually stopped
        if (tnow < last_pilot_yaw_input_ms + 250) { // give 250ms to slow down, then set target heading
            target_yaw_rate = 0; // Stop rotation on yaw axis

            // call attitude controller with target yaw rate = 0 to decelerate on yaw axis
            attitude_control.input_euler_angle_roll_pitch_euler_rate_yaw(target_roll, target_pitch, target_yaw_rate);
            last_pilot_heading = ahrs.yaw_sensor; // update heading to hold

        } else { // call attitude controller holding absolute absolute bearing
            attitude_control.input_euler_angle_roll_pitch_yaw(target_roll, target_pitch, last_pilot_heading, true);
        }
    }

    // Update z axis //
    control_depth();
}
#endif  // POSHOLD_ENABLED == ENABLED