ecl_wheel_controller.cpp

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/**
 * @file ecl_wheel_controller.cpp
 * Implementation of a simple PID wheel controller for heading tracking.
 *
 * Authors and acknowledgements in header.
 */

#include "ecl_wheel_controller.h"
#include <float.h>
#include <geo/geo.h>
#include <mathlib/mathlib.h>
#include <matrix/math.hpp>

using matrix::wrap_pi;

float ECL_WheelController::control_bodyrate(const struct ECL_ControlData &ctl_data)
{
    /* Do not calculate control signal with bad inputs */
    if (!(ISFINITE(ctl_data.body_z_rate) &&
          ISFINITE(ctl_data.groundspeed) &&
          ISFINITE(ctl_data.groundspeed_scaler))) {
        return math::constrain(_last_output, -1.0f, 1.0f);
    }

    /* get the usual dt estimate */
    uint64_t dt_micros = ecl_elapsed_time(&_last_run);
    _last_run = ecl_absolute_time();
    float dt = (float)dt_micros * 1e-6f;

    /* lock integral for long intervals */
    bool lock_integrator = ctl_data.lock_integrator;

    if (dt_micros > 500000) {
        lock_integrator = true;
    }

    /* input conditioning */
    float min_speed = 1.0f;

    /* Calculate body angular rate error */
    _rate_error = _rate_setpoint - ctl_data.body_z_rate; //body angular rate error

    if (!lock_integrator && _k_i > 0.0f && ctl_data.groundspeed > min_speed) {

        float id = _rate_error * dt * ctl_data.groundspeed_scaler;

        /*
         * anti-windup: do not allow integrator to increase if actuator is at limit
         */
        if (_last_output < -1.0f) {
            /* only allow motion to center: increase value */
            id = math::max(id, 0.0f);

        } else if (_last_output > 1.0f) {
            /* only allow motion to center: decrease value */
            id = math::min(id, 0.0f);
        }

        /* add and constrain */
        _integrator = math::constrain(_integrator + id * _k_i, -_integrator_max, _integrator_max);
    }

    /* Apply PI rate controller and store non-limited output */
    _last_output = _rate_setpoint * _k_ff * ctl_data.groundspeed_scaler +
               ctl_data.groundspeed_scaler * ctl_data.groundspeed_scaler * (_rate_error * _k_p + _integrator);

    return math::constrain(_last_output, -1.0f, 1.0f);
}


float ECL_WheelController::control_attitude(const struct ECL_ControlData &ctl_data)
{
    /* Do not calculate control signal with bad inputs */
    if (!(ISFINITE(ctl_data.yaw_setpoint) &&
          ISFINITE(ctl_data.yaw))) {
        return _rate_setpoint;
    }

    /* Calculate the error */
    float yaw_error = wrap_pi(ctl_data.yaw_setpoint - ctl_data.yaw);

    /*  Apply P controller: rate setpoint from current error and time constant */
    _rate_setpoint =  yaw_error / _tc;

    /* limit the rate */
    if (_max_rate > 0.01f) {
        if (_rate_setpoint > 0.0f) {
            _rate_setpoint = (_rate_setpoint > _max_rate) ? _max_rate : _rate_setpoint;

        } else {
            _rate_setpoint = (_rate_setpoint < -_max_rate) ? -_max_rate : _rate_setpoint;
        }

    }

    return _rate_setpoint;
}