mc_att_control: move rate control to RateControl class

This makes the controller more modular, more readable and hence
better maintainable.

src/modules/mc_att_control/RateControl/RateControl.cpp

@@ -0,0 +1,155 @@
+/****************************************************************************
+ *
+ *   Copyright (c) 2019 PX4 Development Team. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ * 3. Neither the name PX4 nor the names of its contributors may be
+ *    used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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+ * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ *
+ ****************************************************************************/
+
+/**
+ * @file RateControl.cpp
+ */
+
+#include <RateControl.hpp>
+#include <px4_defines.h>
+
+using namespace matrix;
+
+void RateControl::setGains(const Vector3f &P, const Vector3f &I, const Vector3f &D)
+{
+	_gain_p = P;
+	_gain_i = I;
+	_gain_d = D;
+}
+
+void RateControl::setDTermCutoff(const float loop_rate, const float cutoff, const bool force)
+{
+	// only do expensive filter update if the cutoff changed
+	if (force || fabsf(_lp_filters_d.get_cutoff_freq() - cutoff) > 0.01f) {
+		_lp_filters_d.set_cutoff_frequency(loop_rate, cutoff);
+		_lp_filters_d.reset(_rate_prev);
+	}
+}
+
+void RateControl::setTPA(const Vector3f &breakpoint, const Vector3f &rate)
+{
+	_tpa_breakpoint = breakpoint;
+	_tpa_rate = rate;
+}
+
+void RateControl::setSaturationStatus(const MultirotorMixer::saturation_status &status)
+{
+	_mixer_saturation_positive[0] = status.flags.roll_pos;
+	_mixer_saturation_positive[1] = status.flags.pitch_pos;
+	_mixer_saturation_positive[2] = status.flags.yaw_pos;
+	_mixer_saturation_negative[0] = status.flags.roll_neg;
+	_mixer_saturation_negative[1] = status.flags.pitch_neg;
+	_mixer_saturation_negative[2] = status.flags.yaw_neg;
+}
+
+Vector3f RateControl::update(const Vector3f rate, const Vector3f rate_sp, const float dt, const bool landed,
+			     const float thrust_sp)
+{
+	Vector3f gain_p_tpa = _gain_p.emult(tpa_attenuations(_tpa_breakpoint(0), _tpa_rate(0), thrust_sp));
+	Vector3f gain_i_tpa = _gain_i.emult(tpa_attenuations(_tpa_breakpoint(1), _tpa_rate(1), thrust_sp));
+	Vector3f gain_d_tpa = _gain_d.emult(tpa_attenuations(_tpa_breakpoint(2), _tpa_rate(2), thrust_sp));
+
+	// angular rates error
+	Vector3f rate_error = rate_sp - rate;
+
+	// prepare D-term based on low-pass filtered rates
+	Vector3f rate_filtered(_lp_filters_d.apply(rate));
+	Vector3f rate_d;
+
+	if (dt > FLT_EPSILON) {
+		rate_d = (rate_filtered - _rate_prev_filtered) / dt;
+	}
+
+	// PID control with feed forward
+	Vector3f torque = gain_p_tpa.emult(rate_error) + _rate_int - gain_d_tpa.emult(rate_d) + _gain_ff.emult(rate_sp);
+
+	_rate_prev = rate;
+	_rate_prev_filtered = rate_filtered;
+
+	// update integral only if we are not landed
+	if (!landed) {
+		updateIntegral(rate_error, dt, gain_i_tpa);
+	}
+
+	return torque;
+}
+
+void RateControl::updateIntegral(Vector3f &rate_error, const float dt, const Vector3f &gain_i_tpa)
+{
+	for (int i = 0; i < 3; i++) {
+		// prevent further positive control saturation
+		if (_mixer_saturation_positive[i]) {
+			rate_error(i) = math::min(rate_error(i), 0.f);
+		}
+
+		// prevent further negative control saturation
+		if (_mixer_saturation_negative[i]) {
+			rate_error(i) = math::max(rate_error(i), 0.f);
+		}
+
+		// I term factor: reduce the I gain with increasing rate error.
+		// This counteracts a non-linear effect where the integral builds up quickly upon a large setpoint
+		// change (noticeable in a bounce-back effect after a flip).
+		// The formula leads to a gradual decrease w/o steps, while only affecting the cases where it should:
+		// with the parameter set to 400 degrees, up to 100 deg rate error, i_factor is almost 1 (having no effect),
+		// and up to 200 deg error leads to <25% reduction of I.
+		float i_factor = rate_error(i) / math::radians(400.f);
+		i_factor = math::max(0.0f, 1.f - i_factor * i_factor);
+
+		// Perform the integration using a first order method
+		float rate_i = _rate_int(i) + i_factor * gain_i_tpa(i) * rate_error(i) * dt;
+
+		// do not propagate the result if out of range or invalid
+		if (PX4_ISFINITE(rate_i)) {
+			_rate_int(i) = math::constrain(rate_i, -_lim_int(i), _lim_int(i));
+		}
+	}
+}
+
+void RateControl::getRateControlStatus(rate_ctrl_status_s &rate_ctrl_status)
+{
+	rate_ctrl_status.rollspeed_integ = _rate_int(0);
+	rate_ctrl_status.pitchspeed_integ = _rate_int(1);
+	rate_ctrl_status.yawspeed_integ = _rate_int(2);
+}
+
+Vector3f RateControl::tpa_attenuations(float tpa_breakpoint, float tpa_rate, float thrust_sp)
+{
+	static constexpr float tpa_rate_lower_limit = 0.05f;
+
+	/* throttle pid attenuation factor */
+	float tpa = 1.0f - tpa_rate * (fabsf(thrust_sp) - tpa_breakpoint) / (1.0f - tpa_breakpoint);
+	tpa = fmaxf(tpa_rate_lower_limit, fminf(1.0f, tpa));
+
+	return Vector3f(tpa, tpa, 1.f);
+}