tailsitter.cpp

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/**
* @file tailsitter.cpp
*
* @author Roman Bapst 		<bapstroman@gmail.com>
* @author David Vorsin     <davidvorsin@gmail.com>
*
*/

#include "tailsitter.h"
#include "vtol_att_control_main.h"

using namespace matrix;

Tailsitter::Tailsitter(VtolAttitudeControl *attc) :
	VtolType(attc)
{
}

void
Tailsitter::parameters_update()
{
	VtolType::updateParams();

}

void Tailsitter::update_vtol_state()
{
	/* simple logic using a two way switch to perform transitions.
	 * after flipping the switch the vehicle will start tilting in MC control mode, picking up
	 * forward speed. After the vehicle has picked up enough and sufficient pitch angle the uav will go into FW mode.
	 * For the backtransition the pitch is controlled in MC mode again and switches to full MC control reaching the sufficient pitch angle.
	*/


	if (_vtol_vehicle_status->fixed_wing_system_failure) {
		// Failsafe event, switch to MC mode immediately
		if (_vtol_mode != vtol_mode::MC_MODE) {
			_transition_start_timestamp = hrt_absolute_time();
		}

		_vtol_mode = vtol_mode::MC_MODE;

	} else if (!_attc->is_fixed_wing_requested()) {

		switch (_vtol_mode) { // user switchig to MC mode
		case vtol_mode::MC_MODE:
			break;

		case vtol_mode::FW_MODE:
			resetTransitionStates();
			_vtol_mode = vtol_mode::TRANSITION_BACK;
			break;

		case vtol_mode::TRANSITION_FRONT_P1:
			// failsafe into multicopter mode
			_vtol_mode = vtol_mode::MC_MODE;
			break;

		case vtol_mode::TRANSITION_BACK:
			const float pitch = Eulerf(Quatf(_v_att->q)).theta();

			// check if we have reached pitch angle to switch to MC mode
			if (pitch >= PITCH_THRESHOLD_AUTO_TRANSITION_TO_MC || _time_since_trans_start > _param_vt_b_trans_dur.get()) {
				_vtol_mode = vtol_mode::MC_MODE;
			}

			break;
		}

	} else {  // user switchig to FW mode

		switch (_vtol_mode) {
		case vtol_mode::MC_MODE:
			// initialise a front transition
			_vtol_mode = vtol_mode::TRANSITION_FRONT_P1;
			resetTransitionStates();
			break;

		case vtol_mode::FW_MODE:
			break;

		case vtol_mode::TRANSITION_FRONT_P1: {

				if (isFrontTransitionCompleted()) {
					_vtol_mode = vtol_mode::FW_MODE;
					_trans_finished_ts = hrt_absolute_time();
				}

				break;
			}

		case vtol_mode::TRANSITION_BACK:
			// failsafe into fixed wing mode
			_vtol_mode = vtol_mode::FW_MODE;
			_trans_finished_ts = hrt_absolute_time();
			break;
		}
	}

	// map tailsitter specific control phases to simple control modes
	switch (_vtol_mode) {
	case vtol_mode::MC_MODE:
		_common_vtol_mode = mode::ROTARY_WING;
		_flag_was_in_trans_mode = false;
		break;

	case vtol_mode::FW_MODE:
		_common_vtol_mode = mode::FIXED_WING;
		_flag_was_in_trans_mode = false;
		break;

	case vtol_mode::TRANSITION_FRONT_P1:
		_common_vtol_mode = mode::TRANSITION_TO_FW;
		break;

	case vtol_mode::TRANSITION_BACK:
		_common_vtol_mode = mode::TRANSITION_TO_MC;
		break;
	}
}

void Tailsitter::update_transition_state()
{
	VtolType::update_transition_state();

	const hrt_abstime now = hrt_absolute_time();

	// we need the incoming (virtual) mc attitude setpoints to be recent, otherwise return (means the previous setpoint stays active)
	if (_mc_virtual_att_sp->timestamp < (now - 1_s)) {
		return;
	}

	if (!_flag_was_in_trans_mode) {
		_flag_was_in_trans_mode = true;

		if (_vtol_mode == vtol_mode::TRANSITION_BACK) {
			// calculate rotation axis for transition.
			_q_trans_start = Quatf(_v_att->q);
			Vector3f z = -_q_trans_start.dcm_z();
			_trans_rot_axis = z.cross(Vector3f(0.f, 0.f, -1.f));

			// as heading setpoint we choose the heading given by the direction the vehicle points
			const float yaw_sp = atan2f(z(1), z(0));

			// the intial attitude setpoint for a backtransition is a combination of the current fw pitch setpoint,
			// the yaw setpoint and zero roll since we want wings level transition.
			// If for some reason the fw attitude setpoint is not recent then don't use it and assume 0 pitch
			if (_fw_virtual_att_sp->timestamp > (now - 1_s)) {
				const float pitch_body = Eulerf(Quatf(_fw_virtual_att_sp->q_d)).theta();
				_q_trans_start = Eulerf(0.f, pitch_body, yaw_sp);

			} else {
				_q_trans_start = Eulerf(0.f, 0.f, yaw_sp);
			}

			// attitude during transitions are controlled by mc attitude control so rotate the desired attitude to the
			// multirotor frame
			_q_trans_start = _q_trans_start * Quatf(Eulerf(0, -M_PI_2_F, 0));

		} else if (_vtol_mode == vtol_mode::TRANSITION_FRONT_P1) {
			// initial attitude setpoint for the transition should be with wings level
			const Eulerf setpoint_euler(Quatf(_mc_virtual_att_sp->q_d));
			_q_trans_start = Eulerf(0.f, setpoint_euler.theta(), setpoint_euler.psi());
			Vector3f x = Dcmf(Quatf(_v_att->q)) * Vector3f(1.f, 0.f, 0.f);
			_trans_rot_axis = -x.cross(Vector3f(0.f, 0.f, -1.f));
		}

		_q_trans_sp = _q_trans_start;
	}

	// ensure input quaternions are exactly normalized because acosf(1.00001) == NaN
	_q_trans_sp.normalize();

	// tilt angle (zero if vehicle nose points up (hover))
	const float cos_tilt = math::constrain(_q_trans_sp(0) * _q_trans_sp(0) - _q_trans_sp(1) * _q_trans_sp(1) -
					       _q_trans_sp(2) * _q_trans_sp(2) + _q_trans_sp(3) * _q_trans_sp(3), -1.f, 1.f);
	const float tilt = acosf(cos_tilt);

	if (_vtol_mode == vtol_mode::TRANSITION_FRONT_P1) {

		// calculate pitching rate - and constrain to at least 0.1s transition time
		const float trans_pitch_rate = M_PI_2_F / math::max(_param_vt_f_trans_dur.get(), 0.1f);

		if (tilt < M_PI_2_F - math::radians(_param_fw_psp_off.get())) {
			_q_trans_sp = Quatf(AxisAnglef(_trans_rot_axis,
						       _time_since_trans_start * trans_pitch_rate)) * _q_trans_start;
		}

	} else if (_vtol_mode == vtol_mode::TRANSITION_BACK) {

		// calculate pitching rate - and constrain to at least 0.1s transition time
		const float trans_pitch_rate = M_PI_2_F / math::max(_param_vt_b_trans_dur.get(), 0.1f);

		if (tilt > 0.01f) {
			_q_trans_sp = Quatf(AxisAnglef(_trans_rot_axis,
						       _time_since_trans_start * trans_pitch_rate)) * _q_trans_start;
		}
	}

	_v_att_sp->thrust_body[2] = _mc_virtual_att_sp->thrust_body[2];

	if (_vtol_mode == vtol_mode::TRANSITION_BACK) {
		const float progress = math::constrain(_time_since_trans_start / B_TRANS_THRUST_BLENDING_DURATION, 0.f, 1.f);
		blendThrottleBeginningBackTransition(progress);
	}

	_v_att_sp->timestamp = hrt_absolute_time();

	const Eulerf euler_sp(_q_trans_sp);
	_q_trans_sp.copyTo(_v_att_sp->q_d);
}

void Tailsitter::waiting_on_tecs()
{
	// copy the last trust value from the front transition
	_v_att_sp->thrust_body[0] = -_last_thr_in_mc;
}

void Tailsitter::update_fw_state()
{
	VtolType::update_fw_state();

}

/**
* Write data to actuator output topic.
*/
void Tailsitter::fill_actuator_outputs()
{
	_torque_setpoint_0->timestamp = hrt_absolute_time();
	_torque_setpoint_0->timestamp_sample = _vehicle_torque_setpoint_virtual_mc->timestamp_sample;
	_torque_setpoint_0->xyz[0] = 0.f;
	_torque_setpoint_0->xyz[1] = 0.f;
	_torque_setpoint_0->xyz[2] = 0.f;

	_torque_setpoint_1->timestamp = hrt_absolute_time();
	_torque_setpoint_1->timestamp_sample = _vehicle_torque_setpoint_virtual_fw->timestamp_sample;
	_torque_setpoint_1->xyz[0] = 0.f;
	_torque_setpoint_1->xyz[1] = 0.f;
	_torque_setpoint_1->xyz[2] = 0.f;

	_thrust_setpoint_0->timestamp = hrt_absolute_time();
	_thrust_setpoint_0->timestamp_sample = _vehicle_thrust_setpoint_virtual_mc->timestamp_sample;
	_thrust_setpoint_0->xyz[0] = 0.f;
	_thrust_setpoint_0->xyz[1] = 0.f;
	_thrust_setpoint_0->xyz[2] = 0.f;

	_thrust_setpoint_1->timestamp = hrt_absolute_time();
	_thrust_setpoint_1->timestamp_sample = _vehicle_thrust_setpoint_virtual_fw->timestamp_sample;
	_thrust_setpoint_1->xyz[0] = 0.f;
	_thrust_setpoint_1->xyz[1] = 0.f;
	_thrust_setpoint_1->xyz[2] = 0.f;

	// Motors: Generating force and torque (optional for FW_MODE)
	if (_vtol_mode == vtol_mode::FW_MODE) {

		_thrust_setpoint_0->xyz[2] = -_vehicle_thrust_setpoint_virtual_fw->xyz[0];

		/* allow differential thrust if enabled */
		if (_param_vt_fw_difthr_en.get() & static_cast<int32_t>(VtFwDifthrEnBits::YAW_BIT)) {
			_torque_setpoint_0->xyz[0] = _vehicle_torque_setpoint_virtual_fw->xyz[0] * _param_vt_fw_difthr_s_y.get();
		}

		if (_param_vt_fw_difthr_en.get() & static_cast<int32_t>(VtFwDifthrEnBits::PITCH_BIT)) {
			_torque_setpoint_0->xyz[1] = _vehicle_torque_setpoint_virtual_fw->xyz[1] * _param_vt_fw_difthr_s_p.get();
		}

		if (_param_vt_fw_difthr_en.get() & static_cast<int32_t>(VtFwDifthrEnBits::ROLL_BIT)) {
			_torque_setpoint_0->xyz[2] = _vehicle_torque_setpoint_virtual_fw->xyz[2] * _param_vt_fw_difthr_s_r.get();
		}

		// for the short period after switching to FW where there is no thrust published yet from the FW controller,
		// keep publishing the last MC thrust to keep the motors running
		if (hrt_elapsed_time(&_trans_finished_ts) < 50_ms) {
			_thrust_setpoint_0->xyz[2] = _last_thr_in_mc;
			_torque_setpoint_0->xyz[0] = 0.f;
			_torque_setpoint_0->xyz[1] = 0.f;
			_torque_setpoint_0->xyz[2] = 0.f;
		}

	} else {
		_thrust_setpoint_0->xyz[2] = _vehicle_thrust_setpoint_virtual_mc->xyz[2];

		// for the short period after starting the backtransition where there is no thrust published yet from the MC controller,
		// keep publishing the last FW thrust to keep the motors running
		if (_vtol_mode != vtol_mode::TRANSITION_FRONT_P1 && hrt_elapsed_time(&_transition_start_timestamp) < 50_ms) {
			_thrust_setpoint_0->xyz[2] = -_last_thr_in_fw_mode;
		}

		_torque_setpoint_0->xyz[0] = _vehicle_torque_setpoint_virtual_mc->xyz[0];
		_torque_setpoint_0->xyz[1] = _vehicle_torque_setpoint_virtual_mc->xyz[1];
		_torque_setpoint_0->xyz[2] = _vehicle_torque_setpoint_virtual_mc->xyz[2];
	}

	// Control surfaces: Generating torque (optional for MC_MODE)
	// VT_ELEV_MC_LOCK=0 enables control surfaces in hover, VT_TS_CS_HVR_DIS can still
	// selectively disable individual surfaces (e.g., those outside propeller slipstream).
	if (!_param_vt_elev_mc_lock.get() && _vtol_mode == vtol_mode::MC_MODE) {
		// In MC_MODE apply torque from multirotor controller
		_torque_setpoint_1->xyz[0] = _vehicle_torque_setpoint_virtual_mc->xyz[0];
		_torque_setpoint_1->xyz[1] = _vehicle_torque_setpoint_virtual_mc->xyz[1];
		_torque_setpoint_1->xyz[2] = _vehicle_torque_setpoint_virtual_mc->xyz[2];

	} else {
		_torque_setpoint_1->xyz[0] = _vehicle_torque_setpoint_virtual_fw->xyz[0];
		_torque_setpoint_1->xyz[1] = _vehicle_torque_setpoint_virtual_fw->xyz[1];
		_torque_setpoint_1->xyz[2] = _vehicle_torque_setpoint_virtual_fw->xyz[2];
	}
}


bool Tailsitter::isFrontTransitionCompletedBase()
{
	const bool airspeed_triggers_transition = PX4_ISFINITE(_attc->get_calibrated_airspeed());

	bool transition_to_fw = false;
	const float pitch = Eulerf(Quatf(_v_att->q)).theta();

	if (pitch <= PITCH_THRESHOLD_AUTO_TRANSITION_TO_FW) {
		if (airspeed_triggers_transition) {
			transition_to_fw = _attc->get_calibrated_airspeed() >= _param_vt_arsp_trans.get() ;

		} else {
			transition_to_fw = true;
		}
	}

	return transition_to_fw;
}

void Tailsitter::blendThrottleAfterFrontTransition(float scale)
{
	// note: MC throttle is negative (as in negative z), while FW throttle is positive (positive x)
	_v_att_sp->thrust_body[0] = scale * _v_att_sp->thrust_body[0] + (1.f - scale) * (-_last_thr_in_mc);
}

void Tailsitter::blendThrottleBeginningBackTransition(float scale)
{
	_v_att_sp->thrust_body[2] = scale * _v_att_sp->thrust_body[2] + (1.f - scale) * (-_last_thr_in_fw_mode);
}