VTOL tailsitter: fix motor spike to 0 when finishing front transition

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/vtol_att_control/tailsitter.cpp

@@ -281,6 +281,12 @@ void Tailsitter::fill_actuator_outputs()
 
 		_thrust_setpoint_0->xyz[2] = -_vehicle_thrust_setpoint_virtual_fw->xyz[0];
 
+		// 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;
+		}
+
 		/* 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();

src/modules/vtol_att_control/vtol_type.cpp

@@ -164,6 +164,8 @@ void VtolType::update_transition_state()
 	_time_since_trans_start = (float)(t_now - _transition_start_timestamp) * 1e-6f;
 
 	check_quadchute_condition();
+
+	_last_thr_in_mc = _vehicle_thrust_setpoint_virtual_mc->xyz[2];
 }
 
 float VtolType::update_and_get_backtransition_pitch_sp()

src/modules/vtol_att_control/vtol_type.h

@@ -299,6 +299,7 @@ protected:
 	// motors spinning up or cutting too fast when doing transitions.
 	float _thrust_transition = 0.0f;	// thrust value applied during a front transition (tailsitter & tiltrotor only)
 	float _last_thr_in_fw_mode = 0.0f;
+	float _last_thr_in_mc = 0.f;
 
 	hrt_abstime _trans_finished_ts = 0;
 	hrt_abstime _transition_start_timestamp{0};