Should roll and yaw set points be zero during transition?

dlwalter · May 1, 2019, 4:25pm

Looking at the VTOL Attitude Controller and I see that roll and yaw setpoints are passed through from the controller. We’ve experienced some stalls and quadchute emergency transitions if excessive roll and yaw commands are send during the transition.

Should the roll and yaw setpoints be set to zero during transition? Are there cases where we would want the aircraft other than straight and level during transition?

mohammad · May 5, 2019, 4:19pm

Roll and pitch shuld set to zero during transition , but how you can set this ?

dlwalter · May 6, 2019, 4:49pm

Using standard.cpp as an example in update_mc_state() _v_att_sp->roll_body should be set to 0 and set yaw_error to 0 then calculate the q_sp quaternion setpoint.

github.com

PX4/Firmware/blob/50bd148f53f1aeca6f1bd4a1caabcc18e4f2888b/src/modules/vtol_att_control/standard.cpp#L467


		// return the vehicle to level position
		float pitch_new = 0.0f;


		// create corrected desired body z axis in heading frame
		matrix::Dcmf R_tmp = matrix::Eulerf(roll_new, pitch_new, 0.0f);
		matrix::Vector3f tilt_new(R_tmp(0, 2), R_tmp(1, 2), R_tmp(2, 2));


		// rotate the vector into a new frame which is rotated in z by the desired heading
		// with respect to the earh frame.
		float yaw_error = _wrap_pi(euler_sp(2) - euler(2));
		matrix::Dcmf R_yaw_correction = matrix::Eulerf(0.0f, 0.0f, -yaw_error);
		tilt_new = R_yaw_correction * tilt_new;


		// now extract roll and pitch setpoints
		_v_att_sp->pitch_body = atan2f(tilt_new(0), tilt_new(2));
		_v_att_sp->roll_body = -asinf(tilt_new(1));
		R_sp = matrix::Eulerf(_v_att_sp->roll_body, _v_att_sp->pitch_body, euler_sp(2));
		matrix::Quatf q_sp(R_sp);
		q_sp.copyTo(_v_att_sp->q_d);
	}

mohammad · May 10, 2019, 5:16pm

In ardupilot code there is a parameter for this but threre is not in px4code.

dlwalter · January 18, 2020, 12:25am

It looks like we should be able to control a level transition from vtol_att_control in update_mc_state and update_fw_state by setting _v_att_sp->roll_body and pitch_body to 0.0f and include a parameter check VT_LEVEL_TRANS or something.

Manual mode transitions don’t seem to follow this (I think they are mapping the manual_setpoints from the rc controller into roll/pitch.