mc_att_control_vector: fixes

src/modules/mc_att_control_vector/mc_att_control_vector_main.cpp

@@ -540,21 +540,24 @@ MulticopterAttitudeControl::task_main()
 			math::Vector3 rates(_att.rollspeed, _att.pitchspeed, _att.yawspeed);
 
 			/* try to move thrust vector shortest way, because yaw response is slower than roll/pitch */
-			/* angle error between current and desired thrust vectors (Z axes) */
+			/* sin(angle error) between current and desired thrust vectors (Z axes) */
 			math::Vector3 R_z(R(0, 2), R(1, 2), R(2, 2));
 			math::Vector3 R_z_des(R_des(0, 2), R_des(1, 2), R_des(2, 2));
-			math::Vector3 e_R = R_z.cross(R_z_des);
+			math::Vector3 e_R = R.transpose() * R_z.cross(R_z_des);
 
-			/* convert angle error from NED to bady frame */
-			e_R = R.transpose() * e_R;
+			/* calculate angle error */
+			float e_R_sin = e_R.norm();
+			float e_R_cos = R_z * R_z_des;
+			float angle = atan2f(e_R_sin, e_R_cos);
 
 			/* e_R has zero Z component, set it according to yaw */
 			/* calculate rotation matrix after roll/pitch only rotation */
 			math::Matrix R_rp(3, 3);
-			float e_R_angle = e_R.norm();
-			if (e_R_angle > 0.0f) {
+
+			if (e_R_sin > 0.0f) {
 				/* get axis-angle representation */
-				math::Vector3 e_R_axis = e_R / e_R_angle;
+				math::Vector3 e_R_axis = e_R / e_R_sin;
+
 				/* cross product matrix for e_R_axis */
 				math::Matrix e_R_cp(3, 3);
 				e_R_cp.setAll(0.0f);
@@ -564,13 +567,14 @@ MulticopterAttitudeControl::task_main()
 				e_R_cp(1, 2) = -e_R_axis(0);
 				e_R_cp(2, 0) = -e_R_axis(1);
 				e_R_cp(2, 1) = e_R_axis(0);
+
 				/* rotation matrix for roll/pitch only rotation */
 				math::Matrix I(3, 3);
 				I.setAll(0.0f);
 				I(0, 0) = 1.0f;
 				I(1, 1) = 1.0f;
 				I(2, 2) = 1.0f;
-				R_rp = R * (I + e_R_cp * sinf(e_R_angle) + e_R_cp * e_R_cp * (1.0f - cosf(e_R_angle)));
+				R_rp = R * (I + e_R_cp * e_R_sin + e_R_cp * e_R_cp * (1.0f - e_R_cos));
 			} else {
 				/* zero roll/pitch rotation */
 				R_rp = R;
@@ -582,6 +586,9 @@ MulticopterAttitudeControl::task_main()
 			math::Vector3 R_rp_x(R_rp(0, 0), R_rp(1, 0), R_rp(2, 0));
 			e_R(2) = R_rp_x.cross(R_des_x) * R_des_z;
 
+			/* don't try to control yaw when thrust vector has opposite direction to desired */
+			e_R(2) *= (e_R_cos > 0.0f ? 1.0f : e_R_sin);
+
 			/* angular rates setpoint*/
 			math::Vector3 rates_sp = _K * e_R;
 			/* feed forward yaw setpoint rate */