From badf146e192d2341df1a76a31798a4ce6900e538 Mon Sep 17 00:00:00 2001
From: Anton Babushkin <anton.babushkin@me.com>
Date: Sun, 15 Dec 2013 16:24:45 +0400
Subject: [PATCH] mc_att_control_vector: independent thrust vector and attitude
 control

---
 .../mc_att_control_vector_main.cpp            | 45 +++++++++++++++++--
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/src/modules/mc_att_control_vector/mc_att_control_vector_main.cpp b/src/modules/mc_att_control_vector/mc_att_control_vector_main.cpp
index 834189a546..93806165d2 100644
--- a/src/modules/mc_att_control_vector/mc_att_control_vector_main.cpp
+++ b/src/modules/mc_att_control_vector/mc_att_control_vector_main.cpp
@@ -539,9 +539,48 @@ MulticopterAttitudeControl::task_main()
 			/* current body angular rates */
 			math::Vector3 rates(_att.rollspeed, _att.pitchspeed, _att.yawspeed);
 
-			/* orientation error between R and R_des */
-			math::Matrix e_R_m = (R_des.transpose() * R - R.transpose() * R_des).transpose() * 0.5f;
-			math::Vector3 e_R(-e_R_m(1, 2), e_R_m(0, 2), -e_R_m(0, 1));
+			/* 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) */
+			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);
+
+			/* convert angle error from NED to bady frame */
+			e_R = R.transpose() * e_R;
+
+			/* 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) {
+				/* get axis-angle representation */
+				math::Vector3 e_R_axis = e_R / e_R_angle;
+				/* cross product matrix for e_R_axis */
+				math::Matrix e_R_cp(3, 3);
+				e_R_cp.setAll(0.0f);
+				e_R_cp(0, 1) = -e_R_axis(2);
+				e_R_cp(0, 2) = e_R_axis(1);
+				e_R_cp(1, 0) = e_R_axis(2);
+				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)));
+			} else {
+				/* zero roll/pitch rotation */
+				R_rp = R;
+			}
+
+			/* R_rp and R_des has the same Z axis, calculate yaw error */
+			math::Vector3 R_des_z(R_des(0, 2), R_des(1, 2), R_des(2, 2));
+			math::Vector3 R_des_x(R_des(0, 0), R_des(1, 0), R_des(2, 0));
+			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;
 
 			/* angular rates setpoint*/
 			math::Vector3 rates_sp = _K * e_R;