Fix signs for fixed wing control, issue resulted from consistently flipped pitch response for IO and FMU

ROMFS/mixers/FMU_Q.mix

@@ -25,13 +25,13 @@ for the elevons.
 
 M: 2
 O:      10000  10000      0 -10000  10000
-S: 0 0  -5000  -8000      0 -10000  10000
-S: 0 1  -8000  -8000      0 -10000  10000
+S: 0 0   5000   8000      0 -10000  10000
+S: 0 1   8000   8000      0 -10000  10000
 
 M: 2
 O:      10000  10000      0 -10000  10000
-S: 0 0  -8000  -5000      0 -10000  10000
-S: 0 1  8000   8000       0 -10000  10000
+S: 0 0   8000   5000      0 -10000  10000
+S: 0 1  -8000  -8000      0 -10000  10000
 
 Output 2
 --------

ROMFS/mixers/FMU_X5.mix

@@ -23,13 +23,13 @@ for the elevons.
 
 M: 2
 O:      10000  10000      0 -10000  10000
-S: 0 0   3000   5000      0 -10000  10000
-S: 0 1   5000   5000      0 -10000  10000
+S: 0 0  -3000  -5000      0 -10000  10000
+S: 0 1  -5000  -5000      0 -10000  10000
 
 M: 2
 O:      10000  10000      0 -10000  10000
-S: 0 0   5000   3000      0 -10000  10000
-S: 0 1  -5000  -5000      0 -10000  10000
+S: 0 0  -5000  -3000      0 -10000  10000
+S: 0 1   5000   5000      0 -10000  10000
 
 Output 2
 --------

apps/controllib/fixedwing.cpp

@@ -323,7 +323,7 @@ void BlockMultiModeBacksideAutopilot::update()
 			_att.rollspeed, _att.pitchspeed, _att.yawspeed
 		);
 		_actuators.control[CH_AIL] = _backsideAutopilot.getAileron();
-		_actuators.control[CH_ELV] = - _backsideAutopilot.getElevator();
+		_actuators.control[CH_ELV] = _backsideAutopilot.getElevator();
 		_actuators.control[CH_RDR] = _backsideAutopilot.getRudder();
 		_actuators.control[CH_THR] = _backsideAutopilot.getThrottle();
 
@@ -355,7 +355,7 @@ void BlockMultiModeBacksideAutopilot::update()
 			_att.rollspeed, _att.pitchspeed, _att.yawspeed);
 
 			_actuators.control[CH_AIL] = _stabilization.getAileron();
-			_actuators.control[CH_ELV] = - _stabilization.getElevator();
+			_actuators.control[CH_ELV] = _stabilization.getElevator();
 			_actuators.control[CH_RDR] = _stabilization.getRudder();
 			_actuators.control[CH_THR] = _manual.throttle;
 		}

apps/px4io/controls.c

@@ -192,6 +192,10 @@ controls_tick() {
 				unsigned mapped = conf[PX4IO_P_RC_CONFIG_ASSIGNMENT];
 				ASSERT(mapped < MAX_CONTROL_CHANNELS);
 
+				/* invert channel if pitch - pulling the lever down means pitching up by convention */
+				if (mapped == 1) /* roll, pitch, yaw, throttle, override is the standard order */
+					scaled = -scaled;
+
 				r_rc_values[mapped] = SIGNED_TO_REG(scaled);
 				assigned_channels |= (1 << mapped);
 			}