Alter UAS.cc so that it transmits MANUAL_CONTROL messages at 5Hz when no inputs have changed.

Otherwise MANUAL_CONTROL messages are still sent at the regular 50Hz. This reduces transmission bandwidth from 0.9kbps when the joystick is used continuously to 0.1kbps when it's idle.
To prevent possible issues from the last high-bandwidth message being lost and the system then not responding for .1s, the last messsage is double-transmit which should prevent those issues.

src/uas/UAS.cc

@@ -2885,29 +2885,65 @@ void UAS::setManualControlCommands(double roll, double pitch, double yaw, double
     Q_UNUSED(xHat);
     Q_UNUSED(yHat);
 
-    // Scale values
-    double rollPitchScaling = 1.0f * 1000.0f;
-    double yawScaling = 1.0f * 1000.0f;
-    double thrustScaling = 1.0f * 1000.0f;
-
-    manualRollAngle = roll * rollPitchScaling;
-    manualPitchAngle = pitch * rollPitchScaling;
-    manualYawAngle = yaw * yawScaling;
-    manualThrust = thrust * thrustScaling;
-
-    // If system has manual inputs enabled and is armed
+    // Store the previous manual commands
+    static double manualRollAngle = 0.0;
+    static double manualPitchAngle = 0.0;
+    static double manualYawAngle = 0.0;
+    static double manualThrust = 0.0;
+    static int manualButtons = 0; //FIXME: Change buttons to a uint16_t, as it is defined by MAVLink
+    static int countSinceLastTransmission = 0; // Track how many calls to this function have occurred since the last MAVLink transmission
+
+    // We only transmit manual command messages if the system has manual inputs enabled and is armed
     if(((base_mode & MAV_MODE_FLAG_DECODE_POSITION_MANUAL) && (base_mode & MAV_MODE_FLAG_DECODE_POSITION_SAFETY)) || (base_mode & MAV_MODE_FLAG_HIL_ENABLED))
     {
-        mavlink_message_t message;
-        mavlink_msg_manual_control_pack(mavlink->getSystemId(), mavlink->getComponentId(), &message, this->uasId, (float)manualPitchAngle, (float)manualRollAngle, (float)manualThrust, (float)manualYawAngle, buttons);
-        sendMessage(message);
-        //qDebug() << __FILE__ << __LINE__ << ": SENT MANUAL CONTROL MESSAGE: roll" << manualRollAngle << " pitch: " << manualPitchAngle << " yaw: " << manualYawAngle << " thrust: " << manualThrust;
 
-        emit attitudeThrustSetPointChanged(this, roll, pitch, yaw, thrust, QGC::groundTimeMilliseconds());
-    }
-    else
-    {
-        //qDebug() << "JOYSTICK/MANUAL CONTROL: IGNORING COMMANDS: Set mode to MANUAL to send joystick commands first";
+        // Transmit the manual commands only if they've changed OR if it's been a little bit since they were last transmit. To make sure there aren't issues with
+        // response rate, we make sure that a message is transmit when the commands have changed, then one more time, and then switch to the lower transmission rate
+        // if no command inputs have changed.
+        // The default transmission rate is 50Hz, but when no inputs have changed it drops down to 5Hz.
+        bool sendCommand = false;
+        if (countSinceLastTransmission++ >= 10)
+        {
+            sendCommand = true;
+            countSinceLastTransmission = 0;
+        }
+        else if ((!isnan(roll) && roll != manualRollAngle) || (!isnan(pitch) && pitch != manualPitchAngle) ||
+                   (!isnan(yaw) && yaw != manualYawAngle) || (!isnan(thrust) && thrust != manualThrust) ||
+                   buttons != manualButtons)
+        {
+            sendCommand = true;
+
+            // Ensure that another message will be sent the next time this function is called
+            countSinceLastTransmission = 10;
+        }
+
+        // Now if we should trigger an update, let's do that
+        if (sendCommand)
+        {
+            // Save the new manual control inputs
+            manualRollAngle = roll;
+            manualPitchAngle = pitch;
+            manualYawAngle = yaw;
+            manualThrust = thrust;
+            manualButtons = buttons;
+
+            // Store scaling values for all 3 axes
+            const double axesScaling = 1.0 * 1000.0;
+
+            // Calculate the new commands for roll, pitch, yaw, and thrust
+            const double newRollCommand = roll * axesScaling;
+            const double newPitchCommand = pitch * axesScaling;
+            const double newYawCommand = yaw * axesScaling;
+            const double newThrustCommand = thrust * axesScaling;
+
+            // Send the MANUAL_COMMAND message
+            mavlink_message_t message;
+            mavlink_msg_manual_control_pack(mavlink->getSystemId(), mavlink->getComponentId(), &message, this->uasId, (float)newPitchCommand, (float)newRollCommand, (float)newThrustCommand, (float)newYawCommand, buttons);
+            sendMessage(message);
+
+            // Emit an update in control values to other UI elements, like the HSI display
+            emit attitudeThrustSetPointChanged(this, roll, pitch, yaw, thrust, QGC::groundTimeMilliseconds());
+        }
     }
 }