Sub: Limit input demand rate of change on motor mixer in manual mode

ArduSub/Sub.h

@@ -320,6 +320,8 @@ private:
 
     AP_Arming_Sub arming {ahrs, barometer, compass, battery};
 
+    uint32_t last_control_mode_update_us; // dt tracking for control mode updates
+
     // Altitude
     // The cm/s we are moving up or down based on filtered data - Positive = UP
     int16_t climb_rate;

ArduSub/control_manual.cpp

@@ -32,4 +32,7 @@ void Sub::manual_run()
     motors.set_throttle(channel_throttle->norm_input());
     motors.set_forward(channel_forward->norm_input());
     motors.set_lateral(channel_lateral->norm_input());
+
+    float dt =  ((float)(micros() - last_control_mode_update_us)) / 1e6;
+    motors.limit_demand_slew_rate(g.manual_slew_rate, dt);
 }

ArduSub/flight_mode.cpp

@@ -139,6 +139,8 @@ void Sub::update_flight_mode()
     default:
         break;
     }
+
+    last_control_mode_update_us = micros();
 }
 
 // exit_mode - high level call to organise cleanup as a flight mode is exited