Copter: no get_throttle_pre_takeoff for TradHeli

ArduCopter/Attitude.cpp

@@ -219,7 +219,13 @@ float Copter::get_throttle_pre_takeoff(float input_thr)
     float in_min = g.throttle_min;
     float in_max = get_takeoff_trigger_throttle();
 
+#if FRAME_CONFIG == HELI_FRAME
+    // helicopters swash will move from bottom to 1/2 of mid throttle
+    float out_min = 0;
+#else
+    // multicopters will output between spin-when-armed and 1/2 of mid throttle
     float out_min = motors.get_throttle_warn();
+#endif
     float out_max = get_non_takeoff_throttle();
 
     if ((g.throttle_behavior & THR_BEHAVE_FEEDBACK_FROM_MID_STICK) != 0) {