Plane: added FBWA_TDRAG_CHAN parameter

this allows for testing taildragger takeoffs in FBWA mode

ArduPlane/ArduPlane.pde

@@ -531,6 +531,9 @@ static struct {
     // should we use cross-tracking for this waypoint?
     bool no_crosstrack:1;
 
+    // in FBWA taildragger takeoff mode
+    bool fbwa_tdrag_takeoff_mode:1;
+
     // Altitude threshold to complete a takeoff command in autonomous modes.  Centimeters
     int32_t takeoff_altitude_cm;
 
@@ -555,6 +558,7 @@ static struct {
     inverted_flight  : false,
     next_wp_no_crosstrack : true,
     no_crosstrack : true,
+    fbwa_tdrag_takeoff_mode : false,
     takeoff_altitude_cm : 0,
     takeoff_pitch_cd : 0,
     highest_airspeed : 0,
@@ -1309,6 +1313,16 @@ static void update_flight_mode(void)
             nav_pitch_cd = 0;
             channel_throttle->servo_out = 0;
         }
+        if (g.fbwa_tdrag_chan > 0) {
+            // check for the user enabling FBWA taildrag takeoff mode
+            bool tdrag_mode = (hal.rcin->read(g.fbwa_tdrag_chan-1) > 1700);
+            if (tdrag_mode && !auto_state.fbwa_tdrag_takeoff_mode) {
+                if (auto_state.highest_airspeed < g.takeoff_tdrag_speed1) {
+                    auto_state.fbwa_tdrag_takeoff_mode = true;
+                    gcs_send_text_P(SEVERITY_LOW, PSTR("FBWA tdrag mode\n"));
+                }
+            }
+        }
         break;
     }
 

ArduPlane/Parameters.h

@@ -122,6 +122,7 @@ public:
         k_param_glide_slope_threshold,
         k_param_stab_pitch_down,
         k_param_terrain_lookahead,
+        k_param_fbwa_tdrag_chan,
 
         // 100: Arming parameters
         k_param_arming = 100,
@@ -457,6 +458,7 @@ public:
     AP_Int16 terrain_lookahead;
 #endif
     AP_Int16 glide_slope_threshold;
+    AP_Int8 fbwa_tdrag_chan;
 
     // RC channels
     RC_Channel rc_1;

ArduPlane/Parameters.pde

@@ -206,6 +206,12 @@ const AP_Param::Info var_info[] PROGMEM = {
     // @User: User
     GSCALAR(takeoff_throttle_slewrate, "TKOFF_THR_SLEW",  0),
 
+    // @Param: FBWA_TDRAG_CHAN
+    // @DisplayName: FBWA taildragger channel
+    // @Description: This is a RC input channel which when it goes above 1700 enables FBWA taildragger takeoff mode. It should be assigned to a momentary switch. Once this feature is enabled it will stay enabled until the aircraft goes above TKOFF_TDRAG_SPD1 airspeed, changes mode, or the pitch goes above the initial pitch when this is engaged or goes below 0 pitch. When enabled the elevator will be forced to TKOFF_TDRAG_ELEV. This option allows for easier takeoffs on taildraggers in FBWA mode, and also makes it easier to test auto-takeoff steering handling in FBWA. Setting it to 0 disables this option.
+    // @User: Standard
+    GSCALAR(fbwa_tdrag_chan,          "FBWA_TDRAG_CHAN",  0),
+
     // @Param: LEVEL_ROLL_LIMIT
     // @DisplayName: Level flight roll limit
     // @Description: This controls the maximum bank angle in degrees during flight modes where level flight is desired, such as in the final stages of landing, and during auto takeoff. This should be a small angle (such as 5 degrees) to prevent a wing hitting the runway during takeoff or landing. Setting this to zero will completely disable heading hold on auto takeoff and final landing approach.

ArduPlane/system.pde

@@ -306,6 +306,13 @@ static void set_mode(enum FlightMode mode)
         autotune_restore();
     }
 
+    // zero initial pitch and highest airspeed on mode change
+    auto_state.highest_airspeed = 0;
+    auto_state.initial_pitch_cd = ahrs.pitch_sensor;
+
+    // disable taildrag takeoff on mode change
+    auto_state.fbwa_tdrag_takeoff_mode = false;
+
     switch(control_mode)
     {
     case INITIALISING:
@@ -351,8 +358,6 @@ static void set_mode(enum FlightMode mode)
     case AUTO:
         auto_throttle_mode = true;
         next_WP_loc = prev_WP_loc = current_loc;
-        auto_state.highest_airspeed = 0;
-        auto_state.initial_pitch_cd = ahrs.pitch_sensor;
         // start or resume the mission, based on MIS_AUTORESET
         mission.start_or_resume();
         break;

ArduPlane/takeoff.pde

@@ -127,22 +127,28 @@ static void takeoff_calc_pitch(void)
 }
 
 /*
-  return a tail hold percentage during initial takeoff for a tail dragger
+  return a tail hold percentage during initial takeoff for a tail
+  dragger
+
+  This can be used either in auto-takeoff or in FBWA mode with
+  FBWA_TDRAG_CHAN enabled
  */
 static int8_t takeoff_tail_hold(void)
 {
-    if (control_mode != AUTO || auto_state.takeoff_complete) {
+    bool in_takeoff = ((control_mode == AUTO && !auto_state.takeoff_complete) ||
+                       (control_mode == FLY_BY_WIRE_A && auto_state.fbwa_tdrag_takeoff_mode));
+    if (!in_takeoff) {
         // not in takeoff
         return 0;
     }
     if (g.takeoff_tdrag_elevator == 0) {
         // no takeoff elevator set
-        return 0;
+        goto return_zero;
     }
     if (auto_state.highest_airspeed >= g.takeoff_tdrag_speed1) {
         // we've passed speed1. We now raise the tail and aim for
         // level pitch. Return 0 meaning no fixed elevator setting
-        return 0;
+        goto return_zero;
     }
     if (ahrs.pitch_sensor > auto_state.initial_pitch_cd + 1000) {
         // the pitch has gone up by more then 10 degrees over the
@@ -150,10 +156,17 @@ static int8_t takeoff_tail_hold(void)
         // early liftoff, perhaps due to a bad setting of
         // g.takeoff_tdrag_speed1. Go to level flight to prevent a
         // stall
-        return 0;
+        goto return_zero;
     }
     // we are holding the tail down
     return g.takeoff_tdrag_elevator;
+
+return_zero:
+    if (auto_state.fbwa_tdrag_takeoff_mode) {
+        gcs_send_text_P(SEVERITY_LOW, PSTR("FBWA tdrag off"));
+        auto_state.fbwa_tdrag_takeoff_mode = false;
+    }
+    return 0;
 }
 
 /*