Copter: added DISARM_DELAY parameter

this allows automatic disarming to be disabled, or set to a shorter or
longer time as appropriate for the user

Originally committed by Tridge, merged to AC3.3 with conflict.

ArduCopter/Parameters.cpp

@@ -447,6 +447,14 @@ const AP_Param::Info Copter::var_info[] PROGMEM = {
     // @User: Standard
     GSCALAR(arming_check, "ARMING_CHECK",           ARMING_CHECK_ALL),
 
+    // @Param: DISARM_DELAY
+    // @DisplayName: Disarm delay
+    // @Description: Delay before automatic disarm in seconds. A value of zero disables auto disarm.
+    // @Units: Seconds
+    // @Range: 0 127
+    // @User: Advanced
+    GSCALAR(disarm_delay, "DISARM_DELAY",           AUTO_DISARMING_DELAY),
+    
     // @Param: ANGLE_MAX
     // @DisplayName: Angle Max
     // @Description: Maximum lean angle in all flight modes

ArduCopter/Parameters.h

@@ -170,6 +170,7 @@ public:
         // 90: Motors
         //
         k_param_motors = 90,
+        k_param_disarm_delay,
 
         //
         // 100: Inertial Nav
@@ -427,6 +428,7 @@ public:
     AP_Int8         ch11_option;
     AP_Int8         ch12_option;
     AP_Int8         arming_check;
+    AP_Int8         disarm_delay;
 
     AP_Int8         land_repositioning;
     AP_Int8         fs_ekf_action;

ArduCopter/config.h

@@ -688,6 +688,10 @@
  # define ALT_HOLD_ACCEL_MAX 250    // if you change this you must also update the duplicate declaration in AC_WPNav.h
 #endif
 
+#ifndef AUTO_DISARMING_DELAY
+# define AUTO_DISARMING_DELAY  10
+#endif
+
 //////////////////////////////////////////////////////////////////////////////
 // Dataflash logging control
 //

ArduCopter/motors.cpp

@@ -5,8 +5,6 @@
 #define ARM_DELAY               20  // called at 10hz so 2 seconds
 #define DISARM_DELAY            20  // called at 10hz so 2 seconds
 #define AUTO_TRIM_DELAY         100 // called at 10hz so 10 seconds
-#define AUTO_DISARMING_DELAY_LONG   10  // called at 1hz so 10 seconds
-#define AUTO_DISARMING_DELAY_SHORT   5  // called at 1hz so 5 seconds
 #define LOST_VEHICLE_DELAY      10  // called at 10hz so 1 second
 
 static uint8_t auto_disarming_counter;
@@ -75,10 +73,11 @@ void Copter::arm_motors_check()
 // called at 1hz
 void Copter::auto_disarm_check()
 {
-    uint8_t disarm_delay = AUTO_DISARMING_DELAY_LONG;
+    uint8_t disarm_delay = constrain_int16(g.disarm_delay, 0, 127);
 
-    // exit immediately if we are already disarmed
+    // exit immediately if we are already disarmed, or if auto
-    if (!motors.armed()) {
+    // disarming is disabled
+    if (!motors.armed() || disarm_delay == 0) {
         auto_disarming_counter = 0;
         return;
     }
@@ -86,14 +85,9 @@ void Copter::auto_disarm_check()
     // always allow auto disarm if using interlock switch or motors are Emergency Stopped
     if ((ap.using_interlock && !motors.get_interlock()) || ap.motor_emergency_stop) {
         auto_disarming_counter++;
-#if FRAME_CONFIG == HELI_FRAME
-        // helicopters do not use short disarm delay as they could be in auto-rotation.
-        disarm_delay = AUTO_DISARMING_DELAY_LONG;
-#else
         // use a shorter delay if using throttle interlock switch or Emergency Stop, because it is less
         // obvious the copter is armed as the motors will not be spinning
-        disarm_delay = AUTO_DISARMING_DELAY_SHORT;
+        disarm_delay /= 2;
-#endif
     } else {
         bool sprung_throttle_stick = (g.throttle_behavior & THR_BEHAVE_FEEDBACK_FROM_MID_STICK) != 0;
         bool thr_low;