APM: removed reset_I() and instead auto-reset integrator in PID library

this prevents us resetting key integrators on waypoint change, while
still preventing old integrators being used when a PID starts to be
used again

ArduPlane/Attitude.pde

@@ -273,18 +273,6 @@ static void throttle_slew_limit()
 }
 
 
-// Zeros out navigation Integrators if we are changing mode, have passed a waypoint, etc.
-// Keeps outdated data out of our calculations
-static void reset_I(void)
-{
-    g.pidNavRoll.reset_I();
-    g.pidNavPitchAirspeed.reset_I();
-    g.pidNavPitchAltitude.reset_I();
-    g.pidTeThrottle.reset_I();
-    g.pidWheelSteer.reset_I();
-//	g.pidAltitudeThrottle.reset_I();
-}
-
 /* We want to supress the throttle if we think we are on the ground and in an autopilot controlled throttle mode.
 
    Disable throttle if following conditions are met:

ArduPlane/commands_logic.pde

@@ -6,11 +6,6 @@
 static void
 handle_process_nav_cmd()
 {
-    // reset navigation integrators
-    // -------------------------
-    reset_I();
-
-
     // set land_complete to false to stop us zeroing the throttle
     land_complete = false;
 

ArduPlane/control_modes.pde

@@ -33,10 +33,6 @@ static void read_control_switch()
 
         oldSwitchPosition = switchPosition;
         prev_WP = current_loc;
-
-        // reset navigation integrators
-        // -------------------------
-        reset_I();
     }
 
     if (g.reset_mission_chan != 0 &&

ArduPlane/events.pde

@@ -75,10 +75,6 @@ static void failsafe_short_off_event()
         (g.short_fs_action == 1 && control_mode == RTL)) {
         reset_control_switch();
     }
-
-    // Reset control integrators
-    // ---------------------
-    reset_I();
 }
 
 #if BATTERY_EVENT == ENABLED

libraries/PID/PID.cpp

@@ -25,6 +25,12 @@ PID::get_pid(int32_t error, float scaler)
 
     if (_last_t == 0 || dt > 1000) {
         dt = 0;
+
+		// if this PID hasn't been used for a full second then zero
+		// the intergator term. This prevents I buildup from a
+		// previous fight mode from causing a massive return before
+		// the integrator gets a chance to correct itself
+		_integrator = 0;
     }
     _last_t = tnow;