Plane: announce throttle limited by Battery Watt Limit

ArduPlane/Plane.h

@@ -590,6 +590,7 @@ class Plane : public AP_Vehicle {
     int8_t  throttle_watt_limit_max;
     int8_t  throttle_watt_limit_min; // for reverse thrust
     uint32_t throttle_watt_limit_timer_ms;
+    uint32_t throttle_watt_limit_last_gcs_ms;
 
     AP_FixedWing::FlightStage flight_stage = AP_FixedWing::FlightStage::NORMAL;
 

ArduPlane/servos.cpp

@@ -443,15 +443,19 @@ void Plane::throttle_watt_limiter(int8_t &min_throttle, int8_t &max_throttle)
 
     } else if (throttle_watt_limit_min == 0 && throttle_watt_limit_max == 0) {
         // no limiting happening, nothing to do
+        if (throttle_watt_limit_last_gcs_ms > 0) {
+            throttle_watt_limit_last_gcs_ms = 0;
+            GCS_SEND_TEXT(MAV_SEVERITY_INFO, "Throttle no longer limited");
+        }
         return;
     }
 
     // check to recover the throttle limit since we're not overloading
-    const int8_t most_limited_of_min_and_max = MAX(throttle_watt_limit_min, throttle_watt_limit_max);
-    const int8_t most_throttle_of_min_and_max = MAX(-min_throttle, max_throttle);
+    int8_t most_limited_of_min_and_max = MAX(throttle_watt_limit_min, throttle_watt_limit_max);
+    int8_t most_throttle_of_min_and_max = (most_limited_of_min_and_max == throttle_watt_limit_min) ? -min_throttle : max_throttle;
 
-    // if we're limiting all the way (min or max == 0) then the delay is larger
-    const uint32_t recovery_delay_ms = most_limited_of_min_and_max >= most_throttle_of_min_and_max ? 5000 : 1000;
+    // if we're limiting all the way (demand - min/max == 0) then the delay is larger
+    const uint32_t recovery_delay_ms = most_limited_of_min_and_max == most_throttle_of_min_and_max ? 5000 : 1000;
 
     if (now_ms - throttle_watt_limit_timer_ms >= recovery_delay_ms) {
         // it has been 1 second since last over-current, or 5s if throttle is pushed all the way down to 0%, check if we can resume higher throttle.
@@ -470,6 +474,18 @@ void Plane::throttle_watt_limiter(int8_t &min_throttle, int8_t &max_throttle)
         }
     }
 
+    // announce to user so they are aware of this event happening every 5 seconds
+    if (now_ms - throttle_watt_limit_last_gcs_ms >= 5000) {
+        if (throttle_watt_limit_last_gcs_ms == 0) {
+            // initial message is handled differently because it will always show max-1 which isn't very useful.
+            // Need to give it a few seconds to see how much we're actually limiting the throttle
+            GCS_SEND_TEXT(MAV_SEVERITY_CRITICAL, "Throttle limited by battery Watt limit!");
+        } else {
+            GCS_SEND_TEXT(MAV_SEVERITY_CRITICAL, "Throttle limited to %d%%", most_limited_of_min_and_max);
+        }
+        throttle_watt_limit_last_gcs_ms = now_ms;
+    }
+
     max_throttle = constrain_int16(max_throttle, 0, max_throttle - throttle_watt_limit_max);
     if (min_throttle < 0) {
         min_throttle = constrain_int16(min_throttle, min_throttle + throttle_watt_limit_min, 0);