AP_ICEngine: add idle throttle percentage

libraries/AP_ICEngine/AP_ICEngine.cpp

@@ -102,7 +102,14 @@ const AP_Param::GroupInfo AP_ICEngine::var_info[] = {
     // @Range: 0 100
     AP_GROUPINFO("START_PCT", 10, AP_ICEngine, start_percent, 5),
 
-    AP_GROUPEND    
+    // @Param: IDLE_PCT
+    // @DisplayName: Throttle percentage for engine idle
+    // @Description: This is the minimum percentage throttle output while running, this includes being disarmed, but not safe
+    // @User: Standard
+    // @Range: 0 100
+    AP_GROUPINFO("IDLE_PCT", 11, AP_ICEngine, idle_percent, 0),
+
+    AP_GROUPEND
 };
 
 
@@ -210,7 +217,7 @@ void AP_ICEngine::update(void)
                 // reset initial height while disarmed
                 initial_height = -pos.z;
             }
-        } else {
+        } else if (idle_percent == 0) { // check if we should idle
             // force ignition off when disarmed
             state = ICE_OFF;
         }
@@ -250,13 +257,20 @@ void AP_ICEngine::update(void)
 
 /*
   check for throttle override. This allows the ICE controller to force
-  the correct starting throttle when starting the engine
+  the correct starting throttle when starting the engine and maintain idle when disarmed
  */
 bool AP_ICEngine::throttle_override(uint8_t &percentage)
 {
     if (!enable) {
         return false;
     }
+
+    uint8_t current_throttle = SRV_Channels::get_output_scaled(SRV_Channel::k_throttle);
+    if (idle_percent > current_throttle && state == ICE_RUNNING) {
+        percentage = (uint8_t)idle_percent;
+        return true;
+    }
+
     if (state == ICE_STARTING || state == ICE_START_DELAY) {
         percentage = (uint8_t)start_percent.get();
         return true;

libraries/AP_ICEngine/AP_ICEngine.h

@@ -89,6 +89,9 @@ private:
     // throttle percentage for engine start
     AP_Int8 start_percent;
 
+    // throttle percentage for engine idle
+    AP_Int8 idle_percent;
+
     // height when we enter ICE_START_HEIGHT_DELAY
     float initial_height;