Add command to split off locomotive

advtrains/trainlogic.lua

@@ -892,8 +892,10 @@ function advtrains.spawn_wagons(train_id)
 	end
 end
 
-function advtrains.split_train_at_fc(train)
-	-- splits train at first different current FC
+function advtrains.split_train_at_fc(train, count_empty)
+	-- splits train at first different current FC by convention,
+	-- locomotives have empty FC so are ignored
+	-- count_empty is used to split off locomotives
 	local train_id = train.id
 	local fc = false
 	local ind = 0
@@ -902,7 +904,7 @@ function advtrains.split_train_at_fc(train)
 		local data = advtrains.wagons[w_id]
 		if data then
 			local wfc = advtrains.get_cur_fc(data)
-			if  wfc ~= "" then
+			if  wfc ~= "" or count_empty then
 				if  fc then
 					if fc ~= wfc then
 						ind = i

advtrains_luaautomation/README.txt

@@ -206,12 +206,16 @@ split_at_index(index, command)
 split_at_fc(command)
 	Splits the train in such a way that all cars with non-empty
 	current FC of the first part of the train have the same FC. The
-	command specified is sent to the rear part, as with split_at_index.
-	It returns the fc of the cars of the first part.
+	command specified is sent to the rear part, as with
+	split_at_index.  It returns the fc of the cars of the first part.
 
-	Example: Train has current FCs "" "" "foo" "bar" "boo" "foo"
-	Result: first train: "" "" "foo"; second train: "bar" "boo" "foo"
+	Example : Train has current FCs "" "" "foo" "bar" "foo"
+	Result: first train: "" "" "foo"; second train: "bar" "foo"
 	The command returns "foo" in this case
+split_off_locomotive(command)
+	Splits off the locomotives at the front of the train, which are
+	identified by an empty FC.  command specifies the command to be
+	executed by the rear half of the train.
 step_fc()
 	Steps the FCs of all train cars forward
 train_length()

advtrains_luaautomation/atc_rail.lua

@@ -73,10 +73,15 @@ function r.fire_event(pos, evtdata)
 			if new_id then
 				minetest.after(1,advtrains.atc.train_set_command,advtrains.trains[new_id], cmd, atc_arrow)
 			end
-			if fc == "" then
-				return nil
-			end
-			return fc
+			return fc or ""
+		end,
+		split_off_locomotive = function(cmd)
+			assertt(cmd, "string")
+			if not train_id then return false end
+			local new_id, fc = advtrains.split_train_at_fc(train, true)
+			if new_id then
+				minetest.after(1,advtrains.atc.train_set_command,advtrains.trains[new_id], cmd, atc_arrow)
+			end						
 		end,
 		train_length = function ()
 			if not train_id then return false end