diff --git a/maidroid/api.lua b/maidroid/api.lua
index daf0293..d036da1 100644
--- a/maidroid/api.lua
+++ b/maidroid/api.lua
@@ -61,12 +61,13 @@ end
 
 -- maidroid.maidroid.get_core_name returns a name of a maidroid's current core.
 function maidroid.maidroid.get_core_name(self)
-	return self.core_name
+	local inv = self:get_inventory()
+	return inv:get_stack("core", 1):get_name()
 end
 
 -- maidroid.maidroid.get_core returns a maidroid's current core definition.
 function maidroid.maidroid.get_core(self)
-	local name = self:get_core_name(self)
+	local name = self:get_core_name()
 	if name ~= "" then
 		return maidroid.registered_cores[name]
 	end
@@ -342,14 +343,15 @@ function maidroid.register_maidroid(product_name, def)
 	end
 
 	local function update_infotext(self)
-		if self.core_name ~= "" then
+		local core_name = self:get_core_name()
+		if core_name ~= "" then
 			local infotext = ""
 			if self.pause then
 				infotext = infotext .. "this maidroid is paused\n"
 			else
 				infotext = infotext .. "this maidroid is active\n"
 			end
-			infotext = infotext .. "[Core] : " .. self.core_name
+			infotext = infotext .. "[Core] : " .. core_name
 
 			self.object:set_properties{infotext = infotext}
 			return
@@ -366,7 +368,6 @@ function maidroid.register_maidroid(product_name, def)
 					local core_name = stack:get_name()
 					local core = maidroid.registered_cores[core_name]
 					core.on_start(self)
-					self.core_name = core_name
 
 					update_infotext(self)
 				end
@@ -386,8 +387,8 @@ function maidroid.register_maidroid(product_name, def)
 
 			on_take = function(inv, listname, index, stack, player)
 				if listname == "core" then
-					local core = maidroid.registered_cores[self.core_name]
-					self.core_name = ""
+					local core_name = stack:get_name()
+					local core = maidroid.registered_cores[core_name]
 					core.on_stop(self)
 
 					update_infotext(self)
@@ -514,8 +515,8 @@ function maidroid.register_maidroid(product_name, def)
 		pickup_item(self)
 
 		-- do core method.
-		if (not self.pause) and self.core_name ~= "" then
-			local core = maidroid.registered_cores[self.core_name]
+		local core = self:get_core()
+		if (not self.pause) and core then
 			core.on_step(self, dtime)
 		end
 	end
@@ -531,16 +532,15 @@ function maidroid.register_maidroid(product_name, def)
 
 	-- on_punch is a callback function that is called when a player punch then.
 	local function on_punch(self, puncher, time_from_last_punch, tool_capabilities, dir)
+		local core = self:get_core()
 		if self.pause == true then
 			self.pause = false
-			if self.core_name ~= "" then
-				local core = maidroid.registered_cores[self.core_name]
+			if core then
 				core.on_resume(self)
 			end
 		else
 			self.pause = true
-			if self.core_name ~= "" then
-				local core = maidroid.registered_cores[self.core_name]
+			if core then
 				core.on_pause(self)
 			end
 		end
@@ -569,7 +569,6 @@ function maidroid.register_maidroid(product_name, def)
 		pause                        = false,
 		product_name                 = "",
 		manufacturing_number         = -1,
-		core_name                    = "",
 
 		-- callback methods.
 		on_activate                  = on_activate,