diff --git a/maidroid_core/register.lua b/maidroid_core/cores/basic.lua
similarity index 79%
rename from maidroid_core/register.lua
rename to maidroid_core/cores/basic.lua
index 963f2f5..b2d0e58 100644
--- a/maidroid_core/register.lua
+++ b/maidroid_core/cores/basic.lua
@@ -3,10 +3,7 @@
 -- https://github.com/tacigar/maidroid
 ------------------------------------------------------------
 
-local state = {
-	IDLE      = 0,
-	ACCOMPANY = 1,
-}
+local state = {IDLE = 0, ACCOMPANY = 1}
 
 local function on_start(self)
 	self.state = state.IDLE
@@ -19,6 +16,10 @@ local function on_stop(self)
 	self.object:setvelocty{x = 0, y = 0, z = 0}
 end
 
+local on_resume = on_start
+
+local on_pause = on_stop
+
 local function on_step(self, dtime)
 	local player = self:get_nearest_player(10)
 	if player == nil then
@@ -55,12 +56,13 @@ local function on_step(self, dtime)
 	end
 end
 
-maidroid.register_core("maidroid_core:core_basic", {
-	description     = "maidroid core : basic",
-	inventory_image = "maidroid_core_basic.png",
-	on_start        = on_start,
-	on_stop         = on_stop,
-	on_resume       = on_start,
-	on_pause        = on_stop,
-	on_step         = on_step,
+-- register a definition of a new core.
+maidroid.register_core("maidroid_core:basic", {
+	description      = "maidroid core : basic",
+	inventory_image  = "maidroid_core_basic.png",
+	on_start         = on_start,
+	on_stop          = on_stop,
+	on_resume        = on_resume,
+	on_pause         = on_pause,
+	on_step          = on_step,
 })
diff --git a/maidroid_core/cores/empty.lua b/maidroid_core/cores/empty.lua
new file mode 100644
index 0000000..163fd05
--- /dev/null
+++ b/maidroid_core/cores/empty.lua
@@ -0,0 +1,14 @@
+------------------------------------------------------------
+-- Copyright (c) 2016 tacigar. All rights reserved.
+-- https://github.com/tacigar/maidroid
+------------------------------------------------------------
+
+maidroid.register_core("maidroid_core:empty", {
+	description      = "maidroid core : empty",
+	inventory_image  = "maidroid_core_empty.png",
+	on_start         = function(self) end,
+	on_stop          = function(self) end,
+	on_resume        = function(self) end,
+	on_pause         = function(self) end,
+	on_step          = function(self, dtime) end,
+})
diff --git a/maidroid_core/init.lua b/maidroid_core/init.lua
index e7f7996..98f0535 100644
--- a/maidroid_core/init.lua
+++ b/maidroid_core/init.lua
@@ -8,4 +8,5 @@ maidroid_core = {}
 maidroid_core.modname = "maidroid_core"
 maidroid_core.modpath = minetest.get_modpath(maidroid_core.modname)
 
-dofile(maidroid_core.modpath .. "/register.lua")
+dofile(maidroid_core.modpath .. "/cores/empty.lua")
+dofile(maidroid_core.modpath .. "/cores/basic.lua")
diff --git a/maidroid_core/textures/maidroid_core_basic.png b/maidroid_core/textures/maidroid_core_basic.png
new file mode 100644
index 0000000..966e2e8
Binary files /dev/null and b/maidroid_core/textures/maidroid_core_basic.png differ
diff --git a/maidroid_core/textures/maidroid_core_basic.xcf b/maidroid_core/textures/maidroid_core_basic.xcf
new file mode 100644
index 0000000..cd96fbb
Binary files /dev/null and b/maidroid_core/textures/maidroid_core_basic.xcf differ
diff --git a/maidroid_core/textures/maidroid_core_empty.png b/maidroid_core/textures/maidroid_core_empty.png
new file mode 100644
index 0000000..37103e1
Binary files /dev/null and b/maidroid_core/textures/maidroid_core_empty.png differ
diff --git a/maidroid_core/textures/maidroid_core_empty.xcf b/maidroid_core/textures/maidroid_core_empty.xcf
new file mode 100644
index 0000000..43b891f
Binary files /dev/null and b/maidroid_core/textures/maidroid_core_empty.xcf differ