diff --git a/maidroid/api.lua b/maidroid/api.lua
new file mode 100644
index 0000000..3d60c85
--- /dev/null
+++ b/maidroid/api.lua
@@ -0,0 +1,114 @@
+------------------------------------------------------------
+-- Copyright (c) 2016 tacigar
+-- https://github.com/tacigar/maidroid
+------------------------------------------------------------
+
+-- maidroid.animation_frames represents the animation frame data
+-- of "models/maidroid.b3d".
+maidroid.animation_frames = {
+	STAND     = {x =   0, y =  79},
+	SIT       = {x =  81, y = 160},
+	LAY       = {x = 162, y = 166},
+	WALK      = {x = 168, y = 187},
+	MINE      = {x = 189, y = 198},
+	WALK_MINE = {x = 200, y = 219},
+}
+
+-- maidroid.get_inventory returns a inventory of a maidroid.
+function maidroid.get_inventory(self)
+	return minetest.get_inventory {
+		type = "detached",
+		name = self.inventory_name,
+	}
+end
+
+-- maidroid.register_maidroid registers a definition of a new maidroid.
+function maidroid.register_maidroid(product_name, def)
+
+	-- create_inventory creates a new inventory, and returns it.
+	function create_inventory(self)
+		self.inventory_name = self.product_name .. tostring(self.manufacturing_number)
+
+		local inventory = minetest.create_detached_inventory(self.inventory_name, {
+			on_put = function(inv, listname, index, stack, player)
+
+			end,
+
+			allow_put = function(inv, listname, index, stack, player)
+
+			end,
+
+			on_take = function(inv, listname, index, stack, player)
+
+			end,
+		})
+		inventory:set_size("main", 16)
+		inventory:set_size("core",  1)
+
+		return inventory
+	end
+
+	-- create_formspec_string returns a string that represents a formspec definition.
+	function create_formspec_string(self)
+		return "size[8,9]"
+			.. "list[detached:"..self.inventory_name..";main;0,0;4,4;]"
+			.. "label[5,0;core]"
+			.. "list[detached:"..self.inventory_name..";core;6,0;1,1;]"
+			.. "list[current_player;main;0,5;8,1;]"
+			.. "list[current_player;main;0,6.2;8,3;8]"
+	end
+
+	-- on_activate is a callback function that is called when the object is created or recreated.
+	function on_activate(self, staticdata)
+		if staticdata == "" then
+			self.product_name = product_name
+			create_inventory(self)
+		else
+			-- if static data is not empty string, this object has beed already created.
+			local data = minetest.deserialize(staticdata)
+
+			self.product_name = data["product_name"]
+			self.manufacturing_number = data["manufacturing_number"]
+
+			local inventory = create_inventory(self)
+
+			if data["inventory"]["module"] ~= "" then
+
+			end
+
+		end
+
+		self.formspec_string = create_formspec_string(self)
+	end
+
+	-- get_staticdata is a callback function that is called when the object is destroyed.
+	function get_staticdata = function(self)
+		local inventory = maidroid.get_inventory(self)
+		local data = {
+			["product_name"] = self.product_name,
+			["manufacturing_number"] = self.manufacturing_number,
+			["inventory"] = {
+				["main"] = {},
+				["core"] = core_name, -- TODO
+			},
+		}
+
+		for _, item in ipairs(inventory:get_list("main")) do
+			local count = item:get_count()
+			local itemname = item:get_name()
+			if count ~= 0 then
+				local itemdata = {count = count, name = itemname}
+				table.insert(data["inventory"]["main"], itemdata)
+			end
+		end
+		return minetest.serialize(data)
+	end
+
+	-- register a definition of a new maidroid.
+	minetest.register_entity(product_name, {
+		product_name = "",
+		manufacturing_number = -1,
+
+		on_activate = on_activate,
+	})
+end
diff --git a/maidroid/init.lua b/maidroid/init.lua
new file mode 100644
index 0000000..65b2e54
--- /dev/null
+++ b/maidroid/init.lua
@@ -0,0 +1,11 @@
+------------------------------------------------------------
+-- Copyright (c) 2016 tacigar
+-- https://github.com/tacigar/maidroid
+------------------------------------------------------------
+
+maidroid = {}
+
+maidroid.modname = "maidroid"
+maidroid.modpath = maidroid.get_modpath(maidroid.modname)
+
+dofile(maidroid.modpath .. "/api.lua")
diff --git a/maidroid/models/maidroid.b3d b/maidroid/models/maidroid.b3d
new file mode 100644
index 0000000..76243ba
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diff --git a/maidroid/models/maidroid.png b/maidroid/models/maidroid.png
new file mode 100644
index 0000000..d9c5f77
Binary files /dev/null and b/maidroid/models/maidroid.png differ
diff --git a/maidroid/staticdata-format.json b/maidroid/staticdata-format.json
new file mode 100644
index 0000000..bc854bf
--- /dev/null
+++ b/maidroid/staticdata-format.json
@@ -0,0 +1,4 @@
+{
+	"product_name" : "maidroid_mk2",
+	"serial_number" : 831,
+}