-- place robot spawner one below bottom left/right corner of tunnel
if not l then
	-- CHANGE VALUES BELOW TO CONFIGURE TUNNEL
	l=20 -- tunnel length
	w=3 -- tunnel width
	h=2 -- tunnel height: 1 or 2
	a="N" -- tunnel direction: N S E W
	s="R" -- side of tunnel spawner is at: L R
	f="default:cobble" -- place block if no floor

	generate_power=0 -- dont use power to dig, fails if node requires power
--	generate_power=0.04 -- amount of power to generate each dig
	fuel="default:coal"

	-- DON'T TOUCH ANYTHING BELOW HERE
	x=0 ; y=0 ; dx=1 ; m=0
	as={["N"]=0,["W"]=90,["S"]=180,["E"]=270} ; turn.angle(as[a])
	if s=="L" then dx=-1 ; x = w end
elseif m==0 then
	node=read_node.forward()
	if node=="air" then
		m=1
	elseif generate_power then
		if machine.energy() < generate_power then
			machine.generate_power(fuel, generate_power)
		else
			if not dig.forward() then self.remove() end
			m=1
		end
	else
		if not dig.forward() then self.remove() end
		m=1
	end
else
	local function check_and_place_floor(where)
		local node = read_node[where]()
		if node=="air" then if not place[where](f) then self.remove() end end
	end

	x=x+dx
	if x==w or x==-1 then
		dx=dx*-1 ; x=x+dx -- reverse X direction

		y=y+1
		if y==h then
			l=l-1 ; if l<=0 then self.remove() end -- tunnel completed

			-- move back to ground before moving forward
			if y>1 then if not move.down() then self.remove() end end
			y=0

			check_and_place_floor("forward_down")
			if not move.forward() then self.remove() end
		else
			if not move.up() then self.remove() end
		end
	elseif dx==1 then
		if y==0 then check_and_place_floor("left_down") end
		if not move.left() then self.remove() end
	else
		if y==0 then check_and_place_floor("right_down") end
		if not move.right() then self.remove() end
	end
	m=0
end