Enrico, there is virtually no limit to what an arduino board can control, for instance, I have successfully controlled my milling machine spindles which has 2 by 2HP three phase electric motors on it! The trick is that the arduino board won't power these sorts of things directly (obviously), so you need to find something to interface with it, eg relays or in my case, a VFD (Variable Frequency Drive) which has a serial port interface. Also, when you get to these bigger items, you need to make sure your board is isolated from any feedback from these motors to protect your board and to ensure it functions properly.