Knock-Cube: hit against a surface to trigger a sound.	Cube construction, showing the central hollow area for sensors and actuators.	The Hub: four cubes at a time can be connected to the hub. The hub contains all of the circuitry required to run the cubes. The hub is also connected to both power, and the computer.	This shows the relationship in size between the cubes.	When not in use, the cubes will stack on top of the hub.