People tend to view goals as admirable things to strive towards. An engineer tends to view these as constraints that begin to define the design. After looking at YouTube videos of various cube sizes I decided to design an 8x8x8 cube. If designed properly I figured it would lend itself to bigger and smaller versions using the same techniques.

Choosing a x8 size (shorthand for 8x8x8) yields the first constraint: 8x8x8 = 512 smart LEDs.

Secondary constraints immediately followed. For example, one secondary constraint is the amount of current to drive that many LEDs -- recall that 512 smart LEDs = (512 Red) + (512 Blue) + (512 Green) = 1536 total LEDs that can pull up to 30.71 A of current.

This amount of current will add further constraints with regards to connectors, the sizes of circuit board, size of power supply, and circuit board trace sizes.

So, that one goal of a x8 cube created several significant derivative constraints.

Another goal would by physical size. There doesn't seem to be any consensus regarding the spacing between the LEDs. The spacing impacts how nice the display will look at a given distance. It also impacts the physical size of the cube. Physical size impacts the cost of the circuit boards to some extent as board cost is usually directly related to board area. Also, shipping costs of the final product relate to physical size and weight.

After looking at other cube designs I decided to settle on 0.75" (19.05mm) spacing to start with. At this point we're looking at a cube that will be a minimum of 6"x6"x6" plus whatever extra dimensions might be necessary. This is small enough to fit comfortably on a table top.