Raspberry Pi Bramble Rack

This simple design lets you stack four Raspberry Pi machines to form a small Hadoop cluster. It requires the use of [my design for a Raspberry Pi case](https://www.thingiverse.com/thing:1728228). I use active cooling (e.g., a fan) to keep the cluster between 30 - 40 C. Without active cooling the pi's would hover around 60 C.