Rasberry PI cluster in a Stackable Tube.

update 12 June 2017 I am finally building it!
Check out the thingiverse page:
https://www.thingiverse.com/thing:1374292
Getting down a bunch of ideas I have been having about building a raspberry pi cluster. I got this idea from reading how cray computers used to be built in a circle to reduce the length of the wires that connected the individual computers together. Evidently this resulted in significant measurable speed ups in message passing latency.

Picture 12 raspberry pi computers in a circle with their GPIO pins on the inside, their hdmi slots facing out, and their memory cards facing up. very short wires from each board going to every other board. Serial networking protocols running on those serial TTL connections, eliminating the need for more hardware and reducing latency to very small values.   Disadvantage would be low bandwidth on any one network segment.

One of the Pi computers acts as the master and connects to local network with a standard network cable and routes to the rest of the computer
s in the cluster.  Alternatively you could run network connections to every computer and use this for high latency, high bandwidth data.

Doing the low latency network connections would speed up the cluster if it was processing many tiny messages that need processed as quickly as possible, such as financial data, or medical HL7 events.

A single brick power supply sends power directly into the GPIO of each board, bypassing all the safety measures on the boards, so the power supply would have to be a good one. This eliminates the need for running a usb cable to each individual board for power.

Right now I am working on printing out tube segments that will fit on top of each other and hold the PIs. These tubes would be passively cooled, the tube acting like a chimney. So it would have to be on a base that allowed air flow from underneath. But also design them to be stacked with a connecting segment on each one with the middle clear so you can drop power and network cables down the middle. This connecting segment would pull in air from the front, let it go up the tube above it, while letting the air from the tube below it go behind the stack of tubes. If need be a small fan on the back of each stacking segment could pull air up through each segment.

Alternatively the tubes could stack on top of each other and a single 120mm fan on the bottom rapidly blows air up through all the tubes.

A topper segment neatly closes the top off from view, while allowing air to blow up easily. The base could accept legs or screw down to a board for better stability. Or the whole thing could hang from a ceiling beam.

With Pi Zeros the cluster would only draw about 7 watts max. With Raspi 2s it could draw up to 25 watts and be 3 times more expensive, but it would be almost an order of magnitude more capable. Power data comes from here. Nodes can power down unused parts of their board for more savings.

A clear plastic tube over them proudly showing the details and directing cooling air flow. This could be done by cutting the tubing and pressure fitting them into 3D printed fixtures at the top and bottom. A 3D printed frame fits into the clear tube and the tube goes into rings top and bottom to make it look finished.