- Category: General
- Published: 05 May 2016
- Hits: 3641
Its been a couple weeks since I ran out of Black ABS filament and it's been back-ordered in China (I was sent 3mm by mistake before they realised they were out of stock, my machine is 1.75mm only). While I waited for this to arrive I decided to use some of my spare blue ABS on a plug and play rack system for my Raspberry Pi servers.
I have a number of Raspberry Pi's performing several server based tasks. These range from the original Model B to the B+, 2B and now a couple of 3's. The form factor of the 2B and 3 are identical so I focused on these, the two remaining servers I have running on the older form factor (Asterisk VoIP system & Direct to Disk SAN backup) will remain as they are. Never one to reinvent the wheel I looked around the web for an existing design and stumbled across this....
Many thanks go to Dave Pedu who did the original design for this project here
I like the design and it has future expandability due to the threaded rod stacking system employed so I decided to use this one. However it was in need of some modification to suit my needs and hardware. The basic rack design is used as supplied and consists of the upper plate which is grooved to allow the blade racks to slide in and out. The lower plate which is also grooved but has receptacles for the power connections.....
....and the back plate which holds the network connectors.
All these parts were printed as is and needed no additional modification from the design. An additional plate holds the network switch and power distribution. This is the plate I had to modify so I imported the supplied SketchUp drawings into my preferred 123D software and proceeded to modify. The attachment points for the network switch were altered as the switch I had bought a while ago contained a circuit board that although was the right size and shape appeared to be upside down to the one originally designed for. I also modified the power distribution section of this plate to suit standard copper strip board rather than the green prototyping board the original design called for (I didn't have any of the green boards)
I also acquired a dedicated 5v 10A power supply from ebay to replace the ATX PC supply in the design. I designed and printed an end cap for this supply to allow for a standard fused connector to be added and for the output to be presented on a plug and socket arrangement.
Once all of this was printed I began assembly starting with end cap for the power supply. I added in the two 'Deans' sockets I would use for 5v output.....
.....and then the fused and switched 240v supply socket.
Finally wiring it all to the supply terminals and closing it with a screw.
Next up was the wiring for the power and network that goes through holes in the bottom plate. Each spot on the rack has to have power and network supplied. I found the network cables could all be the same length which made making then easier. One end of the custom network cable has the locking tab removed and the RJ45 pushed through the back plate, the other will eventually be plugged into the network switch on the plate blow the rack. The Cat5e cable had to have the outer sleeve removed to make it fit through the supplied holes but as this is unshielded cable this would have no detrimental effect. The power connector is a simple 0.1" 2 pin PCB connector and thanks to the Wall-E project I have loads of those. A female connector attached to the mounts on the lower plate ready to receive the male pins that are on the blade itself. The wiring for these connectors are all different lengths and go to a distribution board on the power and network plate. These were soldered in as was a large power cable with a 'Deans' plug on the end to fit the new connectors on the 5v 10A supply.
With all the wiring completed I assembled the rack and started working on the blades that hold the Raspberry Pi's in place.
Each of the Blades consist of a single Raspberry Pi positioned exactly in line with the RJ45 mounted in the chassis. Each of these plastic blades has a spot for the 0.1" 2pin male connector to be mounted exactly in line with the female in the chassis. The 0.1" power connector has two wires coming from it that are 5v and GND. The original design attaches the end of these wires to the GPIO 5v and GND pins of the Raspberry Pi's however I was not comfortable with this arrangement since it bypasses the fuses, regulation and protection on Pi itself. I therefore decided to solder my wires to the back of the Pi circuit board at the factory test point locations for the 5v and GND lines of the USB power therefore utilising all the protection the Pi has to offer on the power side.
For those that are interested the connection points for the Raspberry Pi's are as follows......
Raspberry Pi B+
PP1 or PP2 - USB 5v
PP3 - USB GND
Raspberry Pi 2 & 3
PP1 or PP2 - USB 5v
PP5 - USB GND
Once all 4 of my existing Pi's were attached to blades I added them to the chassis and tested everything. As you can see from the last image I have 6 bays in this chassis all have there blades wired and ready. 4 of these are populated with Raspberry Pi's already and 2 remain for expansion.