The Evolution of a Raspberry Pi2/3 Cooling Tunnel

Well after receiving my 3D printer I gave some thought to what I would make.  Yoda’s and the like don’t interest me.  After giving it some consideration I decided to build a Raspberry Pi2/3 wind tunnel (cooler).  This thread will show the build and estimated times to build the various components.  There are a total of 11 components – one 100 mm power cylinder,  two cylinder extenders, two cylinder couplers,  two end caps, a plate on which to mount the Pi2/3, and three filter grates.  This is the minimum number of parts you will require to support a PI2 with a wifi dongle.  If using a Pi3 with built in WIFI then less parts are required.  You will need to supply your own nuts and bolts, printer, etc. to fabricate the finished product.  Don’t have a 3D printer?  Check in your area.  There are libraries or professional businesses which provide such services for a price.  But bear in mind that one component takes 7.5 hours.  Many “public” locations might not allow such a long print.  And the cost of printing large parts might be $ prohibitive.  You best option might be a friend so be sure to offer to pay him for the filament used.

The goal:  mount a Raspberry Pi2/3 used for distributed computing (Einstein@Home is a great example) in a tunnel to which a fan is attached.  This will provide ventilation/cooling for the Pi2/3.  The fan will be initially powered from the Pi2/3’s +5V and ground pins and a LED will be powered by the Pi2/3’s GPIO pins to alarm a temperature violation and send email.

Here is a picture of my printer:IMG_1377

It came as an unassembled kit and took 2/3 days to assemble.  There is a learning curve in 3D printers so unless you are will to spend some time learning how to 3D print it might be best to avoid them altogether.  I did not use the filament holder that came with the kit but designed my own out of extruded aluminum channels from Adafruit.  Adafruit also has lots of cool stuff for electronic projects which include the Raspberry Pi2/3, 3D printers, filament (I am using a black PLA/PHA filament available through their website), etc.  In fact the Raspberry Pi3, LEDs, LED holders all came from Adafruit

I used a RepRap cartesian printer to print these parts.  Total print time:  ~21 hours.  The 100mm power section with access ports took 7.5 hours, the end pieces 1.5 hours each (3 hours), the Pi plate 30 minutes, the 2 couplers 1 hour each, the 2 extenders 3 hours each, and the fan grates 1 hour each (3 hours).  With respect to the cylinder you might want to outsource that because of the time it takes (I tried this but it was cost prohibitive – $200).  A big problem with 3D printing is that if you loose power during a print you also loose the part.  There is no way to start over using entry level printers.  This is why I decided to go with  smaller parts for shorter print times even though it meant having to have more pieces in the project.  The chance of a failure in 7 hours is greater than in 3 hours.  I can’t address the use of a UPS.  I don’t think it would be feasible because of the power draw on both the extruder hotend and the heated bed.

What follows are a series of pictures showing the tunnel.  There are also videos embedded of the prints for some of the components.  The video for the filter grate/End Cap grate is the most interesting to watch.  It was the most complex print.  I no longer use that part it because it impeded airflow.  Instead I went with  circular design/grate.

What follows are pictures of the major components.  Other components such as the extenders and couplers, standoff  have been omitted at this point but will be shown in the assembly portion.

A.  100mm power cylinder – has two internal channels running the full length.  This channels accept the Pi plate to which is mounted the Raspberry Pi2/3.  The current design provides 3access ports, 1 for power, 1 for HDMI,  and 1 for sound.


B.  2 End Caps – They are identical.  Both have ports/holes for the led housing and the fan wiring to pass through.


C.  1 or more  Pi2/3 Plates – the plates provides 4 holes which align with the mount holes in a Pi2/3.  It’s width is wider to allow a snug fit in the cylinder.  One end is flat and butts up again the fan while the other end has a concave cut out to allow for easier cable storage.  Two of these can be used together if you use tunnel extenders.

D.  3 filter grates – two are used on the fan end.  A filter material of your choosing is “sandwiched” between two grates and then mounted to the fan end-cap.  The other filter grate is directly mounted to the other end-cap without filter material.

Some Assembly required (there, I have warned you):

Normally the components shown at the right would allow you to build a tunnel for a Pi3.  This assumes support for the LED and the fan.  No other devices.  If you wanted to add additional stuff then you will need to extend the tunnel by using the 50mm extenders and 30mm couplers. IMG_0272
Here is a normal assembled tunnel for just a Pi2/3 without any other hardware compared to my proposed configuration using an mSATA drive.  As you can see the tunnel is “short”. What I am proposing
So I will extend the tunnel by using 2 30mm couplers and two 50mm tunnel extenders followed by an exhaust end cap.  The couplers shown are 20mm.  When assembled there was sway in the tunnel so I made the couplers 30mm long for more support and tightened up their inside diameter slightly. This required an extension of the tunnel.  Yes I could print a 1 200mm tunnel but long prints entail greater risk of failure due to power fluctuations, etc. so I decided on a “more parts” approach. 
Begin assembly: place 3m bolts in the 4 holes on the fan shroud.IMG_0287
followed by 1 circular grateIMG_0288
followed by filter material
followed by another circular grate
install fan into shroud – be sure the standoffs stay in place.  they provide space between the last grate and the fan so there is no contact. IMG_0308IMG_0309
install LED holder IMG_0312
and secure with nut
mount fan to fan end cap pass the fan wires through the small hole on the front of the end cap.IMG_0316IMG_0320IMG_0322secure with nuts
attach 100mm  power cylinder IMG_0324
pay attention to orientation.  the holes are power, hdmi, audio.IMG_0326the “other” side.  note the bridging material covering the GPIO slot – necessary during printing.  easily “snapped off” with needle nose pliers.IMG_0327from the front
now for the Pi part Pi3 with USB mSATA mounted on Pi plate. 
extending the tunnel components are extremely tight fitting.  be patient.  looks pretty good though

a look down the barrel with extenders attached
Pi insideIMG_0339
oops.  video part not quite right (too low) – fixed in drawing.  IMG_0369

wiring for LED and FAN The left pair is for the FAN.  Note the pin placement 5V and Grnd.  Maintain polarity.  Yes the fan will spin in the other direction if reversed but the fan’s blades are meant to be efficient going in one direction only.  The second pair of wires is for the LED.  Again maintain polarity or the LED won’t light.  And don’t forget the inline resistor. 
Pi violating high temperature limit.  The software runs as a cron job every 15 minutes.  If the temperature violates a specified limit (your choice) it will email you and then enter a one minute loop flashing the led.  At the end of one minute it will extinguish the LED and exit until the next 15 minute period. IMG_0218

4/2/16 – I removed the compressed download for the Pi Tunnel *.stl files.  I have instead provided a new download for the PiVE.  The PiVE is 4 or more tunnels joined together to make a hive.  You will be able to download the actual sketchup files which will enable you to resize the components to your needs.  One thing that has forced me to do this is that depending on your power brick used for the Pi the USB end might not fit the port in the tunnel.  Because they are .stll files it might not be possible for most to resize the port to accommodate their USB connector.  I apologize for any inconvenience this has caused.  Here is a link to the  PiVE.

Here is a tar file for the 3D components for the cooling tunnel:

pi_tunnel.tar.gz (820 downloads)

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