Going into the process of writing up and publishing this design, I knew I’d never publish it if I waited for it to be perfect and I knew I’d put it off indefinitely if didn’t publish it as soon as I could get a writeup put together.
Of course, this means it was inevitable that there would be problems to solve. I intend to list known issues here as I become aware of them.
Assembled with the materials listed in the bill of materials from 1. What You Need, the cluster will get too hot when it’s been running a while. I’ve never seen it get so hot that it exceeds the BCM2835’s rated maximum temperature of 85°C, but I’ve noticed that network connections will get flaky after a while.
My current solution to this issue is to run the cluster without air filters. (It runs even cooler with the left panel off, but I’m not sure this is necessary.) I see this as temporary; I believe I allowed enough space in the case to redesign/rework the fan and filter harness so that it’s the only part that should need to be changed. I intend to post a redesigned part once I have a solution.
2. SD Card/Socket Issues
The 8 GB SD cards I listed will also warp, as I mentioned in a previous update, even though I believe they are also still below their rated maximum temperature as well. Though, technically, they do still function if you can get them to make contact will all the pins in the SD card socket. That can be accomplished by replacing the Pi’s original SD card socket with one that supports the other side of the SD card. There’s a Wurth brand socket in the same form factor that works well, but the Pi isn’t quite as pretty after it’s installed.
I’ve been replacing the SD card sockets on my own Pis with the Wurth model so I can still use my original SD cards. However, I believe the warping issue will solve itself once I have an updated fan and filter harness installed.
3. Flaky Short Network Cables
I seem to have some problems with a few of my shortest network cables. They work, but seem to have intermittent connection problems. I’m unsure at this point if it’s due to a minimum length issue or that I simply made a few bad cables. Really, neither should be a problem, but the fact that my shortest cables seem to have the most problems suggests that it may be a length issue.
It’s entirely possible this issue is also related to the heat issue mentioned previously, as the longer cables still get rather warm, which I assume means they’re effectively functioning as heat sinks for the Ethernet ICs on the Pis.
So far, I’m getting around this issue by bypassing flaky cables with slightly longer cables (10 inches or more). This is reasonably easy to do, but isn’t as pretty as I’d like it to be.