Mox Part 2

After having my Mox for over a month now, I’ve made a few changes, and have a few more complaints.

I ended up salvaging an internal antenna from another device, and using the original WLE900VX card instead of the SDIO WiFi for 2.4GHz. It only has two antennas for the time being, but that’s still no worse than SDIO card (and, you know, it doesn’t have bug-riddled firmware).

I’ve also slowed down the fan a little bit more, so that the card still stays under 70C under most ambient temperatures. It is a tiny bit hotter with the extra card running in it.

So, what are the problems?

The first is a bit of instability. There is a known issue with soft rebooting some Moxes, and mine seems to be one of them. However, since the Mox has the same auto-updates as the Omnia (including kernel updates, which require a reboot), it’s hard to tell what really happened when you come home and the Mox is unresponsive.

The main problem I have is the case design. It certainly looks fine, but there are some functional issues I have with it:

  • Thermal management, or utter lack thereof
  • Have to disassemble large parts of the case to access one module
  • Limited places to put antennas, and high risk of accidentally pulling a cable

Read on for the details.

Thermal Management

This is the biggest one, since a lot of my challenges have been heat-related. It’s safe to say the Mox was probably not designed for really hot WiFi cards (though for a device advertised as being modular, I’d hope they’d keep it in mind) like the 1216, but even then, the CPU heatsink runs pretty hot as well. Unfortunately, I can’t seem to figure out if there is a way to read the CPU temperature (there’s a thermal sensor at /sys/class/hwmon/hwmon0/temp1_input, but I’m not sure what it’s actually measuring).

The Omnia was able to at least solve CPU heat issues by using solid block of metal as a thermal bridge between the CPU and the metal case. The Mox has no such device. Combined with the poor airflow, anything that generates heat inside the Mox is effectively heating up everything else inside.

As a test, I decided to run the Mox with the front/back pieces on the 1216’s module removed. Lo and behold, the temperatures dropped by 2-3C. This tells me that internal temperatures could have been improved by simply providing more air holes.

The interior of the case is reminiscent of a large rackmount server, where there are some shrouds and baffles to force airflow into places where it’s needed, rather than just blowing air from one end to the other without it actually cooling anything. But the Mox doesn’t have any fans, so I can only guess that these pieces must be purely structural.

Disassembly

This is another annoying point. The case has several different plastic pieces that form one module’s worth of case:

  • Bottom inner case (what the board snaps into)
  • Top inner case
  • Top/Bottom outer pieces
  • Front/Back outer pieces
  • Endcaps

The problem is that there isn’t a very good way to access just a single module. You can sometimes get away with just removing the two front/back caps, the two adjacent top caps, and then bending the combined case a little while pulling out the top (then doing the reverse to reassemble it), but that seems risky as, as it sometimes crashes the router if you do it hot (probably momentarily breaks the PCIe connection). To properly disassemble it, you have to do it fully (i.e. all the front/back caps first, then the outermost top caps, then the endcaps, then finally you can separate the top from the bottom).

On top of that, the pieces are held together using those small plastic “hooks” (I’m not sure what they’re actually called), which can break.

Antenna Mounting

In my original post, I said I made a mistake by not ordering enough extra antennas. This would have been an even bigger mistake, because the large antennas I bought can realistically only be mounted on the top case pieces, front-to-back. This would not make a good antenna setup, because they would all be at the same axis. I’m not an antenna expert, but I know that generally, that is conducive neither to improving coverage nor enabling devices to use multiple spatial streams.

The included antennas do it right – they are at a variety of angles. No two antennas belonging to the same card are positioned alike.

However, the included antennas are also very small. I know size isn’t everything, but these things are smaller than all of the various internal antennas I took from other devices. This means that it is more difficult to find compatible antennas, and more difficult to actually position them.

Next Steps

The good news is that I think I can fix the thermal and antenna issues in one go. I’ve filed a support ticket to see if I can buy some spare case parts (the front/back caps). If I’m able to get them, I’ll see about drilling some holes in them to allow for both better airflow, and external antennas. I could possibly even make one that provides a place to put a 40mm fan. It should be as simple as drilling some holes in the plastic.

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