Temperature Testing, Round One

So far we haven't done any temperature testing other than the failed attempt with the first prototype and a propane torch which melted the USB connector's plastic. Our investigation into being the toughest USB drive in the world showed that a good temperature rating is one thing we are currently lacking.

We will perform some initial temperature testing with the one of the third prototypes which has been destined for eventual destructive testing, although we will try to be careful and not destroy it so we can get as much data from it as possible.

Failure Modes

Before going ahead with the testing it may be useful to review exactly how our VIUD may fail at high temperatures:

• Plastic in USB connector melts
• USB flash drive fails
• O-rings Melt
• Internal epoxy melts/fails
• Body melts

The primary failure modes we're interested in would be the first two. The plastic melting in particular is the most likely failure as, depending on the exact type of plastic, it occurs at relatively low temperatures of 150-315 °C (300-600 °F)  although Wikipedia states a melting temperature for Polyethylene as low as 105 °C (220 °F).

It is difficult to determine at what temperature the flash memory will fail at although it appears to be a gradual process: the higher the temperature the more likely bits will flip by themselves. There is an interesting paper that shows results for accelerated temperature testing in the range of 170-250 °C (340-480 °F) and gives the data retention for their device at 105 °C (220 °F) as 10 years. We can assume from this that the failure temperature for the flash memory is also relatively high and not likely to occur before the connector plastic melts.

Similarly the last three failure mechanisms occur at temperatures above that of the plastic melting point. If Viton o-rings are used they are rated to 200 °C (390 °F) and probably won't completely fail somewhere above that. The epoxy used in this prototype is only rated to 125 °C (260 °F) but again won't completely fail somewhere beyond this temperature and the actual epoxy that is going to used is rated much higher (300 °C, 570 °F). The melting of Aluminum (660 °C, 1220 °F) and Titanium (1670 °C, 3030 °F)  is so high as to be mostly irrelevant.

Procedure

The procedure for temperature testing will be relatively simple:

1. Let test object return to room temperature.
2. Let test apparatus achieve desired temperature (if applicable).
3. Subject test object to the desired temperature for a set amount of time.
4. Cool object after test in water for at least 5 minutes.
5. Examine object for any obvious signs of damage.
6. Test USB for any new file blocks with errors.
7. Test USB contents for any changes in data.
8. Repeat test at slightly higher temperature and/or longer period as desired.

The test for bad blocks is done using HD Tune Pro which is a basic drive benchmark and tester. The test for changing bytes during a test is simply done by creating random files that fill the USB and using a MD5 sum to ensure their contents are identical before and after the test.

Test Results

The following table summarizes all the temperature test results so far:

Test Type	Temperature	Length of Time	Error Test	Bit Change Test	Notes
Oven	90 °C (200 °F)	5 min	Passed	Passed
Oven	120 °C (250 °F)	5 min	Passed	Passed
Oven	150 °C (300 °F)	5 min	Passed	Passed
Oven	180 °C (350 °F)	5 min	Passed	Passed
Oven	200 °C (400 °F)	5 min	Passed	Passed
Oven	230 °C (450 °F)	5 min	Passed	Passed
Oven	260 °C (500 °F)	5 min	Passed	Passed
Oven	290 °C (550 °F)	5 min	Passed	Passed	Case exterior exceeds 100 °C
Oven	290 °C (550 °F)	6 min	Passed	Passed
Oven	290 °C (550 °F)	7 min	Passed	Passed
Oven	290 °C (550 °F)	8 min	Passed	Passed
Propane Torch	1800 °C (3300 °F)	10 secs	Passed	Passed
Propane Torch	1800 °C (3300 °F)	20 secs	Passed	Passed
Propane Torch	1800 °C (3300 °F)	30 secs	Passed	Passed	Case exterior exceeds 100 °C
Propane Torch	1800 °C (3300 °F)	40 secs	Passed	Passed	Minor damage to external o-ring
Propane Torch	1800 °C (3300 °F)	2 min	Failed	Failed	Prototype #1, USB plastic melted
Oven	200 °C (400 °F)	15 min	Passed	Passed
Oven	290 °C (550 °F)	9 min	Passed	Passed
Oven	290 °C (550 °F)	10 min	Passed	Passed
Boiling Water	100 °C (212 °F)	60 min	Passed	Passed	Turned Aluminum black
Wood Fire	600 °C (1100 °F)	30 sec	Passed	Passed	Case exterior exceeds 100 °C
Wood Fire	600 °C (1100 °F)	45 sec	Passed	Passed	Damage to external o-ring
Wood Fire	600 °C (1100 °F)	60 secs	Passed	Passed	Damage to external o-ring

One interesting thing to note is that the boiling water test turned the drive a black color with tints of gold that actually looks rather nice (resembles a black anodized Aluminum). I'm assuming it is something in my water (a very hard water) that turned it this color.

Surprise...it's Black Now!

Comparing the Competition

Most USB drives don't have explicit temperature ratings but of those that do the LaCie Xtremkey has the highest:

• Operating temp.: 5 to 35°C (41 to 95°F)
• Non-operating temp.: -20 to 60°C (-4 to 140°F)
• Fire test: 30 sec. fire exposure
• Heat test: 200°C (392°F) / 3 min

Since we easily beat both of the listed tests by a considerably margin it is safe to say our VIUD would be the toughest USB drive available for temperature ratings.

Tentative Ratings

We still have to test our final design although I wouldn't expect too different results with the possible exception of the Titanium model performing a little better. We can still estimate our temperature ratings based on the tests so far:

• Operating Temperature: ? to 60 °C (? to 140 °F)
• Storage Temperature: ? to 90 °C (? to 200 °F)
• Air Storage: 290 °C (550 °F) for 5 minutes
• Boiling Water: 100 °C (212 °F) Indefinitely
• Wood Fire: 1 minute exposure (600 °C, 1100 °F)
• Propane Torch: 40 seconds exposure (1800 °C, 3300 °F)

The operating and storage temperatures may be changed by the specifications of the USB flash memory used. Next up will be testing the cold side of the temperature scale which should be interesting to see how low we can go.

The Toughest USB Drive in the World

I was thinking last night while I was trying to fall asleep about the following question:

What do I need to do to honestly be able to call the VIUD the world's toughest USB drive?

While I think we're already pretty close to this point we'll look at a few areas that a USB drive needs to excel at to be called "tough":

1. Pressure
2. Temperature
3. Acceleration / Shock
4. Force / Load

The pressure rating is an immediate win for our VIUD: currently rated at 3000 psi it is at least ten times higher than any other USB drive out there except for the old Tyukalov which was rated at 2000 psi.

So far we haven't done any temperature tests except the failed 2 minutes at 1100 °C propane torch test on prototype #1. Most USB drives don't have explicit temperature ratings or they are simply set incredibly low but the LaCie Xtremkey is rated for 3 minutes at 200 °C and 30 seconds fire exposure. I hope I can beat both these ratings despite using essentially off-the-shelf USB drives since the failure mechanism is the plastic in the USB connector melting.

Most drives are also not rated for shock/acceleration with the Xtremkey again topping the chart with a rating of 50G. I haven't done any shock testing yet although the high-speed camera has been ordered and some basic calculations seem to indicate that a 50G rating should be easily beaten.

The force/load tests are really the most important ones for a "tough" USB drive and there are actually no drives out there with explicit force or load ratings. There are a few with unofficial "car/SUV drive over rating" but this is actually a relatively low bar to pass. Even a large moving truck driving over a USB only exerts around 2 tons of force which even our low strength brass prototype could withstand. Stress modelling of our Aluminum and Titanium VIUD design shows a worst case failure in end-to-end stress to be in the area of 8-10 tons. This would seem to point towards a win this category although actual destructive stress testing of competing drives will have to be done to be sure.

So while the prospecst look very good that we will be able to call our VIUD the "world's toughest USB drive" we have a bunch of testing to do first.

Looking at the Competition

Looking at existing products in the rugged, waterproof or otherwise indestructible USB drive market is useful for a few reasons:

1. It may be that our "best" VIUD already exists.
2. Compare and possible change our design with what is available.
3. Get a better idea of prices if we wish to market our drive.

The following are a selection of better products found from searches of rugged, waterproof or indestructible USB drives.

Corsair Survivor

The Corsair Survivor looks like a relatively nice consumer level rugged and waterproof USB drive. It has a nice waterproof rating of 300 psi and its Aluminum case looks like it would take a pretty good beating. The design, in my opinion, is not ideal with a very large cap which may be easily lost. It has a relatively low price range of $30-85.

LaCie XtremKey  

The LaCie XtremKey looks like a decent candidate for a VIUD with a 300 psi waterproof and to a 10 ton pressure resistant rating. The "resistant" qualifier is suspect but with an all metal case it looks like it could handle being run over by a large car depending on the exact type of metal used (they mention a Zamac alloy but not which one). It has a large cap design like the Survivor which I dislike. Its price point is slightly higher at $85-140 but is not unreasonable for such a rugged device.

One notable specification for this drive is its large range of temperatures, particularly its high temperature limit of 200 °C. Although they again say "resistant" this is much higher than any other USB drive I've seen that actually has any temperature ratings (most don't).

Imation Ironkey Basic

The Ironkey Basic from Imation is a very nice looking drive with what looks like a basic metal case which would protect it from everyday bumps and drops but probably not larger accidents. It is rated waterproof under specification MIL-STD-810 which, as far as I can tell, is close to IP67/68 or essentially just waterproof from basic immersion and not pressure rated.

The drive's price is significantly higher than other rugged drives at $90-300 despite being less rugged. This is likely due to the Ironkey's main purpose of being an encrypted drive. Overall a great looking drive but not exactly what we're looking for our own VIUD. In theory if we wanted encryption it could be done at the software level.

Tyukalov USB Drive

The Tyukalov drive is a unique, one of a kind, custom USB drive which is interesting to compare to the consumer type drives previously found. It was made in a limited quantity of 100 at a relatively high price of $200-250 each but managed to sell out in a short period of 3 weeks. Its unique dual cavity design is not particularly convenient but it boosts the highest waterproof rating of 2000 psi of any USB drive I've seen and undoubtedly an equally high rugged rating.

Eternal Case

The Eternal Case is a product that wasn't out when I initially researched and came up with my VIUD design in the fall of 2012 but is remarkably similar. It just goes to show that if you think of a good idea there's a good chance someone else already has or soon will.

There are no explicit ratings for this custom product but from its design I would guess it should be waterproof to at least 300 psi and would easily withstand being run over by a car. Its price is amazingly low at only $40-75, even for a 32GB Titanium model. Based on what I've researched for prices I'm unsure how they can make a profit at this price. The only negative thing I can see is that the design/manufacture is relatively rough looking.

Wrapping Up...

There are other drives that are marketed as "rugged" but the majority don't actually have an explicit mechanical or waterproof specification. Most appear to be just cheap drives surrounded by a thin metal case with a "rugged" label which is not what I'm looking for my own VIUD. 

Even with this relatively small collection of existing true rugged drives it gives us a relatively good baseline on what is currently available and at what price. It also helps narrow down some of our design constraints, or at least what we would like them to be:

• >2000 psi waterproof rating
• >10 ton crush rating
• >200°C for 3 minutes temperature rating
• $40-300 (depends on capacity, quality, and ultimate rating)

Time will tell whether any of these are actually possible or not....