The Finished Product!

While it took much longer than I had anticipated I'm happy to say I can hold in my hand the world's toughest USB drive!

The Completed Revision 5 VIUD Prototypes

The completed VIUDs are even better looking than the individual parts and work great. I've been carrying two in my pocket for the last two months and while they are definitely on the heavy side for a USB drive they are not excessively so. There's a bit of chipping on the corners/edges of the Aluminum model which is expected and probably mostly due to the Titanium model being next to it. The Titanium model still looks flawless.

The magnetic cap works great and is strong enough to hold the VIUD to the fridge door or other metal surface as designed. I haven't tested the lanyard attachment but my initial concern of the edges being too sharp were fortunately unfounded. I've only done a quick 3000 psi pressure test so far but both test units passed easily.

Assembly

Adding the Internal Epoxy

Assembly of the 15 prototypes went well but did reveal a few minor design and assembly flaws:

• The anodized threads were just barely too tight and required manual retapping. I'll specify a looser thread tolerance for the internal threads to compensate.
• The slots for the magnets were just barely too small and had to be made a bit larger. Slightly larger OD dimension for the slots are needed depending on how shock testing goes. I fear if I make it too loose the cap magnet will come free too easily.
• Weighing the amount of epoxy in the base worked great but the magnet caused havoc with the scale. Adding a few non-magnetic spacers fixed this easily.
• The scale used has an annoying tendency to turn off in the middle of deploying the epoxy into the base. Hopefully there's a way to disable the auto-power off feature or a different scale will be needed.
• The amount of epoxy needs to be reduced slightly as when it is cooked in the oven it expands and overflows. The overflow is actually good in a sense as it means there are no air pockets in the base but it requires more time consuming clean up afterwards.
• Oven baking to cure the epoxy worked just fine. The magnets help to keep the base secure the metal pan.

Baking at 90°C (200°F) to Cure the Epoxy

What Next? 

There will have be a small break in the VIUD development this summer due to my personal schedule...who knew getting married would keep you so busy! Sometime in the fall I'll get back into more testing of the finished revision 5 VIUD prototypes to see exactly what sort of punishment they can take.

Assuming no significant design change is required (I doubt it but you never know) I hope to be able to get a KickStarter going for the initial VIUD production run later this fall. Stay tuned to the blog for the eventual announcement.

Prototype #4: The Last One?

After a long overdue wait I finally have the pieces of prototype #4 in my hands, ready for assembly, and they are looking great!

Fresh from the Shop and Looking Good!

Prototype #4 has a number of design changes from the previous prototypes originating from a variety of tests, feedback, and research:

• Magnetic base and cap (it works very well...not sure how I overlooked this design initially)
• Slightly longer for a combination of aesthetics and to hold long-style USB boards if I ever need to
• Hole in the cap for a lanyard attachment
• Slightly simpler interior design for cheaper production (at a small cost of strength)
• Very high strength materials (Aluminum 7068-T651 and Titanium Grade 5)
• Hard anodized Aluminum (dark red)
• Laser engraved logo and serial number

Close-up Showing the Laser Engraving Details

The production itself was basically flawless with only a few minor issues encountered:

• Thread in base was 0.05" deeper than specified (makes assembly a little trickier)
• Threads in the Aluminum base were a bit tight (re-tapped manually after anodizing)

Other than the smaller quantities (10 Aluminum and 5 Titanium) the production process was identical to that of the (hopefully) eventual larger order. This minimizes any surprises and gives me a good idea on the base material cost and time required for assembly.

All that is left now is the final assembly of the USB boards and epoxying before I can get back to destructively testing a few units for fun!

Prototype #4 Production: How to waste 4 months....

I haven't updated this blog in a few months as I was waiting for a small production run of prototype #4 to be completed. I only expected this to take a few weeks but it ended up being a annoyingly painful 4-5 month process.

The Quotes

I originally tried to get quotes from 5 different machine shops from (names have been removed to protect the guilty):

Shop 1	Shop 2	Shop 3	Shop 4	Shop 5
High-end CNC shop Used for prototype #3 Al = $70/set for x100 Ti = $130/set for x50	Advertised as a large, high-volume CNC shop Did not respond to several quote requests and inquiries	US company via internet Has simple CAD software for instant quotes Al = $25/set for x100  Ti = $80/set for x50 Many production issues	Local machine shop Took 2 weeks to respond to initial quote request Could not source desired Al alloy Al = $160/set for x100 Ti = $350/set for x50	Local machine shop Did not source or work with desired materials

I don't understand why I never got a response back from shop #2 despite them looking like a large and reputable shop. I guess they're doing so much business they don't need to reply to quote requests although a simple "We cannot do this order for you at the moment" type reply would be nice.

I tried shops #4 & 5 as they are close in the area as me but both had issues with my material choices. I understand not wanting to work with certain materials, like Ti Grade 5, but I'd expect a machine shop to be able to source materials better than an amateur like myself can. ...or perhaps I'm overestimating how commonly Al 7068-T651 is used. Even with cheaper materials shop #4's quote is more than double that of shop #1 and 4-6 times that of shop #3.

I've used shop #1 for a large number of orders in my previous job as well as for making two pieces of the VIUD prototype #3. They produce excellent quality parts and are very easy to work with. I've always considered them as an "expensive" shop although after this episode I've warmed up to their prices...you get what you pay for after all.

An Unfortunate Choice

Given the wide range of quotes I went with the cheapest one from shop #3....unfortunately I choose poorly. Shop #3 has a slightly different operating practice than most other machine shops. It supplies a very simple custom CAD program that you use to create designs and submit them for instant quote requests. While their CAD application is very limited compared to SolidWorks or AutoCad it works well enough and being able to get instant quotes for simple parts is very convenient. Their quotes for the parts were also far cheaper than anything else I could find by over a factor two.

While shop #3 appears to have a lot going for it they had multiple issues actually delivering them. Trying to contact an actual person is difficult and usually you end up talking with someone who can't, or doesn't, actually answer your questions. Their lead time was longer than most shops at one month but this was extended twice to two and three months without explanation.

Oh....but it gets so much worse. After finally actually completing my order of 15 pieces after 3 months there were three serious quality control issues:

1. Knurling was the incorrect type (straight instead of diamond)
2. The internal thread in was made at the incorrect depth



Worst Knurl Ever

3. The depth of cut in the threaded plug was wrong.

I could probably live with the incorrect, and poorly made, knurling but the other two issues were a deal breaker. I know that mistakes happen in production but these parts are so simple and the mistakes so basic I'm at a loss to explain how they might of occurred. Call me crazy but I expect a competent shop to have the basic ability to make things according to the drawing, especially trivial parts like this. Coincidentally they messed up on each of three parts.

I asked, and the agreed to remake everything, but after another few weeks and several more manufacturing issues I was told they "couldn't find anyone to make it" and I had to cancel the order. The only nice thing I can say is that it didn't cost me anything...except 3 months of time.

The End Result

So +3 months after placing the order for prototype #4 I had nothing to show for it. At this point it is close to Christmas which scratches off another couple of weeks before I can source and place an order with shop #1. I finally get the 15 pieces in my hands some 5 months after the initial order with shop #3.

This whole process highlights a simple wisdom I've learned over the years:

Supplier relationship is often more important than price

Shop #1 may not have had the best price but they are incredibly easy to work with and produce excellent quality work (the prototype #4 pieces look great). I'm looking forward to using them in the future for larger production quantities of the VIUD.

Prototype #3: First Machining

Our last two prototypes (#1 and #2) were made by myself to simply reduce the cost and time involved. Now that our design is more refined we can make our next prototype from a machine shop (i.e., from someone who actually knows how to machine metal correctly) hopefully in preparation for an actual production run. 

For manufacturing I used a local CNC machine shop in Mississauga that I regularly used at my previous job which does great work although it is typically a little more expensive than other shops. For a material we will use Aluminum 7075-T6 which has a yield strength of around 65,000 psi. We will make two units of the same design: one for destructive testing and one we can keep. The price for making just two units was very high at around $250 per unit for just the machining costs although this is reduced to around $50/unit if the quantity is increased to 100. For the USB flash drive I just purchased some off-the-shelf consumer models and removed the plastic case. At around $350 total per unit these are definitely one of the more expensive USB drives out there.

The end result can be seen in the pictures below and it looks great! Note that the following pictures were taken after the drive spent a year in my pocket so it is a bit scratched up. The most notable design change from the previous prototypes is the addition of the engraved logo and serial number which turned out well. Our previous issue of a crooked cap on the first two prototypes has disappeared: the cap fits perfectly indicating that the issue was indeed the manual tapping process or my machining inexperience. The only notable issue was the knurling (the diamond grid pattern for grip) was a bit coarser than what I wanted at 0.08" pitch instead of 0.05".

For now only pressure testing has been performed and we again achieved success the first time at 3000 psi for one hour. A variety of destructive testing including temperature, shock, and force will be performed on one of the units later on.

This prototype was made in the fall of 2012 and one of the units has been in my pocket ever since then and has seen a lot of use. Much like the second prototype there were no usability issues noted and it looks and works like a charm.

Prototype #2

VIUD Prototype #2

I learned a lot from making, and subsequently destroying, our first VIUD prototype and we'll quickly jump to making a second one. This prototype will essentially be the same design as the first one but be made of 6063 Aluminum instead of Brass. In this case I choose a cheaper Aluminum merely for convenience but we will likely not want to use 6063 in the end as it is one of the weaker alloys.

Machining will again be done by myself with a few tricks learned from the first prototype. The process went well although I did have issues with the cap not lining up perfectly with the body when closed despite trying to be very careful when tapping the threads. I believe the issue here is merely due to the inherent inaccuracies of manual tapping. 

Despite a slightly crooked cap pressure testing at 3000 psi for 1 hour passed the first time without any leakage. There is little point in destructive stress testing this prototype as we won't be using the same type of Aluminum in the final design, and it should be same strength as the Brass prototype anyways.

One notable observation is that this prototype is significantly lighter than the first one weighing in at only 60 g despite using a Brass thread plug. This is much nicer than the 150 g of the Brass prototype and while it is heavier than most consumer level USB drives you see it is light enough to not really notice it in your pocket, at least no where near enough to be annoying.

Prototype #2 With the Cap Off

I should note that while I am writing this blog entry in the summer of 2013 I actually made this prototype nearly a year ago in the fall of 2012. Since then this prototype has been in my pocket or backpack almost everywhere I go. After using it some hundreds of times I can't really find any fault in the design other than it not fitting some closely spaced USB connections with other things plugged into them. Its convenient, works well, nothing has broken or worn noticeably, it is relatively pretty despite my limited machining skills, and it has turned a few heads from co-workers and friends (always a good sign)!

The First Prototype

Now that we've done our basic design and research for our rugged USB drive it's time to start making something! I'm a very amateur machinist and the basic design for the drive case is simple enough for me to attempt to make, at least for the testing prototypes. 

I choose Brass for the first prototype's material for a number of reasons: 

Brass Pros Easy to machine Cheap Shiny!

Brass Cons Mechanically Weak Heavy

This is fine for a simple prototype but the Brass cons are more than enough to consider other materials for the final product (materials are to be discussed in a future blog entry).

The design of the VIUD case is relatively simple and is composed of three parts:

1. Cap - Removable part that covers the USB connector and attached with thread.
2. Base - Main body of the USB 
3. Plug - Threaded plug which the USB fits into and is permanently mounted into the base.

Basic Components of our VIUD Design

Machining these parts is relatively simple, even for an amateur, although there are a few "gotchas" to note:

• Using a tap to manually create the threads is difficult at best. You have to tap before machining the case OD or else the body walls buckle outwards. 
• It is difficult/impossible to create a perfectly straight thread with manually tapping (even with a jig) which causes the cap to not sit perfectly on the body. This can be corrected by filing the edge of the cap but is tedious. 
• The hole in the plug for the USB connector is machined with round corners and needs to be filed out square.
• The groove in the plug for the main o-ring seal was done after assembly and the epoxy had hardened to ensure a perfect fit.
• The mount for the cap at the end of the base was added afterwards by press fitting an additional piece into the base.

For the USB flash drive itself I merely purchased a cheap 2GB consumer level drive and removed the plastic case. Assembly merely required to insert the USB into the rear side of the plug, fill the base with epoxy (enough to squeeze out when assembled) and screw the plug into the base. After letting the epoxy dry and machining a groove for the o-ring seal in the plug the first prototype VIUD is finished! Unfortunately I don't have any pictures of the prototype before its destruction in stress testing.

Testing

End-to-End Stress Modelling

Our first VIUD prototype may not look too pretty but it is fine for basic testing of our design. First is a simple handling test: How does the drive feel in terms of weight and size. The size feels fine although it is significantly larger than most USB flash drives these days. It is a little on the heavy side, however, at around 150 g. Not terrible but a little too noticeable when held in your pocket. The overall physical operation of the drive is also fine and doesn't reveal any unforeseen difficulties.

Next, with our simple and cheap pressure testing rig we can easily see what pressure our prototype can handle. Fortunately, even with a slightly crooked cap it successfully passed a 1 hour test at 3000 psi with no leaks! 

Temperature testing was next and I was evidently a little too eager at this stage by using a propane blow torch. Even with just a 2 minute external exposure of 1100 °C the plastic in the USB connector melted completely and a quick repair attempt failed to get the USB drive to respond when plugged in to a computer.

Since the drive was already toast the next and final test was the destructive stress test. I purchased a basic 10 ton hydraulic press from my favourite store Princess Auto. I had done some basic stress modelling using Solidworks and Autocad Inventor which showed the failure of the Brass prototype should occur at around 4000-5000 lbs on the threads of the cap with a vertical load. The modelling proved very accurate as that is exactly when and where the prototype failed! We usually assume modelling is reasonably accurate but it is always nice to see it verified once and a while.

Brass VIUD Prototype #1 -- After Destructive Testing

Lessons Learned

Despite the first prototype being destroyed during testing it yielded a number of important insights:

• Validated the overall design.
• Handling pressures up to 3000 psi should be no issue.
• Brass is too heavy and too soft a material for a true VIUD.
• Manually trying to tap the threads myself doesn't work very well.
• The mechanical stress modelling agrees very well with the actual stress testing.
• Temperature testing will have to be done a little more carefully (no propane torch)!

More prototypes, testing and research await for us on our quest for the ultimate VIUD....