Introduction: Make a Lego Mini-figure FlashDrive

About: Freelance mechanical engineer from the Bay Area.

This tutorial shows you how to make an awesome, unique flash drive out of a Lego Minifigure of your choice and a Verbatim "Tuff 'N' Tiny" flash stick.

I wanted to make something for my brother for his birthday, and this seemed to be the perfect thing. I took a lot of measurements off of Lego minifigures and many different flash sticks, and found that this particular Verbatim flash stick is the only one out there that will fit inside a lego guy (with some modification). They are pretty cheap on Amazon, and there are several different memory amounts (I got the 8 GB one).

My brother and I share a lot of inside jokes about Batman, so naturally I chose a Batman minifigure, but this tutorial works for whatever minifigure you want.

Lets get started!

Step 1: Designing

As always, the first step is designing. If you use the same flash stick I did, you won't have to do much of this, but if you want to try a different model you should make sure all the dimensions work out. 

My original sketches are included, all measurements are in mm. 
I've also included a sketch of an official lego-minifigure with accurate dimensions (also in mm).***

(official mini figure sketches:
*** I dont own these

Step 2: Modifying the Flash Drive

The flash drive is coated in a plastic resin which can easily be cut with an X-acto knife or box cutter. The actual electronics are about half a millimeter under the plastic surface, so as long as you go slowly and carefully, you won't cut into the electronics inside. 

First, I cut the key-chain loop off the back of the flash stick, and then I beveled the back corners a little.

Thats all the modification I had to do for the flash stick!

Note: Save the lanyard that comes with the flash stick! You will be using it later.

Step 3: Modifying the Mini-figure

This part was a little more laborious then the last. Basically, you have to carve out everything inside of the mini figure's torso, or at least everything in the 'back half' of the torso (look at first picture above for explanation).

First, pop the arms out of their sockets. Then, use a thin x-acto knife to carve away the plastic inside the torso. Using a thin x-acto knife is preferred because you will have to stick it in through the arm-holes to reach some of the plastic, and if the knife is thin it will reach further into the body. You want the inside of the back of the torso to be relatively smooth and flat to give you a nice bonding surface to glue the flash drive to. 

When you are done, you will notice the flash drive still doesn't fit all the way into the body. Unfortunately, you will have to carve some slots out of the sides of your mini figure near the arm-holes to make room (this means you will have to glue the arms in place: they won't be able to pivot / rotate) Look at the photos above to see how to cut the slots.

Once you have the slots cut, check to see if the drive fits all the way into the torso. The pictures above should give you some indication of how far in my flash drive went. 

Now, cut off half of the ball-joint on each arm so the remaining half will fit into the semi-circle hole created by the flash drive. Reference the pictures above, it will make more sense.

Step 4: Gluing the Torso Together

Once all of your modifications are dont, the torso is ready to glue up!

I used super glue with a fine applicator tip. First, I applied some drops of glue to the back of the flash drive (the solid purple side) and slid it into the torso so the glue bonded with the inside of the back of the torso. Then I applies some more drops near the edges, and where the flash drive comes out through the arm-holes. After that dried, I put some drops of glue on the arm ball-joints and fit them in place. 

Step 5: Making New Legs

This is the trickiest part. The flash stick needs to slide into the legs, but carving a slot into the lego legs is near impossible. The individual leg pieces connect to the 'pelvis' through a one-sided joint that connects right where the slot needs to be. So, if we carve out a slot, the legs will fall apart. The solution is to make our own legs from scratch.

I suppose there are several ways to do this, but I think the easiest is to make a mold out of silicon, and then make a replica out of urethane resin. This may sound a little daunting if you've never molded and casted before, but its actually very simple, and I believe any DIY-er or garage tinkerer should have molding and casting capabilities anyway, so this is a good place to start!

Purchase silicon-RTV rubber and urethane resin online or at a store like TAP Plastics. It's a little pricy, but you only use a little at a time, and it's got a pretty long shelf life. 

Silicon rubber comes in two liquid parts, a base and a catalyst. The base contains a bunch of floating silicon molecules, and the catalyst is some chemical which makes the silicon stick to itself. When you mix the catalyst into the base, the silicon in the base polymerizes and in about 12-24 hours goes from a liquid to a rubbery 'solid'. 

Urethane resin also comes in two liquid parts, but the chemistry behind the reaction is slightly different. In the silicon reaction, all the 'structural' elements are in the base, and the catalyst just causes the base to solidify. In urethane resin, both liquid components (A and B) contain their own type of monomer (free floating molecules) that dont bond with themselves, but bond with the other type. A doesn't bond with other A's, B doesn't bond with other B's, but A bonds with B. So, when A and B are stored separately, they stay in liquid form, but when mixed together they start to form long chains of alternating A and Bs. These long polymer structures form a solid in anywhere from 2 to 10 minutes after being mixed, depending on what type of urethane you buy. 

Like I said, molding and casting is a great skill to have, and the basics are very simple. The idea is you start with something you want to replicate, in this case it's some lego legs, which is referred to as your 'master mold'. Then you construct a little container where you can suspend your master mold so you can pour the silicon around it. This creates a silicon 'negative' of your master. When the silicon dries, you remove your master and are left with a cavity which is the same shape as the master. This is why its called a negative, because the negative space of the silicon is your master mold. Then, you mix the two parts of the urethan resin together and pour it into the silicon 'negative' mold, forming a 'positive' of your master mold in resin. When the resin dries, you pull out the solid resin part, and ta-da! you have replicated your original master mold in plastic resin!

Since you want to waste as little as possible, make the container for the silicon pour just a little bigger than your master mold. I made mine out of foam core and hot hot glue, and I left about 1 cm in each direction around the master. Since we want a solid replica of the legs, make sure to fill in all gaps in the legs with modeling clay. When the silicon is in its liquid form it has astounding 'resolution', it can pick up the details of cell structure, so it will seep into the smallest of cracks and crevices in your master mold, so make sure that clay is really sealing all those little gaps in the lego legs! 

To position your mold inside the container, make sure that it's equidistant from the walls of the container (make sure its centered), and make sure you will be able to 'see' part of it once you are done with pouring the silicon. Basically, dont completely cover the mold with silicon, cause you won't be able to get the mold out when the silicon dries, and you also won't be able to pour in the resin after (since you will eventually be pouring resin into the empty cavity, you need a hole to pour in the resin).

When you are ready, mix much less of the silicon and catalyst than you think you need. Even though I've been doing this for years, I still always prepare to much silicon and resin. Use it sparingly! You can always mix more if you run out, because solidified silicone can actually bind with liquid silicon, so even if your first pour dries, you can add more on top later. 
Because this mold was so small, I actually poured the silicon in the container first, and then I pushed the master mold into the silicon after.

Let the silicon dry in a warmish place for a day or so. When its dry, remove the master mold.
Since I didn't want to have to carve out a cavity for the flash stick, I actually made the replica with a cavity in it. I cut out a piece of cardboard the same dimensions as the flash stick and wrapped it in plastic wrap very tightly.
Mix a very small amount of urethane resin, and pour the resin into the negative cavity in the silicon. Once the resin is poured, push the plastic-wrapped cardboard into the liquid resin where you want your slot to be. This should only take several minutes to solidify, but putting it in a warm place will speed up the process if you are impatient (like me). I usually use a blow drier to blast it with hot air, and it dries in less than a minute. 

Poke it with a pencil to make sure its hard, then pull the replica out of the silicon. The plastic wrapped cardboard should slide out easily, and leave you with a slot in your new legs that fits the flash drive nicely. 

Wasn't that easy! And now you know how to mold and cast with urethane. Exciting!

Step 6: Finishing Touches

Now that you have your legs made and your torso glued up, its time to attach the lanyard.

Using a 1/64" drill bit, I drilled a hole in the very top of the Batman mask / helmet thing, and drilled a similar hole in the top of the head inside the lego 'stud'. I fed the lanyard through the mask and then the head, and then put a small zip-tie through the lanyard loop to make sure the lanyard wouldn't pull out through the head and mask. 

Next, I put the cape on the torso's head-stud, then I glued the head onto the torso, and then glued the mask over the head. 

I painted the legs semi-gloss black with modeling paint (model paint binds well to plastics). There was still a lot of purple showing on the flash stick, so I painted the flash stick black too (except the metal contacts). Of corse, match the paint color to whatever color the original legs were, not necessarily black.

You may have to do a little extra tinkering to make sure the legs fit snuggly over the flash stick so they dont just fall off randomly. You can either layer up several coats of paint inside the leg slot, or you can shove a little modeling clay down into the leg slot. Sticking some electrical tape in there might also work, since its a little rubbery it might hold the flash stick in there nicely.

Once you've done that, you are finished! Find a computer, plug in your awesome new flash drive, and after making sure it still works, name it something witty!