This Instructable will lovingly guide you along the process of embedding a retro game loaded Raspberry Pi Zero within a cement Thwomp.

Why? Why not? The notion of permanently sealing a functioning computer in a chunk of cement is compelling to me for some reason. This flies in the face of the modern notion of upgradability, patches, updates, & the unspoken reverence for a computer (even this cheap one) and I love that about this project.

This build presented a number of unexpected challenges as you can see in the above video... :D

The inspiration for this project came as my response to the Concrete/Cement USB HUB Challenge on YouTube and Giaco Whatever's MAKE video.

This was a result of my desire to combine several different materials and disciplines into one fun build. It incorporates 3D modeling, 3D printing, molding, casting, cement, painting and electronics with a dash of video game references.

Enough with the intro, let's begin with a list of some of the materials you will need:

Project Materials:

Cement & Casting:

Quikrete Sand Topping Mix: https://goo.gl/m4ySLV

Smooth-On Silicone Rubber (Get Two Kits of this to cover this project!): http://amzn.to/2gPB0s8

Smooth-On Release Agent Spray: http://amzn.to/2hGZ6Yi

FoamBoard: http://amzn.to/2xFt1e3

Orbital Sander (without sanding pad) is useful for this project.

3D Printing:

My Thwomp 3D Model: https://www.thingiverse.com/thing:1930500\

Smooth-On XTC-3D 3D Print Coating: http://amzn.to/2z8LEDh

LulzBot Taz 3D Printer: http://amzn.to/2xFG4Hy

3D Printing Filament (PLA): http://amzn.to/2xGDKoI

Electronic Related:

Raspberry Pi Zero:http://amzn.to/2znx4cc

USB Gamepad: http://amzn.to/2ymLxoM

Mini HDMI to HDMI Adapter: http://amzn.to/2znxrn6

USB OTG Cable/Adapter: http://amzn.to/2z9Qal7

Liquid Electrical Tape: http://amzn.to/2xFuYT3

Software:

Autodesk Fusion 360: (Free for Students, Hobbyists and Start-Ups) http://www.autodesk.com/products/fusion-360/overvi...
RetroPie: https://retropie.org.uk/

Step 1: Model Your Thwomp!

Using Fusion 360, begin the modeling process. While this is not a full tutorial of the modeling process, it covers some of the basic steps required in the workflow.

If you would rather just 3D print out the model, proceed to Step 2. There I link my Thwomp model that is ready for 3D Printing.

Begin by importing your Thwomp image into Fusion as a Canvas. This will let you sketch against the model to help get an accurate look!
Using the Sketch line tools, begin tracing the outline of the character. make sure to sketch out complete shapes that connect. Broken sketch lines cannot be extruded.
Extrude the shape.
Continue to add details with the sketch tools
Use the Extrude tool, but the Cut function to carve out the details.
Adding fillets on the corners of rectangles help round out the shape.
Repeat these steps as needed until your character is complete!
Imagine the Thwomp laying on his back...Any vertical surfaces on his face should be beveled or have a draft angle added to them so that they release from the mold well.
Export your model into your 3D Printing Slicing software of choice.

Step 2: 3D Print Him!

Using your model from the previous step or the Thwomp model I designed (http://www.thingiverse.com/thing:1930500), toss him in your slicer software and prepare him to be printed.

I recommend printing him at a .2mm resolution with 20-30% infill with 3 layers for the walls and top/bottom. We want this guy to be solid and not flex at all in the mold making process. Due to the large surface aream I recommend using PLA as it doesn't have a tendency of pulling up off of the printbed as some filament materials do. (LOOKING AT YOU ABS!!)

After printing, coat the model with Smooth-On XTC-3D. This is a resin helps fill in the print striation lines which definitely show up in the final cement casting. Mix up very small batches of the XTC-3D and paint them on quickly with a foam brush. This may take several little coats and mixes to cover the model. Move qucik aas the stuff begins curing quickly, but try not to slop it on.

Step 3: Build a Mold Box Around the Thwomp

Take some foamboard and a generous amount of hot glue and fashion a box around your model. You want between about 1/2" of space all the way around the model.

Make sure to seal the joining surfaces very well, and apply a bead of glue on both sides to make sure it is watertight.

Finally glue down your Thwomp in the box. he will float otherwise, and this is bad M'kay?

Spray your model and the inside of the box with release agent. While it is not 100% necessary, as silicone generally avoids sticking to anything besides other silicone, it is a good practice.

Allow about 30 minutes for agent to dry.

Step 4: Prepare Silicone and Pour It Up!

Using the recommended silicone on the first page, mix them in equal parts in a large container. If you would like to do two batches, that is fine, as it has a pretty slow setup time.

When mixing the two parts together, be sure to not whip it up too vigorously. This can trap air in the silicone, potentially causing air bubbles to form against your piece. Air is your enemy here. Slow and steady mixing is best. Try to ensure a good mix by scraping the sides and bottom of the cup with your mixing stick.

Once well blended, pour the silicone in as small of a stream as possible, high above the part. This thin stream will help squeeze air bubbles out of the mix. Avoid pouring it directly onto the part you are molding, as this can also cause air bubbles. Pour it in just one corner of the mold box and let the silicone flow around naturally.

After the model is covered with about 1/2 inch of silicone, tap the sides of the mold box to encourage any trapped air bubbles to rise to the surface. Also lightly spraying the surface of the liquid silicone with release agent can help air bubbles to pop.

Give the silicone a couple of hours to cure well.

Step 5: Remove the Print From the Mold

After allowing sufficient time for curing, tear away the sides of your foam board box. Carefully extract your 3d print and admire your awesome mold! I try to leave the backing board for rigidity.

Step 6: Prepare Some Pi. Mmmmmm. Pi.

Gather your Raspberry Pi Zero, microSD card, USB OTG cable, USB 2.0 A-Male to Micro B Cable. and Mini-HDMI cable together.

Set up the Raspberry Pi Zero with it's operating system designed for emulating older video game systems, RetroPie.

Make sure to load whatever ROMs you will want now. While you can technically load them when the Pi is embedded in the cement, it is much easier if you do it at this step.

If you need help with setting up the Raspberry Pi, I recommend checking out this great Instructable on the topic.

After you are good to go software wise, plug in your USB On-the-Go (OTG) cable into the USB jack, the USB 2.0 A-Male to Micro B Cable into PWR and mini-HDMI cable in securely. Also make sure your loaded SD card is in there well too.

Now you have to waterproof the electronics from the potential hazards of giving it a pair of cement shoes so to speak. ;)

The best way I have found to do this is to paint Liquid Electrical Tape all over the Pi and cable connections. You may need to do this is many coats, inspecting each coat for gaps and holes. Make sure it is good and covered. This is a crucial step in this project.

Step 7: Mix It Up!

I found that the Quikrete Sand Topping mix gives an excellent surface for your Thwomp. This lacks any large stone aggregate that can cause him to look a bit more ragged, but if that is the look you want to go for, more power to you! :)

Spray the silicone mold with release agent. Cement, unlike silicone, wants to stick to everything. Coat the inside with release and wait 30+ for it to dry.

Mix up a small amount of cement. You want this to be about a runny oatmeal consistency.

Pour in a small amount of cement and use a wide stick to lightly tamp the facial features of the Thwomp. Air bubbles are again your mortal enemy here and stabbing the small features of the face will help the cement get in.

Use an orbital sander without sanding pad on the sides and back of the mold. This vibration helps get the trapped bubbles out as well. It also has a cool liquefaction side effect on the cement, allowing it to freely flow around into the features of the mold.

Continue to add a bit thicker cement and vibrate the mold with the sander until it is halfway full.

Step 8: Tell Your Pi to Take a Dip

Carefully lay your coated Raspberry Pi zero into the cement.

Continue to cover the Pi until the cement is level with the top of the mold. Be sure to keep vibrating the mold with the sander. How much do you vibrate it? When you think you did it enough, vibrate it a bit longer. This is the last defense protecting your casting from air bubbles which can ruin an otherwise perfect part.

Route and secure the cabling so that it exits the back of the Thwomp near the bottom. you may have to suspend the cabling so that it is in the proper position while cement cures.

Step 9: Remove the Cement Thwomp From Mold.

Give the cement a solid 2 or more days to cure, the more the better. The wet cement may break off fragile facial features when demolding your part. Play it safe and be patient!

After a few days, here comes the first moment of truth, the demold! Carefully pull the edges of the silicone mold away and flex the back of the mold until the cement guy comes out. Hopefully he looks good! Take a moment and marvel at your work. :)

Ok, get back to work.

Step 10: Painting and Finishing Your Thwomp!

You may need to sand or file some bits off of the cement casting to pretty him up a bit before this last big step.

Using a medium brush, apply a splotchy coat of watery black acrylic paint in the crevices and all over your model. Go crazy and have fun with this step, as the next step can bring it back if it goes too far.

After the black coat is dry, pour some isopropyl rubbing alcohol in a small cup. Drip your paint brush in the alcohol and re-activate the black wash on your model. Using a rag, scrub the wet areas to remove some paint. what gets left behind is the magic part. This dirt and grime is what helps make it the details in the model pop!

I like to use isopropyl alcohol here instead of water as it evaporates quickly and allows you to work quickly without worrying if the wet paint is causing drips etc. you can even mix more black and other colors with the alcohol to help texture your Thwomp.

Step 11: Final Touches!

Using moss normally used in hobby train landscapes, smudge it around on model sparingly. This leaves a great/gross green that adds another level of realism.

Take a bit of white PVA glue and place some bits of moss in the lower corners of the model. Once the glue is dry, you can even go back with some more black and other colors to add some variants to the moss.

As a nice finishing touch, take some rubbery furniture pads that have an adhesive backing and make feet for the Thwomp to help prevent it from scratching up a table, bookshelf or TV stand.