This project is a few years old now. I made this for my son when he was 6 (now 9) and figured it was a good first Instuctable for me to post. He is/was a a big Star Wars fan, as all 6 year olds should be. I figured I would document the build since it was more project build thank a cake.
As a disclaimer this was for my son, and I don't consider my decorating skills to be that great.
This mostly started as a joke and got out of hand. The original thought was a 2D sheet cake in the likeness of R2D2. However that wasn't really good enough for my son, he wanted it to stand up. I started by looking up pictures of R2D2, and quickly realized to do it correctly it really needed a custom stand. This is what I started with, but it occurred to me that if I was building a stand and a vertical cake I might as well make it project Princess Leia on the wall in true R2D2 fashion.
Step 1: Cake Stand
It is cardboard and wood wrapped in Saran Wrap. A trunk of PVC pipe ran up the center for stability and gave me a place to feed wires to a laptop nearby, as my Raspberry Pi could not keep up the frame rate.
The cakes are Pillsbury, Betty Crocker, or similar box-o-cakes. Nothing special here.
My wife was nice enough to bake six 9" round chocolate cakes for me. After the layers are cooked take a cake cutter or knife and level the tops, and approximate the PVC hole size with a small cup to pre-cut the hole (does not need to be exact).
I then stacked the cake layers, and slid them onto the frame. Then applied butter-cream frosting in-between each layer to hold it together more. The recipe for butter-cream is simple. I do it from memory, but I used something like the one found here with just butter and no shortening. Buttercream-Icing
This was way more cake than we needed, but I couldn't scale it down much more due to the dome size.
This whole thing was topped with a cardboard ring to provide a crisp edge at the top. The outside was then frosted with a modestly thick layer to make a cylindrical shape.
Step 2: Fondant, Domed Head, Legs
I make a marshmallow fondant myself to save time and money, but store bought would work well in this application. I needed a couple batches of white, and 1 batch of blue. I find it is easier to mix the color into the melted marshmallow (30 seconds), rather than the standard of folding it into white fondant (30 min).
Fondant recipe I use is here. Rolled-Marshmallow-Fondant
To make to top dome I added CMC powder to some of the marshmallow fondant. This turns the fondant into gum paste, and turns the fondant hard after it dries. This was then molded into the inside of a 9" semi-spherical bowl that was coated in vegetable spray and powdered sugar.
I am not the best artist, so I did my best to decorate the head after it setup in the mold. The body was then covered in white fondant and decorated with black icing and blue fondant cut to shape.
Rice crispy treats were used for the legs. They were covered with icing and fondant. I didn't document this beforehand there is a posthumous picture of the leg from the inside.
This was all assembled and decorated with fondant and black decorative icing.
Step 3: Projector
First I needed the video to project, which I found unsurprisingly on youtube.
Next I pulled out my raspberry pi and pico projector, but quickly abandoned the raspberry pi as it was having trouble playing the video. I landed on a netbook on the outside running VGA to the projector in the cake. The PVC selected allowed all the cables to fit up and through the cake to the outside. The setup looked like this.
For the finish touches I added a birthday message to the end of the Leia Message, and topped the cake with R2D2's head.
And a video showing the whole thing in action.