It was our toddler’s birthday and in the weeks leading up to it he made it very clear that he wanted a robot cake. We felt that a cake that looks like a robot should also move like a robot, and with Smartibot we definitely have the technology to make that happen. (The Crafty Robot also has form combining food and robotics, like our Gingerbread House, Pineapple Bot and Botato Wars).
Designing a motorised cake
As we wanted to eat the cake, I was keen to keep the actual robotic parts as contained and separate from the cake part, whilst still keeping them totally hidden. A motorised ‘cake base’ the same diameter as the cake tin, which could be iced along with the cake, seemed like a good way to do that. I got to designing a puck-shaped Smartibot chassis.
I wanted it to be as flat as possible, and we needed torque to move the cake and not speed (as it was only going to drive around on the table top) so I went for more or less the smallest wheels that keep the Smartibot motor casings off the ground, when they are mounted horizontally. I designed the wheels so that two R-17 (ID 20 mm, section 3.5 mm) ’O’ rings would fit on as tyres, and put a feature on the chassis to hold one of the marbles from the Smartibot kit as the third point of contact with the ground.
Building a robotic cake base
Once the chassis and wheels were 3D printed the build was simply a matter of attaching the wheels to the motors, them in the chassis, popping in the marble, and then flipping the chassis over and connecting the motor wires to the Smartibot circuit board. Finally I connected the battery box and popped it and the circuit board into the recess on the top.
We planned to ice and decorate the cake the night before the toddler’s birthday and then leave it in the fridge over night. In order to make sure we could switch it on in the morning I put the battery box in with the switch facing down and, instead of using a plate, we assembled the cake on a piece of cardboard with a hole cut in it, that would allow us to lift the whole thing up and access the switch, without touching the cake.
Assembling the robot cake
When we first assembled the cake we made an absolutely elementary and disastrous error. We put a piece of aluminium foil between the top of the robotic base and the bottom of the cake. This meant that when we came to switch it on, we ended up shorting out the circuit board and had to quickly open up the cake and replace it with another one. If you make one of these make sure you don’t do this!!! Grease-proof paper works great. Remarkably, after we’d fixed it, the cake went back together quite well and it was difficult to notice that any drastic last minute surgery had been performed.
Apart from the foil debacle the cake assembly was quite straightforward. We popped the main part of the cake on top of the base, iced over the whole thing, put on a smaller rectangular bit of cake we used for the head, iced that and then decorated it with chocolate buttons, chocolate raisins, shiny sugar balls, strawberry liquorish, strawberries and a blueberry cut in two for the eyes.
To make the arms I 3D printed some simple moulds (open at the top and bottom) lay them on grease-proof paper, poured in melted chocolate, left them to solidify in the fridge, popped them out of the moulds and then stuck them into the cake.
The big reveal
You can see the moment we first drove it around with the candles lit in the video. The toddler seemed very happy with it, though, as you can probably guess, he’s seen quite a few robotic things so I don’t think he views it as particularly remarkable. My wife and I were both really please with the effect and it was really fun to combine baking and engineering.
3D printing your own robot cake base
If you want to make your own robotic cake, the files to 3D print the chassis and wheels are here and you can get a Smartibot kit here.
If you want to make one of these but need a different diameter base (to fit a bigger cake tin) get in touch and I should be able to adjust the CAD model and do another variant.