August 29, 2015

Transforming Birthday Cake - Animated Platform

Since uploading Transform Birthday Cake - Optimus Prime on You Tube I have heard from many people wanting to know how the "animated cake platform" works. I have used my fair share of open source software and hardware in my time so I am only too happy to share and give something back.

You can read on to see how I made the machine you see in the video or you can follow my build project where I am making an easy to build version so you can make your own.

Its worth pointing out I am not a mechanical engineer, I simply enjoy designing and making things for a hobby. Its important for me to say this because I don't want people (especially my kids) to dismiss an idea because they "arn't smart enough". The internet is jam packed with information on every subject, if it interested you got for it! Thats is what I did here: find out just enough information to make this idea become reality.

The Challenge

This idea came simply from my eldest son asking for a Transformers cake for his birthday, my wife makes our two boys cakes each year. My inner child immediately pictured a cake that actually transformed and that was it, I was hooked. I pondered the idea for a while and concluded that yes it could conceptually be done but I knew it couldn't just be a machine covered in icing, it needed to be first and for most an actual cake, the machine would need to work around the cake. Also I wanted to the final cake to have a sense of wonder about it, yep, wonder. I wanted it to be like a magic trick and fool the viewer (mostly 6 year old children) into thinking the cake was standing up by itself. So that was the challenge, make Optimus Prime come to life in an invisible way.


The first few months of the project (of any of my projects) were all paper sketches and doodles, throwing ideas around in my head. As a parent I have very limited time between the kid,s myself and going to bed. So I have no time to waste in the evening. My way around this is to think, design and sketch before hand, I have a 45min train ride to work so this is the perfect time for me to do this. That way when I do step into the workshop it is 100% time on the tools.

I started sketching in January 2015 and by about March felt I was ready to start entering the design in a CAD package.

The whole design centers around the concept of using wire under tension, I don’t know the exact engineering term but I got the idea when I recalled an episode of Richard Hammonds Engineering Connections. (Though I can’t recall which episode) In it Richard holds up an old fashion toy man standing on a base. When he pushes a button on the bottom of the toys its arms, body and legs go limp, when he releases it the toy stand erect from the tension in the spring loaded wires. He did this to illustrate this properties of wire under tension.

The Skeleton

The skeleton has two modules: the legs (blue and grey parts) and the Cab (Red parts). 

The legs have 2 different types of lift connections, for sake of explanation let’s call them the shin connection (connecting the two blue blocks) and the thigh connection (connecting the middle block to the cab).

The cab has two L-shaped arms, and a center column holding the mechanism for simultaneously raising the head and opening the arms.


The blue and grey sections have steel fishing wire weaved through them in such a way that when the wire is pulled the connections want to climb (see this YouTube video), just like the toy man that inspired it. The wire is pulled by a gear-down stepper motor, more on that  later. Each corner that the wire threads around has a small v-grooved bearing (gotta love ebay) to make the transformation nice and smooth.

Not only is steel fishing wire strong, skinny and flexible, it also of course conducts electricity.

Shin connection

Notice in the picture to the right the shin connection has a motion range of 180deg. This is important because the middle blue block needs to swing around clear of the rear blue block when it transforms. Also the blue pieces need to remain parallel throughout the movement,.That is what the belt is for. I got the idea for the belt off this video from this amazing Channel via an article on Makezine.  
First try: "Bent Parallel Bar" 
My hope was that the belt would give me high strength and accurate movement, something I wasn't confident my first design would deliver. The down side to this approach were many: the 3D printed pulleys teeth didn’t quite align right (by the tinniest amount) so the belt teeth didn’t grip properly, so then it needed super tight (custom sized) belts to compensate, but the force of the tight belts caused the plastic to bend, which then required reinforcing the connecting rods and caused friction issues plus having to assemble and disassemble this fiddly mechanism over and over, it was all very frustrating.

Copy this particular design at the risk of your own sanity! Instead I hope you take inspiration and the principles used and make your own improvements on this design.
The belt design was actually my second design, In hindsight I should have tried to refine my original “bent parallel bar” design, see pic. (which I found after studying one of my boys transformer toys.)

Thigh connection

Fresh from the printer
This connection was simple 90deg hinges and probably because of that fact they worked just fine. The end of each wire attaches to the middle of lower connection. Many springs and elastic bands were used to assist the stepper motor and ensure the cab lifts before the legs. The elastic bands are used to pull and the springs to both pull and push. The cab did not naturally fall from vertical under its own weight as I had hoped it would. I improvised and over stretched the springs so by the time the connection is vertical the strings are actually applying a pushing force to help the cab fall when the cable slackens for the downward journey.

The Cab

This was the second most difficult part. It took many train rides to try and figure out a simple way to make it all work.  I originally wanted not only the head to lift and the arms to open but also the forearms to descend. I eventually had to concede that the forearm descend element was going too far and it was dropped in favor of the L-shaped arms.

Hiding under the cab is a geared dc motor attached to a lead screw that I stripped out of an old CD/DVD drive. The lead screw raised a small platform that the head sits on. To move the arms each one has a "curved triangle" piece that the platform pushes against with small bearings. Sort of like a cam-and-follower.

The rear door is also actioned by the upward motion of the platform. Note the curved profile on the door so it opens early in the movement clearing space for the head.

Elastic bands are used to pull the arms and the rear door closed when the platform is lowered.

The dc motor gets its power through the primary wires, sneaky huh :) Look on the side of the rear blue block and you will see black wires connected the rear most bearing. The power travels through the metal bearing, along the fishing wire through the connecting pin then up to the motor. Simple and ultra invisible.

3D printing

 Everything was designed with 3D printing and cake in mind. The printing was done via a local printer iprimin on 3Dhubs on his Ultimaker 2.  PLA was the material of choice because it is considered food safe. I actually got 3 batches of prints done: the first so I could get a feel for the PLA material and feed that back into the design before the other two batches for legs and cab.

The underbelly

The underbelly.
The winch system is simple enough: the stepper motor is gears down from a 20 tooth to a 32 tooth pulleys and additionally geared down by using a very small diameter on the spindles. The bearing and stepper mounts are 3d printed also.

An Arduino is used along with an easyDriver, 2amp DC motor driver and mp3 player module. The black cylinder is a portable music speaker and the 4 buttons (top right) are just for development purpose to move the stepper and head motors when I needed.

The based I had CNC cut at (Who are always very helpful with my custom designs and reasonably priced )

The base is covered with metal look contact sheet bought from Kmart (Australia). Credit to my wife for that nice finishing touch.


To lower the legs a secondary set of wires uses more elastic bands (see the underbelly pic) to pull when the primary wires slacken. Note in the picture that there are 2 groups of elastic bands, one connected to the rear of the base and the other to the middle. This is so I could control the amount of force and when it is applied. The middle mounted elastic bands work only for the first 5-6 downward centimeters to pull the shin connection over the initial lump. The second set of elastic bands is used to take up the slack for the rest of the downward movement.


mmmm cake. Plus a random cup cake.
The cake is where all very nearly came unstuck. I drastically under calculated (totally stuffed up actually) how much mud cake weighs. So the cab had some Styrofoam in it to help lighten the load a little.

The cake was chocolate mud cake covered Bakels Pettinice (Fondant) rolled as thinly as possible to reduce weight. Rolkem Super silver was used where a metal look was needed. 

Whilst I and a good portion of the internet think the cake looks great, my wife did have much grander plans for other icing based decorations which I vetoed as I was so worried it would fail to lift on the day. Yes it came that close to being overweight.

I had so much fun designing, problem solving, building and also having a project to share with my wife. We are thrilled with how it turned out and are totally overwhelmed with the positive responses it has received.

If you have any questions please feel free to ask in the comments. If this inspires you to make one of your own please let me know  I would love to hear about it. 

Birthday boy gets the first piece!

More pics:

Sketch 2
Sketch 3
Sketch 4
Sketch 5
Sketch 6
Sketch 7
Sketch 8
Screws, bearing, wire, glue
Cab close up
Cab close up 2

Parts List

M3 machine screws - various lengths - button head - allen socket
24x M3 10mm - countersunk - allen socket
49 stand fishing wire
Glue - Rapid Fix (CA)
Plastics screws - wide head various - taken from old kids toys and discarded computer printers
GT2 Belt 1meter for making shin connection belts
Base - MDF - 300x390x55mm

Cab ----
2x 3mm rod
Leadscrew from computer CD/DVD - cut to size
Universal joint - 3mm and 6mm ends to match leadscrew and cd motor shaft
6x Hinges - model aircraft

38mm Nema17 Stepper Motor
1x 240mm GT2 Belt

36 tooth pulley
20 tooth pulley
Tiny washers for bearing spacing
Elastic bands - various
2x Springs
10x V-Groove bearing - 12mm OD - 3mm ID
4x BallBbearing 10mm OD - 5mm ID
5mm rod
Grease - food grade

12v 1 amp power supply (minimum)
Arduino Uno
2A DC motor controller - externally power
Ezy driver
38mm Nema17 stepper motor
DC motor with gear box 60-400 rpm range
Mp3 module
Portable speakers - battery powered, samplers, 3.5mm connector
Start switch

3D parts-----
Bearing mounts
Steeper mount
Foot - base join
Foot - inner
Knee - inner
Knee - outer
Knee platforms
Shin - connecting rod
Shin - pulleys
Shin - caps
Thigh connections
Cab center column
Cab rear door
Cab head platform
Cab roof
Cab arms
Cab cam triangle's
Cab front


  1. you are an amazing father to do this for your son, I also wanted to know where did you get the costume for the birthday boy?My son is crazy about transformers and I just challenged my husband ( who will totally enjoy making it ) to make this for his upcoming birthday :)

    1. Thanks! The costume was from Ebay, not sure where specifically. Good luck to your husband, I can can email you the STL (3D print files) files if you like?

    2. I am helping a friend build this for his nephew. can I have the 3d print files please.

    3. hi, can you email me the 3d print files pls. Thank you

  2. Are you able to provide a list of the parts you used in constructing this?

  3. my husband really wants to try this. Would you be willing to share the plans for what you 3D print was? Do you have plans and instruction even for sale?

    1. No I don't have any plans or instructions to sell sorry. This fiddly design would be a customer support nightmare for me. But as this machine is proving so popular I am begin to design a version that it uses 3D printable gears/cogs (not wires and bearing) which 'should' be much simpler. I will update my blog when I produce a satisfactory design but it will likely be a few month away. Sorry I cant help you right now.

  4. What a great Daddy. The smile on your Sons face was so beautiful and made my day. He in all honesty is a handsome little sweetie, he was so happy & surprised. Well I know I can't wait to see what you make for your other son. Great job daddy. Your awesome. ..

  5. Hi, I'm a cake maker and are you willing to sell the robotic used on the cake and if yes how much? Thanks

    1. Thank so much for your interest, I would love to sell it to you but it is very complex and fiddling and I couldn't in good conscience sell it. BUT I am working on a version that I would likely to be able to sell, the target market being cake makers like yourself, those who can reuse it. Perhaps I could contact you in the future about it? I would like to make sure it is a viable product for you and others. Or you could follow me on twitter, I will be tweeting about development. @lownlazy

  6. hello, you beautiful cake you done , my son is a fan of chili and transformers are not getting anything accomplished and so , for number five birthday is in a month, you sell it ? I hope you can answer me my email is .. greetings

    1. I am not selling at the moment but I am currently developing a version you can buy but it wont be available for some months.

  7. amazing father and great design! just featured it on our facebook page about 3d printing!

  8. Hey I am making the cake and I was wondering if you could share the stl files with me so I can print them on my 3D printer.

    1. Hi Max if you are still interested I will be documenting and release files for the cake in a new hackaday project

  9. This comment has been removed by a blog administrator.

  10. I was just challenged by my cousin to make this in February. Any chance on you having the new servo plans available yet? If so, please let me know! I was so happy to find that you were so generous to post your process but I don't have access or experience with a 3d printer so I'm a little intimidated!

  11. I said this on Youtube just a bit ago when I first saw your video, but this is simply amazing.

    With your files and the parts list, do you think this would be possible to do in a two month time frame? I'd love to be able to do this for my own little transformer this year.

    1. Thanks for your interested in this project Jordan. For various exciting reasons I have (hopefully temporarily) stopped handing out the STL files.
      Sorry but its a legal thing so I have to play of the safe side and withhold them for now.

    2. Hi Jordan

      If you are still interested I am going to document and release files for a simpler version of the transforming cake

  12. Amazing cake!!! Great job!! I would like to try this for my son's 6th birthday. Would you mind sharing your 3d print files.

    1. Thanks for your interest in this project Rene. For various exciting reasons I have (hopefully temporarily) stopped handing out the STL files.
      Sorry but its a legal thing so I have to play of the safe side and withhold them for now.

    2. When you get everything worked out, can you PLEASE let us know. I would LOVE LOVE LOVE to purchase the plans for my husband & son's birthdays in May. They are HUGE Transformer's fans! Thank you so much!

  13. Are you able to send of the parts of it so people can make it themselves

    1. Sorry fo the slow reply, if you are still interested I have started documenting the build process you can follow along here

  14. Hello interested in buying the setup already made. Do you mAKE IT AND SELL IT? please let me know thank you

  15. I will like to buy the final version. Do you already finish your project?

  16. No not at the moment but possibly 2017.

  17. It's been several months since anyone had asked so I figured I would give it a try :) do you have this for sell yet?

    1. No not yet sorry but there are things happening.

    2. No not yet sorry but there are things happening.

    3. Unfortuately the commercialisation deal I was working has fallen though. However I still want to share this with everyone. You can follow my new build project here:

  18. Hi there.. Have to say that's an amazing job you have done.. Really hats off.. I believe you aren't able to send the stuff files for the 3d template for the structure of the robot? Is it possible to provide the normal template or size for it? You can mail me at We could correspond there if it's ok with you.. Cheers mate

    1. Hi Keith, sorry for the slow reply. If you are still interested I have just started a project to document how to make your own here:

  19. Want to make your own? Follow the project at:

  20. wow, only wow. please, sell this in a kit for the father that no are very inteligent, wow

  21. This is so amazing. I read above that you might make a version that you could sell...I'm just checking in to see if you ended up doing so?

    1. I tried commercialising it but it was not considered a economical viable product (cost to much to make, sell for too little)