Idea and Concept
Our initial idea was to buy a toy train and modify its wagons by adding two compressing springs with a set and release mechanism. Positioned on each spring would have been a coloured ball that would jump out of the wagon when the mechanism was released.

The reset of the system would have had to be manual and only two balls per time and wagon could have been made jump each time the apparatus was released. We also intended a second surprise mechanism that made it hard to connect the wagons in the first place and to make it somehow difficult to put the balls onto the wagon so it would have been all the more frustrating when the balls flew off. Also the wagons would have automatically separated after a certain time.

What became of the concept you can see here in the video of the final result:


Getting to work and solving the unsolvable

The concept was then split into two Major assignments:

First: Finding a toy-train in the appropriate size with enough space for our modifications and
Second: Finding springs with the required properties (not too hard to draw back (tensile force) but with a good enough take off power) and designing an apparatus that made balls jump with them.

What we did not know at that point: With our final solution of the second assignment came a third major assignment we did not know of while scheduling our time.

After wasting two costly days on solving both major assignments the planned way we decided to solve it by adding work to reduce it:

Instead of buying a toy-train (and wasting precious time looking for it) we decided to built it ourselves as a made-to-measure solution. Using the leftover-stock we took some wood and learned to use Adobe Illustrator for the vector design.

The base for all the measurements was the remote controlled toy-car we had found in the workshop on a coincidence. We designated the chassis to be our towing vehicle. Later followed the self-made chassis and wheels for the wagons. (We could not find any to buy in the required dimensions)

Lesson learned: I am convinced that despite the additional work we put in making it up from zero we did save a lot of time and learned a lot in the process as well. (Using the lasercutter, working with Adobe Illustrator,how to use the tools in the workshop, AND: improvise, improvise, improvise)


The second major assignment turned to the most unexpected result. After focusing days on first finding the perfect spring (which turned out to be a disaster) and make it work SOMEHOW. The solution lay somewhere totally different. A frustration-solving stroll through the workshop brought me to a discarded piece of acrylic glass. It was both: surprisingly flexible and yet dimensionally stable. And immediately a totally new idea took shape. The prototype on the new concept took only a few minutes and worked on the first run. Here a demonstration:

The new concept brought several more advantages: We no longer had to reset the system for every new round. a hacked 360° servo  could keep the springless construction running infinitely. That also meant we were no longer limited to a 1:1 ratio on balls and springs: we now could shoot around a whole load of balls in every wagon.

Lesson learned: Stop trying to reinvent the car when all  need is a wheel.

With the train and the spring-less construction done the day before the presentation, we thought nothing could go wrong now. We thought the electronics would be easy. A mistake that literally cost us our sleep the last night.

Taking up an idea we had had quite in the beginning we used popsicle-sticks with a copper coating to transfer signals plus energy and keep the train able to make turns because the coupling was flexible. It was a rather simple but effective solution. Still it turned out to be very very time consuming and starting a task that requires a focused mind and a still hand after 12 hours of work is not the best idea. Yet we managed it and after 6 more hours everything was working just fine.

The Arduino gets its power from a 9V battery on the first train. From the Arduino emerge 5 cables: A Voltage cable with 5V and a Ground cable that serially connect to every servo. Three seperate Signal cables, so every servo can be controlled autonomosly.

Lesson learned: Do not sleep in the CIP-Pool. You risk freezing to death while asleep. Seriously.
Things that were left out – Ideas for the future

The whole “Trains falling apart just before the balls start jumping out”. We threw the idea aboard after realizing it would require one arduino and a battery per wagon. Plus a strong repellant like an electric stud or electromagnets. Two things that are highly energy consuming. And by adding those the space for the eggs would have been considerably minimzied.

Springs. As mentioned above it didn’t work out. Not only the mechanism was catastrophic, but also aquiring fitting springs… It seems that springs are usually only produced for companies that use them for their tools. The springs we found were all too big or had too much tensile force. Thinking around the corned helped here. A stroll through the lab and we really simply ran into the solution.

Buying a toy train. Looking for something extremly specific (exact measurments, size, material) is really hard. If you have any talent in “do it yourself” then do just that. No point in fearing failure. Just do it. At the very least you will learn a lesson.

Acoustics: At one point we intended the train to make some funny childisch train sounds, time killed the idea rather soon, but we still liked it

Light effects: Blue subfloor illumination. Again time was the killer but this would be the simplest of all to add as we have already designed the wagons with extra space for an additional battery and space left for some LEDs.

A stronger towing vehicle: Altough we tested the admissable total weight of the toy car to be 1,5 kg it still had trouble towing the wagons. Either the last wagon has to go, or the towing vehicle needs a stronger engine.

A remote controlled starter: We still have to start the arduino manually. Adding a remote would certainly improve the effect.


Things that were added

Easter Eggs instead of balls (spontanously)

Selfmade train + wheels

10 Eggs rather than two balls. The more eggs the more the fun


Final words by the author

Despite the batch of chaos in the final 24 hours I really really enjoyed the course. The project with all its ups and downs was really cool, the learning curve amazing and the people were not only helpful but especially the lunchtimes were real fun. For every stressful moment (including having to sleep on the CIP-Pool floor): it was worth it.