Always on the look out for material suitable for handiwork/DIY, I found the following kit: kit.
This kit is made up of black and yellow foam pieces of different thicknesses and of plastic screws / nails which can be screwed / planted in this material. There are also four wheels, with which vehicles can be made. Finally there are some tools.
Here is a detail view of some foam pieces fixed together with a plastic screw, using a suitable screwdriver:
With this material it is easy to make structures of medium size and with reasonable solidity, which of course depends on how the structure is conceived.
Here are some steps in the construction of a locomotive. The first step is to make the front part of the body:
The funnel can be made using the cylindrical foam pieces, while the rest of the structure is made using the flat pieces of various thicknesses:
The pieces are held together with the various sizes of plastic screws. Here the main structure is fixed together using the longest screws:
A base plate serves to hold the different parts together. This is also useful to fix the wheels:
The yellow pieces provide decoration for the construction and also to round off some parts:
The wheels are equipped with plates so as to be fixed easily to a horizontal surface:
Finally here is the complete structure of the locomotive without Thymio:
The Thymio II is fixed to the front of the locomotive with a screw which passes through the central pencil hole and is screwed into the foam of the main body.
The whole moves quite elegantly, as can be seen in this video: