Here is an example of Thymio II powering a boat. This construction is based on parts from the LEGO Technic 8258 construction kit and a Playmobil boat which no longer exists, only the image
there). Thymio II is used to drive the paddles of the boat. It can be controlled directly or using a remote control, in the basic modes.
The boat looks like this:
It can go quite fast, is stable and can carry a useful cargo.
Operating in a fountain gives the the following result:
The construction is quite simple, based on a structure which sits in the boat hooking on to the sides. The basic structure looks like this:
Placed in the boat it has added stability by being supported by the sides of the boat. The bars which carry the axles of the paddles make the whole more rigid and stronger.
The power transmission from the wheels to the axles of the paddles is effected by gears which provide a slight speed reduction. There is a single fixation point per side of the structure to Thymio II (in addition to the wheel).
Finally here are some details of the construction: