Thank you for this very nice feedback! I came to this after having done the balance with flexible joins ( https://www.instructables.com/Robot-Thymio-Avec-Balance/ but is in French, would it be useful to translate?) that makes a simple spring. But here the goal was to have a omnidirectional spring.
To please you high-school teacher next time you can even put in the comment in French :-DEn tout cas encore merci beacoup pour le joli commentaire!!!!! ;-)
But I see now you looked to the French version. Have you seen https://www.instructables.com/Wood-Flexible-Wheel-for-the-Thymio-Robot/ or do you feel more comfortable reading French?
Roue Flexible En Bois Pour Le Robot Thymio
Wood Flexible Wheel for the Thymio Robot
Robot Thymio Avec Balance
Thymio Prompteur / Liseuse