the "physical" movement that I would like to do and that you see in the video also works without constraints; if you look at the tutorial the constraints and relationships are used only by minute 2:20 then when paul hamilton creates a new relationship to attribute to the pin the function of the "fixed" part, but the chain drag works regardless of this bond, the introduction of the bond only serves to prevent the pin from moving and forcing the pinion to rotate around it when it is dragged by the chainHi, in the tree I don't see any constraints, they have to be created to see the movement.