but i'have a little trouble,
for each iteration i want to rotate then move from the center of the iteration of the moment and not from the center of the first iteration
You can't do this in Context Free right now. What you are trying to do is have the loop iterate with the {r -27.7} rotation and the {x 5} translation separately and combine them before invoking the base shapes. But Context Free can only loop through a single transform. Your best solution is to write a Perl or Python script to generate the jj rule, which would look something like this:
Where $0 represents the index of the inner {x 5} loop and $1 represents the index of the outer {y 5} loop. But, don't hold your breath for Context Free 3.0.