module stack_of_spheres(w,r) {
    for(layer = [0 : w -1])
        for(x = [0 : w -1 - layer])
            for(y = [0 : w - 1 - layer])
                translate([x * 2 * r + r * layer, 
                           y * 2 * r + r * layer, 
                           r + (r * layer * sqrt(2)) ]) sphere(r);
}
$fn=20;
stack_of_spheres(10,3);