h = 15;
w = 7;

module notchesSphere (HowMany){
    for(i = [0:HowMany]){
        rotate(i*360/HowMany)
        translate([15,-4,0])
        square([h, w]);
    }
}

module sphere(){
    difference(){
        circle(30);
        notchesSphere(4);
        circle(5);
    }
}

sphere();