$fn=60;

module spike(H) {
  sph=1;
  difference() {
    cylinder(d1=9, d2=sph, h=H);
    translate([0,0,-0.005]) cylinder(d=2.9, h=15);
  }
  translate([0,0,H]) sphere(d=sph);
}

translate([00,0,0]) spike(H=80);
translate([10,0,0]) spike(H=50);
translate([20,0,0]) spike(H=30);