$fn = 50;
tube_length = 4; // tube length in studs
piston_length = 3; // piston length in studs
travel_length = piston_length-2; // piston travel in studs

travel = min(travel_length, piston_length-2, tube_length-2);

//difference() { union() {

difference() {
  translate([0, 0, 2.3]) cylinder(r=4, h=tube_length*8-2.3);
  translate([0, 0, 2.3]) ball_end_n();
  translate([0, 0, 8]) cylinder(r=3.2, h=tube_length*8);
  translate([-5, -0.5, tube_length*8-6]) cube(size=[10, 1, 3], center=false);
}

color([1, 0.5, 0.5]) translate([0, 0, (tube_length+piston_length-1)*8]) rotate([180, 0, 0])
{
  difference() {
    translate([0, 0, 2.3]) union() {
      cylinder(r=3, h=piston_length*8-2.3);
      cylinder(r=4, h=8-2.3);
    }
    translate([-5, -0.7, (piston_length-travel-1)*8+3]) cube(size=[10, 1.4, travel*8+3], center=false);
    translate([0, 0, 2.3]) ball_end_n();
  }
}

//rotate([90, 0, 0])
color([0.5, 0.5, 1]) translate([-4, -0.5, tube_length*8-6])
cube(size=[8, 1, 3], center=false);

//} translate([0, -50, -1]) cube(size=[10, 500, 500]); }

//rotate([10, 0, 0]) axleround(h=8);

// ball end shift 2.3mm down
module ball_end_n() {
  translate([0, 0, 1.7]) sphere(r=3.05);
  translate([0, 0, -0.1]) cylinder(r=2.9, h=2);
}

module axleround(h = 24, axleradius = 2.3, axlemesh = 1.7) {
  translate([0, 0, -h/2]) difference() {
    cylinder($fn=16, r=axleradius, h=h);
    translate([axlemesh/2, axlemesh/2, -1]) cube([axleradius, axleradius, h+2]);
    translate([axlemesh/2, -axlemesh/2-axleradius, -1]) cube([axleradius, axleradius, h+2]);
    translate([-axlemesh/2-axleradius, axlemesh/2, -1]) cube([axleradius, axleradius, h+2]);
    translate([-axlemesh/2-axleradius, -axlemesh/2-axleradius, -1]) cube([axleradius, axleradius, h+2]);
  }
}