$fn=50;

dims = [74, 24.5, 6.3];

module screwpost(h) {
  //  2.7d, 3.5h over lip
  difference() {
    cylinder(d=2.7, h=h);
    cylinder(d=1.7, h=h);
  }
}

union() {
  difference() {
    union() {
      cube(dims);
      // outer lock
      translate([0, -2.5, 1]) {
        difference() {
          cube([6, 29.5, 3]);
          translate([1, 1.5, 1.01])
            cube([6, 26.5, 2]);
        }
      }
      // center fins
      translate([39.7, -2.25, 1])
        cube([6.8, 29, 1]);
    }
    // inside
    translate([1,1,1])
      cube(dims - [2,2,0]);
    // lip
    translate([0.5,0.5,dims.z - 1])
      cube(dims - [1, 1, 0]);
    // pcb slot
    translate([dims.x - 3.7, 0.5, 1])
      cube([2.7, dims.y - 1, dims.z]);
  }
  // battery connector lip
  translate([dims.x - 1, dims.y - 10, 0])
    cube([1,6.7,8]);

  translate([3.35, 3.35, 0])
    screwpost(10.25);
  translate([3.35, dims.y - 3.35, 0])
    screwpost(10.25);

  translate([dims.x - 3.35 - 2.7, 3.35, 0])
    screwpost(8);
  translate([dims.x - 3.35 - 2.7, dims.y - 3.35, 0])
    screwpost(8);
}