set '$fn' globally based on develop or print for wheel

[challenge-bot] / wheel.scad

// challenge-bot
// GNU AGPLv3 (or later at your option)
// project available at these locations:
// https://gitorious.org/ozzloy/challenge-bot
// https://github.com/waynegramlich/challenge-bot

// use $fn = 20 while developing, 100 when about to print
//  20 will make previews fast
//  100 will make printing smooth
$fn = 20;

wheel_depth = 6;
wheel_radius = 68/2;

module encoder_shaft(){
  // measured with calipers, checked against the motor shaft
  motor_shaft_big = 3.7; // radius, gets doubled in cylinder
  motor_shaft_small = 4.8; // total length of box
  motor_shaft_length = wheel_depth * 3 / 4;

  intersection(){
    cylinder(h = motor_shaft_length, r = motor_shaft_big, center = true);
    // x direction is multiplied by 2 because the radius of the cylinder
    // goes in both directions.  the extra .1 is for overlap
    cube([motor_shaft_big * 2.1, motor_shaft_small, motor_shaft_length],
         center = true);}}

module mounting_screw(){
  cylinder(h = wheel_depth * 1.1, r = 1, center = true);}

module wheel(){
  translate([0, 0, wheel_depth / 2]){
    difference(){
      cylinder(h = wheel_depth, r = wheel_radius, center = true);
      translate([0, 0, wheel_depth / 4]){
        scale([1, 1, 1.1]){
          encoder_shaft();}}
      mounting_screw();
      for(i = [1 : 5]){
        rotate(i * 360/5, [0, 0, 1]){
          translate([0, 0, -0.6 * wheel_depth])
            between_spokes();}}
      translate([0, 0, wheel_depth / 4]){
        difference(){
          cylinder(h = wheel_depth / 1.2,
                   r = 0.85 * wheel_radius,
                   center = true);
          cylinder(h = wheel_depth / 1.2,
                   r = 0.23 * wheel_radius,
                   center = true);}}}}}

module wheel_block(){
  cube([wheel_radius, wheel_radius, wheel_depth]);}

module pie_slice(){
  intersection(){
    translate([0, 0, wheel_depth / 2]){
      cylinder(h = wheel_depth,
               r = 0.85 * wheel_radius,
               center = true);}
    translate([0, wheel_radius * 0.3, 0]){
      rotate([0, 0, (360 / 5) / 2]){
        intersection(){
          wheel_block();
          rotate([0, 0, 90 - 360 / 5])
            wheel_block();}}}}}

module between_spokes(){
  minkowski(){
    pie_slice();
    cylinder(h = wheel_depth / 2, r = 1);}}

wheel();