log-spiral.scad

// chirp screw: parameterized on 0 <= t <= 1

t_steps = 500;

major_d = 50;
major_facets = 71;

minor_d = 4;
minor_facets = 17;

turns = 10;
length = 50;

//function z_func(t) = length * t;
function z_func(t) = 3*length * t*t;
function freq_func(t) = turns * t;

module spiral(){
  for (i = [0:(t_steps+1)]){
    t = i/t_steps;
    theta = 360 * freq_func(t);
    x = 0.5 * major_d * cos(theta);
    y = 0.5 * major_d * sin(theta);
    z = z_func(t);
    
    t1 = (i-1)/t_steps;
    theta1 = 360 * freq_func(t1);
    x1 = 0.5 * major_d * cos(theta1);
    y1 = 0.5 * major_d * sin(theta1);
    z1 = z_func(t1);    
    
    hull(){
      translate([x, y, z]){
	rotate([90, 0, theta])
	  cylinder($fn=minor_facets, d=minor_d, h=0.1);
      }
      
      translate([x1, y1, z1]){
	rotate([90, 0, theta1])
	  cylinder($fn=minor_facets, d=minor_d, h=0.1);
      }
    }
  }
}


difference(){
  cylinder($fn=major_facets, d=major_d, h=z_func(1));
  spiral();
}