$fn=60;
l1=[48,24,8];
l2=[24,18,5];
treads(n=15,link_size=l2);
module treads(n, link_size){
    tread_link(link_size);
    for(i=[1:1:(n-1)]){
    translate([(link_size[1]-link_size[2])*i,0,0])
    tread_link(link_size);
        translate([(link_size[1]-link_size[2])*(i),0,0])
        pin(link_size);
    }
}

module master_pin(){

}
module pin(s){
    pin_diameter = floor(s[2]/2);
    union(){
        translate([0,0,2*0.2])
        cylinder(h=s[0]-4*0.2,r=pin_diameter/2);
        translate([0,0,2*0.2])
        union(){
            cylinder(h=s[2]/2,r=s[2]/3);
            translate([-(s[2]/3),-s[2]/2,0])
            cube([(s[2]/3)*2,s[2]/2,s[2]/2]);
        }
        
        translate([0,0,s[0]-2*0.2-s[2]/2])
        union(){
            cylinder(h=s[2]/2,r=s[2]/3);
            translate([-(s[2]/3),-s[2]/2,0])
            cube([(s[2]/3)*2,s[2]/2,s[2]/2]);
        }
    }
}

module tread_link(s, gap=0.2){
    pin_diameter = floor(s[2]/2);
    echo("Pin diameter: ", pin_diameter);
    difference(){
        union(){
            tread_base(s);
            translate([s[1]*0.16,s[2]/2,s[0]/2])
            rotate([180,0,90])
            chevron(1,s[0]*0.48,135);
            translate([s[1]*0.88,s[2]/2,s[0]/2])
            rotate([180,0,90])
            chevron(1,s[0]*0.48,135);
            
            translate([s[1]*0.50,s[2]/2,s[0]/2])
            rotate([180,0,90])
            chevron(1,s[0]*0.50,135);
        }
        pin_holes(pin_diameter, s, gap);
        insets(s, gap);
        tooth_hole(s);
    }
}

module tread_base(s){
    union(){
        linear_extrude(s[0])
        hull(){
            circle(r=s[2]/2);
            translate([s[1]-s[2],0,0])
            circle(r=s[2]/2);
        }
    }
}

module pin_holes(d, s,gap){
        cylinder(h=s[0], r=((d+gap)/2)+0.1);
        translate([s[1]-s[2],0,0])
        cylinder(h=s[0], r=((d+gap)/2)+0.1);
}

module insets(s,gap){
    i_d=s[0]*0.25;
    
    rear_inset(s,i_d,gap);
    translate([0,0,s[0]-i_d])
    rear_inset(s,i_d,gap);
    front_inset(s,i_d,gap);
}

module rear_inset(s,i_d,gap){
    translate([-s[2]/2,-(s[2]*2)/2,-gap])
    cube([s[2]+gap,s[2]*2,i_d+gap*2]);
}

module front_inset(s,i_d,gap){
    translate([(s[1]-s[2])-(s[2]/2)-gap,-(s[2]*2)/2,i_d])
    cube([s[2]+gap+2,s[2]*2,s[0]-(2*i_d)]);
    
    translate([(s[1]-s[2])-(s[2]/2)-gap,-s[2]/2,-(s[2]/2)+3*gap])
    cube([s[2]+gap,s[2]+2,s[2]]);
    
    translate([(s[1]-s[2])-(s[2]/2)-gap,-s[2]/2,s[0]-(s[2]/2)-3*gap])
    cube([s[2]+gap,s[2]+2,s[2]]);
}

module tooth_hole(s){
    w=s[0]*0.5;
    d=s[1]*0.25;
    translate([s[1]*0.25,-(s[2]*2)/2,(s[0]-w)/2])
    cube([d,s[2]*2,w]);
}

module chevron(s,l,a){
    union(){
        rotate([-(90-(a/2)),0,0])
        translate([s/2,-s/2,-l/2])
        cube([s+0.1,s,l],center=true);
        rotate([90-(a/2),0,0])
        translate([s/2,-s/2,l/2])
        cube([s+.1,s,l],center=true);
    }
}