module strand(ysep,see){  // rand at 20
      
    //  ty=ysep+10+rands(-2,2,1)[0];
    //  by=ysep+rands(-2,2,1)[0];
    // the above two rands, generate the y end points,
    // but they should not change for each iteration of block
    // but should change for every iteration of strand within a block
      ty=10+ysep;
      by=0+ysep;
      
         b=[0,ty];
          c=[for (j=[1:1:(len/2)-1]) [j*20,ysep+10+rands(-2,2,1)[0] ]];
           d= [(len/2)*20,ty];
            e=[(len/2)*20,by];
             f=[for (j=[(len/2)+2:1:len])[(len-j+1)*20,ysep++rands(-2,2,1)[0]]];
              g=[0,by] ;     
          p=concat([b],c,[d],[e],f,[g]); 
      polygon(p);
 
}
    
module block(){
  for (j=[0:1:ns-1])
        strand(sep*j,j*7);
}       

ns = 50; // number of strands
sep = 20; // strand separation
len = 10;  // length of strand



for (j=[2:1:10])
translate([j*100,0,0])block();

block();