I have a game coded in jQuery where bots are moved around the screen. The below code is a loop that runs every 20ms, currently if you have over 15 bots you start to notice the browser lagging (simply because of all the advanced collision detection going on).

Is there any way to reduce the lag, can I make it any more efficient?

P.s. sorrry for just posting a block of code, I can't see a way to make my point clear enough without!

$.playground().registerCallback(function(){ //Movement Loop
        if(!pause) {
            for (var i in bots) {
                //bots - color, dir, x, y, z, spawned?, spawnerid, prevd
                var self = $('#b' + i);
                var current = bots[i];
                if(bots[i][5]==1) {
                    var xspeed = 0, yspeed = 0;
                    if(current[1]==0) { yspeed = -D_SPEED; }
                    else if(current[1]==1) { xspeed = D_SPEED; }
                    else if(current[1]==2) { yspeed = D_SPEED; }
                    else if(current[1]==3) { xspeed = -D_SPEED; }

                    var x = current[2] + xspeed;
                    var y = current[3] + yspeed;
                    var z = current[3] + 120;
                    if(current[2]>0&&x>PLAYGROUND_WIDTH||current[2]<0&&x<-GRID_SIZE||
                        current[3]>0&&y>PLAYGROUND_HEIGHT||current[3]<0&&y<-GRID_SIZE) {
                            remove_bot(i, self);
                    } else {
                        if(current[7]!=current[1]) {
                            self.setAnimation(colors[current[0]][current[1]]);
                            bots[i][7] = current[1];
                        }
                        if(self.css({"left": ""+(x)+"px", "top": ""+(y)+"px", "z-index": z})) {
                            bots[i][2] = x;
                            bots[i][3] = y;
                            bots[i][4] = z;
                            bots[i][8]++;
                        }
                    }
                }
            }
            $("#debug").html(dump(arrows));
            $(".bot").each(function(){
                var b_id = $(this).attr("id").substr(1);
                var collision = false;
                var c_bot = bots[b_id];
                var b_x = c_bot[2];
                var b_y = c_bot[3];
                var b_d = c_bot[1];
                $(this).collision(".arrow,#arrows").each(function(){ //Many thanks to Selim Arsever for this fix!
                    var a_id = $(this).attr("id").substr(1);
                    var piece = arrows[a_id];
                    var a_v = piece[0];
                    if(a_v==1) {
                    var a_x = piece[2];
                    var a_y = piece[3];     
                        var d_x = b_x-a_x;
                        var d_y = b_y-a_y;
                        if(d_x>=4&&d_x<=5&&d_y>=1&&d_y<=2)  {
                            //bots - color, dir, x, y, z, spawned?, spawnerid, prevd
                            bots[b_id][7] = c_bot[1];
                            bots[b_id][1] = piece[1];   
                            collision = true;
                        }
                    }
                });
                if(!collision) {
                    $(this).collision(".wall,#level").each(function(){
                        var w_id = $(this).attr("id").substr(1);
                        var piece = pieces[w_id];
                        var w_x = piece[1];
                        var w_y = piece[2];
                        d_x = b_x-w_x;
                        d_y = b_y-w_y;
                        if(b_d==0&&d_x>=4&&d_x<=5&&d_y>=27&&d_y<=28) { kill_bot(b_id); collision = true; } //4 // 33
                        if(b_d==1&&d_x>=-12&&d_x<=-11&&d_y>=21&&d_y<=22) { kill_bot(b_id); collision = true; } //-14 // 21
                        if(b_d==2&&d_x>=4&&d_x<=5&&d_y>=-9&&d_y<=-8) { kill_bot(b_id); collision = true; } //4 // -9
                        if(b_d==3&&d_x>=22&&d_x<=23&&d_y>=20&&d_y<=21) { kill_bot(b_id); collision = true; } //22 // 21
                    });
                }
                if(!collision&&c_bot[8]>GRID_MOVE) {
                    $(this).collision(".spawn,#level").each(function(){
                        var s_id = $(this).attr("id").substr(1);
                        var piece = pieces[s_id];
                        var s_x = piece[1];
                        var s_y = piece[2];
                        d_x = b_x-s_x;
                        d_y = b_y-s_y;  
                        if(b_d==0&&d_x>=4&&d_x<=5&&d_y>=19&&d_y<=20) { kill_bot(b_id); collision = true; } //4 // 33
                        if(b_d==1&&d_x>=-14&&d_x<=-13&&d_y>=11&&d_y<=12) { kill_bot(b_id); collision = true; } //-14 // 21
                        if(b_d==2&&d_x>=4&&d_x<=5&&d_y>=-11&&d_y<=-10) { kill_bot(b_id); collision = true; } //4 // -9
                        if(b_d==3&&d_x>=22&&d_x<=23&&d_y>=11&&d_y<=12) { kill_bot(b_id); collision = true; } //22 // 21*/
                    });
                }
                if(!collision) {
                    $(this).collision(".exit,#level").each(function(){
                        var e_id = $(this).attr("id").substr(1);
                        var piece = pieces[e_id];
                        var e_x = piece[1];
                        var e_y = piece[2];
                        d_x = b_x-e_x;
                        d_y = b_y-e_y;
                        if(d_x>=4&&d_x<=5&&d_y>=1&&d_y<=2)  {
                            current_bots++;
                            bots[b_id] = false;
                            $("#current_bots").html(current_bots);
                            $("#b" + b_id).setAnimation(exit[2], function(node){$(node).fadeOut(200)});
                        }
                    });
                }
                if(!collision) {
                    $(this).collision(".bot,#level").each(function(){
                        var bd_id = $(this).attr("id").substr(1);
                        if(bd_id!=b_id) {                           
                            var piece = bots[bd_id];                                
                            var bd_x = piece[2];
                            var bd_y = piece[3];
                            d_x = b_x-bd_x;
                            d_y = b_y-bd_y;
                            if(d_x>=0&&d_x<=2&&d_y>=0&&d_y<=2) { kill_bot(b_id); kill_bot(bd_id); collision = true; }
                        }
                    });
                }
            });

        }
    }, REFRESH_RATE);

Many thanks,