It has become the mark of football's great freekick takers - the ability to strike the ball so it moves unpredictably through the air, leaving goalkeepers standing. Players like Christiano Ronaldo and Gareth Bale have become famous for using the so called'knuckleball' shot. Now researchers have built a robot that kick a'knuckleball' just like Ronaldo every time, but without the fear of crying if it loses, or stripping off its shirt if it wins. Researchers have now built a robot (pictured) that can kick the ball in a'knuckleball' way every time, and used a wind tunnel and high-speed camera to work out what forces cause this zigzag trajectory of balls through the air Knuckleball is a technique developed by baseball player Eddie Cicotte. Cicotte's method involved holding the ball between his knuckles with the intention of avoiding the rotational spin created by throwing a ball normally.