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Football Focus: Ball tracking device takes guessing out of the game

The days of football’s chain gang might be numbered, if researchers at North Carolina State University, Carnegie Mellon University and Disney Research get their way. A team of electrical engineers has developed a new technology that could make the measuring chain redundant on tough first-down decisions—and could also take the subjective factor out of goal line calls.

Many other sports already employ some sort of ball-tracking technology. The Hawk-Eye system in tennis uses a set of high-speed cameras to trace the trajectory of a ball and to determine whether a shot landed in or out. Baseball uses both PITCHf/x (high speed cameras) and TrackMan (Doppler radar) to analyze the trajectories of pitches and hit balls. Though these aren’t used to make umpiring calls in baseball, they help generate some of the statistics used by teams, media and fans to understand the game.

Goal line technology also debuted at this summer’s soccer World Cup in Brazil. GoalControl-4D, which uses high-speed cameras similar to Hawkeye, awarded a goal to France in its game against Honduras on June 15, when the system detected that the ball had just barely crossed the line.


None of these technologies can be used for football, however, because the ball is often completely hidden from view by players. “I always wondered where the ball was,” said David Ricketts, the professor at NC State who ran the research project together with Joshua Griffin from Disney Research. Ricketts was also a lineman in high school. “I’ve been in a pile on, and it wasn’t until they peeled me off that I knew where the ball was.”

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So the team at NC State, Carnegie Mellon and Disney converted a football into the equivalent of a bar magnet. The researchers did this by coiling copper wire around the internal bladder and adding a small battery and some electronics. By passing electrical current through the loops of copper wire a magnetic field was generated around the ball.

Instead of being blocked by players’ bodies, the magnetic field passed straight through. By flipping the direction of the field — switching the north and south poles of the magnet — 400,000 times a second, a signal was generated that could be picked up by receivers placed around the football field. Finally, computers were used to process the data and determine exactly where the football was.

One of the main tasks of the computer algorithm was to remove the effect of the earth, which interferes with the magnetic signal. This effect would be slightly different at each different field, but the system can be calibrated to account for this.

The electronics add less than an ounce to the weight of the ball, and can be placed beneath the stitching so that the shape of the football is unchanged. Working out how to lace the football was a challenge, though. According to Ricketts it took Michael Sibley, an intern at Disney, 10 hours the first time to figure out how to package and re-lace the modified ball. However, a specially built power rack charges the battery wirelessly, so team equipment managers won’t need to learn this skill themselves. The cost of building everything into a football is estimated to be about a dollar, though the receivers and computer system will cost tens of thousands of dollars.


The modified ball has been used in practice at Carnegie Mellon, testing both the robustness of the electronics and the ability of the system to track it. The results show that more work is needed to fine-tune the accuracy, which is currently a couple of feet. The position would need to be known to less than half the length of a football for the system to be used to assist refereeing decisions.

The team is now hoping to find a partner to turn its cyborg football from science experiment into NFL game changer.