Olympic luge racers earn their medals by some of the narrowest margins in sport. Athletes add the times of four runs down an icy track, producing almost identical sums.
At the 1998 Nagano Winter Olympics, the gap between gold and silver for women's luge was just two thousandths of a second, as Germany's Silke Kraushaar (3:23.779) edged out her teammate Barbara Niedernhuber (3:23.781). The bronze medal was a whopping (relatively-speaking) four-tenths behind, with the Austrian Angelika Neuner at 3:24.253.
When medals are lost by slices of seconds, timing is everything. So victory in the 21st Century is judged with precision tools, including RF chips, lasers, and digital cameras. Given that each technology has specific strengths and weaknesses (see chart pg 44), the choice isn't always easy.
Stringent demands. It should be a simple engineering challenge—figuring out who is first to the finish line—but it's not. The demands include:
Accuracy (even a perfect clock errs by its reaction time)
Redundant systems (if your clock fails, you can't ask world-class athletes for a do-over)
Portability (events are held in different places every day)
Scalable accuracy (alpine ski racers need more precision than marathon runners)
Knowledge of rules in each event (what stops the clock, an athlete's leg? chest? ski pole? skate blade?)
"Smart" systems (in a cycling or nordic skiing time-trial, every athlete on the course is racing his own clock)
Weather (an indoor cycling race is warm and dry; a ski race is neither)
Networking (to calibrate the start and finish clocks, and to broadcast instant results to a scoreboard, Internet, and television)
For generations, the only technology found at a race was a gun and a clock. But sluggish human reflexes allow us to use stopwatches only to an accuracy of 0.25 sec.—far too slow to have picked a winner in Kraushaar's winning luge run.
Modern tools have smaller margins of error, but race officials often ignore the math, says Bob Fayfield, CEO of Banner Engineering (Minneapolis, MN), maker of optical sensors used in timing applications, including Olympic events.
"We analyzed the hypocrisy in using one millisecond time places; it's just not accurate," he said. "Where it really came out was luge and bobsled."
For instance, a typical photoelectric sensor has a one-inch diameter eye. Athletes who race early in the day must break the entire beam to stop the clock. But by afternoon, frost and snow have clouded the eye, so racers can finish by covering just a fraction of the beam.
"Athletes are making or missing the Olympic team by the third decimal point," he says. "Is that a valid thing to do?" Given the best technology, the only response is to combine times from multiple runs (as luge does) or to drop a decimal point for finish times—creating more ties, but fewer false winners.
There will always be a margin of error. To avoid false stops, Banner's photoelectric must sense four consecutive pulses signaling a change of state in light before it trips. "You'll always have the ambiguity of plus or minus one pulse," Fayfield says, "because you don't know if the racer broke the beam just before or just after the pulse."
Another way to avoid false trips is to use a bigger eye, so snowflakes and ski poles won't stop the clock (ski racers often lunge with their poles to stop a beam before their legs reach it). But the variation in how much beam must be broken to stop the clock introduces more error.
So the primary challenge in precision timing is not logistics—it's accuracy, agrees Tom Westernberg, the U.S. Olympic Committee's manager of timing and scoring for the 2002 Winter Olympics at Salt Lake City, UT.
An Olympic luge event is timed to the thousandth of a second, so the clocks are accurate to 0.0002 sec., Westernberg says. He achieves this by shooting a 0.5 to 1.0-inch wide infrared beam across the track, stopping the clock when the receiver is blocked. He won't use lasers because their beam is so narrow they produce many false trips. In the weather-prone outdoor sports, beams can be tripped by heavy snowfall, or by ice chips thrown by speed skates. And many electronics wander off calibration when temperatures drop below -15C.
"Theoretically, a laser beam would give the best repeatability," he says. "But out in the real world, there are too many sources for error; it's an optically noisy environment."
Luge timing, in particular, has changed a lot in the two years leading up to the 2002 Winter Games. Previous beam systems would act perfectly calibrated in the test lab, but until recently, "their modulation rates were down in the few-hundred hertz range," he says. Since jitter (the change in frequency) equals one over the modulation rate, Westernberg went looking for faster beams.
As he tested some of the older timing systems, he found error rates up to 20 milliseconds—a gap that could create vast mistakes when multiplied over dozens of competitors sliding four races apiece.
Another fault of some older systems was that lugers with bright-white suits could avoid tripping the beam until their black helmets passed through—the last part of their body to do so. Those suits would essentially act as reflectors. And variables like the curve of a bobsled nose can trip the beam at different times, depending on sled design.
Beams must be calibrated to account for snowfall—judges who didn't dig out after a recent blizzard watched the first luge racer pass completely underneath the beam, says Giles Norton, director of corporate communications at Lynx Systems Developers (Woburn, MA), a precision sports timing company.
Another weakness is that the beam system can time just one athlete at a time, so for an event with simultaneous racers—like speed skating—Westernberg will use a "line camera." This high-speed, digital camera takes multiple pictures of the finish line, each photo just one pixel wide and 1,000 pixels tall. A judge can eyeball when the skater's blade crosses the line, then read the time-stamp when that frame was recorded.
That's why Westernberg chose cameras from Lynx System Developers for short-track speed-skating at this winter's Olympic Games. For that application, they will adjust the camera to shoot 2,000 pictures/sec—good for accuracy to 0.0005 sec—because of the great speed and close finishes in the event.
As opposed to beams, cameras can also identify each athlete. But they would be unwieldy to use for mass finishes like nordic skiing, where dozens of racers per minute could cross the line.
So mass races like marathons often use RF tags attached to each athlete's foot. Each April, the Boston Marathon times its thousands of competitors this way. Every runner registers a time as he jogs over a carpet in the street, allowing race organizers to collect split times throughout the course. That 2 to 4-hour race is timed only to 1.0-sec accuracy. But on close finishes, the chip may not be sufficient, since the finish is judged by an athlete's chest breaking the line. If the chip is on his trailing foot, a close winner could appear to be beaten by an athlete with the chip on his leading foot.
And when Olympic gold is on the line, that's too large a margin to leave to chance.
Gold medal margin (over silver) at Nagano Games
||0 sec (tie for Gold) (two-man bobsled)
||0.002 sec (women's singles)
||0.02 sec (men's giant slalom)
||0.059 sec (women's 500m)
||8.0 sec (men's 10k freestyle)
|Timing is everything
Typical event, speed
||tracks only single athletes, wide beams boost margin of error
||alpine skiing, luge, bobsled
||tracks only single athletes, narrow beams often false-tripped
||tracks multiple athletes
||expensive, not very accurate
|Digital line camera
||tracks multiple athletes
||expensive, bad for mass finishes
||bicycling, horse racing, rowing, speed skating, track and field
||foolproof, portable, cheap
||low accuracy, tracks only single athletes