TFT (formally FOE) Timing Lights

A Brief History

Following a conversation with Ted Reading of the National Sprint Association, it was decided it would be useful for me to provide a technical description of how TFT/FOE timing light and drag/sprint systems work, especially for competitors new to the sport.

Back in 1985, we were approached by Performance Bikes magazine, who were then having difficulty in measuring the top speed of motorcycles. They did have a Radar system, but it frequently missed bikes completely, especially above 150mph. Eventually after about 2 years of development, we produced a speed trap system consisting of 2 modulated infra red light beams and a control box. The system was designed to measure speed to an accuracy of 0.5mph at 200mph.

Several of these systems were made and sold to motorcycle magazines and proving grounds. In 1988 we were contacted by the NSA to make a sprint system, consisting of a start beam a stop beam and a speed start beam. Two of these systems were purchased by the NSA to replace white light equipment. Over the following years these basic sprint systems were developed into twin lane systems with a complete drag racing start line system (NSA North, now run by Trevor Duckworth of Straightliners) and a simplified drag racing start line system (NSA South).

National Sprint Association Technical Description

For each lane, two start line beams, a speed start and an et/speed stop beam is employed. A simplified drag race start line tree is used with white (stage), green (go) and red (false start) lights for each lane.

The start line system consists of two beams both modulated at 6KHz set approximately 4 inches apart. The rider needs to block either (or both) of these beams with his front wheel for the stage light to come on. Once both bikes are staged the tree will automatically go to Green after 3 seconds. A fraction of a second (<0.001mS) before the Green is illuminated, the control box logic checks that each rider is still staged, if he (or she) still is, then the Green is switched on, if not a Red is displayed. Once a Green light is illuminated, the elapsed time clock is enabled, but will not start until the rider comes out of stage, which effectively means both start line beams are no longer broken. Note that if a Red is illuminated the elapsed time clock will not be enabled, as it means the rider was not in stage at the correct time. If the rider was not in stage, he (or she) cannot come out of stage to trigger the elapsed time counter, therefore no time will be recorded.

At the end of the track, normally a quarter of a mile from the start, a speed start beam is placed 32ft in front of the speed et stop beam which is at the quarter mile mark. On breaking the speed start beam a second (speed) timer is started. On crossing the finish and breaking the speed et stop beam both speed and elapsed time (et) timers are stopped. The et timer can measure to within 1/100^th or 1/1000^th of a second. The mph timer measures the time taken to cover the last 32ft to 1/10000 of a second. The logic in the control box converts this time into a mph reading and displays it on the front panel to within 0.1mph.

The control box also identifies which rider crosses the finish line first and displays a win light on the front panel. Once the timekeeper has recorded the times the reset switch is depressed which resets all clocks and allows the next two riders to stage.