Why don’t you use RFID chips for CX races?
While RFID chip timing works great and can be used at a CX race, its just not necessary. Using a good number caller and properly positioned bibs, its possible to produce 100% correct results with CrossMgr even with field sizes of 75 riders or more and fast finishes. Most CX races are selective enough that after the first lap, riders are spread apart, making it easy to call numbers.
The benefit to chip timing a CX race increases as there are more race day walk-ups. As race day registrations exceed 50, it becomes increasingly difficult to enter the walk-ups and also enter bib numbers during the race. With a chip timed race, the timer can spend more time entering registration data while the RFID system collects chip numbers on each lap.
Races with more than 50 race day walk-up registrants benefit from using RaceDB, registration software that integrates with CrossMgr. This allows a second operator to enter the walk-ups and race changes while the timer is entering bib numbers during the race.
What is the difference between active and passive RFID tags for racing?
Active RFID tags can be identified by their hard plastic shell. They have a small lithium battery inside that can last up to 5 years or longer. These tags are programmed with a unique number that cannot be changed, so there is additional work required during registration to link the tag numbers to the racer and bib. Active tags offer high reliability and high precision; 1/100 second for J-Chip and 1/1000 second for Race|Result tags.
Active tags have a very high replacement cost of $20 to $60, so they must be collected after events. Active tags rely on an inductive loop to activate and transmit. This inductive loop provides a narrow area around 1-meter wide where the chip will activate. However, tags must pass over the inductive loop to activate, so tags will fail to read when the inductive loop is not long enough to cover the finish line.
Passive tags lack a battery, so they rely on the radio antenna signal to both activate the tag and read the tag data. Passive tags have the advantage of low cost (less than $1) and are reusable unless damaged by bending or folding.
Passive tags have lower positional consistency since they can be read in a wider range by the antenna. Antennas vary from 30 deg to 60 deg beam width, resulting in a read zone that may be up to 10 meters wide. For RFID readers and software that record only the first or strongest signal from the chip, this can result in a chip time that is widely different than the time of the bike and RFID tag on the finish line.
However, using quadratic regression analysis on 3 or more chip times can result in generating a calculated finish time with 0.01 second precision, resulting in accuracy of 6 inches or less for a tag in front of the antenna.
An Impinj RFID tag reader can process up to 600 tags per second. At a speed of 34mph when tags are moving 50 feet per second, it is possible to read a passive tag 3 to 6 times, or up to 20 times at lower speeds.
Support for quadratic regression analysis on passive tags became available in CrossMgrImpinj v2.20.1 released in March 2018. Both J-Chip and Race|Result use a proprietary method encoded in the reader firmware for analyzing their active chips to calculate and report a high precision time.
For any RFID tag, a camera is necessary to correctly position finishers on the finish line. CrossMgr software features integrated digital pictures that show where the finisher is at the time the passive or active RFID tag was read.
Where can results be found from completed races?
There are three sites providing long-term hosting for race results produced by CrossMgr. Results are organized in folders by year and then by event date.
- Results pages for cyclocross races in Western New York
- Results pages for the Buffalo Bicycling Club
- Results pages for events produced with CrossMgr
Why isn’t GPS used for timing events?
While GPS data provides positioning data, the resolution of that data can vary between 3 to 30 feet or more. GPS data is sent from satellites orbiting 23,000 miles away, so the signal is very faint when it reaches the ground and can easily be blocked or lost. It can also take up to 30 seconds to receive the complete sequence of data providing the location information. While these capabilities are great for finding a location, they are unsuitable for the high precision and high speeds involved in racing.