Wireless Bike Brakes Fail Three Times in a Trillion
Computer scientist Holger Hermanns on his wirelessly-braking bike.
CREDIT: Angelika Klein
Many people have had their cell phone calls dropped or their wireless Internet connection interrupted while they're browsing online. What if in the future, airports or subway systems relied on wireless devices? To test the idea of a critical, life-and-death wireless system, researchers at Saarland University in Germany created and tested something a little less high-stakes: A wireless bike brake.
A bike is a "playground" for testing ideas that may be applied to more critical systems, said one of the researchers, computer scientist Holger Hermanns, in a statement. Nevertheless, testing can't be fun for at least one rider. In their paper, the programmers called the experiment their "mad bike project." Hermanns and his colleagues ultimately created a brake that works more than 99.999 percent of the time. They'll present their results Mar. 6 at a computer science show in Germany called Cebit.
The braking system has sensors in the bike bell, the rider rings the bell when he wants to stop. The sensors convey a "stop!" message to a sender device, which transmits the message to a receiver, which tells an engine to pull the brakes. An alarm turns on red LED lights when the system fails. An external battery powers everything.
Hermanns and his team tested the brakes with mathematical models they wrote and with real-life rides with other wireless devices, copy machines and microwaves nearby. They found that each step in the wireless system takes time, at least 125 milliseconds altogether. As long as every step works correctly, that's fast enough for everyday use, they decided. As long as the brakes work within 250 milliseconds, they calculated, someone pedaling at 19 miles an hour can brake in six feet.
Just as with dropped calls and Internet connections, the brakes' wireless messages sometimes failed to send. The researchers created two models of the bike brake. In the first, the brakes failed almost two percent of the time. But in the second, the brakes' rate of failure was about three for every trillion braking attempts. "That is not perfect, but acceptable," said Hermanns.