Reaching 99.999999999997 percent safety: Computer scientists present their concept for a wireless bicycle brake

The cruiser bike is more similar to an Easy Rider motorcycle without an engine block than it is to a traditional bike. However, looking at the straight, elongated stem, it is readily apparent what makes the newly developed system so special. The bicycle has neither a protruding brake lever to control the front brake, nor a brake cable snaking down the frame.

But the wireless bicycle brake represents much more than just an academic gadget to the scientists. Professor Holger Hermanns, who holds the chair of Dependable Systems and Software, and who developed the wireless bicycle brake together with his group, explains: "Wireless networks are never a fail-safe method. That's a fact that's based on a technological background." Nonetheless, the trend is to set up wireless systems that, like a simple bicycle brake, have to function all the time.

"In the field of the future European Train Service, for example, concrete plans already exist," Hermanns reports. Furthermore, he says that train and airplane experiments are far too sophisticated, and could even endanger the life of human beings in case of malfunction. Therefore, the Saarland computer scientist's mathematical methods should now verify the correct function and interaction of the components automatically. "The wireless bicycle brake gives us the necessary playground to optimize these methods for operation in much more complex systems," Hermanns adds. Therefore, his research group examines the brake prototype with algorithms that normally are used in control systems for aircraft or chemical factories. As a result, they found out that the brake works with 99.999999999997 percent reliability. "This implies that out of a trillion braking attempts, we have three failures," Hermanns explains and concludes: "That is not perfect, but acceptable."

To brake with the wireless brake, a cyclist has just to clench the rubber grip on the right handle. The more tightly the grip is clenched, the harder the disk brake on the front wheel works. It seems as if a ghost hand is in play, but a combination of several electronic components enables the braking. Integrated in the rubber grip is a pressure sensor, which activates a sender if a specified pressure threshold is crossed. The sender is integrated in a blue plastic box which is the size of a cigarette packet and is attached to the handlebar. Its radio signals are sent to a receiver attached at the end of the bicycle's fork. The receiver forwards the signal to an actuator, transforming the radio signal into the mechanical power by which the disk brake is activated. To enhance reliability, there are additional senders attached to the bicycle. These repeatedly send the same signal. In this way, the scientists hope to ensure that the signal arrives at the receiver in time, even if the connection causes a delay or fails. The computer scientists at Saarland University found that increasing the number of senders does not result in increased reliability. "If it is not configured correctly, it is possible that three out of five braking attempts fail," Hermanns says.

Its current configuration enables the cruiser bike to brake within 250 milliseconds. This means that at a speed of 30 kilometers per hour, the cyclist has to react two meters before reaching the dangerous situation. But the Saarland University computer scientists are not satisfied with this functionality. "It is not difficult to integrate an anti-lock braking system and traction control. That takes only a few adjustments," Hermanns explains. After first talks with bicycle brake manufacturers, Hermanns is looking for engineers who will realize the concept of a wireless bicycle brake.

Researching the wireless bicycle brake was funded within the special research field "Automatic Verification and Analysis of Complex Systems (AVACS)" by the German Research Foundation. Its results are documented in the scientific paper "A Verified Wireless Safety Critical Hard Real-Time Design," published by the Institute of Electrical and Electronics Engineers (IEEE).