Scientists Build Wireless Bicycle Brakes

itwbennett writes "Computer scientists at a German university have built a set of brakes controlled using a small motor for a braking mechanism and a wireless signaling device to tell it when to brake and how hard. 'Making a popular set of bike brakes wasn't really the point of the project,' says blogger Kevin Fogarty. 'The project was to find out how to make the wireless connections between two components of a system that has to operate in real time – with milliseconds of difference between success and failure (PDF) – more reliable than systems that are normally connected by a wire.'"

Stop whining

[hackertourist]

This isn't about wireless bike brakes, it's about reliable, real-time wireless connections. Surely that's something nerds can find a use for?

Re:Awesome...

[Crudely_Indecent]

I hope there is some sort of Make sure you mix up the levers and calipers so the radio pairs aren't installed together on the same bike.

Yeah, no thanks. This sort of technology adds multiple potential points of failure to a system that is currently reliable and simple.

Whereas a bicycle brake system can experience a cable failure (among others which are shared with a wireless system, such as pads) a wireless system can experience transmitter failure, receiver failure, radio interference, battery failure (transmitter or receiver). This team tries to mitigate that potential failure by adding more transmitters. That reminds me of a SNL skit - Christopher Walken "More Cow Bell"

In my time as a cyclist (3 decades), I've only experienced brake communication failure (broken cable) a couple of times - after which I learned to stop buying cheap cables and I've never experienced brake failure again.

I realize this is not a product that will likely see the light of day. It was an exercise in the reliability of critical communication as indicated by a quote early in TFA:

"Wireless brake" and "hit by a truck" sound the same to a cyclist

Re:Awesome...

[Migraineman]

Most of the responses so far are people getting hung-up on the example and responding "wireless brakes on a bike are teh shitz." If you read the PDF, they're pretty clear that the experiment is about real-time control systems using wireless communications links. The wireless bike brake is a convenient structure to do some real-world prototyping, and provides some environmental bounds (response time, lag, bandwidth, etc.) that ratchet this up one level above being a purely academic exercise.

That said, the authors are faced with the horrible reality of wireless links - they are completely unreliable. Fundamentally. Period. The aether is a shared medium, and as such, you have to deal with collisions from other transmitters and interference from unintentional radiators (microwave oven, I'm looking at you.) The objective response time in this experiment is 150mS in the wireless link, and 100mS in the physical actuator. Ignoring the actuator time, 150mS is an abstract number without context. If you're brewing coffee wirelessly, 150mS to close the loop on the temperature control is effectively "instant." [no pun intended] However, if you're measuring RPM feedback on a turbine shaft, 150mS may be an eternity.

If you're placing the wireless link in the feedback path of a control loop, which these guys are doing, you have to account for the characteristics of the wireless link as part of the control loop stability analysis. Modeling packet loss and transmission delay as the equivalent phase shift and frequency characteristic of a classical analog component can be quite challenging. Further, the characteristics of interference sources may place you squarely in the "doomed from the start" category. If the above mentioned microwave oven can impair your wireless link for the duration of a bag of popcorn, your 150mS response time is irrelevant.

Wireless links and hard real-time control systems go together like fish and bicycles do.