What's a great gift for the cyclist who already has a digital speedometer, ultra-light aluminum frame, rear-view mirror, and horn? How about a "smart" bike that will find the right gear, no matter what the incline, or what the cyclist's energy level.
Just as many cars have automatic instead of manual transmission, so the bicycle built by a group of University of Rochester undergraduates shifts automatically. The bike can even learn the nuances of a cyclist's riding style and customize the shifting accordingly. The bike is on display at the University this week as part of National Engineers Week.
The "brains" behind the operation -- besides the students -- is a computer chip similar to those found in microwave ovens or air bag safety systems. The students programmed the chip to measure wheel speed and how fast the cyclist is pedaling. An algorithm uses these numbers to determine whether the chain is under tension or not, an important factor in shifting.
The cyclist decides how fast he or she wants to pedal, and programs the information into the chip by pressing a few buttons. The chip then "remembers" how fast the cyclist is supposed to be pedaling. When the bike rider tires and begins to pedal slower, the bike automatically shifts to a lower, easier gear. And when the cyclist pedals faster going down hill, the bike shifts to a higher gear.
"Many people wait until they're pedaling too fast to shift up, and they don't shift down until they're working too hard," says senior Ezra Gold, a mechanical engineering major and one of the bike's developers. "This lets the rider keep the right cadence, which can be adjusted by pushing a couple of buttons.
"It's also easier to ride," says Gold, a cyclist himself. "The bike automatically puts you in the right gear, so you can ride further faster. But it is weird to keep reaching for a lever that's not there."
The bike has six speeds, but more can be added. While there are a few automatic shifting bicycles on the market, their complex and sometimes jerky mechanical features, as well as added weight and cost, have discouraged most riders. Computer- controlled shifting is virtually unheard of. Student Emily Hackett did a patent search to see what systems had already been developed. "There were tons of ways to do this mechanically -- just about every way imaginable," says Hackett, a mechanical engineering major. "But there were only a couple of systems that tried to use computers to help control the shifting."
The chip and shifting system run on two small 7.2-volt batteries. Instead of a cable that adjusts the rear derailleur, the chip triggers a motor that moves a screw, sending the bike into a higher or lower gear.
The main difference from a conventional bike, says Gold, is that when the cyclist stops pedaling, the chain keeps turning so that the bike can continue to shift.
The chip, motor and batteries are contained in a small box that weighs between one and two pounds and sits below the rider. The students say the control box could be much more compact and light to make it commercially viable. The unit would probably add about $200 to the cost of a bike, say the students. Besides Gold and Hackett, the project team included former students Mark Spencer, Gregory Lukins, and Frank Duver.
"There were a lot of people who didn't believe we could do this well, without adding much weight," says Gold. "But it hasn't failed once."
The project was the idea of Bruce Arden, William F. May Professor of Engineering, vice provost for computing, and an avid bicyclist who makes the 15-mile commute to work by bike whenever possible. And it's commuters like himself, says Arden, who would get the most benefit.
"This makes the most sense for commuters, since they're the ones who start and stop the most often," says Arden. "If you're a bicycling fanatic, you'll probably want to manually shift gears, just as some people prefer a car they can shift manually."