Cooper Union student builds flywheel-powered bike

Concept bike stores braking energy, and returns it on command

The constant quest to ride waves of green lights in New York City, inspired Cooper Union's engineer student, Maxwell von Stein, conceptualize a method to harness a bike's braking energy when stopped at a red light and then return it on command to help give riders a boost when green flashes.

And von Stein wanted to do it without a battery: the solution, integrate a 15-pound steel flywheel from a Porsche into a Continuously Variable Transmission (CVT) drivetrain for a bicycle.

As part of his senior project at New York City's Cooper Union for the Advancement of Science and Art he integrated a mechanical flywheel into a bicycle; one that could be ideal in urban environments. "The bicycle is already the fastest way to get around NYC," von Stein told BikeRadar. "A bicycle with a flywheel could make you even faster! The model I built helps when you need to slow down, but not when you need to come to a full stop. Incorporating a clutch between the flywheel and rear wheel would allow the flywheel to keep spinning when you come to a full stop. When the light turns green, you’d engage the clutch and accelerate."

While this might not sound all that complicated, one aspect raised has been whether this system would add more weight? But von Stein counters that the system only adds 20 pounds to the weight of the bike. "That's a 10 percent increase when you consider the weight of the rider and the bike," says von Stein. "Why do you want a light bike? You want a light bike so it's easier to pedal up to speed. That's where the flywheel comes in. It's another means of propulsion."

He does admit that the benefits depend on how you ride, and notes that a rider who rarely uses the brakes—say on a long training ride— would only be slowed by the flywheel. But he notes that in cities, where brakes are used quite often the weight might be outweighed by the assist in getting back up to speed.

Von Stein maintains that in a ride where speeds vary from 12- to 15mph (20- to 24 kph) the system can actually produce about 10-percent energy savings. That would certainly be helpful for the daily commute. And the concept was intriguing enough that it has attracted a bit of attention; so far von Stein has been awarded the Nicholas Stefano Prize, which Cooper Union presents to outstanding mechanical engineering senior projects. "The Flywheel Bicycle is a hybrid bike that uses a spinning flywheel to store and release energy," said von Stein. "You want high capacity with minimum weight. Instead of a heavy flywheel, it’s best to have one that spins as quickly as possible."

For this reason von Stein used a large chainring on the output of the transmission and a small sprocket at the flywheel. "Ideally an infinitely variable transmission would allow the rider to use the full capacity of the flywheel," he said, adding that flywheels have another advantage over batteries and electronic powered motors. "Flywheels provide greater acceleration because they can be charged and discharged quickly."

No plugs required, just a bit of pedaling.

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