In order to help boost their range, many electric and hybrid cars employ regenerative technology where braking energy is stored in the battery instead of simply being wasted. This idea can also be applied to electric-assist bikes, but what about bicycles of the plain old human-powered variety? Isn't it a shame that after having built up some good momentum, you just have to write it all off once you stop? Maxwell von Stein, a student at New York City's Cooper Union for the Advancement of Science and Art, thought so. As his senior project, he recently rigged up a flywheel to an existing bicycle, in order to harness the energy that's lost during braking. That energy can then be used to boost the bike when needed.
The Flywheel Bicycle has a continuously variable transmission in the rear hub. This is linked to a 6.8 kilogram (15 lb) flywheel from a car engine mounted in the middle of the frame. When the cyclist wishes to slow down, such as when they're going down a hill or coming to a stop, they shift the transmission to maximize the flywheel-speed-to-bike-speed ratio. This "charges" the flywheel with kinetic energy - effectively a mechanical version of what happens in an EV where a battery stores the scavenged energy.
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Once they want to accelerate or climb a hill, they do the opposite - they shift the transmission to minimize the ratio. This lets the energy stored in the flywheel drive the transmission, giving the bike and its rider a boost. In a ride where speeds vary between 20 and 24 kph (12.4 to 14.9 mph), the system is claimed to not only increase acceleration, but to also produce 10 percent in energy savings.
Although the added weight of the flywheel would certainly need to be taken into account, the concept behind the Flywheel Bicycle is still definitely intriguing ... enough so that it won von Stein the Nicholas Stefano Prize, which Cooper Union awards to outstanding mechanical engineering senior projects.
Maxwell explains and demonstrates his invention below:
Source: Scientific American