In a new spin on the bicycle, a Yale mechanical engineering class has created a bike whose spokeless wheels appear to rotate around thin air.
The bicycle, which its inventors believe to be the first of its kind, was the fall project of nine Yale mechanical engineering majors in MENG 489, “Mechanical Design: Process and Implementation.” The bike was unveiled in a presentation Dec. 10, and it is currently on display at the Yale Engineering and Applied Science Library on Prospect Street.
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The class chose to build the bike because its design was counter-intuitive and challenging, said class instructor Vern Van Fleet, a mechanical engineer at the Stratford, Conn.-based Sikorsky Aircraft Corporation. While numerous designers have toyed with the idea of a spokeless bike, and the Internet abounds with concept drawings, Van Fleet said he was not aware of any of these designs ever actually turning into a functional prototype — until now.
“There’s plenty of conceptual drawings out there that industrial designers have come up with that look pretty cool, but an engineer would say that would never work,” Van Fleet explained. “We wanted to come up with something that would actually work.”
There are several advantages to having a spokeless wheel, team member Derek Zhao ’10 said. For example, the space could be used to house an electric motor.
But, more importantly, Zhao said, the bike just looks cool.
Strictly speaking, the actual bicycle is only half spokeless, Van Fleet said. Due to time constraints and material costs, the class was only able to make a spokeless rear wheel and attach a standard bicycle wheel to the front.
“It’s still not ideal, not fully developed at the point,” said Van Fleet. “In a semester, you can only get so far into the design process. To get to a first stage functional prototype is a big achievement.”
But the fact that only one wheel is spokeless was of little significance to the students’ goal, which was to prove that a spokeless bike is mechanically feasible, team member Sean McCusker ’10 said.
The spokeless rear wheel, which is the source of the bike’s power, was by far the most challenging aspect of the design, McCusker said. Zhao explained that most bikes are propelled by a gear in the center of the rear wheel, which turns the spokes. The spokeless model uses a gear placed on the inside of the wheel’s rim, Zhao said. Instead of turning spokes, the gear grips the teeth of an industrial timing belt fixed to the inside of the wheel. The lack of spokes meant that the bike had to structurally reinforced by adding a heavy frame, Zhao said.
The project gave the students a realistic experience of working on a design team, Van Fleet said. The team’s initial enthusiasm sometimes gave way to friction when faced with the project’s challenges, but all remained friends and came away with a great sense of accomplishment, he said.
In specifying areas for improvement, Zhao said the bike’s weight was the group’s main concern.
Although its weight made it “a little slow to start,” the bike was quite rideable, said Kevin Webb ’10, who attended the bike’s presentation in December.
“It’s not something that you’re going to be speeding around the streets on, but it definitely gets around,” McCusker said.
Materials for the project were provided by Sikorsky, Zhao said. There are no plans to market the bike, he added.