A team of Penn Engineering students has designed a bike that offers cyclists the best of both worlds, as part of the school's annual Senior Design competition.

This year the champion was the ALPHA, a novel bicycle, designed by Mechanical Engineering and Applied Mechanics seniors Lucas Hartman, Geoff Johnson, Katie Savarise, Evan Dvorak, and Katie Rohacz, that can switch from fixed-wheel mode to freewheel mode, and has a unique drivetrain and embedded electronics inside its frame.

Members of the ALPHA bike team began the process of creating the bike at the start of their senior year when, along with advisor Jonathan Fiene, they sat down to brainstorm dozens of potential projects. The decided on the ALPHA because switching from fixed-wheel to freewheel modes posed an engineering challenge.

The distinction between fixed and freewheel bikes has to do with how directly the pedals are connected to the wheels. Freewheels have multiple gears that allow riders to coast without the pedals moving (think of a 10-speed bike). Fixed gears, or “fixies,” have a single gear and direct drivetrain, meaning the pedals always rotate along with the wheels, in both directions (think of a tricycle). And while fixies have experienced a resurgence in popularity in recent years, the single gear can make steep hills challenging, or even dangerous. 

The ALPHA provides riders with both configurations, plus the ability to switch from one mode to the other. At the push of a button, a clutch engages or disengages the part of the drivetrain that allows the pedals to rotate freely. 

“To our knowledge, there is nothing out there that can switch on the fly like this,” says Hartman. To fit everything inside the frame, while still making parts easily accessible for maintenance and repair, required extreme engineering precision.

“We pretty much took the machine shop here to, and beyond, its capabilities,” says Hartman. “You need half-a-thousandth-of-an-inch accuracy—an eighth of the thickness of a sheet of paper—on some of these parts. It’s mind-blowing.”

While most of ALPHA’s components were machined on campus, one key part was made at Midwest Composite Technologies. Fabricating the driveshaft pulley involved a new technology called Direct Metal Laser Sintering, where layers of powdered metal are melted by a laser, gradually building up otherwise impossible-to-make shapes. 

The team has also won design competitions outside of Penn, and plan on entering more, but have already succeeded in one of their original goals: turning heads.

“The idea was to get people to do a double take and say, ‘How the heck is this thing working? What is this thing?’” says Hartman. “And we have definitely gotten that reaction.”