Electronically switchable chainless drivetrain developed for Alpha Bike concept

The Alpha Bike is an interesting prototype out of the University of Pennsylvania featuring a fully internal chainless drive that can be switched between fixed gear drive and freewheel electronically.

Fabricated entirely in-house, the bike's drivetrain, brake systems and onboard electronics are all concealed inside the custom-machined frame and an LCD display on the handlebars updates the rider on important journey information.

The bottom bracket of the Alpha Bike is home to the Switchable Integrated Free-Fixed Transmission (SWIFT) Drive system designed by University of Pennsylvania Mechanical Engineering seniors Geoff Johnson, Lucas Hartman, Katie Savarise, Evan Dvorak, Katie Rohacz, with Dr. Jonathan Fiene as advisor.

SWIFT uses an electronically-controlled clutch for switching between fixed-gear and freewheeling modes and incorporates a central shaft made from AMS-6514 Maraging steel, a Titanium 6Al4V clutch plate and belt pulleys made from stainless steel.

A front hub houses a drum brake and dynamo which provides power for the electronics, charging two super capacitors which in turn power a suite of sensors and a microcontroller. At the rear there's a compact three-speed planetary gear set actuated by a standard push-pull cable.

The LCD display on the 16 ounce (458 g) 3D-printed handlebars offers the rider useful information such as time, distance, cadence, wheel speed and chosen gears. Bike dynamics information is stored to SD card, which can be examined after completion of a ride.

Sadly, there is no information available on how the performance of the prototype drivetrain compares to more familiar designs. Nor is there any indication that the development might result in a production model.

The purpose of the design project was to "create a bicycle push the boundaries of integrated systems." In that regard, the Alpha team was recently rewarded for its efforts, receiving the Gemmil Award in the University's 2011 Senior Design Competition.