Ben Johnke, Bill Engelking, and Matthew Stout from CSU teamed up on a self-shifting bike prototype. As the rider picks up or drops in speed, the bicycle shifts gears to accommodate. The stock derailleur and cable system are paired with electronic sensors and computer code. When starting the bike, the rider keys in initial gearing on the bar-mounted main computer. While pedaling, a sensor reads speed as an LED light bounces off reflective tape on the rear wheel.
A detailed presentation after the break…
- This is the main computer. All code is run through this. It features an interface where the initial gearing is keyed before the ride. While riding, the speed and current gear are displayed.
- This mechanism does the physical shifting of the chain ring.
- This mechanism does the physical shifting of the freewheel.
- This is the absolute rotary shaft encoder. It senses whether the rider is pedaling forwards, backwards, or not pedaling at all. Due to this sensor, the bike will only shift if the rider is pedaling forward.
- This is an infared LED sensor with a photo transistor. As the reflective tape (6) passes by the sensor, the system records it and reacts as necessary.
- This is the reflective tape that is essential for reading the speed of the bike.
A close-up of the main computer (1). When the ‘On’ switch is engaged, it asks for the initial gear of the chain ring and freewheel. After that, the bike senses the speed and takes the shifting from there.
A close up of the rotary shaft encoder (4). Without this, the system wouldn’t know if the rider were pedaling or coasting. It is essential that the gearing change while the rider pedals and not while the rider coasts.
A closeup of the cable that relays signal from all of the components to the main computer.
This story is from Design News. They list the parts used and feature a video where students explain the system in greater detail (for those more electronically-oriented).