The next phase of this project is to build some kind of feedback display. We've found that even just a light that goes on when energy is being generated provides a reward for the rider. I have prototyped a string of individually addressable RGB LEDs doing different animations depending on how much electricity is being generated. Now it's time to build a final version and (ahemm...) a teensy would be a perfect lightweight controller.
The problem is I'm not sure where to put it or what to display. The original idea was to wire LEDs around the whole bike, but the massive range of adjustability to the bike just made it unfeasible. I also considered doing lights on a rear flag, then deploying it somehow in front of the rider. The flag pole could act as a big energy meter. Another idea is simply some kind of display attached to the handlebars. I would love to hear some other ideas!
In addition to the display, some simple games would be fun and add a competitive component. "How long will it take you to generate 1Wh of stored energy?," Who can make the most electricity in 30 seconds," etc.