Here is an instructable on how to add a servo motor to your back-wheel derailleur with electronic control. This is one part of a much larger fully automatic bicycle project to make gears change automatically based on parameters such as heart rate, cadence, incline, speed, gps, etc…
After seeing the electronic shift mechanism at a Trek store, I thought having autoshift based on cadence would be nice to have. I was wondering if this could be accomplished using an existing bicycle computer for the cadence monitoring. Oh, that’s right; it would not contain the parameters and algorithims for the shift instructions. I just found this site and will keep an eye on your progress. Thanks