I'm looking to make an automatically shifting bicycle for my senior design project (along with some additional features TBD). However, I come from an electrical/software background; not a mechanical one. So I need to figure out a decent way to shift gears. I was thinking of leaving the gear system in place as is and using some sort of motor (servo or stepper motor with worm gears) to pull and release the wire cable as needed. However, I have some concerns with this; namely the amount of torque needed to pull the wire and finding something with enough holding torque. Perhaps my best option is to use the trigger shifters on as well and perhaps use a solenoid. My other concern (namely with the worm gear) is that it'll be too slow.
So I would like to pick your brains here for a moment. Thanks