# Mechanism for changing gears on a bicycle

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

• Do you have the ability to measure the tension required to pull the shifter to its limit? Knowing that measurement would be the first step toward making any type of informed decision. – Ian Sep 28 '13 at 18:25
• I could probably use a tension gauge to measure it once I obtain a donor bicycle. – audiFanatic Oct 2 '13 at 20:28
• I have seen a very simple unit on a 3 speed hub gear that was bolted to the chain guard and would actuate the read hub rear link as the pedal cadence increased. It certainly looked like a old bit of gear from the 80's. – KalleMP Oct 27 '15 at 13:40
• This is a exploded view of a commercial gear cable actuator, very nice. schaeffler.com/remotemedien/media/_shared_media/04_sectors/… – KalleMP Oct 27 '15 at 14:11

One of the fancier ones I've seen is the Shimano Di2 Dura Ace 7970 It's not cheap though, it's about \$2200 for the set or \$500 for the rear derailleur alone, \$690 for the shifters, plus another \$85 for the battery.