Electric Derailleur for bike shifting


I have a project to electrify my bike shifting derailleur (Shimano Di2 like).

My plan is to not modify the derailleur itself, but pull the cable, like a normal shifter will do.

The cable stroke is around 35mm in total, with the following requirements:

  • quite high position accuracy
  • keep position when not powered (to save battery)

I have 2 ideas in mind:

  • use a servo motor, probably the most simple but cannot keep position without power. I would need to implement some clutch to release the shaft or not, which might be complex. Any other idea ?

  • use a geared DC motor or geared stepper motor, which keeps position better by itself. Next issue is to sense the position "remanently", even after Arduino will be switched off then on. I have no idea about what sensor use ? potentiometer (stroke 180°), or whatever else ? Any idea ?

Interested by your valuable ideas :wink: !

Thanks !