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 !
First of all, you remove the spring from both derailleurs, which breaks your gears (in the case of the rear - not the one that tightens the derailleur carriage). This is very important as these servos do not have that much power and overheat while holding the derailleur in its position. If the chain is on any gear on the cassette, it will stay there even if you remove the spring, but the servo will be safe and will not burn.
As for the motor or servo, if you understand the code, the engine will be pretty cool, because you can attach a screw with a thread to the engine and put a nut on the derailleur and by turning the gears will change.
Oh, as this is a project and the setting of the servo or motor will probably be inaccurate, the determination of the servo stroke is best required for each gear - then you can set the gear perfectly
On this page you have code, not mine, but it's good. it's intuitive, so adding or subtracting a few gears shouldn't be a problem.
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