Ultimate DI3000,000 gears

[brucelee]

I've been mulling this for a while :
A stepper motor mounted on a mech with a pully that pulls the cable, a 3D printed housing, a microcontroller, some flat cable, a couple of switches, motor driver, couple of 18650's. This would put a lot of gear compatibility problems to bed for good just by reprogramming the controller for the appropriate spacing. Could even throw in some overshoot and non-linearity for good measure. The stepper motor could be the sacrificial component if the mech got smacked - they're pretty cheap. Anyone know how much force it would take to overcome the spring on a typical mech ?
Cheers,
Bruce.

[scottg]

Is this what you're talking about ?

Note, it isn't powerful enough for a pull chain mech, so don't expect it to run
your Benelux Tourist mech, also no overshift control, so it won't work with a
Osgear SuperChampion.

https://archercomponents.com/collection ... nd-remotes

[Brucey]

Anyone know how much force it would take to overcome the spring on a typical mech ?

IIRC campag have introduced a load of RDs fairly recently that pull less hard (~1kgf) on the cable because otherwise some of their ergos might throw in the towel prematurely. i thunk it is unlikely that any recent spring-loaded mech pulls harder than ~5kgf.

[rjb]

Why not remove the spring completely and use a threaded rod driven by the stepper motor to change gear.

[brucelee]

Why not remove the spring completely and use a threaded rod driven by the stepper motor to change gear.

I toyed with that but there is the issue of mounting the servo so that it can push as well as pull. With a short piece of cable outer, the mechanism can be mounted on the frame. Installation could be simpler and universal.