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I am doing a project on automatic gear shifting. I need to choose which motor will be used to change the gear.
I have found a previous question on this topic. An answer mentioned:

If you used a fairly hefty RC servo motor I think it could work

Which motor is used nowadays for automatic gear shifting? Which motor will be perfectly suitable for my application? How much power will be required for a gear shift and to hold the wire in a particular position?

I am interested in the exact value of torque/power required for a single gear shift in 7 geared cycle.

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    I assume you plan to simply pull the shift cable with a servo motor? I think the easiest way you’ll get a good answer is by pulling the shift cable on your bike with a luggage scale and convert that to pulling force (or measure the force in any other way). – Michael Oct 20 '20 at 16:12
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    If you expect the motor to hold the cable against the springs in the derailleur on its own you need a stepper motor – Affe Oct 20 '20 at 17:18
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    A stepper motor will consume far too much power. For this application (pulling and holding a cable), we should use a worm and worm-gear arrangement. This will hold the cable in position with the motor turned off, and it also offers a high ratio of often 20:1 or 50:1, which will enable use of a smaller and higher-RPM motor. – BetterSense Oct 20 '20 at 17:35
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    TRy to read how electronic shifting is implemented, you can learn a lot from that. I am sure that patent applications for Shimano Di2 or SRAM eTap will have a lot of information and some of it may be relevant. (they use stepper motors) – Vladimir F Oct 20 '20 at 17:36
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    @Affe there is at least one "converter" that allow turning a conventional mechanical derailleur into a wireless one, e.g. Archer D1x. It is mounted on the chainstay and does pull a short run of the cable from the derailleur. – Grigory Rechistov Oct 22 '20 at 10:10

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