which motor is used to change gears in automatic gear shifting cycle now-a-days?

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.