We can use expression editor (under windows>animation editors) or node editor to make linked animation between gears. And we need to freeze transformation of the mesh before we create the expression.

Also, in order to make sure different sizes of gears match with each other, we need to make sure the ratio of the number of gear teeth to the radius of the gear is equivalent.

Therefore, I tried to design and make an animated steampunk style gear clock, I found some online pictures as inspiration.

In this case, I just combine diffrent types of gears together, and made a antique style pendulum and clock face. I also linked four gears with the same modulus to do the rotation.