Base for Robot Arm

[nickwalt]

I'm making a robot arm (my first one) and I'm trying to figure how to actuate the base. The arm will have a rotatable base with a 20cm tall tower on it, but I'm worried if I simply attach the servo to the tower then the moment from the outstretched arm will be too much stress on it. What's a good solution for this? Do I just have two discs touching each other so they hold the force and have the servo actuate the upper one? Or will that cause too much friction?

Any resources or help would be great!