How to attach a potentiometer to a servo motor shaft

So what's wrong with these ?

I may need to pick out a Servo motor first. I found a couple of hours, they look simple enough to build. But all of the servo Motors on Amazon seem to be for little plastic robots. I need something big

I worked with the kind of servo motors you are talking about with wafer lifters and they are hella
expensive.

Servo motors

What are the specs for the motor in question ?