I am kind of new to the whole CNC thing, but have a strong electronics / electrical background.
Basically.. I would like to build a CNC machine that uses an outside sensor to tell the CNC program when the machine has reached the desired location instead of the CNC machine just telling a servo motor to move a certain number of steps.. I want the freedom to use whatever motor I want to drive the machine in the desired direction, and use a sensor like an encoder, or some other type of sensor to tell the CNC software the location that the machine is at.

This will give me the option of using anything to drive the machine to the desired location, even pneumatic pistons if I wanted.. I just don't want to be limited to the power / speed / size of a servo.. even tho I know they come in lots of different sizes etc.

So how do I go about using a sensor to tell the machine where it is instead of the software telling a servo to move a certain number of steps?

I plan to use Mach3.