Thank you for your reply Admin
I dont need to know the voltage, I only need to modify it, so I can control the signals from the RC controller from the parallel port.
I think I have found a easy way to do it:
I am going to replace the potentiometer with a small circuit with two relays. They will work like this:
Both off - Sending 0v through where the potentiometer was before. This will make the servo reverse.
A On - Sending 1.5V through where the potentiometer was before. Will make the servo stand at default / zero.
B On - Sending 3V through where the potentiometer was before. Will make the servo move in the positive direction.
(The above is not the right voltage!)
And here is a very professional circuit drawing:
Anyone know if a setup like that will work? It does in my mind