Hi ejector,
building your own RC control takes about four to five times the investment you'd have to consider when buying a complete RC transmitter and receiver off the shelf.
You will need a transmitter using a common (license free) frequency in the 27, 40, 315, or 433MHz band emitting coded information for each servo you want to control. Those devices are commonly known as digital-proportional RC transmitters.
The transmitter sends a sync pulse for the receiver which starts counting up from zero.
Thereafter the transmitter sends steering commands of 1.0 to 2ms length (with 1.5ms being the neutral servo position) in sequence according to "channels". (one channel has double function, e.g. rudder right, left and neutral).
The steering commands are normally transmitted at a frequency of 100Hz.
The receiver sends the info to the dedicated servo making it rotate one or the other way. The built in potentiometer (has to have a mechanical link with the rudder lever) moves the servo to the desired position and makes the servo stop within the dead band provided by the circuitry within the servo electronics.
That game continues until you switch of battery power to either the transmitter or the receiver.
My suggestion: Find a complete RC set at "ebay". There are cheap offers of the "Futaba F14", a 7/14 channel transmitter and receiver.
Kind regards
Boncuk