Here is what a guy from AsTeRICS (Assistive Technology Rapid Integration & Construction Set) told me.
My thoughts about your setup:
I assume you get binary signals on the wires forward, reverse, left and right.
The problem with digital signals for the steering is, that it’s very difficult to get a real sensitive control, but just cruising around should be no problem.
The next problem with digital signals is that you can’t just solder them to the remote directly. You would need a microcontroller to translate your control commands – Arduino would be perfect.
I can suggest the following two setups:
First of all you need a radio transmitter with a trainer jack (Buddy box - Wikipedia). These are used to connect the remote of a trainer and a beginner to practice driving, flying or whatever. In our system we hook up the Arduino to the trainer jack and get the possibility to send steering commands to the transmitter which then sends the appropriate radio signal to the model. The communication between the Arduino and the remote is done via a PPM signal. Attached you find some code for the Arduino to generate such a signal but you would need somebody who adjusts it to your needs. Maybe you have a RC hobby club around your home, normally you can find very interested people there who are into electronics and share their passion for RC cars or RC models with you.
Pinout for the Arduino for the ppm generator:
Connect pin 12 with the ppm in of the trainer jack
Connect GND from the Arduino to the GND pin of the trainer jack
Connect your signals to digital inputs and connect GND of the Arduino and the 9 pin cable.
Read the buttons state and set the channels in the Arduino loop method according to your inputs
The code should be very easy to write and also people with low programming experience should be able to be successful.
The second (easiest) option would be to get a remote with two joysticks, take one joystick out of the radio and mount it to your chin. We used soft balls from wheelchair chin controls which we glued on the stick to make the steering more comfortable, but I don’t know if this would be an option for you.
I hope I could help you, and if you have further questions just drop another email.