communication on long distances

Hi all,
I need your help and suggestions in this problem:
I have a robot which have two motors and a car battery, and I control its direction forward, reverse , to right and to left without any problems, but when I use a long wire for control about 300 m there are not anything work, and I test to run motor directly from the car battery throgh the cable (200m) and it's working but very slowly I think the wire is the problem , so how I can control the robot form long distance so I send only the control signals to robot and all circuits and driver and car battery on the robot ?

If you want to stay with wires look into RS422 or use a radio link.

oky I will use rs485 or rs422 but is there any porjects I can find with schematics ?

Maxum makes a converter chip 232 to 485. I do not remember the part number.

Once the signal is converted you will use two wires for RX and two wires for TX.