Sounds exciting right, i had the same excitement in making and playing it. I used the same computer controlled r/c car for this project.
In this project I have managed to control my r/c car through a motion detector that i built at home. The motion detector is tied on the hand and connected to the remote controller of the r/c car.
The idea behind this motion sensor is very simple and logical. We all know that for a circuit to work it must be closed, the push buttons in the car's remote close the circuit and make the car work.
The same idea is applied in this motion detector, instead of push buttons I used a set of screws and a metal washer[a thin ring put in between nuts and bolts to make them tight]. Three screws are drilled in a row on a plastic sheet and a washer is put freely on the middle screw, touching only the middle one. When tilted the washer touches a side screw and thus establishes a connection between the middle and a side screw acting as a switch.
This sensor is connected to the controller's switch connections and now acts as a real motion sensor switch when tilted in some direction.
I had to make two sensors i.e one for driving front and back and one for direction. After many trials and fine adjustments I placed all the parts on a plastic piece and glued it together.
The motion sensor can be connected with any toy or relay to control them with motion of hands!