To have I4WS, you need at least 3 channels. Furthermore, to get the most from I4WS, I feel that you must use a 3 or 4 channel stick radio instead of a pistol style radio.
Requirements:
A 3 or 4 channel radio. One channel steers the front tires (left stick in left to right direction), another channel steers the back tires (right stick in left to right direction), and a third channel controls the throttle (left or right stick in up and down direction).
When getting your radio, you must be sure to get a ground based frequency radio (for cars and boats). An air-frequency based radio (for planes and helicopters) will work, but is not very legal to use on your monster truck.
A method to mount the extra steering servo:
How to:
Modify your transmitter: "Oh no! I have to take apart my transmitter ??!!" you are thinking. Well, if you can handle controllong your throttle with the right stick (in up and down direction), then you are off the hook and don't have to modify your transmitter. However, a normal 2 channel radio uses the left stick to control the throttle, so if you are used to the throttle being on the left stick like me, then you will need to do some modifications to make your 4 channel radio work that way.
The problem with with the 4 channel stick radio is that the left stick in the up and down direction (the one you use for throttle) is a rachet type instead of a spring type. Plane and helicopter users know what I'm talking about. They like to keep throttle at a constant position for long periods of time. The ratchet type makes it so that if you put the throttle at a certain position and release the stick, the stick remains there, it doesn't spring back like how car radios are designed. Imagine using your throttle control without that spring that brings the stick (trigger) back to neutral position. That would be tough huh? So if you want to use the left stick for throttle, you will have to make that stick from a ratchet type to a spring type.
The left stick is a rachet type, but the right stick is the spring type like how we want. Good!! So Plan A is to trade sticks; Put that right stick on the left side and put the left stick on the right side.