look at the 2 rear wheel speeds and pick the fastest travelling one and compare it to the speed of the propshaft and if it is going slower execute it into another piece of code to lock the diff up.
That seems unnecessarily complex. Unless your diff has broken you know that the propshaft speed is proportional to the average of the two wheel speeds so all you need to do is look at the ratio of the two wheel speeds.
If the car is not going in a straight line the outer wheel will turn faster than the inner wheel.
I have been assuming that you have done at least a few of the example projects that came with your IDE. They do require some hands-on to teach basics.
Suppose you hook up the sensor and wheel you have and see what you can get from that?The sensor is digital right? It's either on or off, LOW or HIGH, 0 or 1?So write code to read the sensor and if it is HIGH you turn a led on (UNO has built-in led on pin 13, I dunno about the MEGA) and if it is LOW you turn the led off. Then turn the wheel and see how the led flickers. If it does not then it's time to check the wiring and the code.
Be sure to put a resistor in the path between 5V to sensor to digital pin unless the sensor already has one. A 1k resistor should keep your Arduino pin safe, even 2.2k is not too much for digital.
i disagree the car is normally a front wheel drive car, when slip is detected it will lock up the rear diff (as it doesnt have a centre diff) to transfer the power to the back wheels. in its original state the car will decide how much lock to put on by looking at the outside temperature, steering angles, throttle position, G force meter and overall speed. so this will be a simple system compared to the original
For that to make sense, the drive to the rear wheels must be very different to a conventional prop shaft and diff. Do you have a clutch in the prop shaft? (I remember there was a very nice hydraulically controlled one from Land Rover a few years ago.)
i tride that sensor out to day and could not get it to work the way we discussed so i tock the 10K pull down resister out and put a pot in then tork the pot down to 1.3k and it did work but very tempermentalthe sensor seems to work between 1.0-1.3kwhat do you think?