It seems we may have been six months late in starting this thread - someone was selling a BMW stalk and radar module rather cheaply last year!
https://www.bimmerfest.com/forums/showthread.php?t=632783
The thread is quite an interesting read, according to them (though it may be BMW's own take on the system?) the ACC doesn't adjust the speed relative to distance but actually adjusts it relative to time. Still uses a four-position 'wheel' to select either one second up to four seconds. I kind of see how this way of calculating it works...providing my maths is correct! Converting the national speed limit of 70mph into mps (metres per second) I get a little over 31mps, now if you selected the highest time setting of four seconds you get a distance from the vehicle in front of 124m, which is round about the range of the first gen. radar module.
But perhaps all that is unnecessary? If in fact the ACC DOES in fact calculate its distance from the car in front based on current speed and time then maybe we can avoid the guesswork of the resistance values for the time setting and have a variable resistor in its place?
https://www.bimmerfest.com/forums/showthread.php?t=632783
The thread is quite an interesting read, according to them (though it may be BMW's own take on the system?) the ACC doesn't adjust the speed relative to distance but actually adjusts it relative to time. Still uses a four-position 'wheel' to select either one second up to four seconds. I kind of see how this way of calculating it works...providing my maths is correct! Converting the national speed limit of 70mph into mps (metres per second) I get a little over 31mps, now if you selected the highest time setting of four seconds you get a distance from the vehicle in front of 124m, which is round about the range of the first gen. radar module.
But perhaps all that is unnecessary? If in fact the ACC DOES in fact calculate its distance from the car in front based on current speed and time then maybe we can avoid the guesswork of the resistance values for the time setting and have a variable resistor in its place?