2009:Traction control function

Traction control function

Requirements

1. When a wheel or wheels start slipping,  stop the slipping and regain traction
2. Allow for special cases such as when one or two wheels is on carpet.

Assumptions

1. We know the power values (L drive and R drive) we gave to the motors 
2. Our only sensor input is the actual motor speed of each of four motors.
3. We do not know robot speed nor direction.

Ideas

1. Compare left-front vs. left-rear wheels.    If one wheel is significantly faster than the other,  assume it is slipping.    Reduce power to the slipping wheel for xxx milliseconds then restore restore full power.     Perform same check for right-front vs. right-rear.