[mikeash]

The lip isn't detected by the sensors. The car stops on it when the tires hit it because of the physical obstacle it presents and the extra force needed to climb it.

It's weird, usually the car actually passed over the lip with the front tires, but then stopped when the rear tires got to it. The threshold for stopping must be very close to what it actually encounters there.

[tclmeelmo]

Someone on Youtube had what I thought was a clever solution: a piece of trim (looked like shoe molding) to bridge the 1" step. Cheap, and they claimed 100% effective.