I am not sure I understand your question, but if you are asking about wheels slipping on soft earth, resulting in odometer errors - it can be a problem. This isn’t usually too much of an issue in a “hall-bot” though, and with the proximity sensors, the robot should be OK. There are a number of published studies on dead-reckoning errors, and how to correct them. Unfortunately, most study robots use a combination of GPS and dead-reckoning, so their methods may not help. I enjoyed reading on the link website, the way the builder improvised and used LEDs for both his emitters and detectors. It reminds me of how in Junior High, we used to saw the “roof” off of scrounged TO-3 transistors, and use them for photo-detectors.