For precision position tracking dedicated unpowered tracking wheels work the best.
While there are multiple threads talking about math associated with position tracking, there are very few good pictures of the actual hardware freely available online.
For some reason, people who do position tracking like to literally keep it under wraps. 
or explicitly tell people (me) not to share the details of their build further. 
Luckily @ranOOm from team 2381 made a video where you can see tracking wheels build details at 27:30 on his robot:
