color sensor aid

[Radiken]

I was doing research for a new robot in the works, and I came across these two videos:

http://www.youtube.com/watch?v=6960jAGCkiA

http://www.youtube.com/watch?v=EzClcwUqtlo

They both have a small black and white disc. As much as I can figure, They are there for the color sensors, but what specifically do they do?

[Somchaya]

The small black-and-white discs are probably encoders, and they're used for feedback on the motors to determine how far they've turned. Encoders like those are usually used on DC motors for feedback.