[mikets]

This year at FTC, our robot couldn't run straight. At first, we thought one of our motors was weak. So we replaced both of the motors. It still couldn't run straight, so we finally took one of the encoders apart and examined the optical disc, it had a minor scratch on it. Apparently, one of our students did not use the spacing tool when putting the disc on. After replacing the disc, the robot can run straight again. So it is critical the disc is free of scratches or dirt. However, if it is really dirt on the disc, can't you use a soft damp cloth to clean it?