Looking at the specs for the Vex line following sensor:
http://www.vexlabs.com/docs/inventor...wer-5-1-06.pdf
It uses IR, probably not desirable to use this year, considering all of the potential interference from remote controls and lap counters.
Can you describe the motor or mechanism you want to count RPMs?
Edit: I also notice that the sensor should be very close to the tape. 1/8" and from the spec sheet:
Because the line follower uses an infrared LED to illuminate its target
and an infrared sensor to detect the reflected light, it will actually
work in low-light conditions or even in the dark! However, this
also means that it can easily become saturated — in other words,
everything will look white to it, like an over-exposed photograph — in
environments where there is a lot of infrared radiation. You’ll find
environments like this in competition settings where tungsten lights are
used for illumination. To avoid saturating the infrared sensor,
consider mounting it underneath the robot or adding a cardboard
shield to block ambient radiation.