Re: vex quadrature optical shaft encoders for cortex
If you check out the VEX Cortex Video Trainer: http://www.education.rec.ri.cmu.edu/products/teaching_robotc_cortex/index.html
and go to the Movement > Shaft Encoders section, you'll find some pretty good tutorials on using the encoders with the Cortex.
Also, if you check out the Setup > Build section, we have several sets of building instructions that show where to plug in the encoders. The two wires for shaft encoders must always get plugged in on neighboring digital ports (1&2, 2&3, ect).