Line Follower

It's a line following robot that stops when there is an obstacle in the way and it can also keep track of time for each run. Currently I really want to include a wheel encoder on it, but it's pretty hard since the diameter of the wheel is so small.

 Originally it was a mouse maze robot, now I've ripped out all but one of the IR sensors and installed a reflectance sensor array to do line following tasks. Two things that really tick me off about those IR sensors. First thing is that the sunlight can really mess things up and the second thing is the positioning. I also want to try ultrasonic sensors which shouldn't be affected by the sunlight, but its response is gonna be slower. 

Please share any good ideas or information with me.

Thanks.