I entered this event, finishing in a three-way tie for third with my entry, "Just a Little BS'er". To learn more about this little guy, just keep reading...
Initially, I broke the problem into 3 components:
Because of the size restriction (8" cube") I decided to stick with a basic 2 wheel drive, one motor per wheel. I intended to make this robot bumperless, and use a rotation sensor to look for wheel stall (i.e. hit something) but this changed when I needed the rotation sensor elsewhere (and I only have one ). Having only one RCX meant that other design tradeoffs had to be made.
I quickly discarded the notion of sorting, as the cost/benifit ratio was too high because of the scoring method. Correct coloured blocks scored according to a Fibonacci sequence with a 1 point bonus per block. By a stack of three, the colour bonus is so overwhelmed by the stack hight score, it wasn't worth doing.
I considered a variety of feeder/stacker options, and in the end, did none of them This is because I became obsessed with the idea of a simple friction tube stacker...just push the tube down on the next block and let friction hold it in place. Of course this cause no end of problems, as I then had to come up with ways to align the bricks as well as drop the stack when done. The final bot is here.