Mindstorms and the original RCX were a huge part of my college memories; I had a professor who used them for one of our classes. I built a substantially large "dragon" robot where the head + neck were actually a robot arm that could grip things, and it moved on treads. It took three RCX's "networked" together to get enough inputs and outputs for all the motors and functions. I accomplished the 3-way communication by making a parabolic reflector for the IR out of white cardstock; the three RCX's sat side by side and all aimed at the same reflector. The one in the middle controlled the outer two; each knew to only reply based on the first part of the message, so there was no contention.

I left that model with university which they kept as a display; I felt a little guilty having used up most of three Mindstorms sets for my project. Later I bought my own Mindstorms set, and then one of my then-wife's coworkers - whom we didn't know, and I don't know how she knew of me - randomly gave her a 2nd Mindstorms set to give to me. I keep meaning to re-create this dragon robot someday, leaner so it only takes two RCX. I have a lighter design now for the gripper + wrist section which, like the rocket equation, would allow the whole rest to be smaller if the last stage is smaller.