I used this classical differential drive design for three projects:
S7: IR proximity sensing. It is possible to use the RCX to send IR messages and the light sensor to detect them in order to realize a sort of infra-red radar. It works very well! I don't know who was the first to suggest this trick on LUGNET™. I'd be pleased to give credit to the author on this page.
S9: line following. A very smooth, fast and precise line follower that uses two light sensors to never loose contact with its path.
S10: odometry. My first serious attempt to solve the "where am I" problem. This project gave me the opportunity to enter the legOS world. To implement odometry, in fact, I needed 32bit ints and arrays, both unavailable using the original firmware. My code includes fixed point calculations and trig to deduce robot's position from rotations of the main wheels. The original S7 differential drive chassis had been modified to host two rotation sensors.
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