Tenacious A and Tenacious B are twins -- hacked "Morphibian" radio-control toys. Driver circuitry, sensors and a microcontroller running a custom firmware application have been added to make these two 'bots come alive.
Both run our own in-house infrared communications protocol that allow all our platforms to "see" each other and interact on a basic scale.
The platforms are differentially steered, four-wheel drive, with lots of room inside for circuitry, sensors, etc. The are designed to be waterproof, and while I had to remove some of the water proofing to make room for infrared sensors, they are very tough physically and can be handled by kids, can fall off tables, run straight into walls and keep going. We made the subsumption programming very robust; these guys don't get trapped.
My goal with these 'bots was to keep them cheap, cheap, cheap, cheap and also have a matched pair that could run some experiments with our in-house infrared communications protocol. These are esp. useful, because unlike some of the larger 'bots and nests, these puppies must use their IR leds/detectors for obstacle sensing AND tx/rx of IR data. Gets quite tricky "talking with your eyes" and without mistaking IR communication (or interference) for actual obstacles. They communicate clearly, sees obstacles, and rarely sees "ghosts" when "seeing" with his "eyes/ears", etc.