One of our earlier ideas was to make Theseus capable of moving sideways, thus making it unnecessary for him to turn around in the maze. Thus, he would always be facing the same direction (say, north) no matter where he was in the maze. To do this, we constructed a robot that could raise and lower a second set of wheels for y-axis movement.

Although we managed to implement a mechanism to raise and lower wheels, we ended up abandoning it for a more traditional two-wheel car. Even if the time to raise and lower the wheels had not been an option, a car like that would never have been able to correct itself had it managed to move at an angle. As we learned the hard way, building a robot for ideal conditions doesn't work. We needed a robot that could auto-correct itself, a robot that could know when it went off-track and then fix itself.

So, rotation it was. Professor Turbak showed us a model of how to implemenent dual differentiated gearing, allowing us to use one motor to turn the wheels and one motor to go forward. This would allow us to make extremely sharp turns, as well as well as have enough control to go forward and turn slightly. We built our own gear train to acheive this affect, and hooked it up to a car powerful enough to hold a HandyBoard and six different sensors. We had a "bathroom" (proximity) sensor on each side of Theseus, as well as two reflectant sensors to enable him to detect the white lines in the maze. White lines were used both to indicate a doorway and to contain the candle. Eventually, Theseus will probably need additional sensing (to detect the candle) as well as a motor (to control the candle snuffer).

Once Theseus was built, he ran smoothly and quickly. The next challenge was programming him to find the candle without knocking himself against the walls of the maze before he got close. We had a full-scale model of the maze used in the competition (and judging by the abundance of smears and cracks, it had seen a great deal of practice). Putting Theseus in the mage, we proceeded to attempt to write a navigating algorithm.

This, too, was not an easy process. While the most obvious path for Theseus to take would be to follow the left wall (putting his hand on the left until he got back where he started, so to speak), this would make him skip one of the four rooms (where the only doorway was on the right-hand side. While all of us had had a fair amount of programming experience prior to this class, the HandyLogo language was too limited for us to implement a great deal of logic in Theseus's actions. We tried to build a stack data structure using global variables to allow Theseus to determine where he had and hadn't been, but this idea, too, was abandoned. Left-hand navigation it was.

From there, the theoretical work in programming Theseus was done, but we needed to translate our ideas into a working way for him to navigate the maze. Questions such as "how sharply to turn (inside and outside a room)?", "how close should he be to the wall before turning", "how sensitive should Theseus be to light colors?", and "how often do we need to straighten Theseus to keep him from crashing?" needed to be answered by trying something and testing him. Theseus had a number of false starts, tries where he'd make left turns just fine but crash into the wall when we needed to turn right, tries where he'd get lost in a circle around a room, tries where he'd get fixated upon a smudge in the maze and not go anywhere else, convinced he had found the candle. Fixing Theseus involved trial and error, and lots of it. The robotics lab and the classroom we hijacked to test our maze became our second and third homes.

Theseus's navigation was fine-tuned again and again, up until the day of the exhibition. We added white and black tape to the maze to make sure Theseus didn't get confused, altered the code to make Theseus back up just the right amount and turn at just the right speed. It wasn't easy; during the exhibition we remained on hand to fix him in case he got stuck (there was one corner he particularly had problems with, although for the most part he behaved just fine). In spite of the difficulties, though, we would certainly consider Theseus a great success!