The rules were simple: if drone makers wanted to compete in the Pentagon's million-dollar, robotic, off-road rally, they had to make sure their creations could navigate a mile-long obstacle course first. The test was needed, Defense Department officials repeatedly said, to make sure the bots had at prayer of completing this Saturday's 210 mile journey across the Mojave Desert.

But when the qualifying rounds began Monday for this "Grand Challenge," run by the Pentagon research arm Darpa, it quickly became clear that only a handful of the bots could pass the exam on the opening day. The array of slight ditches and wide passages set up at the California Speedway were just too much for the drones.

So Darpa has re-written the rule book, at least a little. Before, teams had to clear a "required demonstration of intelligent autonomous behavior and safety features around a short demonstration course." Now, it looks like just about any robot car will be on the starting line in the desert town of Barstow, California.

My Wired News story has more.

THERE'S MORE: Seven driverless cars have now made it through the obstacle course, MSNBC's Alan Boyle says. The final Grand Challenge lineup is set to be announced later today.

AND MORE: 15 teams will be at the Grand Challenge starting line in Barstow, California tomorrow. The Palos Verdes High School crew -- which eventually made it about a third of the way through the mile-or-so-long qualifying obstacle course -- will be in 10th position.

Darpa "loosened the rules a bit," said Palos Verdes parent mentor Cecille DeSimone. "Any team that wasn't an obstacle to the others was let in."

AND MORE: Interestingly, Darpa is now calling its Mojave Desert jaunt a "field test" -- as if the agency isn't really expecting anyone to actually pass the challenge this time around.