It's been almost exactly a year since Zodiac Pool Systems last expanded its line of Polaris-branded pool-cleaning robots, and it's now back with two more additions that fill out the top and bottom end of its lineup. That includes the company's most advanced robot to date, the $1499 Polaris 9400 Sport (pictured above), which adds four-wheel drive for the first time, as well as the company's new accelerometer-enhanced ActivMotion Sensor technology -- something Polaris says allows the robot to continually sense where it is in the pool
