They are about the size of a box of tissues. Each has an infrared sensor, an ultrasonic device and a battery-driven motor. And their task is to detect and avoid obstacles and fish little boxes from a maze of grid lines. At the controls of the tiny robots were 32 students taking part in Polytechnic University's annual robotic project competition. The machines were placed on identical grids divided into 49 sections, with cardboard obstacles placed at various intersections. The robot designers had to make their creations intelligent enough to stay on the grid, avoid the obstacles, locate the boxes and drop them outside the grid. 'The contestants had no idea about the obstacle course in advance,' said Alex Wai Ping-kong, head of the university's electronic and engineering department, which organised the contest. Department associate head Daniel Lun Pak-kong said the ultrasonic device had helped locate the obstacles. The photo sensors, or infrared detectors, distinguished the black grid lines from the white floor, keeping the robots on track. Sixteen two-member teams took part in the contest. 'The hardest part was starting from nothing and coming up with an idea of how to solve the problem,' said Chung Siu-chak, a member of the winning team, which won $1,000 in book tokens.