In the case of other sensing strategies, the agent should find the ball, (in Level II and III, obstacles, too) and know what the target is. Beside vision, typical sensors used in mobile robot research are range finders (e.g., sonars) and contact sensors (e.g., bumpers). However, it seems difficult for each or any combination among them to discriminate the ball (obstacles, too in higher levels) and the target unless special equipment such as transmitter is positioned inside the ball or the target, or a global positioning system besides on-board sensing and communication lines are used to inform the positions of all agents. The simplest case is no on-board sensing but only a global positioning system, which is adopted in the small robot league in the physical agent track because on-board sensing facilities are limited due to its size regulation.
In Level II and III,requirements include an obstacle avoidance behavior and the coordination of this behavior with a ball-carrying (or passing/shooting) behavior. One good strategy is assign the sensor roles in advance. For example, sonar and bumper sensors are used for obstacle avoidance while vision sensor is used for the target reaching. One can make the robot learn to assign the sensor roles [Nakamura et al. 1996].