1. A harvesting system, comprising: a frame, which is configured to move between multiple positions along a row of trees to be harvested; multiple robots, which comprise movable robot arms and which are mounted on the frame facing a respective area to be harvested at each position, wherein each of the robots is configured to harvest crop items by reaching and gripping the crop items using the robot arms from a respective angle of approach that is fixed for that robot; one or more sensors, which are all fixed relative to the frame and do not move with the robot arms, and which are configured to acquire images of the area only from outside the trees; and one or more computers, which are configured to identify the crop items in the images acquired by the sensors fixed relative to the frame, and to direct the robots to harvest the identified crop items.