Before the sensor came, we built a linear actuator from a Lego Mindstorms kit, to move the sensor across the detection field. When the sensors arrived, we realized that they would be too heavy for the light-weight actuator. We came up with some options, but were not happy with any of them. One idea was to use a conveyor belt system, which would have worked, but we didn't have the parts for it. Another idea was to have the table's smooth surface support the weight of the sensor and use the actuator to slide the sensor across the table. Finally, we came up with a plan that made sense and that we could build: a train. By combining a Lego train set with our existing actuator, we created a system able to haul the weight of the sensor smoothly, predictably, and precisely. Click on the picture to enlarge.