The Design of a Pair of Identical Mobile Robots to Investigate Cooperative Behaviours

Abstract

The reduction in the range of the infrared sensors in bright sunlight indicates that it is advisable to include additional obstacle avoidance sensors. Laser range finders are an attractive solution; however they tend to be expensive, requiring either high speed electronics or a dedicated digital camera system (often with an associated frame grabber card). A simple alternative is the incorporation of ultrasonic sensors. These can reliably project out to a distance of several meters, and detect obstacles that the robot is likely to encounter. By narrowing the transmitted beam, multipath reflections can be reduced, and simple time-of-flight calculations can easily yield the robot-to-obstacle distance. Accurate localisation of the robots will need further development. The several meter accuracy of the GPS units is not adequate for fine positioning of the robots. Whilst infrareds and/or ultrasonics can provide accurate relative positioning once the robots are closer than 5 meters apart, it would be desirable to have sub-meter absolute positioning. This could be achieved with the purchasing of more expensive GPS modules (US$10K), this would negate the low-cost emphasis of this construction. Odometry and inertial sensing are accurate over short distances, so it is anticipated that use will be made of landmarks to reset the accumulated odometry error, and provide for more accurate localisation. Unfortunately, this constrains the robots to operating in a known environment, and is not an optimal solution. Finally, the manipulator arm obviously needs to be designed and mounted on the robots. This is a significant task, and is not the focus of this article.