Levin Alexander, Jonas Pfeil, Reiner Schäfer. Original title: 'GPS im Kinderzimmer – Navigation eines autonomen Roboters in dynamischer Umgebung'. Second place at the national level of the German contest for young scientists 'Jugend forscht'.
The 'GPS robot' uses a ceiling-mounted ultrasonic tracking system and builds a map of its environment for navigation. Inspired by the GPS satellites, we developed ultrasonic and infrared transmitter and receiver circuits that determine the robots location with an accuracy of a few millimeters.
The ceiling-mounted part of the tracking system comprises four ultrasonic transmitters arranged as a cross roughly 2m x 2m in size and an array of infrared LEDs in the middle. The LEDs provide a time reference to enable the measurement of the sonic time of flight for each of the four transmitters. These are used to calculate the position of the ultrasonic receiver on the robot. The infrared and ultrasonic signals are pulsed to make the systems more error-resistant.
We fitted our custom built robot with sensors for obstacle avoidance. Their location is transmitted to a PC using our own low-level protocol that automatically retransmits packets with bad checksums and thus establishes a reliable link over FM 433 MHz radio modules. We basically implemented the protocol from OSI-layer 2 up.
The PC builds a map of all obstacles that is dynamically updated. Objects which have not been seen for while fade and eventually disappear. We use the D* algorithm to plan a path to a user-set location. The path is simplified and its points are sent as subgoals to the robot. The robot then tries to follow the path, avoiding newly found obstacles which in turn can cause dynamic re-planning on the PC.