This Tribot has a fixed caster and moves back and forth into one direction only. The special receiver from our infrared/ultrasonic beacon system is mounted on the NXT. Not visible on the picture is the beacon itself that periodically sends out IR/US bursts, which are used to measure the distance between the robot and the beacon. The robot is programmed to follow a 1D-path that corresponds to an inverted cosine in the time domain. It’s the goal that the robot should move along the planned trajectory with best timing.
Valuable distance cues are only available rarely. Errors in the localization system may occur. In order to estimate the position and control the robot’s speed, we are using a scalar Kalman filter. The program has been realized with the LabVIEW NXT toolkit. (It was particularly tricky to do the job with integer numbers.)