Lego RCX Self Balancing Two-Wheel Robot (2004)

In February 2020, we heard the creator of the iconic Lego figure J.N. Knudsen passed away. Sad news. I am a fan of LEGO, especially the Mindstorms series. I don't have a habit to document my works of LEGO. One of them was so impressive at that time that I took a short video. This is a balancing robot I made in 2004 (Robotics Invention System, with the NXT 2.0 brain brick CPU)) in which I put a PID controller software (C language) to keep the robot stands up-right. No gyroscope sensor or other advanced sensors (at that time it did not exist), just one light sensor was used to measure the inclination angle of the robot. The error of the inclination angle was then used as the input of the PID software and finally to drive the motor forward or backward with optimum speed. The duration of the video is short but the robot managed to keep its balance longer.