This is a simple dual worm gear drive. It turns two turntables using two worm gears spinning in the same direction at the same speed using one motor. It was really quite easy to build.

In this study, a path correction and obstacle avoidance method for a bipedal intelligent robot, using an ultrasonic sensor and electronic compass sensor, is proposed. The proposed method is implemented on an autonomous humanoid robot (the ARSR) comprised by the Lego NXT Intelligent Bricks. One ultrasonic sensor and one electronic compass sensor are installed on the ARSR to detect environmental information including obstacles, the distance to the obstacle, and the directional angle of the robot. Based on the obtained information, an obstacle avoidance and path correcting method is proposed to decide the ARSR’s behavior so that it can avoid obstacles automatically and move effectively to the destination area. Three obstacle avoidance experiments are carried out to confirm the effectiveness of the proposed method.

while cleaning up. It's beautiful and surprising. I always assumed it worked with using some sort of grid, but that clearly isn't the case at all

The Ultrasonic Sensor uses the same scientific principle as bats: it measures distance by calculating the time it takes for a sound wave to hit an object and return – just like an echo