This isn’t the first Lego Segway (defined as a balancing bot on two wheels) — that honor would probably go to Steve Hassenplug’s Legway. However, the Legway used two EOPDs (Electro-Optical Proximity Detector) from HiTechnic Sensors to balance. What’s cool about this project is that it needs only those parts found in a standard NXT 2.0 set. Most notably, it uses a light sensor in place of the expected (and non-standard) gyro sensor.
By using the NXT Color Sensor as a simple proximity sensor to the ground to detect the approximate tilt angle of the robot, the robot can actually balance itself!
For more fun, if you have a second NXT brick, you can make the Segway rider on this robot lean forwards and backwards via Bluetooth remote control, which will cause the robot to start rolling forward or backwards while staying balanced, just like a real Segway!
Most self-balancing robots (including the actual Segway PT) use one or more gyroscopic sensors to detect the actual tilt angle of the robot from true vertical. This robot uses only the NXT Color Sensor (in light sensor mode) by aiming the sensor at the ground and measuring reflected light, which will change slightly depending on how close the sensor is to the ground.
[via The NXT Step]