A compass sensor is very useful for a mobile robot. This gives him a fixed reference. Coupled with other sensors such as encoders and distance sensors, you can get mobile robots able to move and to locate independently and effectively in an environment.
There are 3 products.
An Arduino-compatible board measuring barely more than 3 cm long and 2 cm wide incorporating an accelerometer, a gyroscope and a 3-axis magnetometer, that’s what Adafruit is offering with its development board based on the LSM9DS0 system-in-package!