Internal VS. external

what is the diffrentse between extrnal gyro and inturnal gen 2 gyro

Well for starters, the built-in inertial sensor on the Gen 2 brain is built-in – no need to take up a smart port.

Secondly, the built-in inertial sensor is a combined 3-axis gyro and 3-axis accelerometer, which means it can measure the pitch, roll, and yaw of the robot all at the same time, and it can do that while the brain is mounted in any orientation relative to the robot. It can detect the brain’s orientation and automatically assign each of the gyro’s axes to pitch, roll, or yaw because the accelerometer can sense which way is down.

The old gyro sensor is just a 1-axis gyro, so it can only measure rotation in one dimension at a time, as indicated by the arrow on top of the sensor.