Spinning Mass Gyroscopes

Spinning mass gyroscopes use a steadily-moving mass with a free-moving axis (gimbal). They are very fragile and require regular maintenance. When a spinning mass gyro is tilted, the gyroscopic effect causes precession – motion orthogonal to the direction tilt sense – along the axis of the rotating mass, indicating that the angle has moved. Because mechanical constraints cause numerous error factors, the axis of a spinning mass gyro is usually fixed with springs. Spring tension is proportional to the precession speed.

Dry-tuned gyros or dynamically tuned gyros are spinning mass gyros that are designed to cause very small mechanical constraints once the spinning speed reaches the specified speed. A dynamically tuned gyro should not be confused with a gyrocompass, a large spinning-mass device that is made to rotate and maintain the same direction as the earth's rotation. Gyrocompasses provide true north readings at all times, whereas dry-tuned gyros provide information about the relative change of angles.