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Elmer Sperry: Gyroscopic Compass, 1914

Heading in the Right Direction

In developing his compass, Sperry was aware of these problems. He knew that the performance of the pendulous gyro aboard a ship differed from the theoretical model, due to acceleration and deceleration on the part of this ship. As the ship changes speeds, changes course, rolls and pitches, it "confuses" the pendulous gyro.

The weight, which makes the gyro subject to gravity and results in its pendulous quality, cannot distinguish between gravity and the motions of the ship, causing the gyro to precess away from the meridian. The gyro instead attempts to align its spin axis with the axis that results from the combination of the earth's spin and the ship movements.

Sperry compensated for this by suspending a weight (called a bail) from a horizontal axis and connecting the gyro and the weight (or bail) by a loose connection. The loose connection allowed the gyro three degrees of freedom within its limits. When the gyro reached the limits of the loose connection its movement around the horizontal axis was effectively restrained, and it was reduced to two degrees of freedom. When on the meridian, the gyrocompass enjoyed three degrees of freedom, when it ventured toward or away from the meridian it was limited to two. Sperry said of his device:

"The important advantages of the pendulous gyro having but two degrees of freedom are retained in the present apparatus, and notably the tendency of the gyro always to seek the north."
The thumbnails and text links at right provide access to a paper entitled, "The Sperry Gyro-Compass in Service," read at the twentieth General Meeting of the Society of Naval Architects and Marine Engineers, which took place in 1912.