`` NEWTON: Torque and Gyroscopes
 
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Name: Ray
Status: educator
Grade: 9-12
Country: USA
Date: Fall 2013


Question:
If an object is rotating, it resists pitch and yaw. Does it also resist lateral motion?

Replies:
Ray

I must work through this a little bit. My familiarity with this subject comes from using inertial navigation systems in aircraft.

A gyroscope is a disk, weighted at its circumference that rotates around an axis. Any perturbation to rotate the axis of rotation to a different orientation is resisted by the gyroscope.

So a gyroscope mounted in a frame that moves will maintain its spatial orientation while the frame moves around it.

Inertial navigation systems that use gyros probably use three gyroscopes in each of the three orthogonal planes. The horizontal gyroscope oriented parallel to the fuselage of the airplane rotates in the roll plane and senses pitch and yaw. The athwartship gyroscope rotates in the pitch plane and senses roll and yaw. The vertical gyroscope rotates in the yaw plane and senses pitch and roll.

My guess is that accelerometers will be necessary to measure lateral motion. Since they are so cheap and have fewer parts, manufacturers probably use accelerometers in three axes rather than gyroscopes in their inertial navigation systems.

Sincere regards, Mike Stewart


Hi Ray

This is a problem in conservation of momentum. The momentum vector is perpendicular to the plane of rotation. That is, if you wrap the fingers of your right hand around the rotating object, your thumb points in the direction of the momentum vector. As long as that vector is pointing in the same direction with the same magnitude, it can happily exist anywhere in three dimensional space. Lateral translation will not change the orientation of the vector, so momentum is conserved, and there will be no resistance to movement either side to side, top to bottom or front to back. Hope this helps!

Bob Froehlich


Hi Ray,

The simple way to put it is that an object rotating around an axis will resist rotation about any other axis. This is the rotational analog to Newton's 1st law, than an object in motion will tend to continue with that same speed and direction unless otherwise acted upon by a force. So a gyroscope can be used to either indicate or stabilize motion in two dimensions, but not in three. For example, an airplane instrument panel will usually contain some gyroscopic instruments. An attitude indicator has a gyro with the axis of rotation in the vertical direction, and it shows changes in pitch and in roll. The gyro is mounted on a gimbal that allows rotation in these dimensions. But it cannot indicate any change in yaw since that would be rotation about the same axis as the gyro itself. The heading indicator, on the other hand, has a gyro oriented with its axis of rotation on the horizontal. This instrument can indicate changes in yaw (i.e., changes in heading), but it wouldn't be able to indicate any change in roll. Theoretically it could also indicate changes in pitch, but this particular instrument has a gimbal mount that rotates in only one dimension.

Regards, John C Strong


Ray

I must work through this a little bit. My familiarity with this subject comes from using inertial navigation systems in aircraft.

A gyroscope is a disk, weighted at its circumference that rotates around an axis. Any perturbation to rotate the axis of rotation to a different orientation is resisted by the gyroscope.

So a gyroscope mounted in a frame that moves will its spatial orientation while the frame moves around it.

Inertial navigation systems that use gyroscopes probably use three gyroscopes in each of the three orthogonal planes. The horizontal gyroscope oriented parallel to the fuselage of the airplane rotates in the roll plane and senses pitch and yaw. The athwartship gyroscope rotates in the pitch plane and senses roll and yaw. The vertical gyroscope rotates in the yaw plane and senses pitch and roll.

My guess is that accelerometers will be necessary to measure lateral motion. Since they are so cheap and have fewer parts, manufacturers probably use accelerometers in three axes rather than gyroscopes.

Sincere regards, Mike Stewart


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