# How do gimbals affect gyros?

"By mounting a gyro on a set of gimbal rings, the gyro is able to rotate freely in any direction. Even though the gimbal rings are tiled, twisted, or otherwise moved, the gyro remains in the plane in which it was originally spinning"

Now I've seen that statement in several different textbooks, but I'm having trouble understanding the terminology used. It's stating that the gyro is able to rotate freely in any direction, but then it also says that the gyro remains in the plane it's rotating. If it can rotate freely in any direction, then it isn't in it's original plane of rotation. So if anyone could simplify that, it'd be helpful.

Also the gimbals allow things to rotate around it while the gimbal doesn't rotate, but then wouldn't you need the gyro to move for precession to take effect?

For an example if I said that I applied a force with regards to precession taking place, would the gyro maintain it's plane of rotation but that force would take affect on the gimbal?

Thank you!

• It's free to rotate, but it doesn't. Really, it's free to stay in its plane while the support for the gimbals rotates. – user_1818839 Apr 2 '17 at 17:50
• Ok so you could say if you applied a force to the gyro, and after precession, the output force will be displayed on the gimbal not the gyro? – ApolloMission4 Apr 2 '17 at 17:52
• I cannot understand the supplementary question. But you could say, if you apply a torque to the gimbals, they will not translate that torque to the gyro. – user_1818839 Apr 2 '17 at 17:54
• Ok, so I understand now that the gimbals rotation will not effect the gyros rotation, however if I was to apply force to the gyro, will that force affect the gimbals, since the gyro must stay in it's plane of rotation. – ApolloMission4 Apr 2 '17 at 17:59

The confusion arises in terminology. What instrumentation engineers call a gyroscope is actually an integrating gyroscope or rate gyro, and what they call a gimbal in gimbal lock isn't the gimbal used to mount the gyroscope itself - the gimbals are used to keep a platform housing three gyroscopes level.

A standard gyroscope will point in the same direction at all times, while a rate gyroscope is used for measuring angular velocity:

The rate gyro will deflect the springs in proportion to how fast the frame is spinning - the faster the spin, the larger the springs deflect, which via strain gauge or similar measurements engineering, can be turned into an electrical signal. Measure the change in rate to derive the angular acceleration. Have a computer integrate the rate over time to derive current angular position.

Note the pivoting gimbals for this device though - they are in the exact configuration of a gimbal lock. A rate gyro's housing can only measure changes in a single axis. If the frame housing the gimbal moves away from the axis, then the device wouldn't measure properly. So, three rate gyroscopes are required to measure angular movement in all three angles. These are mounted on a platform that maintains a fixed orientation in space, so the rate gyroscopes can function properly. In other words, motors specifically move the platform that the rate gyroscopes are mounted onto so it stays on the same plane.

When the rate gyroscope feeds a porportional signal to the instrumentation panel, it also feeds this signal to three motors. They turn the platform in response to the signal, keeping the platform level.

The point of a gyroscope is that, because it has a substantial amount of angular momentum is will tend to stay in the same plane that it is rotating in unless a fairly significant amount of force is applied to it.

What actually happens with a gimbal mounting is that the gyroscope stays still and whatever it is attached to rotates around it (although this is of course relative to your frame of reference)

To put it another way the gimbals isolate the gyroscope from external forces.