What is gimbel lock?

In the movie “Apollo 13” there are several references to “gimbel lock.” Apparently it’s a bad thing. As the capsule swings wildly and they try to get it under control, there is much concern about going into gimbel lock.

I have a basic idea of what a gimbel is, but that’s it.
Tried Google and a SDMB search but found nothing.

– Greg, Atlanta

try using “gymbal”.

Try your Google search again, but spell it “gimbal”. Turned up a number of results [sub]most of which I do not understand.[/sub]

Gimbal
gim·bal 'gim-b&l
noun
Org: alteration of obsolete gemel (double ring)
Date: 1780
a device that permits a body to incline freely in any direction or suspends it so that it will remain level when its support is tipped – usually used in plural; called also gimbal ring

Used for mounting gyroscopes, among other things. If you exceed the range of motion of a gimbal, or move the gimbal in such a manner that it binds, whatever it’s supporting will no longer be free to move independantly. Do that to your navigational gyros and you’re screwed in a royal fashion.

“What is gimbel lock?”

—The reason you have to go across the street to Macy’s?

I read Apollo 13, and as I understand it, it seems that the gimbals (i think it is with an “i”) are three ball bearings - each one of which roll in the x,y, and z directions, respectively. The problem is that the instrument can cause these balls to to roll to an extreme position where two balls can become aligned. At that point, you lose the ability to distinguish between the two. This is “gimbal lock”. It can only be fixed by a re-calibration of the instrument. I agree - it sounds a little primitive, but maybe it was more sophisticated than we laymen will know!?!?!?

It is described as like working with that child’s toy “labyrinth”, a “floating” maze in which the object is to move a steel ball from start to end (without falling through some holes along the way) by “tilting” the maze with two turning handles permitting the maze to move slightly upwards or downwards from the plane in which it lies.

Apollo 13, the book, is AWESOME and more went wrong than the movie had time to explain. You won’t be able to put this book down! BTW, don’t look for it under the original title “Lost Moon”.

  • Jinx

Duuh, Jinx! Naturally, any two points ARE ALWAYS aligned by the definition of a line from geometry! What I mean is that there is risk any two of the three balls (gimbals) can appear as coincident to the user of this instrument.

  • Jinx

Try looking up gyroscope in the dictionary.
If you understand the rings then imagine one gimbal locking up.

Yeah, it might have been rings lying in three orthogonal planes of XY, YZ, and XZ, respectively. But, I believe a parallel was drawn to that kid’s toy, the “labyrinth” puzzle I mentioned above…the book has an index, so I’ll see if I can find a better description for you. - Jinx

The descriptions so far are pretty good. In general, a gimbal is a type of joint that allows the mounting platform to move without shaking the instrument within the gimbal. For instance, a compass on a ship at sea is mounted on a gimbal so that as the ship rolls with the waves, the compass remains level.

On the Apollo Lunar Module, gimbals are used to mount the gyroscopes that control the attitude and orientation (which way it points in 3 dimensions). In order for the spacecraft to track where it is going and which way it points, it uses a “stable platform” that provides the baseline orientation, and then compares the orientation of visible stars. The gimbals mount the stable platform to the vehicle to ensure it stays intertial and is not affected by vehicle orientation changes.

The gimbals have gyroscopes attached that keep them in the correct position. But the gimbals have a set range of motion. If the gyroscopes extend the gimbals too far, the joints lock up.

Here’s a link from the Apollo Saturn Reference Pages, giving technical description of the vehicles and systems.
http://www.apollosaturn.com/Lmnr/gn.htm

Scroll down to “GUIDANCE AND THE LUNAR MODULE”.

According to Michael Collins, in his wonderful book Carrying the Fire (about his experiences in the space program and as CM pilot on the Apollo 11 mission), the original design for the gyroscopic stabilizers had four gimbals and was not subject to gimbal lock problems. They changed to the three-gimbal setup due to weight and cost limitations. He mentions an exchange between himself and Mission Control early in the Apollo 11 mission that went something like:

HOUSTON: Columbia, we show that you’re very close to gimbal lock. Please correct your attitude thrusters.
COLLINS: Yeah, thanks, Houston. (muttering) How about you do something useful and send me up a fourth gimbal.
HOUSTON: Come again, Columbia? We didn’t copy that last remark.
COLLINS: Never mind.

:slight_smile:

On some boats (mainly on maxi race boats), tables and seating for the crew is gimballed about the longitudinal axis (fore to aft) to accommodate port or starboard tack heeling angle. Tied-up in port or at anchor, it would be customary to use pin(s) to “lock” this piece of furniture to a fixed position. Same thing for gimballed stoves and navigation station seating on other race boats.

Otherwise, the gimbals may get loose.

Okay, a little more precisely:

A gyroscope has a property that allows it to remain fixed in position in space, due to conservation of angular momentum. So if you spin up a gyroscope and put it on gimbals, , then attach a pointer to it, the pointer can show your attitude as the spacecraft rotates around the gyroscope. Use one for each dimension, and you can build instruments that will tell your exact pitch, yaw, and roll.

However, if the vehicle rotates past the range of motion of the gimbal, it will force the gyroscope to move with the rotation of the ship. This in turn will cause it to precess, and often ‘tumble’, which means it completely loses its orientation. Now you don’t have a clue where you are, and you’d have to reset your gyros (if you haven’t damaged them) by shooting star sightings with a transit.

The same gyroscope setup is used in aircraft for heading and attitude indicators, and aerobatics in the plane can tumble the gyros if they aren’t designed for it.

Aaahhh, now I understand. Thanks.
Tom Hanks should have just said all that in the movie.
– Greg, Atlanta