1. Apr 25, 2007

### PH7SICS

Hi everyone, 1st post on this forum and I have a question about gyroscopes

I have noticed that a gyroscope wheel if spinning rapidly will resist motion along the plane of the axis or spindle of the spinning wheel. For example if the wheel is horizontal and you try to move it in a vertical direction you can feel that there is a resistance to that motion.
My question is if you were to assemble 3 gyroscope wheels so that the axis of each wheel were along the X, Y & Z planes would the resulting assembly resist motion in all directions or would the result be that there would not be any resistance to movement in any direction, assuming that all wheels are of the same value and of equal rpm.

2. Apr 25, 2007

### Staff: Mentor

They would cancel each other out (via forces in the interconnecting structure), and you would not feel the resistance of "precession" anymore.

http://en.wikipedia.org/wiki/Precession

< EDIT -- Turns out I was wrong in the above assumption -- there will still be a net vector angular momentum in an x-y-z gyroscope. See the following posts. >

Last edited: Apr 27, 2007
3. Apr 26, 2007

### lpfr

I don't agree. In fact gyroscopes DO NOT oppose to rotation. They just rotate in a direction different from what "normal" objects do. You can "force" a gyroscope to turn in any direction.
But when you do it, you realize that the forces (in reality the torque) that you are actually applying are not what intuition predicts.

When you put three gyroscopes in X, Y and Z, their angular momentum add vectorially and the sum is never zero. The resulting object behaves as a gyroscope whose angular momentum is the sum of the moments. It is not simple to treat each gyro and its forces separately. I have never tried.

4. Apr 26, 2007

### mezarashi

I counter disagree. Gyroscopes tend to resist changes to its orientation due to its the angular momentum. By resist, I don't mean you cannot change their orientation, but that it will require more force than if it were not spinning.

I do agree that the addition of the angular momentum of 3 perpendicular gyroscopes would result in a non-zero sum.

Back to the original post: With that last note in mind, by having three gyroscopes built into one, you would only be creating a new device that behaves exactly like a single gyroscope.

5. Apr 26, 2007

### lpfr

As you like.

6. Apr 26, 2007

### rcgldr

Using right hand rule, assume that the angular momentum vectors point forward, left, and up. The sum of these vectors would point 45 degrees left of forward and 45 degrees up, with magnitude of the square root of the sum of the squares of each magnitude. If all magnitudes are the same, then it would be SQRT(3) x the magnitude of one of the vectors.

Angular momentum vectors can't cancel each other if they are perpendicular to each other. Some parallel and opposing components between two or more vectors is required.

A link for almost everything you might want to know about gyroscopes, as a series of videos of lectures.

http://www.gyroscopes.org/1974lecture.asp

Last edited: Apr 26, 2007
7. Apr 26, 2007

### PH7SICS

Thank you everyone! Are we all agreed then that the resulting device would behave like a single gyroscope and will not resist motion in the X, Y& Z planes?

8. Apr 26, 2007

### lpfr

NOOO! We all agree that the new object will behave as a gyroscope!
No one said this: will not resist motion in the X, Y& Z planes.
As any gyroscope, it will not resist rotation motion whose axe is parallel to the resultant angular momentum.

Last edited: Apr 26, 2007
9. Apr 26, 2007

### PH7SICS

Sorry, that is what I meant, the device would behave as a regular gyroscope ie a single gyroscope????

10. Apr 26, 2007

### lpfr

Ouf! That's better!

11. Apr 27, 2007

### Brock

Thanks for THAT link jeff, I must have missed it before.:surprised

12. Apr 27, 2007

### vanesch

Staff Emeritus
Also, as any gyroscope, it will not resist any translational motion...

13. Apr 27, 2007

### lpfr

Also, as any anything, it will not resist any translational motion...

14. Apr 29, 2007

### rcgldr

Better stated as: it will not resist any translatonal motion any different than any object with the same mass. It still has momemtum relative to it's mass.

15. Apr 30, 2007

### vanesch

Staff Emeritus
Correct.

.

16. Apr 5, 2009

### Rockmore

If you have two Gyroscopes rotating on the same axis in opposite directions would it change the resistance?

17. Apr 6, 2009

Staff Emeritus
Then there is no net angular momentum, so it would not act as gyroscope.

18. Apr 6, 2009

### rcgldr

The external resitstance would be the same as zero angular velocity (not spinning) of the gyroscopes, but internally there would be large and opposing torques on the common axis between the 2 gyroscopes in reaction to any rotation component perpendicular to the axis. It would have to be a strong connection or else it would break.

19. Apr 6, 2009

### Rockmore

gyroscopes staying level

I want to make a gyroscope stabilizer for my video camera. If I make a gyroscope with a horizontal rotation using a small electric motor and start the gyroscope exactly level to the horizon will it remain level or will it begin to drift at some point?