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[Iacopo]

I'm guessing that twisting modes will develop causing the height of rotor CM to go up and down changing the dynamics from that of free precession.

You are right.  The horizontal stick between the strings should be as light as possible and the strings too.
Still to some extent it should happen what you predict.

[Russpin]

The horizontal stick between the strings should be as light as possible and the strings too.

True with a light stick this might work. I wonder if you would need a slightly curved stick for balance?

[Iacopo]

True with a light stick this might work. I wonder if you would need a slightly curved stick for balance?

Slightly curved it would give a bit of balance but not sure how desirable it would be ... it would add a bit of torque when spinning.
The axis of precession would stay pointed in a stable direction by itself, while spinning, so I suppose the curved stick is not necessary.

[Iacopo]

I find formulas most useful, not to calculate things, but to remind me of the players directly involved and how they influence the outcome in a qualitative way. That's pretty valuable even if it doesn't really explain the phenomenon.

It's the same for me.

[ta0]

Yes, a nice little derivation similar to the one Feynman used in this Lectures in Physics.

Off Topic but I was in a bookstore years ago and came very close to buying them. I'm glad I didn't because they are online for free.

I had read a few parts of the 3 volumes when I was a student. But when I saw a special deluxe hard bound commemorative publication for the 25th anniversary of the original publication (1988, the same year Feynman passed away) I could not resist. The funny thing is that the binding is mostly blueish instead of the iconic red. I made a point of reading them cover to cover. 

[ta0]

gyro would be useful in demonstrating inertial "floating" behavior without having to go to space.

A poor's man gyro of that kind could be a rotor suspended to thin strings, it would oscillate with a ratio very near to 2:1...

I love the way you think. Another elegant experiment to do.

[Russpin]

I made an animation of the free precession of a thin disk.
Euler's equations for a rigid body where solved to generate this animation. The red line is the angular momentum vector and is stationary because there are no torques acting on the disk. The blue line is the symmetry axis of the disk. For small angles between the angular velocity vector and the symmetry axis, the precession rate is twice the spin rate.

[Iacopo]

I love the way you think. Another elegant experiment to do.

Maybe Jeremy and his Legos could help ?

I am making a video about gyroscopic effect and precession (about 20 minutes long), it's nearly ready and I will post it here soon.

[Iacopo]

This is the video I made about the gyroscopic effect and precession.
It is very simple, there is no math, I just explained intuitively what I know about all this.
Above all I tried to explain these things with clarity, to make it as easy as possible the understanding of this motion: in this sense it has been a challenge, because this motion is very little intuitive.
 

[ta0]

I made an animation of the free precession of a thin disk.
Euler's equations for a rigid body where solved to generate this animation. The red line is the angular momentum vector and is stationary because there are no torques acting on the disk. The blue line is the symmetry axis of the disk. For small angles between the angular velocity vector and the symmetry axis, the precession rate is twice the spin rate.

Great! When I first saw your video I was surprised because on the simulation the precession and spin appeared to be in the same direction and not retrograde. Then I realized that the spin is in fact opposite (and half the value) than the precession but, because the precession "carries" the spinning axle, with respect to fixed space it spins in the same direction (and also at half the precession speed):  w - 1/2 w = 1/2 w.

This is the video I made about the gyroscopic effect and precession.
It is very simple, there is no math, I just explained intuitively what I know about all this.
Above all I tried to explain these things with clarity, to make it as easy as possible the understanding of this motion: in this sense it has been a challenge, because this motion is very little intuitive.

Wonderful video! Very ambitious, clear and beautiful!.
But I will have to watch it again tonight to analyze it in detail. Your explanation of precession reminds me somewhat the one in the appendix of Crabtree. I may scan it an post it. The old book is available online, for example here: Spinning Tops and Gyroscopic Motion (pages 134 and 135.)

[Iacopo]

Your explanation of precession reminds me somewhat the one in the appendix of Crabtree. I may scan it an post it. The old book is available online, for example here: Spinning Tops and Gyroscopic Motion (pages 134 and 135.)

Thank you Ta0. I will try to read it.

[Russpin]

Great! When I first saw your video I was surprised because on the simulation the precession and spin appeared to be in the same direction and not retrograde.

Thanks Ta0.
I was having difficulty visualizing this motion so I decided to make an animation of it.

[Iacopo]

The red line is the angular momentum vector and is stationary because there are no torques acting on the disk.

There are no torques acting on the disk from the outside, but what about from the inside of the disk itself ?
The disk is not spinning about one of the main axes of inertia;
this means that there is couple unbalance in the spinning disk.  Couple unbalance means that there is a torque acting on the disk.

[Russpin]

There are no torques acting on the disk from the outside, but what about from the inside of the disk itself ?

All the internal forces cancel out.

[Iacopo]

All the internal forces cancel out.

So there is not a gyroscopic effect here ?
I looked for some infos about this but haven't found any useful for me.  It is easier to find simple explanations about how precession works, but not pure nutation, (nutation alone, not mixed with precession), or free precession.