Unusual spin of silver finger top

[ta0]

The first top I bought in Cremona busted my budget:



It's made of sterling silver (16.5 gr) with natural onyx stone above and a tip of synthetic corundum. It was made by master jeweler Leonardo Conte.
I generally don't buy jewelry-type tops or tops made of expensive materials. But what sold it to me (besides a 30% discount) was an usual behavior:



I don't find a top with a new behavior everyday, so I had to have it!
Actually, when I first got it, it would only spin vertical if spun softly. If spun a little harder it would always flip to spin sideways. However, after a couple of high drops into a carpet, trying to see if it flipped in mid air (it didn't) it started to spin normal even for hard spins. Now, to make it flip I need to give it enough wobble so the rim touches the base.

This was the only one of a couple of dozen different silver tops Leonardo had for sale that had this behavior. The dimensions and mass distribution of the top must be just right for this behavior.

[ortwin]

Ha! ta0, is your post really meant as an unspoken, yet very clear, challenge for me to build a curtain ring top with the same behavior?
I will see what I can do. If I succeed, you can buy one from me for half the price you paid for that silver top.

[ta0]

Ha! ta0, is your post really meant as an unspoken, yet very clear, challenge for me to build a curtain ring top with the same behavior?

I was hoping that you, Iacopo or Jeremy would take up the challenge.
I'm curious to see how difficult it's to reproduce the effect. What should be the ratio of moments of inertia? How critical is the diameter of the flywheel?

I think the ideal top would be one that spins for a while vertically and then flips sideways. I saw that behavior a couple of times on mine before the high drops. Or perhaps one that spins consistently one way or the other depending on the type of start.

One interesting thing at the end of the first clip of the video is that after the top settles down and starts to spin straight, a very noticeable buzzer sound starts. I believe it's a resonance of the plate. I probably should have let it play longer.
To top also spins upside down very nicely.

[Jeremy McCreary]

Beautiful top, intriguing behavior! Could the high drops have raised the ring by bending the spokes?

Can't take your challenge now, as we're busy prepping for a move to San Diego in late August. But here's a very different top that's happy to sleep and spin sideways when configured just so:



I call these high-CM, high-TMI/AMI tops "sidewinders". They consistently spin down through 3 distinct "phases":
1. Quiet sleep.
2. Rapid precession about the vertical through the CM. As the CM slowly descends, tilt grows, and the tip rolls in a widening spiral.
3. Quiet sideways spin about the CM once the tilt reaches 90°.

Phase 2 requires a broad tip, and you need a very high release speed to get a good Phase 3. To prolong the sideways spin, the final contact -- here, the edge of the blue disk -- should be exactly at CM level. Shaping the lower body to smooth the Phase 2-3 transition also helps.

Your new top differs from a sidewinder on nearly all counts. In particular, its ring is below its CM, and tilt must make a big jump as the contact jumps from tip to ring.

[ortwin]

The tip length seems to be the most critical factor. If the (rubber) rim of the wheel catches on the surface of the base, it starts to rotate "sideways".

[ta0]

Jeremy: I think you are right and there is a relation between the two, even if the shapes of the tops are very different.

Ortwin: I think you are very close. The wheel probably has too much friction for a long sideways spin.

[Jeremy McCreary]

Jeremy: I think you are right and there is a relation between the two, even if the shapes of the tops are very different.

Curious, what relation do you see here?

A prolonged Phase 2 is very common in high-CM, higher-TMI/AMI tops -- even peg tops -- but I've never seen one in a top with a mass distribution like yours. For one thing, the latter tend to scrape and stop before ever reaching the large tilt angles required.

I don't see any Phase 2 to speak of in your videos.

PS: Here's a 3" Relampago with a long Phase 2. Skip to 2:35.



The Relampago thought about spinning sideways at the end, but the required contact would have been too far off CM level. In this run, a sloppy release eliminated Phase 1, but you can see long one at 1:40.

Every peg top I've tested behaves this way if left undisturbed.

[ta0]

Curious, what relation do you see here?

Well, perhaps not that much. But at the end it's spinning around the center of mass which is over the point of the wheel that touches the ground for a slight tilt of the stem from the horizontal.



It just occurred to me that if it's spinning clockwise and therefore precessing clockwise, then as the ring touches the surface it applies a friction force against to the precession. When the precession is slowed down, the tilt increases. This mechanism might help it jump to spinning on the side.

I suspect the change in behavior of the top after the big drops might be in the tip. Currently the corundum tip is flash with the silver. Perhaps before it was sticking more and making the top wobble enough to make the ring touch the surface.

[ta0]

Yoshihito Fujita posted a video of a finger top with the same curious effect:

[Iacopo]

Interesting and inspiring for me, because it seems in some way related to the tippe top, which I am thinking about, how it could work.
I should make one top like that and observe it in slow motion. Probably in the next days, as soon as I will have some free time.

[Iacopo]

I turned it, tomorrow I will add a stem.
But, I tried spinning it, and even without stem, (not very comfortable to spin), it already works, it ends spinning on the side.
I will add a video later.

[ta0]

Nice!

I like the idea of a new class of finger tops.

Perhaps by putting a little bump as a tip, the top will spin normally for a while before leaning, touching the surface with the body, and changing axis. By measuring the time it takes to flip you could determine how "good" it was spun (stronger plus straighter).

[Iacopo]

Perhaps by putting a little bump as a tip, the top will spin normally for a while before leaning, touching the surface with the body, and changing axis. By measuring the time it takes to flip you could determine how "good" it was spun (stronger plus straighter).

Good idea. Today I wasn't at home but tomorrow I will try. To add a little bump is easy because there is a hole passing through the top from side to side, so I can simply let the stem to protrude a bit from below.
I anticipate that, to my surprise, this object behaves like an Euler disk, after it falls from spinning on its side.