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Author Topic: Japanese spinner like some of Iacopo's  (Read 10624 times)

Jeremy McCreary

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Japanese spinner like some of Iacopo's
« on: April 12, 2017, 02:45:04 PM »

Somebody's been taking cues from Iacopo...

https://m.youtube.com/watch?v=lbWR8aWCths

The CM is clearly near the tip, but above or below?

You know, we never decided what to call top-like finger spinners with CMs below their tips. Even though they can't really fall over, I still like "pendulum tops" after the "conical pendulum" of classical mechanics. But there were lots of other propsals.

And that brings us to a favorite sport in these parts: Debating what should and should not qualify as a top. Some day, we might even agree on some criteria -- if not for everywhere and all time, then just for our use as players and connoisseurs of real (not just textbook) tops.
« Last Edit: April 12, 2017, 08:51:48 PM by Jeremy McCreary »
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ta0

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Re: Japanese spinner like some of Iacopo's
« Reply #1 on: April 13, 2017, 01:19:48 AM »

Tim didn't try very hard to spin it upside down, did he?  ;)

The one I have is from Philippe Dyon. It is smaller but was the first one I ever saw.

I consider a proper top one that falls when not spinning, or a least one that would fall if it didn't have extra unnecessary constrains (like the feet of many plunge tops).
This one would still qualify if you spin it upside down. Iacopo's are tops by the slightest margin.
The others we can call top look-alike.  ;)
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #2 on: April 13, 2017, 02:24:21 AM »

Tim didn't try very hard to spin it upside down, did he?  ;)

No, he should have had one of us on the show. A snappy underhand twirl might have worked.

I consider a proper top one that falls when not spinning, or a least one that would fall if it didn't have extra unnecessary constrains (like the feet of many plunge tops).
This one would still qualify if you spin it upside down. Iacopo's are tops by the slightest margin.

I think that's the most practical solution for our purposes. Basically, a bicycle with detachable training wheels is still a bicycle.

The others we can call top look-alike.  ;)

Or maybe a single-word generic term like "spinner".
« Last Edit: April 13, 2017, 03:57:23 PM by Jeremy McCreary »
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Iacopo

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Re: Japanese spinner like some of Iacopo's
« Reply #3 on: April 13, 2017, 06:50:04 AM »

Somebody's been taking cues from Iacopo...

I didn't know that top but I don't think someone made it after having seen the mine. There are some other tops with the recessed tip, older than the mine.  I didn't invent something new, I took the idea of the recessed tip from a malaysian gasing, the first one I saw made in that way.

The CM is clearly near the tip, but above or below?

It seems to me that in this top the CM is still well above the tip.  In my tops I have to insert the tip deeper, (if I want to meet the CM).
« Last Edit: April 13, 2017, 06:55:15 AM by Iacopo »
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ta0

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Re: Japanese spinner like some of Iacopo's
« Reply #4 on: April 13, 2017, 12:15:15 PM »

It seems to me that in this top the CM is still well above the tip.  In my tops I have to insert the tip deeper, (if I want to meet the CM).
You are right. It does seem to have the center of mass above the tip.
On the other hand, Philippe's top has the CM below the tip. One way he achieves that is by having windows on the bell. I called it "top" because it also spins well upside down on the stem. A neat thing is that it becomes transparent when spinning so you can see the finger.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #5 on: April 13, 2017, 12:44:30 PM »

Quote from: ta0 link=topic=4924.msg51651#msg51651
You are right. It does seem to have the center of mass above the tip.
On the other hand, Philippe's top has the CM below the tip. One way he achieves that is by having windows on the bell. I called it "top" because it also spins well upside down on the stem. A neat thing is that it becomes transparent when spinning so you can see the finger.

Wonder which came first for Phillipe, the transparency effect or the CM placement? I enjoy playing around with apparent transparency so much that it often drives my designs nowadays.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #6 on: April 13, 2017, 12:49:32 PM »

Somebody's been taking cues from Iacopo...

I didn't know that top but I don't think someone made it after having seen the mine. There are some other tops with the recessed tip, older than the mine.  I didn't invent something new, I took the idea of the recessed tip from a malaysian gasing, the first one I saw made in that way.

Yes, but you've elevated the art form to new heights. I always think of you when I see spinners like this now.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #7 on: April 13, 2017, 12:59:26 PM »

The CM is clearly near the tip, but above or below?
It seems to me that in this top the CM is still well above the tip.  In my tops I have to insert the tip deeper, (if I want to meet the CM).

On watching the video again, I also think that the CM is above the tip, as the spinner looks about to fall off Tim's thumb at the very end. So it's a proper top after all.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #8 on: April 13, 2017, 07:14:21 PM »

I consider a proper top one that falls when not spinning, or a least one that would fall if it didn't have extra unnecessary constrains (like the feet of many plunge tops).
This one would still qualify if you spin it upside down. Iacopo's are tops by the slightest margin.

I think that's the most practical solution for our purposes. Basically, a bicycle with detachable training wheels is still a bicycle.

The others we can call top look-alike.  ;)

Or maybe a single-word generic term like "spinner".

What about "spinner" for any device that entertains in large part by spinning rapidly about some designated axis? Examples would include tops, fidget spinners, bicycle wheel "gyroscopes", playground turntables, and even bamboo copters. Practically speaking, the spin would have to be about the spinner's greatest or least principal axis of inertia to be useful.

A "top" could be a gravitationally unstable spinner (i) supported only at a single point (tip) below its CM, and (ii) kept from falling over only by spinning on its tip faster than a certain speed. At rest, it would topple immediately.

Some additional spinner categories alongside the top category:

1. Spinner with one-point support that achieves gravitational stability (and therefore doesn't fall over) simply by virtue of having its CM below its tip. Technically, this is a conical pendulum with spin. Iacopo has some beautiful examples.

2. Spinner that's gravitationally stable (doesn't fall over) by virtue of having multiple points of support. Don made a LEGO prototype with 3 points of rolling support two decades ago (see here). Below is a 4-point spinner I came to independently in 2015.



Still don't know what to call Category 1, but I'm liking "rolling Olney" for spinners like this one. Gould might call some Category 2 spinners "supported tops".
« Last Edit: April 13, 2017, 07:17:16 PM by Jeremy McCreary »
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Iacopo

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Re: Japanese spinner like some of Iacopo's
« Reply #9 on: April 15, 2017, 09:12:15 AM »

CM below its tip. Technically, this is a conical pendulum with spin. Iacopo has some beautiful examples.

I like more the real tops, which topple down at the end of the spin.
Nearly all of my tops with a recessed tip topple down at the end of the spin, (they spin at 30 - 60 RPM when they do so).
Their CM is above, not below the tip.
I also tried to put the CM below the tip, to see what it happens, but it was just an experiment, nothing more.
I like to see the toppling down of the top, and I like that it happens at slow speed, so the top stays safely on the base without risk of tumbling down and damage.

The rolling olney could still be a top if (and until) the wheels do not touch the ground while spinning.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #10 on: April 15, 2017, 01:08:53 PM »

I like more the real tops, which topple down at the end of the spin.
Nearly all of my tops with a recessed tip topple down at the end of the spin, (they spin at 30 - 60 RPM when they do so).
Their CM is above, not below the tip.
I also tried to put the CM below the tip, to see what it happens, but it was just an experiment, nothing more.
I like to see the toppling down of the top, and I like that it happens at slow speed, so the top stays safely on the base without risk of tumbling down and damage.

Thanks for clarifying, Iacopo. Somehow I had the impression that you had some finished spinners with CMs below their tips.

It's fun to watch a top stay up at speeds that seem improbably low. Your critical speeds are exceptionally low by any standard but not surprising given your very high AMIs per unit mass and very short CM-to-tip distances.

My lowest critical speed ever with a LEGO top is 90-100 RPM, but 300 RPM is much more representative. At the other extreme, the thin spherical shell tops below need almost 1,000 RPM to stay up. (I can barely twirl them by hand, and then only with lots of practice. If they didn't have internal masses close to the tips to nudge their CMs below the geometric centers of the spheres, they wouldn't stay up at all.)



The rolling olney could still be a top if (and until) the wheels do not touch the ground while spinning.

Yes, that's what I did here. If I lengthen the tip downward on the red one above, it does function as a top, but it doesn't stay up long. I have to keep release speeds low to maintain centrifugal integrity, and drag brings it down to critical speed pretty quickly.
« Last Edit: April 15, 2017, 01:39:04 PM by Jeremy McCreary »
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ta0

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Re: Japanese spinner like some of Iacopo's
« Reply #11 on: April 15, 2017, 02:32:16 PM »

Here is a photo (without flash) of Philippe's low center mass "top" spinning on my finger:



My lowest critical speed ever with a LEGO top is 90-100 RPM, but 300 RPM is much more representative. At the other extreme, the thin spherical shell tops below need almost 1,000 RPM to stay up. (I can barely twirl them by hand, and then only with lots of practice. If they didn't have internal masses close to the tips to nudge their CMs below the geometric centers of the spheres, they wouldn't stay up at all.)

I believe our regular size trick tops need at least 1200 RPMs: they are not easy to snap start!
But I am surprised you spherical shell tops don't spin easier. They remind me some metal sheet tops, generally with the Earth painted on them. Here is another version from the Sputnik age:



They spin easily using the fingers, the orange one up to 45 seconds. That's good because the starter gizmo that came with them needs to be repaired, although by hand I cannot make them whistle. The center of mass seems to be not too far from the center of the sphere. In fact, I can spin them as easily upside down.
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Iacopo

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Re: Japanese spinner like some of Iacopo's
« Reply #12 on: April 15, 2017, 03:34:09 PM »

Somehow I had the impression that you had some finished spinners with CMs below their tips.

Your impression is correct.  My top Nr. 12 is a "conical pendulum with spin", and it was designed intentionally to be so.    Nr. 14 is the other one.  Probably you have seen the videos about them and you remember them.   About the Nr. 14, there was an error, because I didn't want it to be self-righting; its tip was near the CM but still above it;  but I used a ball tip in it, without thinking that a ball tip, near the CM, even if above it, makes the top self-righting in any case.
The rule in this case should be that the center (and not the contact point) of the ball tip must be below the CM, to avoid the self-righting effect.   
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Iacopo

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Re: Japanese spinner like some of Iacopo's
« Reply #13 on: April 15, 2017, 03:38:24 PM »

Here is a photo (without flash) of Philippe's low center mass "top" spinning on my finger:

I didn't know it, it's nice. I too like its transaparency effect.
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Jeremy McCreary

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Re: Japanese spinner like some of Iacopo's
« Reply #14 on: April 15, 2017, 08:42:47 PM »

My lowest critical speed ever with a LEGO top is 90-100 RPM, but 300 RPM is much more representative. At the other extreme, the thin spherical shell tops below need almost 1,000 RPM to stay up. (I can barely twirl them by hand, and then only with lots of practice. If they didn't have internal masses close to the tips to nudge their CMs below the geometric centers of the spheres, they wouldn't stay up at all.)
I believe our regular size trick tops need at least 1200 RPMs: they are not easy to snap start!
But I am surprised you spherical shell tops don't spin easier. They remind me some metal sheet tops, generally with the Earth painted on them. Here is another version from the Sputnik age...
They spin easily using the fingers, the orange one up to 45 seconds. That's good because the starter gizmo that came with them needs to be repaired, although by hand I cannot make them whistle. The center of mass seems to be not too far from the center of the sphere. In fact, I can spin them as easily upside down.
Man, those are some really cool tops, ta0! Wonder what their secret is?

As you know, truly spherical mass distributions (including thin shells) are inherently unstable as tops at any speed. To stabilize my LEGO shells, I started by adding internal mass as close to the tip as possible in order to minimize CM-tip distance as best I could given the low average density of LEGO parts. At the same time, I tried to add mass as far from the spin axis as possible in order to maximize AMI/TMI ratio without straying too far above the tip.

Unfortunately, these goals are geometrically incompatible inside the bottom of a sphere -- at least in the LEGO realm. So I had to find the best compromise, and that took a great deal of trial and error. Below are some early solutions that worked reasonably well.



Perhaps your tops have dense internal mass rings just inside their equators. That wasn't an option for me, but it would explain why your tops work about the same right-side up and upside down. Mine have no chance upside down.
« Last Edit: April 15, 2017, 08:45:33 PM by Jeremy McCreary »
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