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Author Topic: Tim's Spiral Top  (Read 825 times)

Heshsha

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Tim's Spiral Top
« on: December 10, 2018, 10:54:00 AM »

I am a new member in this forum.

I teach Science to kids and I am trying to make a spinning top. It is called Spiral Top by Tim:

 https://www.youtube.com/watch?v=DC8YxGzTwzA


I found it very interesting and have decided to make one.
 
I need some guidance for making it.

What are the key things I must take care off. In fact I tried making one, but failed miserably. I will upload video tomorrow.

Any suggestions how to go about it ?     

Thanks,

Heshsham 
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ta0

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Re: Tim's Spiral Top
« Reply #1 on: December 10, 2018, 11:05:20 AM »

First, welcome Heshsha from New Delhi, India!

That top is most commonly called a Maxwell top, although it also goes by other names. You can read about the history of the top on this thread: Maxwell Top

Something important is that the tip of the top needs to be at the center of mass so it does not precess when it's not touching the track.
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Jeremy McCreary

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Re: Tim's Spiral Top
« Reply #2 on: December 10, 2018, 04:11:12 PM »

Welcome aboard! ta0's right...

Concentrate first on getting your top's center of mass (CM) exactly at the "contact" (support patch). If not too much wobble, the "pointer" (end of stem opposite contact) will then be happy to follow "guides" of many different shapes -- not just spirals.

Now have several working LEGO versions of this spintoy with a number of different guides, but it took a lot of guess-and-check to get there, and it may be the same for you. If I had to do it again... (Search this forum or Wikipedia for unfamiliar terms.)

Step 1. Pick a design with at least 3-fold rotational symmetry and make the built top as rigid as you can. In Tim's example, the 3 evenly spaced hanging balls reduce the top's overall rotational symmetry from infinite (circular or axisymmetric) to 3-fold. This design's plenty rigid -- partly due to the chosen material, and partly due to the bell's double curvature. However, suspect that it could also work in wood or stiff plastic.

Step 2. Bring the built top into good static balance by adding mass to its "light side" or shaving mass from its "heavy side". (Many practical discussions on this forum.) Physically, this brings the CM to the symmetry axis. Balance each structural level separately, as in Tim's top, and you'll likely have enough dynamic balance to avoid most wobble.

Step 3. Shift CM along symmetry axis to coincide with contact by adding, subtracting, or shifting mass without breaking your dynamic balance. With Tim's design, you might just slide the bell along the stem before fastening it down.

Test CM height by observing what happens after a smooth release...
1. No consistent horizontal drift in pointer direction => CM at contact. This absence of precession is the goal for your finished top.
2. Precession in same direction as spin => CM above contact.
2. Precession in opposite direction as spin => CM below contact.

Precession direction and absence of precession are easy to observe and very sensitive to small CM-contact offsets.

One last point: Guide following (mainly a matter of rolling with or without slip) will suffer if there's too much hopping due to wobble.
« Last Edit: December 12, 2018, 12:02:06 AM by Jeremy McCreary »
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Playing with the physical world through LEGO

Mermouy

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Re: Tim's Spiral Top
« Reply #3 on: December 11, 2018, 07:38:59 AM »

Welcome on board Heshsha!
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Heshsha

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Re: Tim's Spiral Top
« Reply #4 on: December 13, 2018, 05:15:19 AM »

Welcome aboard! ta0's right...

Concentrate first on getting your top's center of mass (CM) exactly at the "contact" (support patch). If not too much wobble, the "pointer" (end of stem opposite contact) will then be happy to follow "guides" of many different shapes -- not just spirals.

Now have several working LEGO versions of this spintoy with a number of different guides, but it took a lot of guess-and-check to get there, and it may be the same for you. If I had to do it again... (Search this forum or Wikipedia for unfamiliar terms.)

Step 1. Pick a design with at least 3-fold rotational symmetry and make the built top as rigid as you can. In Tim's example, the 3 evenly spaced hanging balls reduce the top's overall rotational symmetry from infinite (circular or axisymmetric) to 3-fold. This design's plenty rigid -- partly due to the chosen material, and partly due to the bell's double curvature. However, suspect that it could also work in wood or stiff plastic.

Step 2. Bring the built top into good static balance by adding mass to its "light side" or shaving mass from its "heavy side". (Many practical discussions on this forum.) Physically, this brings the CM to the symmetry axis. Balance each structural level separately, as in Tim's top, and you'll likely have enough dynamic balance to avoid most wobble.

Step 3. Shift CM along symmetry axis to coincide with contact by adding, subtracting, or shifting mass without breaking your dynamic balance. With Tim's design, you might just slide the bell along the stem before fastening it down.

Test CM height by observing what happens after a smooth release...
1. No consistent horizontal drift in pointer direction => CM at contact. This absence of precession is the goal for your finished top.
2. Precession in same direction as spin => CM above contact.
2. Precession in opposite direction as spin => CM below contact.

Precession direction and absence of precession are easy to observe and very sensitive to small CM-contact offsets.

One last point: Guide following (mainly a matter of rolling with or without slip) will suffer if there's too much hopping due to wobble.

Dear Jeremy  and others, First of all thank you very much for welcoming me on this forum. You have really given details I was looking for. I hope to start working on this in next 4-5 days.  I also need to revise a few concepts in Physics. Glad to meet you physics geniuses :)   
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the Earl of Whirl

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Re: Tim's Spiral Top
« Reply #5 on: December 13, 2018, 07:47:31 PM »

Yes, welcome Heshsha!!!  Good luck with this project.
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Happiness runs in a circular motion!!!

vegabomb

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Re: Tim's Spiral Top
« Reply #6 on: December 15, 2018, 03:26:04 AM »

I’d like to buy one of these.  :)
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Jeremy McCreary

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Re: Tim's Spiral Top
« Reply #7 on: December 15, 2018, 01:42:47 PM »

Tim found the persistent "cling" between his top's stem and the spiral guide "extraordinary". I do, too. Even more remarkable: Nothing magic about spiral guides. My LEGO knock-offs follow linear, rectangular, circular, and S-shaped guides equally well.

Question is, whence the "cling" if not magnetic? I think it's rooted in the reaction forces generated on first contact between guide and stem and sustained thereafter by a gyroscopic feedback manifesting as "cling".

I'd elaborate, but so far I've been unable to translate the 3D reaction force, torque, and angular velocity vectors involved into plain English that still does justice to the dynamic.

Anyone have a less technical explanation that doesn't mislead?

« Last Edit: December 15, 2018, 06:45:26 PM by Jeremy McCreary »
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ta0

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Re: Tim's Spiral Top
« Reply #8 on: December 15, 2018, 02:49:23 PM »

Crabtree's book has a detailed explanation (but not too technical) of how this top works. I can post it after I come back from visiting family for Christmas. I guess my 10,000 post will also have to wait until then.  :o
« Last Edit: December 15, 2018, 02:52:58 PM by ta0 »
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Iacopo

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Re: Tim's Spiral Top
« Reply #9 on: December 16, 2018, 03:57:33 AM »

Question is, whence the "cling" if not magnetic? I think it's rooted in the reaction forces generated on first contact between guide and stem and sustained thereafter by a gyroscopic feedback manifesting as "cling".

Yes, I believe you are right.

When the top spins, (clockwise in the schetch below, grey arrow), with the stem leaned on the spiral, the stem is constrained to go in the direction of the blue arrow.  Consequently, the top tilts, with the side of the flywheel in front of you going upwards, (green arrow).
Because of the gyroscopic effect, the upwards movement would want to happen 90 degrees later, in the direction of spinning, (red arrow);
this makes the stem of the top to be pressed against the spiral, (orange arrow).



Whatever the position of the top relatively to the spiral, the schema works always in the same way, with the result that the stem is always pressed against the surface on which it is rolling, because of gyroscopic effect, with that deceitful feeling of magnetic attraction.
« Last Edit: December 16, 2018, 11:37:20 AM by Iacopo »
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Jeremy McCreary

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Re: Tim's Spiral Top
« Reply #10 on: December 18, 2018, 01:57:12 AM »

Question is, whence the "cling" if not magnetic? I think it's rooted in the reaction forces generated on first contact between guide and stem and sustained thereafter by a gyroscopic feedback manifesting as "cling".
When the top spins, (clockwise in the schetch below, grey arrow), with the stem leaned on the spiral, the stem is constrained to go in the direction of the blue arrow.  Consequently, the top tilts, with the side of the flywheel in front of you going upwards, (green arrow).
Because of the gyroscopic effect, the upwards movement would want to happen 90 degrees later, in the direction of spinning, (red arrow);
this makes the stem of the top to be pressed against the spiral, (orange arrow).
Whatever the position of the top relatively to the spiral, the schema works always in the same way, with the result that the stem is always pressed against the surface on which it is rolling, because of gyroscopic effect, with that deceitful feeling of magnetic attraction.

I like your diagram and explanation. The clinging motion indicated by your orange arrow may also introduce a positive feedback involving stem-guide friction and the rate at which the stem rolls forward (blue arrow) along the guide. Faster rolling (perhaps due to less slip) should enhance the cling.
« Last Edit: December 18, 2018, 12:04:32 PM by Jeremy McCreary »
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Jeremy McCreary

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Re: Tim's Spiral Top
« Reply #11 on: December 18, 2018, 02:04:25 AM »

Dear Jeremy  and others, First of all thank you very much for welcoming me on this forum. You have really given details I was looking for. I hope to start working on this in next 4-5 days.  I also need to revise a few concepts in Physics. Glad to meet you physics geniuses :)

My pleasure! Looking forward to seeing what you come up with.

Not much genius involved -- at least on my part. We've just been collectively thinking and reading and experimenting and discussing top physics for some time now. And since tops turn out to be a lot more complicated than they look, we're all still learning. Glad you'll be joining us.
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Iacopo

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Re: Tim's Spiral Top
« Reply #12 on: December 18, 2018, 11:42:11 AM »

The clinging motion indicated by your orange arrow may also introduce a positive feedback involving stem-guide friction and the rate at which the stem rolls forward (blue arrow) along the guide. Faster rolling (perhaps due to less sliding) should enhance the cling.

You said it well with your words, there is a feedback mechanism involved; I didn't repeat the concept, but I totally agree.
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