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Author Topic: Maxwell Top  (Read 83756 times)

Jeremy McCreary

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Re: Maxwell Top
« Reply #15 on: March 09, 2016, 04:21:28 PM »

Lourens: Thanks for the book and historical info. I'll be in touch about the former.

Didn't know that all those big names used tops in their research as well, but I'm not surprised. Tops make good demonstration platforms for lots of interesting science.
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Art is how we decorate space, music is how we decorate time ... and with spinning tops, we decorate both.
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the Earl of Whirl

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Re: Maxwell Top
« Reply #16 on: May 19, 2019, 10:10:06 PM »

Found the top container and contents called Ptolemy's top.  I took it to Sunday School and fooled around with it a bit.  Looks like what I have is the same in Lourens's collection.  The little piece of rubber that runs along the track is in pretty bad shape.  I am not sure if I need it.  There are also discs of different designs one can use.  They do not fit over that rubber piece.
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Happiness runs in a circular motion!!!

ta0

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Re: Maxwell Top
« Reply #17 on: May 22, 2019, 10:48:38 PM »

Found the top container and contents called Ptolemy's top.  I took it to Sunday School and fooled around with it a bit.  Looks like what I have is the same in Lourens's collection.  The little piece of rubber that runs along the track is in pretty bad shape.  I am not sure if I need it.  There are also discs of different designs one can use.  They do not fit over that rubber piece.

A rubber piece over the axle would add some grip and increase its diameter, what would make it run faster along the track. But it shouldn't be needed to make it work.
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Jeremy McCreary

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Re: Maxwell Top
« Reply #18 on: May 23, 2019, 04:14:56 AM »

A rubber piece over the axle would add some grip and increase its diameter, what would make it run faster along the track. But it shouldn't be needed to make it work.

Experiments with several crude but successful LEGO knock-offs of the Maxwell/Ptolemy top confirm some of the observations noted above...
1. Speed along the track increases with increasing stem diameter, as you said.
2. Speed along the track also increases with increasing stem-track friction, as that reduces slip at high spin rates. Still, metal-metal friction might be enough to get some of the effect.
3. Speed along the track also increases weakly with decreasing CM-tip distance, whether the CM is above or below the tip. So fastest when the CM is at the tip -- in which case, no precession bucking opposing stem motions along the track. (Hence the bell-shaped rotors.)
4. Nothing magic about a spiral track. S-shaped, circular, linear, and polygonal tracks also work well. Fingers, too.
« Last Edit: May 23, 2019, 05:10:08 AM by Jeremy McCreary »
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ta0

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Maxwell dynamical top
« Reply #19 on: April 04, 2021, 12:19:19 PM »

Yesterday I received a Maxwell Dynamical Top from Machined Marvels of Calgary, Canada.



It's a 1/2 scale reproduction. The weight of the top (without base) is 130 gr vs. the 930 gr. on Maxwell's original paper.
It's made of brass except for the central shaft and the spinning concave surface which are made of steel.
The base is heavy (337 gr) so it doesn't move at all.
As far as I can tell it's a faithful reproduction and the quality is very good. It's serial number 011.



It stays spinning several minutes with a finger start. It can also be started with the included string but that's because the color disk gets in the way of the fingers, not to give it more spin. In general you don't want to spin it too fast or the color wheel won't be helpful.

I look forward to getting acquainted with all the adjustments and to reproducing Maxwell experiments.  :)

« Last Edit: April 04, 2021, 01:41:21 PM by ta0 »
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Jeremy McCreary

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Re: Maxwell Top
« Reply #20 on: April 04, 2021, 04:28:11 PM »

@ta0: Wonderful find! Gorgeous instrument! Eager to hear your findings. Hopefully, you'll also do some experiments in top mode (CM above contact).

Unfortunately, just blew half of the cost on LEGO's new Space Shuttle set (very cool). So I'll be asking for this top for my birthday, wedding anniversary, Christmas, and Bastille Day combined!
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lincolnrick

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Re: Maxwell Top
« Reply #21 on: April 05, 2021, 08:53:26 AM »

What a cool piece. Even if you didn't collect tops, this would be a fine piece of art in anyones' collection. Congrats on the acquisition.
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Texture

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Re: Maxwell Top
« Reply #22 on: April 05, 2021, 01:04:45 PM »

Cool top.  8) Makes me want one, but they are too expensive...
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ta0

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Re: Maxwell Top
« Reply #23 on: April 05, 2021, 01:18:50 PM »

The Maxwell Dynamical Top has a total of 11 adjustment!  :o It's going to take patience to adjust it correctly. As Maxwell himself wrote:

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It is necessary, therefore, to make the moments of inertia about the principal axes very nearly equal, and in this case a very small change in the position of any part of the top will greatly derange the position of the principal axis. So that when the top is well adjusted, a single turn of one of the screws of the ring is sufficient to make the axle no longer a principal axis, and to set the true axis at a considerable inclination to the axle of the top.
All the adjustments must therefore be most carefully arranged, or we may have the whole apparatus deranged by some eccentricity of spinning. The method of making the principal axis coincide with the axle must be studied and practised, or the first attempt at spinning rapidly may end in the destruction of the top, if not of the table on which it is spun.

The instructions that came with the top say:
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The fist adjustment that is done is the distance the spin point protrudes into the interior of the top:
This adjustment is set when we assemble the top and should not be changed!
It is locked in place by the locknut on the top of the bell of the top and is difficult to get adjusted properly.

Well, I stopped the top when it was spinning fast and that locknut became lose, so I have already changed this settinig!  ::)

To be continued . . .
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Jeremy McCreary

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Re: Maxwell Top
« Reply #24 on: April 05, 2021, 06:08:47 PM »

@ta0: Bummer!

Q: Is your inadvertent adjustment the one that sets the axial location of the overall CM relative to the tip contact?
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ta0

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Re: Maxwell Top
« Reply #25 on: April 05, 2021, 06:57:22 PM »

@ta0: Bummer!
Q: Is your inadvertent adjustment the one that sets the axial location of the overall CM relative to the tip contact?
Actually, it may be better in the end, as now I won't be afraid of adjusting it myself.  ;)

That locknut sets the depth of the tip inside the bell, which should also coincide with the center of mass of the top. The axial position of the center of mass is determined by the position of the bob along the screw (and the axial screws to a lesser degree), so you can always make it coincide with the tip. BUT, you also want the axial moment of inertia to be very close to the transversal moments of inertia and those also depend on the position of the bob. The instructions that came with the top (and Maxwell's paper) don't say how to do that, but I think I know how to achieve it.

I made a preliminary measurement with a torsion balance and got that the AMI was 5% greater than the transverse moment with all the adjustment screws all the way in. I need to do it again more precisely. In any case, I want the AMI just slightly less, so when I extend the screws in the perimeter I can equalize all the moments of inertia and then bias them in any direction.
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Jeremy McCreary

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Re: Maxwell Top
« Reply #26 on: April 05, 2021, 10:49:48 PM »

Sounds like equalizing the moments will be the hard part. But while working with spindulums, I found a trick for getting the CM exactly at the contact that might be useful to you.

Turns out that the direction of precession is exquisitely sensitive to the sign of the CM-contact distance. When the CM is even a small fraction of a millimeter above the contact, this distance is positive, and precession is prograde (same direction as spin). That's top mode.

And when the CM is even a tiny fraction of a millimeter below the contact, the CM-contact distance is negative, and precession is retrograde. That's spindulum mode.

The sensitivity of the precession reversal is quite amazing.
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Jeremy McCreary

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Re: Maxwell Top
« Reply #27 on: April 14, 2021, 11:42:52 AM »

Sent my wife the link to the company's page for the top as a birthday request. Nary a squawk about the price.

So, possibly good news for August. But to quote a favorite childhood TV hero,

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Tarzan no like it, Cheetah. Jungle too quiet.
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ta0

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Re: Maxwell Top
« Reply #28 on: April 14, 2021, 12:50:56 PM »

Jeremy: wait until she sends you a link to a website with a present for her birthday. Then you will know why she hasn't said anything!  >:D

I'm still working on equalizing the moments while making the tip coincide with the center of mass. I'm getting there.
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Jeremy McCreary

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Re: Maxwell Top
« Reply #29 on: April 14, 2021, 01:41:36 PM »

Jeremy: wait until she sends you a link to a website with a present for her birthday. Then you will know why she hasn't said anything!  >:D

Uh-oh, hadn't thought of that!
[Cue Jaws theme music]
« Last Edit: April 14, 2021, 01:53:03 PM by Jeremy McCreary »
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