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 91 
 on: September 23, 2021, 05:15:40 PM 
Started by ta0 - Last post by ta0
El reglamento del campeonato mundial está traducido al español: https://spintops.org/es/world-contest/2021-rules/

Ya hay registrados jugadores de Colombia en Tradicional, Femenino y Juvenil.

 92 
 on: September 23, 2021, 04:22:38 PM 
Started by Iacopo - Last post by ortwin
...
I lean to believe, without being sure, that the hidden drag detected by Bill is air drag.

Well, soon Bill will have better vacuum equipment. I am sure he will redo the experiments and the outcome will lead to some clarification. Maybe he will even perform some more experiments before that to confirm or falsify the eddy current hypothesis.

 93 
 on: September 23, 2021, 04:00:10 PM 
Started by Iacopo - Last post by Iacopo
" perfectly centered and aligned" and no wobble or precession is maybe asking a lot. Even if you manage to align and center the magnets near perfectly by geometry, there might still be inhomogeneities in the magnets present that lead to eddy currents.

Very interesting your experiments with magnets under the top, photos A, B, and C. My simple tests suggest the same. Holding a magnet at the edge of an aluminum top results in obvious pull on magnet. But I could never detect any drag with the magnet aligned directly above the spinning top.



I had the highest magnetic drag with the magnet placed at the side of the top, as shown in the photo above.
The magnetic drag increases gradually as the magnet is shifted from below the top to its side.

So, if the magnet is above the top, even if not perfectly centered, the magnetic drag should be little, maybe insignificant.
Also, the magnet used by Bill is not so big like the mine.
Wobble and precession are not an issue because the top with the magnet above is forced to spin always in vertical position by the magnets.

I lean to believe, without being sure, that the hidden drag detected by Bill is air drag.


 94 
 on: September 23, 2021, 03:23:21 PM 
Started by Iacopo - Last post by Iacopo
DETAILS OF VACUUM CHAMBER.

I have been asked to provide details of the vacuum chamber I use for spinning top experiments. The attached photos provide the general idea.
The Plexiglass (transparent acrylic) tube has dimensions of 203 mm ID x 305 mm high, wall thickness 6.35 mm. It was purchased online from ePlastics.com, as Cast Acrylic Tubing 8.000" OD x .250" Wall Thickness. The 6.35mm wall (1/4”) is adequate for full vacuum for this diameter tube.
The end pieces are 12.7 mm (1/2”) thick UHMW. It is available online also. This thickness is OK for full vacuum on the 203 mm tube, but do not use anything thinner. Do not use wood, unless it is sealed with epoxy. Do not use wood inside the chamber, it will leak air into the chamber under vacuum. Using a lathe, I cut a shallow groove in the end pieces to contain a Neoprene gasket. 
I used ¼” tubing for vacuum lines. If you use tubing that fits tightly over fittings, there is no need for hose clamps. It is a good idea to use a check valve between vacuum pump and vacuum chamber. This prevents any chance of pulling oil out of the pump and into the chamber.

Thank you for your detailed informations.  I will look around what I can find.

 95 
 on: September 23, 2021, 02:55:46 PM 
Started by Iacopo - Last post by ortwin
...
... But I could never detect any drag with the magnet aligned directly above the spinning top.
Is that you never "felt" any drag, or did you measure those comparative spin decay curves I suggested?

 96 
 on: September 23, 2021, 02:26:28 PM 
Started by Iacopo - Last post by Jeremy McCreary
Hey, it's not that crazy! I put my own body in a hot water bath just last night.

Thanks for the specs! I must have added Q5 while you were replying. It just asked for the CM-contact distance. Guessing the CM 's pretty close to the rotor's center.

 97 
 on: September 23, 2021, 02:22:24 PM 
Started by Iacopo - Last post by BillW
Would putting your chamber in a hot water bath be workable?

I do have my limits when it comes to wild and crazy schemes.

 98 
 on: September 23, 2021, 02:18:50 PM 
Started by Iacopo - Last post by BillW
Bill: Some questions regarding the 1,370 g test top you used in Reply #109 if you don't mind...

Q1: Is the reported AMI of 0.004 in kg m²?
I recalculated AMI, it is closer to 0.0035 Nm^2. Made of aluminum, but has some lead rod inside. 0.0035 is very close.

Q2: What's the radius and axial length of the rotor?
Radius = 750 75mm, length= 30mm

Q3: Do you know the steel used for the ball tip?
No,  it is a bearing ball purchased online from Boca Bearings. Steel. Still smooth and undamaged.

Q4: Is the carbide disk under the tip flat? If not, any idea of the surface's radius of curvature?
The tungsten carbide disc is flat, and very smooth. Diameter 32mm. No longer available.

 99 
 on: September 23, 2021, 02:09:09 PM 
Started by Iacopo - Last post by Jeremy McCreary
Geez, ebay's out of accelerators again??

Would putting your chamber in a hot water bath be workable?

 100 
 on: September 23, 2021, 02:01:18 PM 
Started by Iacopo - Last post by BillW
But you'll have to get time on your nearest particle accelerator to reduce the kinematic viscosity by reducing pressure alone.
To attack the kinematic viscosity directly, your best bet would be to raise the air temperature. Any good way to heat your rarified air?

Could not find a particle accelerator for sale on EBay.
But maybe running a vacuum spin test on a very hot day vs cold day.

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