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[ortwin]

JBB looks great! Eager to see it in action. Spartan can be forgiven for getting desperate.

Since I asked for some "ad ons" and some little changes it will be at least another week until it comes back.

[ortwin]

...
I guess you have to spin it and then rush to cover it and pump out the air as fast as possible. It should be possible to start one inside a vacuum chamber using magnets. My idea would be to have the top hanging from the chamber ceiling because of a rotating spinning magnet above. The top would either have a magnet or a non circular stem so as to rotate with the driving magnet. After it reaches the necessary speed, you take away the external magnet and the top falls on the surface.

I would like to have a vacuum setup. Perhaps one day . . .

Yes I have to do it like you suspect. There surely are different ways to start tops in a vacuum chamber. I would like purely mechanical ones best, but then again why exactly would you want  that?
With Something like "top secret" you can start the top, then close the vacuum chamber while the base sits outside and drives the top until you pumped down as far as you like (or can do it) . After that you can observe how it spins down when you take away the base.

[Jeremy McCreary]

Since this is the happenin' place for toroidal tops, my latest, in bronze and blue...



If I pack all 5 metal rings downward in their hangers before twirling, this top spins ~30 s by hand without visible wobble. Pretty happy with that considering the rotten aerodynamics and all the opportunities for unbalance.



Compared to the stainless ring I used before (left), the bronze rings are significantly smaller in all dimensions. The stainless ring has 4 times the AMI of the 5 bronze rings put together, and its top spins 11 times longer due to the added AMI, a much lower CM, and much cleaner aerodynamics.

But to give the bronze rings their due, note that their low-AMI, high-drag plastic "chassis" stays up a mere 1 s by itself. By adding many times the AMI of the chassis alone and reducing CM height from 33 to 25 mm, the rings greatly reduce critical speed.

I think the rings are also likely to reduce air resistance. If so, then the added AMI further reduces the slope of the top's spin decay curve from release to fall. Result: A 30-fold increase in spin time.

[ortwin]

Since this is the happenin' place for toroidal tops, my latest, in bronze and blue...


...

Super cool photo !


Will you submit this to our contest?

[Jeremy McCreary]

Super cool photo !
Will you submit this to our contest?

Thanks! The chance of a non-throwing top winning is slim to none, but why not?

[ortwin]

...The chance of a non-throwing top winning is slim to none, but why not?

Let me tell you, winning is not everything ! 
But maybe it would make our corner of the forum more visible to the "sports section"?

[Jeremy McCreary]

But maybe it would make our corner of the forum more visible to the "sports section"?

Good point! I like "sports section".

[ortwin]

Update on Junior Brass Band:  "comeback postponed - important part of my friends lathe broke" 

That lathe is probably older than the oldest member in this forum, so replacement parts need to be specially manufactured. 

[ortwin]

The return of JBB (Junior Brass Band) - Listen up!

There is still a little part missing, but the main components are there.
Being at the age it/she/he is at, it is probably normal to have an identity crisis.
"Am I a stemless top? Do I want to be a top with this stem and a ballpoint pen tip or do I prefer this other one?"

 
Via the screw spokes the tip can be centered. The nuts on the spokes are for (static) balancing. At the moment centering and balancing needs still to be worked on, but I wanted to post this update first.
The best time so far with this version (stemless) is 18:44. So already a small improvement of 5 seconds in comparison to an earlier version. I am quite confident that when I can get rid of most of the wobble times of over 20 minutes are realistic.

[Jeremy McCreary]

Wow, looks and sounds great, and 18 mintes is very impressive.

Love the stem options. Eager to see time trials with and without! Which of the 2 stems feels better for single twirls?

[ta0]

You seem to have a Simonelliesque flair for detail. I wonder where this path into ring tops will take you . . . 

[Jeremy McCreary]

Rats, wanted to look at the details of this beauty, but the security app on my phone says they're on a "suspicious site".

[ortwin]

You seem to have a Simonelliesque flair for detail. I wonder where this path into ring tops will take you . . . 

Thank you, that is a very big compliment. Although I am not sure what detail exactly you mean. There really is not much. The screws/spokes are stainless steel, there were none available in brass. The nuts for balancing are not so great looking I think. I consider having same changed for round brass parts that are longer so they can manipulated just by the fingers.
The hub, yes that is were I asked for it to have about the same curvature as the flywheel ring. The ring itself has now a flattened top and bottom. I hope I can use that area for some laser balancing.The stems don't fit in the whole design package so far, at this point they are basically just to check  if they improve over all performance.

Wow, looks and sounds great, and 18 mintes is very impressive.

Love the stem options. Eager to see time trials with and without! Which of the 2 stems feels better for single twirls?

The smaller thin stem that is knurled does not feel great. That was one I never asked for though. The larger stem has a much better feel to it. I wanted it that flat on the outside. I will try applying sand paper to it for better grip, or a piece of rubber/silicon hose that fits.
With the stemless version I reached 520 RPM to start with and after those 18:44 it fell with 90 RPM.
With the bare larger stem (same scraping angle) 630 RPM at start, after 17:18 falling with about 93 RPM.
As a base I used that large concave mirror that came with the original Euler's Disk.
So besides the centering and balancing the stem business can use some improvement. The stem surface, its length and its diameter need optimization. With less than 750 RPM at the start I will not be happy.The one part that is still missing, is a longer axle to which that ceramic ball is glued. It should be so long that its upper end is flush  with the upper end of that larger stem. Since the stem screws on the axle, I will be able to vary the stem length from about 2.5 cm to 4.5 cm (there will be a counter nut). That range should be  enough to find a good value for the stem length.

[Jeremy McCreary]

It took 86 s to spin down from 93 to 90 RPM??

For a given top, higher release speed should yield longer spin times -- unless the longer stemless spin in this case just happened to hang in a metastable state between spinning down through critical speed and actually falling. It happens.

Nice that you can swap out stems, cuz the only way to optimize stem diameter, length, and texture for this particular top is to test, test, test.

A Simonelli-like low-density stem would have less of an adverse effect on critical speed.

[ortwin]

It took 86 s to spin down from 93 to 90 RPM??
...

No, no, with the stem it seems to lose its speed faster over the whole range. I can't prove that with data I recorded and I do not know why exactly but I suspect that more wobble with the stem leads to a faster loss of energy. Of course I also expected longer times with the higher starting speed using the stem - especially after I saw that critical speed did not go up by so much - BUT it turned out to be different! Maybe we should not try too hard to explain this, since no proper balancing was performed for these cases, differences could also stem from that side?

..
A Simonelli-like low-density stem would have less of an adverse effect on critical speed.

The effect on critical speed does not seem to be sooo bad. With all the runs I performed over the last two days, I would judge it to worsen only by about 6 RPM on average.  The Simonelli low density stem would not make such a big difference: It is solid wood, but my brass stem is hollowed out.

I think the main thing for me should be the centering, balancing and thereby wobble reducing adjustments.Just before I applied some sand paper wrapped around  that stem with double sided sticky tape. I really had one start at around 730 RPM, so a big improvement there, but it "only" led to 18:29.  The big problem in this specific run was the sand paper: one end came a bit off the stem so it could act almost like a braking parachute!