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[Jeremy McCreary]

Jeremy, I think that it is just all that wobble you have that makes your top to slow down so rapidly under the shroud.
My top does not wobble at all with the shroud, but I have a spiked tip, and a very little base.

Nice test and totally agree -- except for the "wobble" part.

I view wobble as a rapid oscillation in tilt angle, regardless of cause. And that's not what I saw under the shroud. But I did see a lot of hula-hooping and precessing without oscillation in tilt angle. And I believe as you do that those motions took energy away from spin -- the only motion that keeps a top from falling.

[Iacopo]

Nice test and totally agree -- except for the "wobble" part.

Sorry, Jeremy..
With "wobble" I just wanted to mean the precession and the hula hooping, nothing else.

By the way, hula hooping happens in the opposite direction of the spin, (contrarily to precession), so if the top spins clockwise, it hula hoops counterclockwise.  If the stem is vertical, there is only hula hooping, and no precession.

The good news: The aerodynamic penalty for removing central mass this way now appears to be quite small. But if you remove it with rotor fenestrations (like the holes between spokes) exposed to the air, the aerodynamic penalty is quite high. And that's where low-mass fairings might help -- as you might be able to remove more central mass with fenestrations, or a fenestrated well, than with a well alone.

I have come to these same conclusions.

[Jeremy McCreary]

By the way, hula hooping happens in the opposite direction of the spin, (contrarily to precession), so if the top spins clockwise, it hula hoops counterclockwise.  If the stem is vertical, there is only hula hooping, and no precession.

Yes! Tried to have some fun with that happy fact below. The yellow flywheel above makes an appearance with a specialized tip assembly at 4:11.



And now that I look at this video again, I was probably seeing hula-hooping with tilt more often than rolling precession under the shroud. You can see a nice transition from hula-hooping to rolling precession at 7:30.

[ortwin]

Gyrocyclotron:
not really really related to the rest of this thread, but to the last fun video.
If you want to feed the spin not from the kinetic energy of the moving bowl (or plate as in the Topnosis) but from gravity, how would your track look like? Some type of spiral downwards. Have you ever seen something like that? If one would be able to make one, we would need to change the rules for the longest run of hand spun top: "starting and end position need to be at the same height above sea-level!" Otherwise someone could built such a track spiraling down the leaning tower in Pisa (Iacopo), the Eiffel tower in Paris (Jim(Cyril?)), or some tall building in Dubai. Then for the record event, when the "Guiness Book" is there, a person gives this top a gentle twirl at the uppermost floor of that building at the start of that track, and then a few hours (or days?) later the top arrives at ground level...........

[Jeremy McCreary]

If you want to feed the spin not from the kinetic energy of the moving bowl (or plate as in the Topnosis) but from gravity, how would your track look like? Some type of spiral downwards. Have you ever seen something like that?

Interesting puzzle! And no, I've never seen such a thing, though I'd love to. Maybe a Mt. Everest to Death Valley track for maximum head.

The key to top acceleration in the gyrocyclotron is to keep the top leaned over on the outer side of a ball tip of favorable radius of curvature. For a non-circular track, some kind of magnetic solution?

As for spin time records, would a Simonelli under a shroud be legit? Bet you could get well beyond an hour that way.

[ortwin]

....
You can see this even better comparing different spin times of the same top in vacuum conditions, (5 millibar residual pressure is very little and essentially you can observe the slowing down due to the tip friction alone).
Large and light tops are better for to measure the air drag, because in them the tip friction is little compared to the air drag, and this reduces the inaccuracy of the measurements.

Yes, it is hard to make sense of the changes introduced in a top if aerodynamic changes are around the same magnitude as tip related deceleration.  With a vacuum chamber you have the tip friction alone, if you have a levitating top you can look at the aerodynamic side by itself. This separation of the problems could help in understanding and towards optimizing both.
electric:



passive:

[ortwin]

As for spin time records, would a Simonelli under a shroud be legit? Bet you could get well beyond an hour that way.

It is a matter of taste really what is legit. To my personal taste something under a shroud would not be legitimate. As recessed tips and multiple twirls would not be. I am not even 100 % sure that I would feel completely happy about a "two handed start" as a stemless top would require. Even the idea I proposed of a self lubing tip by filling oil into a ball pen mine used as a spinning top tip - no there is a moving part involved. And no magnets whatsoever of course, that is a different hobby of mine.

[ortwin]

The key to top acceleration in the gyrocyclotron is to keep the top leaned over on the outer side of a ball tip of favorable radius of curvature. For a non-circular track, some kind of magnetic solution?

You are thinking of something like the "magnetic gyro wheel" but with only one rail?


 Hm, are you going to look into this further? So many things to explore, so little time........

[Iacopo]

if you have a levitating top you can look at the aerodynamic side by itself.

A Levitron in the vacuum doesn't spin for long, there is a magnetic drag. 
It doesn't seem to me a so good way to measure the air drag of a spinning top.
It seems complicate, also.

It is a matter of taste really what is legit.

"Legit" doesn't sound a correct term here, if there are not rules to obey.  You can say "I like traditional tops", "I dislike new ideas", ok... a matter of taste in any case, as you say.

As for spin time records, would a Simonelli under a shroud be legit? Bet you could get well beyond an hour that way.

I don't know, it would be not up to me to decide. But I am not looking for a new official record, and I will not do it.
I am just trying to make something different; it can become boring to make things always in the same way.
I think I can reach maybe 65 minutes with a shroud, not much more, because my best tops have already low air drag by themselves.
 

[ta0]

With "wobble" I just wanted to mean the precession and the hula hooping, nothing else.
By the way, hula hooping happens in the opposite direction of the spin, (contrarily to precession), so if the top spins clockwise, it hula hoops counterclockwise.  If the stem is vertical, there is only hula hooping, and no precession.

I'm sorry, I missed the definition. What exactly is hoola hooping?
I thought it was the rolling precession, but from what you say it's not.

As for spin time records, would a Simonelli under a shroud be legit? Bet you could get well beyond an hour that way.

For my taste, covering the top with a glass enclosure (but not vacuum) is valid for a record. I'm going to start looking for a nice glass to cover my Simonelli top (just for my personal record).

not really really related to the rest of this thread, but to the last fun video.
If you want to feed the spin not from the kinetic energy of the moving bowl (or plate as in the Topnosis) but from gravity, how would your track look like? Some type of spiral downwards. Have you ever seen something like that?

I would say that the Topnosis works by gravity. You are continuously lifting it and gravity makes it fall and roll on the plate.
Same with the Radiaculum.

[Jeremy McCreary]

Electromagnetic Letivation Device youtu.be/AU0q4wVohF8

Is that one of your creations? Very cool.

You are thinking of something like the "magnetic gyro wheel" but with only one rail?...  Hm, are you going to look into this further? So many things to explore, so little time........

Maybe and no, respectively. You're the guy with the magnetic skills.

[Jeremy McCreary]

"Legit" doesn't sound a correct term here, if there are not rules to obey.

Exactly.

I am just trying to make something different; it can become boring to make things always in the same way.

Hey, you can't just drop a teaser like that and walk away!

[ta0]

Electromagnetic Letivation Device youtu.be/AU0q4wVohF8

Is that one of your creations? Very cool.

You are thinking of something like the "magnetic gyro wheel" but with only one rail?...  Hm, are you going to look into this further? So many things to explore, so little time........

Maybe and no, respectively. You're the guy with the magnetic skills.

Jeremy: the levitating thing is something we discussed before (Levitron Revolution) and was used for a pseudo top (Infinity).

A one-track magnetic gyro wheel would be either the Spiraculum or the Radiaculum. These were invented by a German guy. Looking for a photo of the Spiraculum I found out that now there is this economical version:

[Jeremy McCreary]

Cool spintoy! Question is, how many points of support for the gyroscope, and should it be free to fall over below its critical speed?

[ortwin]

[

No clear difference in this limited test of Top C (lower fairing only), no shroud, spokes blowing...

Upward: 166, 172
Downward: 165, 163

Well, thank you anyways for performing these measurements!


The Radialaculum would have only one point of support and could go down asimple but long spiral it seems.  But it seems ta0 is implying that the topnosis could do it without magnets and also in a more upright traditional top like position.

[/size]

I don't know, it would be not up to me to decide. But I am not looking for a new official record, and I will not do it.
I am just trying to make something different; it can become boring to make things always in the same way.
I think I can reach maybe 65 minutes with a shroud, not much more, because my best tops have already low air drag by themselves.
 

I am also not looking seriously for a world record - be it official or not. The way is the goal!


Even thinking about making things different is great. What about large spinning tops that can be started with one hand? A bicycle wheel type top where you have something like a door handle instead os a stem to start?
A bowling ball with some kind of flywheel around it? You can twirl a bowling ball using its holes.
I think I remember seeing  some calculations done by Jeremy that suggested big size tops would not spin as long, but did that cover these cases? There seem to be different muscles of the arm involved, so maybe there is a chance?