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[ortwin]

... I must say your design is quite efficient, reaching almost half an hour with brass and 'only' 600 RPM starting velocity, and while I do not know typical starting velocities of one-twirl finger tops, it is certainly way less than the 1hr+ record setters out there starting with 2000+ RPM and spending half their spin times above 600RPM.
Sapphire lens is a good recommendation, I forgot they existed. Have you noticed any wear on either the base or the top after all this time?

RPM by itself does not matter much, it is always in relation to AMI and other factors. You might have seen that just today I posted a video of a throw top that reaches almost 10.000 RPM but loses most of it very fast.
With my Spartan brass top (there is a video on one of those in the channel you posted as well) I can reach 2000 RPM to start with, and something close to 20 minutes of spin time.


Yes, I notice wear in the sapphire base, but I am not sure if it is from the regular spin of the top or from "special occasions" like when there is some stronger impact when starting the top or from particles that get between tip and base during a spin.

[zaggernut]

RPM by itself does not matter much, it is always in relation to AMI and other factors. You might have seen that just today I posted a video of a throw top that reaches almost 10.000 RPM but loses most of it very fast.
With my Spartan brass top (there is a video on one of those in the channel you posted as well) I can reach 2000 RPM to start with, and something close to 20 minutes of spin time.

True, designs with a higher RPM potential usually have to sacrifice elsewhere, plus it really is diminishing returns increasing RPM, given the nature of air resistance. But matching the starting RPM of Iacupo's WR run and your run at 600 RPM, the spintime difference is really not that much, which I find impressive given your top is both lighter and has a less dense flywheel. Even though Iacopo's design has a much higher RPM potential and could have been even more streamlined had it been designed with a max RPM of 600 in mind.

Yes, I notice wear in the sapphire base, but I am not sure if it is from the regular spin of the top or from "special occasions" like when there is some stronger impact when starting the top or from particles that get between tip and base during a spin.

But no noticeable performance-affecting wear on the carbide ball bearing itself? It is much less troublesome to tilt the base to a fresh spot than it is to replace the tip and then rebalance the top.

[ortwin]

Yes, the design with flywheel and thin spokes might have some more potential than half an hour, but it is probably out of my reach to have one machined from one piece of brass according to my ideas.
What I am still hoping for, is to go past the half hour without the use of a pedestal.

[ortwin]

 

...
But no noticeable performance-affecting wear on the carbide ball bearing itself? It is much less troublesome to tilt the base to a fresh spot than it is to replace the tip and then rebalance the top.

I do not have a good microscope to see anything on that little ball (which was not made for a bearing as such).
And I did not do any specific experiments to determine if wear of the sapphire or the tungsten carbide tip is more relevant for decreasing performance. When I was still using regular mirrors there was a clear relation to the wear of that surface.

[ta0]

When the top finally topples, it does so quite abrubptly, going from minor wobble to a violent destabilization almost instantly. Furthermore, just a few seconds before toppling over, you can see the tilt of the top rotating at exactly the same rate as the top itself (focus on the interior of the hollow axle going slightly darker periodically, due to some discoloration). Both these points combined lead me to believe that just like in the first standing stop video I posted, there is a flat spot on this top too, allowing it to keep rotating below what its critical speed would otherwise have been.

What you see as a discoloration I think is a reflection that changes with the inclination of the stem and that's why it changes at the same time as the tilt.
But I think on this one you can follow the knurling on the stem at the end, of about 1 second per revolution, or 60 RPM:



That's pretty low and similar to what Iacopo gets for a recessed tip, so it's somewhat suspect.
The sudden fall is perhaps to be expected for a very well balanced top with an protruding tip on a flat surface.

I'm not sure if a flat spot that is not big enough for the top to remain standing would extend the duration time. My guess is that it would be detrimental. The exception would be a tip large enough for the top to rest but small enough that environmental vibrations would make it likely to fall before completely stopping.

One note about critical speed. The equation for critical speed is derived in several theoretical papers. But I have never seen an experimental confirmation. It's something we need to verify one day, probably with some very simple tops made for this purpose.

[Iacopo]

I'm not sure if a flat spot that is not big enough for the top to remain standing would extend the duration time. My guess is that it would be detrimental.

In my tests I could see that generally the tip friction is slightly higher if the contact point is larger, when the top is in sleeping position.

Nevertheless, this probably wasn't a big problem for the top in the video, because for the largest part of the time that top "precesses", so that the part of the ball tip in contact with the base was not exactly its flattened area.
The "precession" is an advantage by itself, (it would be so even without a flattened area in the tip), because the tip friction of ball tips is a bit lower while the top walks and the tip rolls, than when the top is steady in sleeping position.
At slow speed, the flattened area in the tip could have helped to reduce the topple speed.
These things together could have favoured the longest spin.   
 

[Jeremy McCreary]

One note about critical speed. The equation for critical speed is derived in several theoretical papers. But I have never seen an experimental confirmation. It's something we need to verify one day, probably with some very simple tops made for this purpose.

Totally agree. For one thing, still bothered by the differences in the formulas for critical total angular speed about the spin axis (w3), and critical spin rate about that axis (s).

Would love to confirm that the simpler — and much more commonly cited — formula for w3 is adequate for our purposes. [Note that w3 = s + p cos(a)  where p is the precession rate about the vertical, and a is the tilt angle measured from the vertical. In a sleeping top (a = 0), w3 = s. We usually don't measure p.]

But testing these formulas won't be easy. Critical speed is just the lower limit of stability against small perturbations in tilt angle. In theory, a top shouldn't fall at or above critical speed, but in a quiet environment, the top might stay up in a metastable state for some time thereafter. This would be especially true of a perfectly balanced top with a worn tip or on a deeply concave support.

HOWEVER, even if the formulas turn out to be poor at predicting first-scrape or topple speeds, I'm already quite comfortable with them as qualitative guides for spin time maximization. I've made thousands of LEGO tops, and I always make them spin as long as possible without compromising higher design priorities. The simple w3 formula has never led me astray.

[ta0]

Another one from the same Youtube channel "spinning top enthusiast" (Hartmut Mentz) , where the top falls 10 seconds after it stopped spinning. Had it fell 10 seconds before stopping, it would have looked like a valid spin until the end. This is certainly a problem.

[Jeremy McCreary]

Another one from the same Youtube channel ("spinning top enthusiast") , where the top falls 10 seconds after it stopped spinning. Had it fell 10 seconds before stopping, it would have looked like a valid spin until the end. This is certainly a problem.

Yes, and just one of several thorny problems with the concept of "spin time".

Another is scrape angle. For lack of a better endpoint, most of us report time to first scrape as "spin time" — usually without saying so explicitly.

But time to first scrape increases with scrape angle, which in turn increases artificially with pedestal height. On a mirror or lens larger than the top, scrape angle also decreases artificially with support concavity.

I have tops with small ball tips designed for shallow, low-friction ball-and-socket supports on pedestals. This arrangement allows scrape angles of over 90°. Nothing stopping the tops from falling off at rest.

Some tops with flat-table scrape angles of 10° or so continue to spiral down slowly to tilts of over 75° before doing anything I'd call "falling". Imagine how much shorter the time to first scrape would have been on the table.

[zaggernut]

The exception would be a tip large enough for the top to rest but small enough that environmental vibrations would make it likely to fall before completely stopping.

That is a possibility I didn't consider, for environmental factors to randomly destabilize tops with center of mass lying within the boundaries of the flat spot. Which absolutely can happen, as evidenced by the video you posted later. And it would not be too hard to covertly induce such environmental factors to reliably make a top topple right before it comes to a standing stop. Muddy waters indeed. 

I think I will do more research on simply getting a top with a spiked tip or a tiny bearing ball, or finding a way to retrofit a ball-ended top. They sell small cone ended sapphire cylinders, but centering and holding them in place rigidly inside a hollow top axle doesn't sound fun.

[ortwin]

The exception would be a tip large enough for the top to rest but small enough that environmental vibrations would make it likely to fall before completely stopping.

That is a possibility I didn't consider, for environmental factors to randomly destabilize tops with center of mass lying within the boundaries of the flat spot. Which absolutely can happen, as evidenced by the video you posted later. And it would not be too hard to covertly induce such environmental factors to reliably make a top topple right before it comes to a standing stop. Muddy waters indeed.

In the case of that video ta0 linked the "environmental factor" was the spinning top enthusiast blowing against the top I am pretty sure. If you turn up the volume on the video you can hear it. I made a comment to one of his videos on youtube by which I invited him to join our discussions here in the forum, lets see.

Is any of you seeing a clean way to come out of the muddy waters? At the moment the mud is diminishing my motivation to continue to play in this field a bit ... 

[zaggernut]

In the case of that video ta0 linked the "environmental factor" was the spinning top enthusiast blowing against the top I am pretty sure. If you turn up the volume on the video you can hear it. I made a comment to one of his videos on youtube by which I invited him to join our discussions here in the forum, lets see.

In the comments of this video down below, he admits it straight up, so no intent to deceive. Of course, the underlying issue still remains.

Nevertheless, this probably wasn't a big problem for the top in the video, because for the largest part of the time that top "precesses", so that the part of the ball tip in contact with the base was not exactly its flattened area.
The "precession" is an advantage by itself, (it would be so even without a flattened area in the tip), because the tip friction of ball tips is a bit lower while the top walks and the tip rolls, than when the top is steady in sleeping position.
At slow speed, the flattened area in the tip could have helped to reduce the topple speed.
These things together could have favoured the longest spin.     

Did not know precession helps reduce tip friction. On further consideration this makes sense, as less of the tip is in contact with the base on tops which have flat spots, when the top itself is tilted. I see the potential to get the best of both worlds by using a tip with a circular ring as a contact point, and you can even buy sapphire nozzles that would fit this purpose, although the needles for sale in the attached link seem to be way too wide. Probably better to manually dig away at the centre of the flat spot of the top to create the ring contact point, if that is possible to do at such tiny scales.

[Iacopo]

On further consideration this makes sense, as less of the tip is in contact with the base on tops which have flat spots, when the top itself is tilted.

It isn't just the flat spot, the tip friction with ball tips is noticeably lower during the precession in any case, flat spot or no flat spot:

https://www.ta0.com/forum/index.php/topic,5248.msg56154.html#msg56154

[Jeremy McCreary]

I see the potential to get the best of both worlds by using a tip with a circular ring as a contact point....

If I understand correctly, I've been using the reverse of this contact in my LEGO tops and really like it for certain purposes when spin time isn't paramount.

Pretty sure that my "ball-on-ring" contacts generate more braking torque than my conventional "point" contacts. But that's with ABS plastic on ABS. Definitely worth investigating with other materials.

I build mostly for play value and appearance at rest and at speed. Here's one application:



In this compound top, the upper top's ball tip (6.0 mm OD) rests on a ring (4.8 mm ID) at the upper end of the lower top's stem. This ball-on-ring joint (see 7:30) allows the tops to spin at different speeds while pointing in directions up to ~80° apart (see 5:30). Despite these degrees of freedom, the upper and lower tops show a strong tendency to spin down to a "rigid-body mode" marked by identical spin rates and perfectly aligned axes (see 1:10). Quite remarkable.

Another application (see 6:13):



You can also use ball-on-ring contacts to spin up tops from below — e g., with the ring mounted on a vertical motor shaft.

[ortwin]

...I made a comment to one of his videos on youtube by which I invited him to join our discussions here in the forum, lets see.

 ...

Hmm, that comment disappeared. Are there rules that you can not put an address/link in a youtube comment? Anyone her knows?