iTopSpin
Current Posts => Collecting, Modding, Turning and Spin Science => Topic started by: Jeremy McCreary on February 24, 2021, 06:34:58 PM
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Over in Spoke wheel performance (http://www.ta0.com/forum/index.php/topic,6404.msg69288.html#msg69288), I suggested that ortwin dress his metal Spartan finger top in a skin-tight shiny black latex fairing -- strictly to reduce drag, of course. Also suggested he call it "Mistress von Karman".
Well, too slow, buddy. This isn't what I had in mind then, but Mistress von Karman is way too good a top name to go to waste...
(https://i.ibb.co/Y7yc5HC/20210224-102749.jpg) (https://ibb.co/hRZBG36)
(https://i.ibb.co/5nh3GCW/20210224-103048.jpg) (https://ibb.co/8dgwNGD)
(https://i.ibb.co/71FgRWp/20210224-102932.jpg) (https://ibb.co/KrHNLqs)
(You know you're too far gone as a topmaker when you start giving your tops names.) :o
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With those spikes she does look like a femme fatale >:D
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Expensive, too. Before they reappeared in some recent sets, those 48 mm red dish fairings were going for to up to $6 each on BrickLink.
Oh wait, Mistress von Karman is summoning me to the dungeon. Right away, Mistress! (Gotta go.)
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Yesterday YouTube informed me, that the video of my "Curtain-Ring-Top Nr. 4" is no longer age restricted. It was their mistake.
But with a video of the Mistress you would not get away that easy! That is why I am only posting this picture of Mr. Spartan in his highly transparent leisure suit.
And no, I won't answer further questions on the brand of the suit!
(https://i.ibb.co/MhNKNjK/DSC-0038-4.jpg) (https://ibb.co/MhNKNjK)
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Great idea! This is what happens when you put unsupervised tops together in bins in the dark without proper protection...
https://youtu.be/Tnhyqw4nADc
Mr. Spartan's suit looks like a promising fairing. How did it work?
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Mr. Spartan's suit looks like a promising fairing. How did it work?
It could be applied easier then the other balloons I tried, but the results did still not show a clear difference in comparison to a naked Spartan.
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That is why I am only posting this picture of Mr. Spartan in his highly transparent leisure suit.
And no, I won't answer further questions on the brand of the suit!
Well, Spartan and Trojan kind of go well together . . . >:D
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Beginning to get the feeling that removing obstacles to von Karman-like swirling flow isn't the answer. You have to shut down the centrifugal pump the flow entails.
How to do that without an external shroud?
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How about counteracting it with a flow directed in the opposite direction? A blow-top turned the wrong way? I don't have the feeling this would work, still I would check for the difference in spinning a blow top. Or build a Lego top where the flat wide spokes can be twisted slightly to give some fan action. Again the influence of the direction of the twirl could be analyzed.
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How about counteracting it with a flow directed in the opposite direction? A blow-top turned the wrong way? I don't have the feeling this would work, still I would check for the difference in spinning a blow top. Or build a Lego top where the flat wide spokes can be twisted slightly to give some fan action. Again the influence of the direction of the twirl could be analyzed.
The spokes in this large, rare 68 mm Znap wheel are pitched so as to blow downward when spun clockwise. When I finally got hold of one years ago, thought I might use the fan action to reduce tip resistance by deweighting the contact. Never thought about disrupting centrifugal pump action.
(https://i.ibb.co/fkzHThr/20210225-100152.jpg)
No go then, but rechecked just now. The starter here turns in both directions at 3,600 RPM with no top loaded. Chucking this top drops max speed to about 3,100 RPM.
Same 130 s spin time in both directions.
Come to think of it, a blowing fan also consumes energy. But this top would probably spin a lot longer without the tread pattern.
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Beginning to get the feeling that removing obstacles to von Karman-like swirling flow isn't the answer. You have to shut down the centrifugal pump the flow entails.
How to do that without an external shroud?
To make the top without the core like in the curtain ring tops of Ortwin is one way, I would like to make a top in that way one day.
The spokes should be very thin, it is not very easy to make a precision top in this way.
Maybe the spokes could be directed not towards the center of the top but could be set obliquely, to better accommodate the flow of the air, (photo below).
(https://i.imgur.com/GNgFqUs.jpg)
Another way could be to look for surfaces slippery for the air, (to reduce skin friction), but I am not sure if this is possible in our case.
I read that it has been found that the surfaces of feathers, (if memory serves), or the skin of the wings of bats, have less air drag than simple smooth surfaces.
There are aerodynamic fabrics, the textures of which reduce the air drag;
they are used by athletes in sports where reducing the air drag is an advantage, like skiing or cycling.
The problem is that, as far as I know, (which is very little), some speed is necessary for these fabrics to work properly, and probably spinning tops spin too slowly. These things can be tested, in any case.
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No go then, but rechecked just now. The starter here turns in both directions at 3,600 RPM with no top loaded. Chucking this top drops max speed to about 3,100 RPM.
Same 130 s spin time in both directions.
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If the ground clearance is large, more then 3mm, that is to be expected, everything quite symmetric. As you and Iacopo found out by experiment, the ground effect needs small spacings. If you could redo the experiment with that in mind it would be great.
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To make the top without the core like in the curtain ring tops of Ortwin is one way, I would like to make a top in that way one day.
The spokes should be very thin, it is not very easy to make a precision top in this way.
No! It is very easy to make spokes 1/10 of a mm or less in diameter that are strong enough for what we need. I try to make my point clear when I present the curtain ring top Nr. 6 .
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Another way could be to look for surfaces slippery for the air, (to reduce skin friction), but I am not sure if this is possible in our case.
I read that it has been found that the surfaces of feathers, (if memory serves), or the skin of the wings of bats, have less air drag than simple smooth surfaces.
There are aerodynamic fabrics, the textures of which reduce the air drag;
they are used by athletes in sports where reducing the air drag is an advantage, like skiing or cycling.
The problem is that, as far as I know, (which is very little), some speed is necessary for these fabrics to work properly, and probably spinning tops spin too slowly. These things can be tested, in any case.
The golf ball dimples and shark skin effect come to mind. Those things have been discussed a few years ago in this forum I found out by a search a few days ago. The last word of ta0 on this was, that those things are only for linear motion, not for the circular motion that is in question here. Is that correct ta0??
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Come to think of it, a blowing fan also consumes energy. But this top would probably spin a lot longer without the tread pattern.
Yes, a fan like rotor is surely to extreme. For a top I was envisioning something more subtle, similar to the ridges on the surface of this billetspin top.I wonder if with this a direction effect would be visible.
(https://i.ibb.co/rytyPJx/Billetspin-Triskelion.jpg) (https://ibb.co/rytyPJx)
This other cheap top here I just ordered, I will keep you informed on its direction sensitivity once it arrives in about four weeks or so.
(https://i.ibb.co/ncbXL8R/mezmocoin-is-an-mesmerizing-spinning-top-that-spins-for-over-12-minutes-thumb.gif) (https://ibb.co/ncbXL8R)
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It's very dangerous to take aerodynamic strategies developed for bodies translating through the air and apply them to a top spinning in place without translation.
For one thing, a top with a smooth outer surface of revolution presents no leading edge to the surrounding air. Nor is there a trailing edge.
That geometry totally changes the induced air flow and largely eliminates the possibility of a boundary layer separation capable of generating pressure drag -- the very thing that many of said strategies were designed to address. At least not a pressure drag directly resisting spin rate.
Also, there may be no such thing as a drag crisis in a top. The dimples on a golf ball are to there to precipitate the drag crisis so as to match it to typical ball flight speeds. That works in part because the ball presents a fairly blunt leading edge to the oncoming air.
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It's very dangerous to take aerodynamic strategies developed for bodies translating through the air and apply them to a top spinning in place without translation.
I would not call it "dangerous". There is not much lost in giving it a thought or try ! It might not work, or it might have a negative effect or it might indeed work for a completely different reason but we will not endanger anybody or lose big money. We invest our spare time and it can be frustrating when we do not reach our goals, but we can enjoy our experiments and discussions anyhow.
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Sorry, no offense meant. We've been struggling with top aerodynamics for a long time.
So let me put it another way: To make progress toward that goal, better to test the hypothesis that an aerodynamic theory or strategy developed for a body translating through the air also works for a top spinning in place than to assume it.
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better to test the hypothesis that an aerodynamic theory or strategy developed for a body translating through the air also works for a top spinning in place than to assume it.
Did I affirm something different, Jeremy...?
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No offense taken at all Jeremy! You don't have to be sorry.
I guess I misunderstood your remark somewhat purposefully so I could make my point: "Let us allow our-self to think in all directions."And the way you put it in your last post is of course perfect. As non native English speaker I can understand it, but I could not come up with with a sentence like that. ;D
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No go then, but rechecked just now. The starter here turns in both directions at 3,600 RPM with no top loaded. Chucking this top drops max speed to about 3,100 RPM.
Same 130 s spin time in both directions.
.
If the ground clearance is large, more then 3mm, that is to be expected, everything quite symmetric. As you and Iacopo found out by experiment, the ground effect needs small spacings. If you could redo the experiment with that in mind it would be great.
Another thing to vary, is not the spacing to the base, but to cover the bottom end of the fan-top with a fairing. Again a check on spin-down rate with different spin direction could be done.
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Did I affirm something different, Jeremy...?
Sorry, not at all. Just got worried that we might be heading for some traps we've fallen into before.
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Mistress von Karman says I'll have to be punished for overreacting. Yes, on my way to the dungeon now, Mistress. Oh no, Mistress! Not more spin time trials! :-* :o
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At ortwin's request in another thread (http://www.ta0.com/forum/index.php/topic,6421.0/topicseen.html)...
"We proudly present: Mistress von Karmann and the fabulous Poledancers!"
(https://i.ibb.co/tqx4FDh/20210310-122250.jpg)
Here, the Poledancers are doing the supine kickline routine with Mistress von Karman dominating them at the center, as her contact of course demands.
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Great! And thank you.How many helping hands would you need, and how many microwave platters to get them dancing all at once for a video?
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Great! And thank you.How many helping hands would you need, and how many microwave platters to get them dancing all at once for a video?
About as many of each as there are tops. With their max release speeds of 7,000 RPM or more, the Poledancers can get quite energetic. And at large tilt angles, they cut a wide swath at high precesdion rates.
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About as many of each as there are tops. With their max release speeds of 7,000 RPM or more, the Poledancers can get quite energetic. And at large tilt angles, they cut a wide swath at high precesdion rates. "
So even that glass table below the microwave platter doesn't really take you anywhere. Maybe you can get a part of that VLT once they put it out of order.
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Over in Spoke wheel performance (http://www.ta0.com/forum/index.php/topic,6404.msg69288.html#msg69288), I suggested that ortwin dress his metal Spartan finger top in a skin-tight shiny black latex fairing -- strictly to reduce drag, of course. Also suggested he call it "Mistress von Karman".
Well, too slow, buddy. This isn't what I had in mind then, but Mistress von Karman is way too good a top name to go to waste...
(https://i.ibb.co/Y7yc5HC/20210224-102749.jpg)
(You know you're too far gone as a topmaker when you start giving your tops names.) :o
Wow that top looks deadly! Love it nice build!
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Wow that top looks deadly! Love it nice build!
Mistress von Karman and I both say thanks, Joah!
Now that I look at Mistress von Karman again, wondering if there's a secure way to put in another layer of spikes upside down to give the spikes smooth surfaces above and below? Off to the workbench...
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Wow that top looks deadly! Love it nice build!
Mistress von Karman and I both say thanks, Joah!
Now that I look at Mistress von Karman again, wondering if there's a secure way to put in another layer of spikes upside down to give the spikes smooth surfaces above and below? Off to the workbench...
Best of luck! That would be cool to see. Are the spikes secure enough to use in battle?
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Wow that top looks deadly! Love it nice build!
Mistress von Karman and I both say thanks, Joah!
Now that I look at Mistress von Karman again, wondering if there's a secure way to put in another layer of spikes upside down to give the spikes smooth surfaces above and below? Off to the workbench...
Best of luck! That would be cool to see. Are the spikes secure enough to use in battle?
None of the spikes are going to come out in battle. The singles might get knocked out of radial alignment, but the doubles are locked down.
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Coincidence? I think not!
(https://i.ibb.co/ncWK1xT/20210416-123243.jpg)
Just junk mail, but Big Data's watching you, too.
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This is too much of a coincidence! :o
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This is too much of a coincidence! :o
I checked on a map on the internet, there is no "Kreisel" on von Karman Avenue.
(KREISEL is the German word for spinning top but the word is also very often used for a "roundabout".)
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See how wrong they got title here:
https://www.snotr.com/video/2364/The_invention_of_the_wheel
It actually is "Giant Top 0.1", and a precursor of Jeremy's pole dancers!
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They got so close to a top! But the invention of the wheel really went down like this...
https://youtu.be/5K1MGXhUxLg