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Author Topic: Curtain Ring tops + follow ups  (Read 40750 times)

ortwin

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Re: Curtain Ring tops + follow ups
« Reply #90 on: April 12, 2021, 03:37:19 AM »

"Kindergarten Brass Band" 

Just a quick update, because I am so surprised and excited that "Brass Band" was able to beat "Easy Listening" that quick and effortless, even in this Kindergarten version:
On the concave mirror base it spun already on its second timed run for 11:40 . Where Easy Listening was struggling to get to 9:50 .
No holes made into the ring, no screws. Only strings attached. The two 0.3 mm nylon strings hold some arbitrary bead (glass or plastic?) from my daughters jewelry kit more or less in the center. The brass thingy visible in the center, is just clamped there between the lines. Its function is to push the bead down a bit to have sufficient ground clearance. The rigging is similar, but not identical to the wedding band top of reply #20 in this topic.
https://i.ibb.co/gMhfwCt/Curtain-Ring-Top-Nr-7b-2.jpg 
I can't even tell you what my starting RPM was because I did not apply the reflector tape yet.
The bead can easily be pushed around, that is how I tried to align it with the center.  But it is not very stable and satisfying to do the adjustments this way, so there will be more versions to come.
Edit/Update: reflector applied, starting at 500 RPM, toppling after 10 minutes at 84 RPM.




« Last Edit: April 12, 2021, 06:02:13 AM by ortwin »
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In the broader world of tops, nothing's everything!  —  Jeremy McCreary

Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #91 on: April 12, 2021, 01:37:08 PM »

A truly elegant top. And a great performer, too! Brass Band is my favorite by far — even in prototype. Well done!
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ta0

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Re: Curtain Ring tops + follow ups
« Reply #92 on: April 12, 2021, 04:15:25 PM »

I cannot believe that you can keep the lines tense and centered to get it balance enough for close to a 12 minutes spin! No drilling, cutting or gluing! :o
Good work!
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #93 on: April 13, 2021, 03:55:04 AM »

I cannot believe that you can keep the lines tense and centered to get it balance enough for close to a 12 minutes spin! No drilling, cutting or gluing! :o
...

Keeping the lines tense is not so hard, but I can make it sound  complicated:
Knot two ends of line together so that you get a loop with a circumference a bit less than four times the radius of the brass ring.  :-\ ??? :-[
Pull this loop over the diameter of the brass ring. Here you make use of the fact that nylon can stretch. 
Do the same thing with a second piece of nylon line, this time you push it over the diameter of the ring at a 90 degree angle to the first one.
You end up with crossed pretty stiff spokes if you chose the length of the lines correctly.
But this is the point when you realize that you forgot to put the bead at its place where it can serve as tip.
So you start all over again with new nylon string (after you convinced yourself that there is no topological way to get the bead where you want it to be without breaking the loops. This might take a while though, and YOU might even find a way, if so then tell me please!).
So you thread the bead on the two strings, knot them to loops, and so on. 


Balancing I did by pushing the bead to whatever direction the top was leaning to, when sitting on a flat, leveled surface. It is still moving quite easily on those strings, even if they are cross and tensioned - of course too easy for good stability sometimes. Still, I had spin times of over 12 minutes in the meantime.



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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #94 on: April 18, 2021, 10:43:40 PM »

ortwin inspired me to try a LEGO spoked flywheel top with a metal ring for the flywheel. Best attempt so far...



The welded stainless steel ring has a mass of 62 60 g and inside and outside radii of 40 and 46 mm, resp. The LEGO parts in the red 4-spoke ring carrier brought the top's total mass to 75 g. Centering the ring securely was the hard part.

Best spin times with the red carrier were quite disappointing: Only 110 s by hand and 125 s with the 1:16 overdrive starter above. And with the yellow 3-spoke carrier below, they were ~5 s worse! Without the metal ring, these carriers stayed up 2 s at most.



Once I installed the round red spoke weights at far left below, the red version wobbled very little at high speed. But a significant low-speed wobble remained. Balancing the top with the yellow carrier was less successful.



Wow, knew spoke drag could be bad, but not that bad!

Based on ortwin's spin times with Brass Band, expected to get at least 300 s here. Instead, I got 125 s at best. Two lines of evidence point to severe spoke drag as the main culprit:

1. Release speeds were ~600 RPM by hand and ~1,300 RPM with the starter. Yet the starter bumped spin time by only 14%. Only one thing can chew up added release speed like that: Severe air resistance.

2. CM height was ~14 mm in the red carrier and ~22 mm in the yellow. Should have been a big spin-time advantage for red, but the added drag produced by its extra spoke largely offset that advantage.
« Last Edit: April 19, 2021, 09:27:35 PM by Jeremy McCreary »
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #95 on: April 19, 2021, 01:35:30 AM »

Really nice! Looks very like StarWars.
Also your post gives me additional arguments to push my coworker towards the thin nylon spokes - he is favoring metal rods.
« Last Edit: April 19, 2021, 01:51:22 AM by ortwin »
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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #96 on: April 19, 2021, 01:50:02 AM »

Really nice! Looks very like StarWars.

Thanks! Really bummed about the spin time, though. What are the specs on your brass ring?
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #97 on: April 19, 2021, 02:56:13 AM »

...
Thanks! Really bummed about the spin time, though. What are the specs on your brass ring?
I really would have guessed five to six minutes spin time would easily be possible when I first saw your ring.
But as I heard someone say again and again:  "spin time is not everything"! Now who said that again?
You are right, I really forgot to give the details on my brass ring, very sorry about that. Depending on the mood of our kitchen scale it weighs in at 119 g up to 124 g.  Inner diameter ~77 mm, outer diameter ~93 mm. Height ~8 mm. 


Would it not be possible to build it so that the spokes are above, not below the ring? CM would be further down.
You could also try to get rid of most of that stem stuff, 600 RPM can be reached by gripping the metal ring.If none of this can be done, you could still build it like my "Kindergarten Brass band". Maybe you could use your wedding band as tip with a different rigging. With that you wouldn't need a spacer as I did. I did not try my wedding band as tip because it is concave.
« Last Edit: April 19, 2021, 09:06:53 AM by ortwin »
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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #98 on: April 19, 2021, 10:34:47 AM »

But as I heard someone say again and again:  "spin time is not everything"! Now who said that again?

OK, OK, you got me there. Maybe I should have said that I was shocked and horrified that spoke drag is really that bad. Two minutes is a good but not great spin time by LEGO standards.

Thanks for the specs. Your metal ring has WAY more AMI than mine about twice as much AMI as mine.

Would it not be possible to build it so that the spokes are above, not below the ring? CM would be further down.
You could also try to get rid of most of that stem stuff, 600 RPM can be reached by gripping the metal ring.

Yes, all good suggestions and easily done. The stem was at worst a minor offender, but I'll try paring it down.

Seldom mentioned fact: Adding a little TMI by beefing up a stem can reduce residual wobble with little adverse effect on CM height. Hence the beefy stem here.

Funny, Plan A was to use gravity and friction to hold the ring in place. Worked pretty well, too. But sometimes the ring would turn out of alignment with the balancing weights during spin-up.

Hence the little white elastics. Why I failed to go the next step and flip the rotor upside down once gravity was no longer needed is beyond me. ::) (This forum really needs a dope-slap emoji.)

Let's see what happens with these tweaks before abandoning a LEGO ring carrier altogether.
« Last Edit: April 20, 2021, 12:28:29 AM by Jeremy McCreary »
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #99 on: April 19, 2021, 11:28:04 AM »

...

Let's see what happens with these tweaks before abandoning a LEGO ring carrier altogether.
You could use nylon fishing line, and one of those LEGO helmets as tip. Would that still satisfy your LEGO contract?
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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #100 on: April 19, 2021, 01:26:32 PM »

You could use nylon fishing line, and one of those LEGO helmets as tip. Would that still satisfy your LEGO contract?

May well end up there, but I have a few more intermediate steps to try, as my doctrine of selective impurism requires.

This iteration stays up 146 s by hand, a 33% improvement.



To balance the top with this yellow 3-spoke ring carrier, had to resort to using a small metal washer as a balancing weight.  Wobble's now minimal at high speed but still unacceptable at low speed, suggesting significant residual unbalance rather than flexure as the cause. Wobble's a big turn-off for me, so not done yet.



Ground clearance below the ring and elastic are now 4 and 3 mm, resp. CM height ~ 10 mm -- a 29% reduction from last time's lowest.

At my current proficiency with stemless starts, I get the fastest scrape-free release speeds with this small residual 2-torque stem.

The Zen Index, however, is now unacceptably low. With scrape angle down to 4°, generally takes 4+ tries to get a fast scrape-free start with the stem and several more without. Very frustrating when you just want to bask in the gyroscopic zen of it all.

As the great Zen masters remind us,

Scape and wobble, yuck!
Spin time isn't everything
Chant previous line

« Last Edit: April 19, 2021, 02:06:35 PM by Jeremy McCreary »
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #101 on: April 19, 2021, 02:14:05 PM »

... scrape-free start ....
Maybe I did not read these unwritten rules often enough, do they really ask for a "scrape-free start" ?
Am I doing everything wrong?
If there is a bit of scraping for the first two seconds or so, that is not a completely lost run in my book. I just start the stopwatch after the last scrape I hear and stop it again at the first one I notice. The scraping takes away a lot of speed so I try to avoid it but not for "spiritual" reasons.
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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #102 on: April 19, 2021, 05:53:50 PM »

@ortwin: You have a very rational view of scrape during spin-up. Not wrong, just to your own taste.

Over the years, my best spin times have consistently come when scrape is gone. Doubt it's just a LEGO thing, but LEGO construction could make it worse. I attribute this correlation more to reduced release speed than to energy lost to transient wobble, but it could be some of both.

Hence, I've become more than a little scrape-phobic. And using a stem to improve tilt control generally helps me avoid it. However, have to concede that a practiced hand might get faster stemless releases by allowing some scrape beforehand.

Question is, which path is ultimately faster? Which excites less transient wobble? Which delivers the longest spin times? And which the most play value?

Who knows? Let's do some tests.
« Last Edit: April 20, 2021, 12:36:56 AM by Jeremy McCreary »
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Jeremy McCreary

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Re: Curtain Ring tops + follow ups
« Reply #103 on: April 19, 2021, 11:18:57 PM »

This latest ortwin-inspired iteration is squarely in skimpy suspension top territory: Just the stainless ring, some low-mass, low-stretch kite string, and 4 g of LEGO parts (including the white elastics) for a total mass of 64 g.



The 330 s spin time by hand is up 127% from last time (Reply #100). Still nowhere near the 700 s ortwin got with his Brass Band top (Reply #90), but much closer to my hope for a LEGO-enabled top deriving most of its AMI from a low-drag metal ring.



Unchanged since last time: Ground clearances under the ring and elastics, a very tight 4° scrape angle, and a CM height of ~10 mm. Though much thinner than I usually use for high-AMI tops, had to resort to the 3.2 mm stem to maintain CM height. (It's a LEGO thing.)



After 2+ hours and several rounds of rigging and balancing, was ready to give up on getting wobble down to an acceptable level. Then it just happened. No idea how.



Under blacklight, the white kite string fluoresces nicely in blue. The bright RBG markers around the stem were for a variant of the paintbrush balancing method. No help balancing this top, turned out, but I like the way they mix to white at speed.





Conclusions: The HUGE gain in spin time since Reply #100 must be largely aerodynamic, as critical speed and tip resistance changed little.

Intuitively, I think that if the spokes are a few thin needles, their drag will be negligible. Still, the optimal radius of the wheel and it's shape are things that have to be determined.

Lookin' pretty good here, ta0! The data accumulated in this thread clearly shows that a suspension top with a large AMI and very thin lines can make a decent endurance top.

This top's a definitly keeper. The long spin time takes some of the sting out of the annoying scrape angle, and I like the way it looks -- especially under blacklight. But if it were ever to lose its balance, not sure I'd put in the work to get it back.
« Last Edit: April 19, 2021, 11:45:15 PM by Jeremy McCreary »
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ortwin

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Re: Curtain Ring tops + follow ups
« Reply #104 on: April 20, 2021, 02:55:49 AM »

....330 s spin time by hand is up 127% from last time (Reply #100). Still nowhere near the 700 s ortwin got with his Brass Band top (Reply #90), ...
CONGRATS! Very well done! Even better when considering the AMI disadvantage (factor two roughly?) you had to cope with.
The black light pictures are very cool. Did you get to filming "Skimpy String Top" in the same black light session?

In one of the pictures it looks to me as if you had used only one string and one knot. I had thought about that possibility, but found it too hard to balance with that setup. It is of course a lot easier if you can tension/position the different spokes somewhat independently.
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