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Balloon tops
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What better use for those long curving panels for hot air balloons than in a LEGO spinning top?
About this creation
Please feel free to look over the images and skip the verbiage.

Few LEGO parts are as graceful or elegant as the long, curving "balloon panel", so called (by me at least) because it was originally used to make hot air balloons.

Here I put balloon panels to even better use in some simple LEGOŽ spinning tops.



The balloon panel made its 2015 debut in the Heartlake Hot Air Balloon set (41097). BrickLink lists it as Panel 4 x 4 x 13 Curved Tapered with Clip at Each End (18969).

I knew I'd be turning these beautiful panels into tops the moment I saw its attachments in person, but they were just too expensive at the time. The 4 "balloon tops" presented here came out of a batch of 25 recently snagged at a good price.







These 4-panel balloon tops qualify as "finger tops" in that they're easy to spin up by hand. Very smooth spins can be had with a little practice and a bit of tweaking (see below).





Unfavorable aerodynamics limit spin times to ~24 sec in the top on the right and ~15 sec in the other with the panels flipped upside down. The difference is due mainly to the latter's much higher center of mass (CM). Differences in the stem, hub, and tip assemblies are minor.

The designs I tend to admire most are simple, elegant, and functional at the same time. These 4-panel balloon tops are about as close as I've come to that ideal in any MOC.



I've been unable to spin up the 8-panel tops by hand, even with practice, but they still have a lot of play value when used with a spin-up tool like the 2-stage planetary spinner in the background.



The top with all-black trim loves to sleep, whereas the red-trimmed version strongly prefers steady precession. This too is largely a reflection of CM height. Both tops spin smoothly.



The aerodynamics here are much cleaner than in the 4-panel case. The top with the all-black trim spins up to 58 sec, while the inverted version with red trim stays up only ~25 sec due to its much higher CM.



This is about as close as you'll ever come to the shape of a typical throwing top (aka "peg top") in the LEGOŽ realm, but I don't recommend throwing it.



All 4 tops in action, from the shortest-spinning to the longest...



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Update: Intersecting balloon tops

After posting this page, I made two more 8-panel tops with the panels pointing both narrow-end-up and narrow-end-down, like so...



These "eggbeater tops" now have their own MOCpage.

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Optional: Design notes

The original 8-panel tops were basically just stock hot air balloons rigged with nearly identical stem, hub, and tip assemblies.



The fact that I couldn't spin them fast enough by hand to keep them up gave me pause. Each balloon panel here attaches to its upper and lower hub (modified 2x2 plate with octagonal bar frame, 30033) with nothing more than a clip at each end. Would these clips really hold at the high speeds (over 2,000 RPM!) attainable with many of my spin-up tools?

Thankfully, the clips have held thus far, but a warning I've given before bears repeating:

Warning! Always wear eye protection when working or playing with high-speed LEGOŽ rotating machinery and keep valuables and bystanders (including pets) a safe distance away -- especially when testing new designs. Really.



The spoked 4-panel tops were much bigger challenges from both structural and performance perspectives. To cantilever each balloon panel from the hub successfully, I'd have to take full advantage of the single clip and single hollow stud at its narrow end.



At the very least, the hub-panel joins would have to withstand the centrifugal stresses generated at speeds attainable by hand (~500 RPM). They'd also have to minimize flapping of the spokes, lest the flapping excite wobbling of the top as a whole.1

The hub solution turned out to be simpler and stronger than I'd imagined.





The key ingredients...



One modified 2x2 plate with octagonal bar frame (30033)...



Four 1x1 round plates with open studs (85861)...



And two 1x5 Technic plates with central axle holes and smooth round ends (32124).

Eliminating all flapping of the spokes would be impossible, as any buttressing of the spokes themselves would only take the aerodynamics from bad to much worse. So instead I weakened the coupling between flapping and wobbling by shifting the spokes' natural flapping frequency away from the top's natural wobbling frequency.



Toward that end, I clipped identical weights to the ends of the spokes, and it worked: The optimal weights (1x2 plates with bars, found by trial and error) took the wobbling from pronounced to minor, and the small residual wobble could be removed by angling the weights relative to one another.

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Specifications
(Presented in "4-panel / 8-panel" format)

Overall dimensions:220x100 / 80x150 mm (DxH) including stems
Masses:36 / 55 g
Spin-up method:Hand or tool / Tool only
Typical spin times:15-24 / 25-55 sec
Typical release speeds:500 / 2,200 RPM
Modified LEGOŽ parts:Tips cut from 4L antennas
Non-LEGOŽ parts:None
Credits:Original MOCs
See also:Intersecting balloon tops

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Footnotes

1 Rhythmic flexure of key structures is the most common cause of pronounced wobbling in LEGOŽ spinning tops, as mass unbalance is rarely an issue once the parts are fully seated in a symmetrical arrangement. This kind of wobbling, a form of whirling in the engineering sense, is distinct from simple gyroscopic nutation, though the two motions can coexist and interact.

The compound curvatures of the balloon panel make it stiffer than its thickness/length ratio might suggest, but it's still flexible enough to bend up and down a bit in a flapping motion when cantilevered from the narrow end.



The abrupt angular acceleration imparted to the top during spin-up tends to excite this flapping. If the natural frequencies of flapping and wobbling are too close together, the two motions will resonate, and the flapping will drive wobbling of the top as a whole to large amplitudes.

The wobbling in turn can feed energy back into the flapping. The strain energy dissipated in this feedback loop comes straight out of the kinetic energy associated with the top's spin, thus reducing spin time.

Moving these natural frequencies apart can reduce the energy exchange between flapping and wobbling dramatically, and the spin will smooth out accordingly. In the 4-panel tops presented here, I simply lowered the natural flapping frequency by weighting the ends of the balloon panels serving as spokes. Shifting the top's center of mass (CM) downward along the spin axis might have helped as well, but ground clearance limitations precluded that approach.

Flexing hub and tip assemblies and damaged tips are also common sources of wobbling in LEGOŽ tops -- especially in heavy tops with large moments of inertia. Hence, I stiffened the hub and tip assemblies as much as I could without raising the CM or compromising ground clearance.

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Comments

 I made it 
  December 7, 2016
Quoting Nirds forprez So.... I am using an adaptation to my username.....hopefully I wont be flagged for review and my comments will be viewed much quicker. Great build here Jeremy. A unique 'twist' to your now-famous tops!
Ah, your subterfuge may be working -- no delay on my first reply! Wait till I tell my wife I'm famous!
 I made it 
  December 7, 2016
Quoting Nirds forprez So.... I am using an adaptation to my username.....hopefully I wont be flagged for review and my comments will be viewed much quicker. Great build here Jeremy. A unique 'twist' to your now-famous tops!
Thanks, NFP! Check back, and I'll let you know if this reply gets delayed.
 I made it 
  December 7, 2016
Quoting Didier B I like that one !
Thanks, Didier!
 I like it 
  December 7, 2016
I like that one !
 I like it 
  December 6, 2016
So.... I am using an adaptation to my username.....hopefully I wont be flagged for review and my comments will be viewed much quicker. Great build here Jeremy. A unique 'twist' to your now-famous tops!
 I made it 
  December 4, 2016
Quoting jds 7777 Hopefully I'll have some time over winter break. Right now I'm on the search for a tiny lithium-ion battery that can power Lego models with the same amount of power, but with a super-small size and weight.
If you find one, I want to hear about it!
 I like it 
  December 4, 2016
Hopefully I'll have some time over winter break. Right now I'm on the search for a tiny lithium-ion battery that can power Lego models with the same amount of power, but with a super-small size and weight.
 I made it 
  December 4, 2016
Quoting D H Your science-ing of these tops never ceases to amaze!
Thanks, DH! Make enough tops, and it becomes a necessity. Early on, I had the exasperating experience of making tops that wobbled like crazy even though I =knew= them to be perfectly balanced with no dings in the tips. Only then did I tumble to the unholy alliance between flexure and wobbling. Turns out to be a common problem in the world of rotating machinery. Better yet, the real-world solutions also work in the LEGO realm.
 I like it 
  December 4, 2016
Your science-ing of these tops never ceases to amaze!
 I made it 
  December 4, 2016
Quoting jds 7777 I love the amount of thought and engineering that goes into your builds! This is about the closest attention to detail I've ever seen anyone put into something as seemingly simple as a top. As you projects show, they are not nearly as simple as they seem! Very interesting read - nice to get my mind of something other than school work and get the engineering side of my brain going again! Makes me wish I still had time for Legos. :) Thanks for posting!
Very gratifying, JDS! I seem to revel in things that turn out to be a lot more complicated than they look, and LEGO is a good playground for that. May you get some brick time soon -- perhaps over winter break?
 I made it 
  December 4, 2016
Quoting gene 3S Amazing experiment with your creations!
Thank you, gene!
 I like it 
  December 4, 2016
I love the amount of thought and engineering that goes into your builds! This is about the closest attention to detail I've ever seen anyone put into something as seemingly simple as a top. As you projects show, they are not nearly as simple as they seem! Very interesting read - nice to get my mind of something other than school work and get the engineering side of my brain going again! Makes me wish I still had time for Legos. :) Thanks for posting!
 I like it 
  December 4, 2016
Amazing experiment with your creations!
 I made it 
  December 4, 2016
Quoting adam thelegofan rutland interesting concept!:D
Thanks, Adam!
 I made it 
  December 4, 2016
Quoting Magma ! I always see those balloon panels being used very creatively on people's MOCs. This is no exception. Also, I see you're having loads of fun with physics behind spinning tops. Respect!
Thanks, Magma! Yes, combining physics and visual design is one of my favorite things, and tops turn out to be an excellent vehicle for that. You can pack a surprising amount of fun engineering into your LEGO if you're so inclined.
 I like it 
  December 4, 2016
interesting concept!:D
 I like it 
  December 4, 2016
I always see those balloon panels being used very creatively on people's MOCs. This is no exception. Also, I see you're having loads of fun with physics behind spinning tops. Respect!
 I made it 
  December 4, 2016
Quoting VAkkron ™ Definitely a good read this morning. You went through quite a process to get to the final product, but that's how the best models are made! I like it a lot, and as people are saying I too want to check out those pieces. Great work, it looks fantastic!
Many thanks, VAkkron! Glad you enjoyed the verbiage. Overcomplicating simple things is one of my centers of excellence, along with losing hats.
 I like it 
  December 4, 2016
Definitely a good read this morning. You went through quite a process to get to the final product, but that's how the best models are made! I like it a lot, and as people are saying I too want to check out those pieces. Great work, it looks fantastic!
 I like it 
  December 4, 2016
Thank you very much Jeremy, that's a big compliment my friend ;) And for that you get a well deserved extra like :)
 I made it 
  December 4, 2016
Quoting Oliver Becker Like these pieces and especially love your use of them, Jeremy! Your tops turn on their charm on many people here, and that's so well deserved! ;)
Kind words, my friend -- especially coming from the master of parts usage.
 I made it 
  December 4, 2016
Quoting Sven ;o) Again some very creative and very good lookin stuff from you. Really like those balloon parts. I think I'll try some flowers with using this parts. But first I have to get the parts XD Keep on brickin my friend ;)
Very kind, Sven! BrickLink prices for balloon panels are starting to come down, and there are several good colors now besides the original white -- including red. If anyone could work them into a firetruck, it would be you! ;^}
 I made it 
  December 4, 2016
Quoting Gabor Pauler The only other good use of these balloon panels could be forming giant flower in "Birth of Venus"-vignette from the Italian MOCer Tiziano
Very good, Gabor. I'll see that and raise you one: Birth of Trump by alt.right MOCer Steven Banning.
 I like it 
  December 4, 2016
Like these pieces and especially love your use of them, Jeremy! Your tops turn on their charm on many people here, and that's so well deserved! ;)
 I like it 
  December 4, 2016
Again some very creative and very good lookin stuff from you. Really like those balloon parts. I think I'll try some flowers with using this parts. But first I have to get the parts XD Keep on brickin my friend ;)
 I like it 
  December 4, 2016
The only other good use of these balloon panels could be forming giant flower in "Birth of Venus"-vignette from the Italian MOCer Tiziano
 I made it 
  December 4, 2016
Quoting Firas Abu-Jaber Really good! It's always satisfying to see your work in action. Keep it up.
Very kind, Firas!
 I like it 
  December 4, 2016
Really good! It's always satisfying to see your work in action. Keep it up.
 I made it 
  December 4, 2016
Quoting Nick Barrett I really must get some of these, such an elegant piece. And now I know how to make an optimally performing spinning top with them.
Thanks, Nick! I'd love to see what you come up with.
 I like it 
  December 4, 2016
I really must get some of these, such an elegant piece. And now I know how to make an optimally performing spinning top with them.
 
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