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Expanding ring tops
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The scissors linkages making up the rings on these centrifugal tops expand during spin-up and contract under rubber band tension during spin-down.
About this creation
Please feel free to look over the images and skip the verbiage.

This page features 2 expanding ring tops (ERTs). Both are "centrifugal tops" in that they bear mechanisms driven outward by centrifugal force and reeled back in by elastic elements. They also qualify as studless tops.



The original video above shows both tops in action. It's the only look you'll get at "Flower Head", the red and yellow one.

The later photos below show "Iris", the black and white ERT, in its brief MOCpages debut with new black rubber bands and a much smaller orange and black centrifugal top of a completely different design.







These are the only ERT photos I have, but the hi-def video shows both tops in plenty of detail. They differ mainly in hub design and the arrangement of the rubber bands used to counter centrifugal force and reel the rings back in.

On this page...


Performance

Larger Iris has a mass of 110 g and a ring that expands from 160 to 224 mm in outside diameter with speed. Smaller Flower Head has a mass of 102 g and an outer ring diameter ranging from 142 to 180 mm.

Twirling these tops by hand takes a good bit of muscle and skill. Of the two, Iris takes more muscle by virtue of its greater axial moment of inertia (details here). Flower Head, on the other hand, takes more skill by virtue of having less ground clearance beneath its rotor.

My best spin times by hand are on the order of 10-12 sec for both. They can also be safely spun up to ~600 RPM with a motorized tool or wind-up spinner like the one shown here. However, the resulting spin times aren't much better due to speed-dependent losses related to the non-rigid rotors and lousy aerodynamics. In this respect only, they resemble my Klingon tops.



Details

The folding circular linkages making up the rings expand under centrifugal force during spin-up and contract under rubber band tension during spin-down. These bent scissors linkages are the planar equivalents of the linkage found in Hoberman spheres.

Most of the wobbling comes from dynamic imbalance due to uneven expansion and contraction of the rings. The root cause is uneven rubber band tension. Iris' rubber band arrangement makes it easier to even out the tension some, but I have yet to eliminate it completely. Additional wobbling comes from fluttering of the rings and whirling of the hub and tip assemblies.

Between the original video above and the later photos, I replaced Iris' original standard-issue tan office rubber bands with more uniform but stiffer black LEGOŽ rubber bands. The new bands seem to help the wobbling at least some of the time, but as seen at 1:48 in the current studless top video below, the ring opens less now all the time. I think I like the original Iris better.



Flower Head's stuck with its office rubber band, because LEGOŽ rubber bands are all too stiff for its return mechanism.




Specifications

Type:Expanding ring centrifugal tops
Construction:Studless
Masses:Iris 110, Flower Head 102 g
Outside ring diameters:Iris 160-224, Flower Head 142-180 mm
Rubber bands:4 on Iris, 1 on Flower Head
Spin times:10-12 sec by hand
Modified LEGOŽ parts:None
Non-LEGOŽ parts:Rubber bands (except on current Iris)
Credits:Original MOCs





Comments

 I made it 
  November 27, 2015
Quoting Clayton Marchetti You come up with the coolest ideas for tops. Awesome!
Thanks, Clayton! The nice thing about LEGO tops is that you're not bound by others' ideas of what a top should be.
 I like it 
  November 27, 2015
You come up with the coolest ideas for tops. Awesome!
Jeremy McCreary
 I like it 
Matt Bace
  November 18, 2015
Wow! These are some of the most creative kinematic LEGO creations I've ever seen. They seem to be simple and complex at the same time.
 I made it 
  November 18, 2015
Quoting Matt Bace Wow! These are some of the most creative kinematic LEGO creations I've ever seen. They seem to be simple and complex at the same time.
Thanks for those very generous words, Matt. Can't claim all the credit, though. Once saw a Hoberman sphere opened up just by spinning it (though not as a top) and just translated that into the MOCs here.
 I made it 
  November 16, 2015
Quoting Nils O. Wow, that's really inspiring. My little son loves spinning tops. I think we'll build one or another during the winter holidays... Great job! :-))
Thanks, Nils. I know you'll come up with some good ones. Hope you'll post them.
 I like it 
  November 16, 2015
Wow, that's really inspiring. My little son loves spinning tops. I think we'll build one or another during the winter holidays... Great job! :-))
 I made it 
  November 15, 2015
Quoting Oliver Becker Well, Jeremy! These gyroskopes are adorable, specially the dynamic ones with rubber bands are fascinating! I can see your great experience with technic- bricks and your professional (?) way to use them, or is this just a hobby? I also love to "go round" with my bricks, technic ones I use more and more, but mostly combining them with the "normal" LEGO... My father and brother are engeneers, myself is a "medicine man" in the country, but it's in the blood... LOL Greets!
Too kind, Oliver! Just a hobby. I'm a retired MD and geologist who uses LEGO to (among other things) feed a life-long passion for science and engineering of all kinds. Of course, we both know that medicine and engineering overlap more than most people think.
 I like it 
  November 15, 2015
Well, Jeremy! These gyroskopes are adorable, specially the dynamic ones with rubber bands are fascinating! I can see your great experience with technic- bricks and your professional (?) way to use them, or is this just a hobby? I also love to "go round" with my bricks, technic ones I use more and more, but mostly combining them with the "normal" LEGO... My father and brother are engeneers, myself is a "medicine man" in the country, but it's in the blood... LOL Greets!
 I made it 
  November 15, 2015
Quoting Didier B Your wife is right Jeremy... You are fully obsessionist !! The visual effect of these expanding tops is excellent. The black and white is my favorite. Didier
Thanks, Didier! That's my favorite, too, but I'm a sucker for black and white with splashes of color.
 I like it 
  November 15, 2015
Your wife is right Jeremy... You are fully obsessionist !! The visual effect of these expanding tops is excellent. The black and white is my favorite. Didier
 I made it 
  November 14, 2015
Quoting Topsy Creatori Most interesting top behavior! I used to do the Bungee Barbie Lab with my students and getting rubber bands with the correct elasticity was always a challenge. :)
Thanks, Topsy! Yes, rubber seems to be part chaos. Visions of possible Bungee Barbie labs are dancing through my head, but some of them can't be right. One thing's for sure, though: Your classes must be a lot of fun!
 I like it 
  November 14, 2015
Most interesting top behavior! I used to do the Bungee Barbie Lab with my students and getting rubber bands with the correct elasticity was always a challenge. :)
 I made it 
  November 13, 2015
Quoting The Royal Brick Beautiful tops, Jeremy! I love the kinetic sculpture nature of these two!
Hey, thanks, Royal! I think tops are very much a form of kinetic art. Glad you think so, too.
 I like it 
  November 13, 2015
Beautiful tops, Jeremy! I love the kinetic sculpture nature of these two!
 I made it 
  November 13, 2015
Quoting Scotty Jones wow..... all that is needed to be said
Many thanks, Scotty!
 I like it 
  November 13, 2015
wow..... all that is needed to be said
 I made it 
  November 13, 2015
Quoting Henrik Jensen A pair of brilliant expanding tops! They look really beautiful and amazing. You really are obsessed with a spinning top craze :-)
Thanks, Henrik! I think "obsessed" is putting it mildly. There are 4 more top posts in the pipeline and more to follow.
 I like it 
  November 13, 2015
A pair of brilliant expanding tops! They look really beautiful and amazing. You really are obsessed with a spinning top craze :-)
 I made it 
  November 13, 2015
Quoting David Roberts I love how the circles on the flower expand and contract with the speed of rotation. I've understood the physics behind it for over 25 years but it's still quite magical! There are also some superb (disturbing!) stroboscopic effects on your second film, especially with the black & yellow at 7 minutes in. Brilliant stuff once more!
Too kind, David. The original markings on black and yellow "Tube Top" were just alternating vertical stripes. A building buddy took one look at it and said, "It needs to be spiral." Boy, am I glad he did. Couldn't agree more: A big reason for my obsession with tops is their way of turning seemingly mundane mechanics into wondrous things to behold. Knowing what's going on under the hood only makes it better.
 I made it 
  November 13, 2015
Quoting Gabor Pauler I immediately started to think about how it could be used in a foldable helicopter rotor. This is one of my psychologic symptoms, and you triggered that...
Please let me know if you find a medication that helps, Gabor. It might help me with tops and boats and flying rotors and tops and boats and flying rotors and tops and boats and flying rotors.... Oh my!
 I like it 
  November 13, 2015
I immediately started to think about how it could be used in a foldable helicopter rotor. This is one of my psychologic symptoms, and you triggered that...
 I like it 
  November 13, 2015
I love how the circles on the flower expand and contract with the speed of rotation. I've understood the physics behind it for over 25 years but it's still quite magical! There are also some superb (disturbing!) stroboscopic effects on your second film, especially with the black & yellow at 7 minutes in. Brilliant stuff once more!
 I made it 
  November 13, 2015
Quoting Walter Lee totally awesome :-)
Thanks, Walter!
 I like it 
  November 13, 2015
totally awesome :-)
 
By Jeremy McCreary
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LEGO models my own creation MOCpages toys shop Expanding ring topsTechnic


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