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Improved fidget spinner and top
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This one nearly doubles previous best spin times, is much easier to use, and functions well as a spinning top.
About this creation
Please feel free to look over the images and skip the verbiage.

Thought I'd get in one more LEGOŽ fidget spinner while the craze lasts.



In my book, the best thing about this new one is that it doubles as a top that spins up to 9 sec!

But the improvements don't end there. Compared to the rather crude color-mixing fidget spinners posted last week, this one spins a lot longer (14 sec vs. 5-8 sec) and is much easier to use.










Design changes

My 1st batch of spinners (the color-mixing fidget spinners) weren't all that ergonomic.

For one thing, the ball grips on their stators were just too slippery -- both to the fingers and to most of the surfaces one might try to stand the stator on during use as a top.



For another, limited hand clearance in the wider 2-spoke spinners (example above) made it hard to get good, clean spins.

This narrower 3-spoke spinner served as the starting point for the current design -- partly because of the added hand clearance, but mostly because tops rarely get by with less than 3-fold rotational symmetry about the spin axis.



The current spinner's greatly improved spin time reflects a much more favorable combination of rotor axial moment of inertia (AMI) and rotor aerodynamics.



Rotor AMI increased a good bit since the earlier 3-spoke, and you can feel it in use. Most of the credit here goes to the higher "specific AMI" (AMI per unit mass) obtained by adding rotor material only in the outermost 8 mm of radius. The gain in total spinner mass (from ~16 to 16.8 g) helped, too, but not as much.

The aerodynamics, on the other hand, may have a taken a step backwards. If so, interference drag added by the new spoke tip geometry is the most likely culprit.



A few words about specific AMI -- arguably the most important measure of pure mass distribution in a top or spinner rotor, at least from a mechanical point of view.

Mathematically, specific AMI is a measure of mass distribution equal to the square of the radius of gyration. The latter is the distribution's second mass moment in the radial direction. The mean/max ratio I suggested is the first radial mass moment as a percentage of outermost radius.

Here in the LEGOŽ realm, however, specific AMI is hard to measure, hard to estimate, and even hard to visualize. A mental measure that may be more accessible is the eye-balled ratio (average radius of the mass present) / (maximum radius). No need to get a number here, of course. Just look at the rotor and imagine where that average radius might lie.

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Specifications

Version:3
Mass:16.8 g
Rotor spokes:3
Overall dimensions:72x51 mm (DxH)
Rotor axial length:16 mm at tips
Stator axle length:5L (40 mm)
Best spin time as spinner:14 sec
Best spin time as top:9 sec
Modified LEGOŽ parts:Tips cut from 4L antennas
Non-LEGOŽ parts:None
Credits:Original MOC
See also:Color-mixing fidget spinners

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Comments

 I made it 
  May 25, 2017
Quoting Sam Sanister Just thought of a question: Have you worn down antenna ends until they've noticeably affected spin characteristics?
Thanks, Sam! All these tips show abrasion after just a few uses, but I don't recall replacing one just for wear, and I'm pretty picky about smooth spins. But I have replaced tips that got dented in falls. Dents can definitely trigger wobble. The black ones seem to hold up best.
 I like it 
  May 24, 2017
Just thought of a question: Have you worn down antenna ends until they've noticeably affected spin characteristics?
 I like it 
  May 16, 2017
Makes me happy, my friend!!! Go on with your great MOCs here, life's to short to miss one... ;)
 I made it 
  May 16, 2017
Quoting Oliver Becker I'd posted the pics via e-mail to the told adress, my friend! Successful? ;)
Yes, success! Sent private email reply as well. Thanks again, Oliver! My new Oliver Becker buddy icon should be up by tomorrow.
 I like it 
  May 16, 2017
I'd posted the pics via e-mail to the told adress, my friend! Successful? ;)
 I made it 
  May 15, 2017
Quoting Oliver Becker I won't tell you what "spinner" means in German, my friend! LOL Yup, another great high- speed top, and: yup, "your" pics are in post production... ;)
But now I have to know! Oh well, I'll ask my German-speaking kid. Thanks and thanks, looking forward to the pix.
 I like it 
  May 15, 2017
I won't tell you what "spinner" means in German, my friend! LOL Yup, another great high- speed top, and: yup, "your" pics are in post production... ;)
 I made it 
  May 14, 2017
Quoting Nick Barrett I wonder how performance differs as you go bigger or is this the optimum size of this design ?
For this particular design, might have been able to thicken the rotor by 1-2 LU and widen its diameter by 2 LU without running into serious hand-clearance issues. The goal here would be to add axial moment of inertia (AMI, about the spin axis) in a way that leaves adequate clearance without backfiring on aerodynamics. That's because maximizing spin time comes down to a delicate trade-off between AMI and drag. Playing this trade-off well is complicated by the narrow range of low mass densities generally available in LEGO realm. (Steel is 7-8 times denser than solid ABS, but don't forget all those air spaces in your MOCs!) Increasing AMI then means increasing bulk -- especially towards the ends of the spokes. But that cuts into hand clearance and increases drag. Where the sweet spot really lies here can only be determined by guided trial-and-error testing. I'll be sharing what I've been able to learn about this core trade-off in my next fidget spinner MOCpage, coming soon.
 I like it 
  May 14, 2017
I wonder how performance differs as you go bigger or is this the optimum size of this design ?
 I made it 
  May 12, 2017
Quoting Henrik Jensen That`s really cool, got to show this to my future son-in-law, he always have a fidget spinner in his hands, and I know he has some Lego-Technic!
Thanks, Henrik! Uh-oh, better warn him: If he's like me, he'll end up wasting more time making the darned things than he ever did spinning them.
 I like it 
  May 12, 2017
That`s really cool, got to show this to my future son-in-law, he always have a fidget spinner in his hands, and I know he has some Lego-Technic!
 I made it 
  May 11, 2017
Quoting TMNS 5097 Great job! I am fascinated at how it works. It hold a spin for a surprisingly long time! Fidget spinners are all the rage at my boy scout troop, I've never used one before but this looks and works great! :D
Thanks! Think of how impressed your fellow scouts will be when you stroll in with a spinner (not necessarily this one) you made yourself from the LEGO you had laying around.
 I like it 
  May 11, 2017
Great job! I am fascinated at how it works. It hold a spin for a surprisingly long time! Fidget spinners are all the rage at my boy scout troop, I've never used one before but this looks and works great! :D
 I made it 
  May 11, 2017
Quoting Sir Flexalot MUST. MAKE. FIDGET SPINNER. :P excellent design!
Thank you, Sir! Sounds like you're already addicted. I fear that the world supply of ball bearings is about to disappear into fancy metal fidget spinners. And since modern civilization runs on ball bearings ... well, it's too scary to think about. ;^}
 I made it 
  May 11, 2017
Quoting Daniel H. Oh man, that's freaking awesome! Great work! I think I'll have to build one like that!
Thanks, Daniel! Just be careful -- for no obvious reason, I'm beginning to get addicted myself.
 I like it 
  May 11, 2017
MUST. MAKE. FIDGET SPINNER. :P excellent design!
 I like it 
  May 11, 2017
Oh man, that's freaking awesome! Great work! I think I'll have to build one like that!
 I made it 
  May 11, 2017
Quoting Sven ;o) Another well crafted spinner/top from you my friend. The video is also pretty nice. Great work!
Many thanks, Sven!
 I like it 
  May 11, 2017
Another well crafted spinner/top from you my friend. The video is also pretty nice. Great work!
 I made it 
  May 11, 2017
Quoting Clayton Marchetti Awesome new fidget spinner and top. Ok I came home from work the other day and my wife says look what I found at Walmart for the kids. (Smacks hand to forehead) I still don't get it. Excellent job!
Thanks, Clayton! Well, I don't quite get it, either, but remember Pet Rocks, Beanie Babies, and Tamigachis? I didnt get those, either, but the kids sure got the latter two.
  May 11, 2017
@Clayton: *x-files theme plays* 0_0
 I like it 
  May 11, 2017
Awesome new fidget spinner and top. Ok I came home from work the other day and my wife says look what I found at Walmart for the kids. (Smacks hand to forehead) I still don't get it. Excellent job!
 I like it 
  May 11, 2017
@ Toa if it keeps spinning, your trapped in your own dreams. Ha ha ha
 I like it 
  May 10, 2017
Ah, okay. Thanks, I was beginning to question my own reality for second :D
 I made it 
  May 10, 2017
Quoting Toa Whero Amazing! And in that video, it appeared to spin one way, and then suddenly spin the opposite. Is that becuase of it's design or just an illusion of the video? And if it's not an illusion, than how did you manage to do that?
Thanks! Your inner physicist was right to doubt your eyes. The apparent reversals are just illusions -- video frame-rate effects related to the stroboscopic effect and the wagon-wheel illusion (see Wikipedia).
 I made it 
  May 10, 2017
Quoting Jonathan Demers Oh yeah, this looks much better than your old version!
Thanks, Jonathan! Works a lot better, too.
 I like it 
  May 10, 2017
Amazing! And in that video, it appeared to spin one way, and then suddenly spin the opposite. Is that becuase of it's design or just an illusion of the video? And if it's not an illusion, than how did you manage to do that?
 I like it 
  May 10, 2017
Oh yeah, this looks much better than your old version!
 
By Jeremy McCreary
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LEGO models my own creation MOCpages toys shop Improved fidget spinner and top


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