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Author Topic: Some unusual construction methods  (Read 148 times)

Jeremy McCreary

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Some unusual construction methods
« on: December 06, 2019, 12:30:06 AM »

This LEGO top does 8-fold rotational symmetry the hard way -- and it's not an easy symmetry to begin with. I like this original rotor color scheme the best...



The 140 g, 160 mm top easily tolerates 1,000 RPM starts with a best spin time of 75 s. Since the chassis allows a bit of (stiff) relative motion between adjacent rotor panels, it takes some fiddling to get the rotor balanced. But wobble's minimal when you do.

As a color-mixing experiment, replaced the rotor's inner yellow ring with red, green, and blue parts adjusted to mix to dark gray at speed, with the goal of matching the adjoining dark gray ring already there...



In person, the color-mixing version looks like this at speed...



But in a photo or video with automatic cameras settings, it looks more like this...



The flat 8-fold rotor is a simplified version of a SNOT (studs not on top) building technique some call the "magic circle". Nothing magic, though. Since 360° / 8 = 45°, you just have to get the 8 identical wedge-shaped panels to meet at 45° angles at every step from the center outward.



The good news: The rotor has a very smooth, low-drag upper surface.

The bad news: You still get a lot of drag from the chassis underneath the rotor. But so be it. Pointing studs inward or outward is a recipe for catastropic centrifugal failure in any LEGO top, and the chassis has to prevent that.



« Last Edit: December 06, 2019, 10:51:32 AM by Jeremy McCreary »
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Playing with the physical world through LEGO

ta0

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Re: Some unusual construction methods
« Reply #1 on: December 07, 2019, 07:17:11 PM »

Yeah, that's not a trivial assembly.
It has rotational symmetry but not mirror symmetry.
I like it!
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Jeremy McCreary

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Re: Some unusual construction methods
« Reply #2 on: December 24, 2019, 06:30:09 PM »

An unusual 6-fold structure made almost entirely of Technic connectors...



The crinkled hexagonal ring holding it all together came within 1 mm of closing naturally. And if that weren't miraculous enough, the bent spokes mated perfectly to the ring thereafter.



Severe drag limits spin time to ~10 s. With a good twirl, you can hear it hiss.


« Last Edit: December 24, 2019, 08:23:20 PM by Jeremy McCreary »
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