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Xenotron
A LEGO top of unusual construction based on Oliver Becker's Xenosphere.
About this creation
Please feel free to look over the images and skip the verbiage.

If aliens ever land right in front of me in a craft like Oliver Becker's Xenosphere, I have a plan: I'll just talk them into letting me turn their ship into a giant spinning top I'll call the "Xenotron". If they find it entertaining enough, maybe they won't eat us right away.

Here's my proof of concept -- a 1:500 working model in various stages of streamlining for operation in Earth's atmosphere...



The streamlined versions work well as finger tops but really shine with this second-generation 2-stage planetary starter.



PS: I knew I'd be building a top around the Xenosphere's cool bar-and-clip space frame the moment I saw it. The schedule just got pushed up a bit when Henrik Jensen commented that "I'm sure Jeremy could make it spin like a UFO!"

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From Xenosphere to Xenotron

To see what I was up against, I built an exact copy of Oliver's "frame"and tested it with a specific goal in mind: A smoothly spinning top with 10 sec spin times or better by hand. From there, a 2-phase plan emerged:

∨ Phase 1. Stiffen the frame with a new hub and add a stem and tip mount like so...



∨ Phase 2. Cover the resulting hub+frame "chassis" with an outer skin designed to (a) boost spin time without introducing wobble and (b) add visual interest at rest and at speed. Play value would hinge on improving the poor spin times of the bare chassis.



For the skin to improve spin time, it would have to do at least one of 2 things: (i) Lower critical speed by improving on the chassis' mass distribution. (ii) Greatly reduce aerodynamic drag by covering key portions of the chassis with low-drag fairings.

Goal (i) called for a less ball-like and more pancake-like overall mass distribution and the lowest possible center of mass (CM) when upright. A lot of guess-and-check went into the inevitable trade-offs between aerodynamics and mass distribution.

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Hub

The central hub transmits torque from the stem to the rest of the top during spin-up. It also works with the frame to keep the top at its resting size and shape at speeds fast enough to deliver spin times with decent play value. This means stiffening the entire structure against torsion and expansion during and after spin-up.

Without the hub, the top would be quick to wobble from elastic vibration, rotating unbalance due to uneven deformation, or both.



Exploded view of the hub with color added for clarity. (The hub actually used is all black.)



Note the 6 black modified 2x2 plates with reinforced octagonal bar frames (75937). These parts actually belong to the frame. I call them "anchors" because they anchor the frame to the hub.

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Frame and chassis

The bar-and-clip space frame surrounding the hub is an elegant piece of LEGOŽ engineering in its own right, and it's straight out of Oliver's Xenosphere.

The hub and frame nicely complement each other's strengths. The combined result is a "chassis" much stronger than either one. The chasis also has to keep the skin from flying off.



Twelve identical "struts" with clips at both ends bind the 6 anchors into a surprisingly strong space frame, with each anchor receiving 4 struts at the corners of a square. A 1L bar with clip (48729b) supplies one of the strut clips. The other comes from a bar holder with clip (11090).



In addition to the 6 identical anchors, the frame has 8 identical hexagonal holes, each bordered by 3 anchors and 3 struts in alternating sequence.

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Skins

The skin adds color, shape, and mass to the top and covers parts of the chassis in the process. In theory, the associated changes in aerodynamic drag and mass distribution could have additive or offsetting effects on spin time. The net effects on spin time turned out to be hard to predict.

NB: All the skins in this section use 6x6 dishes as chassis fairings. In the following update section, however, 8x8 dishes enter the mix with a very favorable effect on spin time.

∨ Case 1. With no skin, the aerodynamically dirty chassis spins a mere 7 sec by hand and 9 sec with the starter.



Here, the aerodynamics and mass distribution are both unfavorable -- with high drag leading to a high spin decay rate, and the ball-like mass distribution leading to a high "critical speed" (above which the top can't fall).



∨ Case 2. Partially covering the sides of the chassis with four 6x6 dishes yields the best spin times I could get with dishes of this size -- 16 sec by hand and 24 sec with the starter.





This skin appears to be the best trade-off between drag reduction and mass distribution attainable with 6x6 dishes alone.

This 4-fairing skin is also my visual favorite, both at rest and at speed. The open top and bottom showcase the frame's cool geometry, and I really like the shapes traced out by the side fairings -- a tulip at low speed and a napkin ring at high.







∨ Case 3. Interestingly, adding 6x6 top and bottom fairings to the 6x6 side fairings actually shortens spin times by almost 20% (from to 16 to 13 sec by hand, and from 24 to 20 sec with the starter).







This 6-fairing skin has its charms but tends to make the Xenotron look rather featureless in motion.

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Update

∨ Case 4. In an early comment, Oliver suggested I try a 6-fairing skin with larger 8x8 dishes at top and bottom, like so...



Relative to Case 2 with just 4 side fairings, this change more than doubled spin times -- from 16 to 30 sec by hand, and from 24 to 51 sec with the starter!

Didn't see that coming, but it makes some sense in retrospect.

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Optional: Fun frame facts

The closer you look at Oliver's frame design, the more remarkable it gets. We'll assume that the frame is properly seated and start by focusing on the clips.



Recall that the frame has 12 struts with 2 clips each for a total of 24. Now imagine a point at the center of each clip. These 24 points are the vertices of an interesting convex polyhedron known as a trunctated octahedron (TO).


Credit: Public domain image contributed to Wikimedia Commons by InductiveLoad.

The TO here is the blue solid left when you lop the red vertices off this regular octahedron. Note the TO's 6 square and 8 hexagonal faces.

To flesh out the TO embedded in the frame, imagine a network of straight lines connecting each TO vertex (clip center) to its nearest neighbors. These lines are the TO's 36 edges (one along each strut and 4 within each anchor), and each and every one of them has a resting length of 19 mm in Oliver's design.

This uniform edge length is critical, because without it, the frame wouldn't balance, and the top would be doomed to wobble.



My new hub had to keep the clips in their resting positions up to a "rated speed" well above the "operating speed" needed for an acceptable spin time and yet well below the top's "break-up speed". The TO could then be counted on to hold its resting size and shape even with an overzealous spin-up, and that would keep the wobble away.



Fun TO facts: Like all convex polyhedrons, the TO obeys Euler's polyhedron formula

V + F = E + 2,

where V is the number of vertices, F is the number of faces, and E is the number of edges. For the TO, V = 24, F = 14, and E = 36.

In a TO, all vertices and edges are identical, and all faces are regular polygons of 2 different kinds -- namely, 8 hexagons and 6 squares. These properties qualify the TO as an Archimedean solid.



The 8 hexagons of the TO have their corners at the clips surround these hexagonal holes in the frame. The frame members bordering these holes (always 3 struts and 3 anchors in alternating sequence) aren't identical in construction, but all frame members have the same clip-to-clip length of 19 mm.



The 6 squares of the TO correspond to the square arrays of clips attached to the anchors. The sides of the squares form 24 of the TO's 36 edges. In the frame, the 12 struts form the rest.

The top reduces the octahedral symmetry of the TO to 4-fold rotational symmetry by using one square face (anchor) to mount the tip and the opposite square face to mount the stem. These are the "polar" faces. The 4 "equatorial" square faces are identical.

Interestingly, the TO and the cube are the only uniform polyhedrons capable of packing (tessellating) 3D space without gaps. If only that were feasible in the LEGOŽ realm!

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Optional: Spin time, aerodynamics, and mass distribution

Further testing in progress.

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Specifications
Data format: No fairings / 6x6 fairings, sides only / 6x6 fairings, sides+top+bottom

Fairings:0 / 4 / 6 6x6 dishes
Overall dimensions:71x101 / 71x101 / 71x102 mm (DxH)
Masses:28 / 41 / 47 g
Release speeds by hand:1,300 / 1,100 / 1,100 RPM*
Spin times by hand:7 / 16 / 13 sec
Release speeds with starter:1,800 / 2,100 / 2,100 RPM*
Spin times with starter:9 / 24 / 20 sec
Modified LEGOŽ parts:Tip cut from 4L antenna
Non-LEGOŽ parts:None
Credits:Frame adapted from Oliver Becker's Xenosphere. Otherwise an original MOC.
See also:My LEGOŽ top folder

* Actual release speeds are a good bit higher than the measurements reported here.

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Comments

 I made it 
  July 24, 2017
Quoting jds 7777 That frame has some pretty crazy geometry going on there! An awesome looking top, I'm digging the curves!
Thanks, JDS! It's become one of my personal favorites for all the same reasons.
 I like it 
  July 23, 2017
That frame has some pretty crazy geometry going on there! An awesome looking top, I'm digging the curves!
 I made it 
  July 17, 2017
Quoting Daniel H. Wow! That's amazing! Love the look of it! Another great top, keep it up! :)
Thanks, Daniel! I foresee many top posts yet to come.
 I made it 
  July 17, 2017
Quoting Sven ;o) For this looooong and understandable explanation you deserve a xtra like my friend ;) I never would glue one of my models XD Thank you very much Jeremy. Was a really good physics lesson.
You're very welcome, Sven. As you can tell, I found the idea of a skyscraper top rather intriguing.
 I like it 
  July 17, 2017
Wow! That's amazing! Love the look of it! Another great top, keep it up! :)
 I like it 
  July 17, 2017
For this looooong and understandable explanation you deserve a xtra like my friend ;) I never would glue one of my models XD Thank you very much Jeremy. Was a really good physics lesson.
 I made it 
  July 17, 2017
Quoting Nirds forprez As expected, while I was away you made some great stuff Jeremy. I especially love this build.... beauty and function wrapped up in one!
Thanks! This is rapidly becoming one of my favorite tops for exactly the reasons you mentioned. Oliver's beautiful polyhedral space frame tickles me no end.
 I like it 
  July 17, 2017
As expected, while I was away you made some great stuff Jeremy. I especially love this build.... beauty and function wrapped up in one!
 I made it 
  July 15, 2017
Quoting Alain Brunel wow, quite impressive, and as mentioned in a previous post, great presentation, it makes us better appreciate your work
Very kind, Alain! The write-ups are certainly part of the fun for me. Nice to hear they're appreciated.
 I like it 
  July 14, 2017
wow, quite impressive, and as mentioned in a previous post, great presentation, it makes us better appreciate your work
 I made it 
  July 13, 2017
Quoting Henrik Jensen I`ll gladly be considered an accomplice in this "theft", as long as we have the blessings from the dispossessed. And to me Oliver seems both involved and happy! :-)
Yes, I think we got away with it.
 I made it 
  July 13, 2017
Quoting Didier B Nice visual effect on that one (without the white part on top) !
Thanks, Didier! Visual effects at speed have become a high priority in my top designs.
 I like it 
  July 13, 2017
I`ll gladly be considered an accomplice in this "theft", as long as we have the blessings from the dispossessed. And to me Oliver seems both involved and happy! :-)
 I like it 
  July 13, 2017
Nice visual effect on that one (without the white part on top) !
 I made it 
  July 12, 2017
Quoting Henrik Jensen I knew it! You just couldn`t let Oliver's Xenosphere spin away without testing it`s potential. It looks great, and I see you got some unexpected help from the inventor himself. Great presentation as usual, and thanks for the mention!
You know me too well, my friend. Two heads are better than one -- especially when one of them is Oliver's. (Imagine the tops when I finally lure him into top-making!) Sorry, my lawyer made me give you up as an accomplice in theft of a Xenosphere. Something about courtroom strategy. ;^}
 I made it 
  July 12, 2017
Quoting Nick Barrett Oliver's in a spin, excellent!
Seems like Oliver pops up new ideas worth stealing every other day. When the Xenosphere popped up, I lost control.
 I made it 
  July 12, 2017
Quoting Sven ;o) Thank you very much my friend ;) Really like your collab with Oliver here. Too bad that my highrises won't be good spinning tops XD
Oliver and I have been egging each other on lately, and I'm enjoying the heck out it. You know, your 3-blade wind turbine rotors have "top" written all over them, and a working LEGO highrise top would be hard but not impossible. We'd just have to willing to (gulp) glue. :O Sure, that tall and slender vertical profile is a challenge, but it can be overcome with speed and strength. Example: A standard wooden pencil will spin on its point like a top above a "critical speed" of ~30,000 RPM. But this works only because the pencil's "break-up speed" is even higher. For a highrise top, it would come down to rotational symmetry about the intended spin axis and a structure able to survive critical speed and then some. But in a working top, tall and slender only increases critical speed. The symmetry requirement is doable: For example, you could build a tower with centered square floors at every level. (Architecturally boring, I know, but bowing to the laws of physics now and then is just a fact of life in the top-making biz.) The structural requirement is a much bigger hurdle. The strength you can pull out of a well-made LEGO structure never ceases to amaze. But I'd be =really= surprised to find a viable LEGO highrise top structure in no need of glue at "operating speed" (critical speed + the extra speed needed to buy an acceptable spin time).
 I like it 
  July 12, 2017
I knew it! You just couldn`t let Oliver's Xenosphere spin away without testing it`s potential. It looks great, and I see you got some unexpected help from the inventor himself. Great presentation as usual, and thanks for the mention!
 I like it 
  July 12, 2017
Oliver's in a spin, excellent!
 I like it 
  July 12, 2017
Thank you very much my friend ;) Really like your collab with Oliver here. Too bad that my highrises won't be good spinning tops XD
 I made it 
  July 11, 2017
Quoting Oran Cruzen Excellent top Jeremy!
Thanks, Oran!
 I made it 
  July 11, 2017
Quoting Clayton Marchetti I just love the internal structure! I like all the changes you made to make it spin longer. Awesome!
Many thanks, Clayton! Thanks to Oliver, the internal structure is my favorite part, too!
 I like it 
  July 11, 2017
Excellent top Jeremy!
 I like it 
  July 11, 2017
I just love the internal structure! I like all the changes you made to make it spin longer. Awesome!
 I made it 
  July 11, 2017
Quoting Doug Hughes I love it!
Many thanks, Doug!
 I made it 
  July 11, 2017
Quoting Sven ;o) First I thought how could I miss this one but it's from today. So lets go ahead and leave some kind words on this really cool creation from you my friend ;) Very well done and thanks for this very good explanation. Ps: regarding your comment at my cameras. Here they are http://www.moc-pages.com/moc.php/384191
Thanks, Sven! Even more great NYC street details at that link!
 I made it 
  July 11, 2017
Quoting Oliver Becker That's a wonderful creation, I love it, my friend! That my little engeneering could give you, Master of spins and tops, some inspiration is just so fine! ;) The video shows the magic at best! If aliens would be confronted with such great technique just out of ABS, they 'll think twice about an invasion or s.th. else like this! LOL Jeremy, a little idea: maybe you could also try an 8x8 disc on top and bottom to make the illusion of a perfect spinning globe...? ;) Best regards! :)
Too kind, my friend! I'm just getting started with the tops you can build around your elegant "little engineering". Tried your suggestion. The rotor got less spherical rather than more, but mass distribution and aerodynamics both improved, and so did the spin times -- dramatically! See the "Update" section I just added for details.
 I like it 
  July 11, 2017
I love it!
 I like it 
  July 11, 2017
First I thought how could I miss this one but it's from today. So lets go ahead and leave some kind words on this really cool creation from you my friend ;) Very well done and thanks for this very good explanation. Ps: regarding your comment at my cameras. Here they are http://www.moc-pages.com/moc.php/384191
 I like it 
  July 11, 2017
That's a wonderful creation, I love it, my friend! That my little engeneering could give you, Master of spins and tops, some inspiration is just so fine! ;) The video shows the magic at best! If aliens would be confronted with such great technique just out of ABS, they 'll think twice about an invasion or s.th. else like this! LOL Jeremy, a little idea: maybe you could also try an 8x8 disc on top and bottom to make the illusion of a perfect spinning globe...? ;) Best regards! :)
 I made it 
  July 11, 2017
Quoting Jonathan Demers Every time I read one of your posts, I learn something new! Great work on the top and thanks for all the info!
Thanks, Jonathan! I try to learn something with every new MOC I make. For better or worse, I just pass it on.
 I like it 
  July 11, 2017
Every time I read one of your posts, I learn something new! Great work on the top and thanks for all the info!
 I made it 
  July 11, 2017
Quoting Gabor Pauler Quite a geometry lesson!
Never met a polyhedron I didn't like, Gabor! Thanks to Oliver, I got a chance here to delve into one I hadn't noticed before.
 I like it 
  July 10, 2017
Quite a geometry lesson!
 
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