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[Jeremy McCreary]

Lots of inspiration for top design in fictional spacecraft. My Deep Space Nine top is a case in point. But turning a TV space ship into a working LEGO top involves many visual and mechanical compromises. If the top ends up with decent play value and recognizability (at least to fans), I call it a success.

Below are 2 successes inspired by the Battlestar Galactica (BSG) TV series aired from 2004 to 2009. Never cared for most BSG ship designs, but the Zephyr (left) and the Mark II Cylon raiders (right) really grabbed me visually.



Zephyr

The Zephyr was originally a human luxury liner with a large spinning habitat ring for passengers, parks, botanical gardens, and science labs in need of some cheap fake gravity. Note how the ring's 4 main spokes angle forward (to the right) in the TV ship below.



My 190 g Zephyr top spins on the ship's tail with the nose as its stem. At 242 mm in max ring diameter and 200 mm in total length, it's one of my largest. The core's way too short for the ring for mechanical reasons, but the shape's still recognizable. As you can see, I think space could use more color.



In the spokes-forward TV configuration above, the top stays up ~45 s with multiple twirls or a 1:4 planetary starter. (Large AMI and high critical speed make single twirls impractical.) Wobble is usually mild but can all but vanish with a lucky release.

Swapping the stem and tip assemblies to make the spokes angle aft rather than forward lowers CM height from 75 to 45 mm. This noncanonical configuration wobbles more but bumps spin time to ~65 s with a starter or multiple twirls and ~45 s with a strenuous single twirl. Scrape angle is still comfortable at 9°.



Cylon raider Mark II

The Cylons evolved from robotic workers and soldiers with AI to sentient biomechanical nasties hell-bent on wiping out their former human masters. (Hate it when that happens!) The small Cylon space fighters the humans called "raiders" were one of the many forms they eventually took. The Mark II raider had an elegant scythe-winged shape...



Doubt even the Disney Research guys (Bächer et al., 2014) could turn this shape into a working top. So instead I made a finger top carrying little raiders made from silver Bionicle monster claws (44036).



This simple 28 g top is 132 mm in max diameter. Drag limits single-twirl spin time to ~15 s. Still rooting out a mysterious wobble, but play value is decent as is. The backstory I tell myself comes from Season 1, Episode 5, wherein a downed human pilot repairs and flies off with a crashed raider. Here, she's chased by 2 hostile raiders as she returns to Galactica with her prize, uncertain of the reception awaiting her.

I like tops with backstories.

[ortwin]

...
Doubt even the Disney Research guys (Bächer et al., 2014) could turn this shape into a working top. .....

...

But I am sure you could if you really wanted to! Think of your offset top and the paper with the spinning elephant.
Edit:   I just realize that the in fact that might be exactly the paper you are citing. 
But if you would use the "jaw" as the tip it does look promising to me.
 
The other design in the movie, the first one, looks as if strongly influenced by the von Braun space station.


Good work by you, as usual!

[Jeremy McCreary]

The other design in the movie, the first one, looks as if strongly influenced by the von Braun space station.

Agree, Zephyr is just a traveling von Braun station with a long core -- presumably to give it directional stability and a visually distinct bow and stern. Still, an interesting adaptation.

Doubt even the Disney Research guys (Bächer et al., 2014) could turn this shape into a working top.

But I am sure you could if you really wanted to! Think of your offset top and the paper with the spinning elephant.
Edit:   I just realize that the in fact that might be exactly the paper you are citing. 
But if you would use the "jaw" as the tip it does look promising to me.

Wish I could share your optimism about the Cylon raider. For starters, this is how big and heavy you'd have to go to approach its true shape in LEGO...



This truly masterful build is remarkably sturdy for its size and weight. But it's obviously not up to the stresses a top version would encounter in play. Doubt glue would change that.

But let's forget about LEGO and durability and look at the 3D printing techniques used by the Disney team. This video is a good summary of their paper...



In the Disney process, you first specify the desired external shape and spin axis A. Then you manipulate the CM location and the principal axes of inertia (PAIs) by varying the internal mass distribution until you get the CM on A and greatest or least PAI perfectly aligned with A. This takes care of both static and couple balance and insures that spin about A is stable.

But for long  spins, A should coincide with the greatest PAI, not the least. Moreover, the moment about A (by definition, the AMI) should be much larger than the moment about the intermediate PAI in order to minimize critical speed.

Succes in this is not guaranteed. And given the raider's long slender tapering arms and the large central void between them, I think it would be a very tall order indeed.

For starters, the raider's shape severely limits the ability to move mass around inside. Note that all of the shapes attempted by the Disney team had a large central volume with smaller appendages around its periphery. The raider's shape is far removed from that favorable configuration.

For any chance of success, I think high-density metal inserts in the arms would be unavoidable. Perhaps the A you proposed could then be something other than the unstable intermediate PAI, but it probably wouldn't be the greatest PAI.

I could go on, but I think you can see now why I'm quite content with my little raider top as is.

[ortwin]

I had this picture of the "Eagle balancing on beak" in mind.
(Please google for the picture, I can't put it in the post at the moment from my mobile.)

[Jeremy McCreary]

I had this picture of the "Eagle balancing on beak" in mind.
(Please google for the picture, I can't put it in the post at the moment from my mobile.)

That eagle sculpture is a very cool static balancing act. But top "spinnability" as defined by the Disney team is about much more than static balance. It's also about the relationship between the desired spin axis and the would-be top's principal axes of inertia.

In which case, the best possible spin axis may still not be good enough if you pick the wrong shape -- even after it gets the Disney treatment.

In my experience, the Disney spinnability index seems to correlate pretty well with the mechanical component of subjective play value.

[ta0]

That eagle sculpture is a very cool static balancing act. But top "spinnability" as defined by the Disney team is about much more than static balance. It's also about the relationship between the desired spin axis and the would-be top's principal axes of inertia.

The principal axis of inertia always goes through the center of mass. Because the balancing bird is kind of flat, the major principal axis of inertia is likely pretty perpendicular to that plane. So those birds are probably close to what it's needed to spin well on the beak.





Somewhere I have one, but I haven't seen it in a long time.

[Jeremy McCreary]

What spin axis are you proposing for the eagle? If it can't fall from its starting orientation, I'm not willing to call it a working top.

[ta0]

What spin axis are you proposing for the eagle? If it can't fall from its starting orientation, I'm not willing to call it a working top.

As is, it's not a top. But if you elongate the beak to make a tip lower than than the center of mass, it becomes a top without changing the main principal axis.

[Jeremy McCreary]

Which principal axis is greatest?

[ta0]

Which principal axis is greatest?

If  you have a planar figure, one principal axis is perpendicular to that plane through the center of mass. The moment of inertia of this axis is always the largest, as it's equal to the sum of the other two principal axis (in the plane). The bird is quite flat (not exactly, of course: the beak is above the center of mass), so this is probably still the case. If you add a thin vertical tip with negligible mass, the principal axes don't change, even though the center of mass is raised with respect to the contact point.

[Jeremy McCreary]

The Cylon raider appears to be even flatter than the eagle.



Its CM is in the right-left mirror plane, probably inside the forward part of the head. So if the raider is horizontal, as in the uppermost image, you envision a roughly vertical spin axis through the CM?

[ta0]

The Cylon raider appears to be even flatter than the eagle.
Its CM is in the right-left mirror plane, probably inside the forward part of the head. So if the raider is horizontal, as in the uppermost image, you envision a roughly vertical spin axis through the CM?

I would bet that is approximately the case. It's probably leaning a little forward because of the "handle" (command bridge?).

[Jeremy McCreary]

Getting less bull-headed about the Cylon raider's potential as a stand-alone top, or rather lack thereof. Thanks to ta0 and ortwin for sticking with me.

In a uniform raider, guessing that the upper end of the near-vertical principal axis would actually tilt a bit aft due to the head mass above the wing plane (as in couple unbalance). If that isn't the best spin axis aerodynamically, maybe the Disney process could improve it. That would presumably involve hollowing of the upper head and, surprisingly, the wing tips as well.

If the CM shifts a bit in the process but remains far enough within the head to mount the stem and tip securely without spokes, so be it.

Still, I'd like to see it actually done. Maybe Disney takes requests.

[Jeremy McCreary]

The Cylon raider appears to be even flatter than the eagle.
Its CM is in the right-left mirror plane, probably inside the forward part of the head. So if the raider is horizontal, as in the uppermost image, you envision a roughly vertical spin axis through the CM?

I would bet that is approximately the case. It's probably leaning a little forward because of the "handle" (command bridge?).

Sorry, missed this. See above about tilt direction.

As sentient biomechanical fighter craft, the raiders are their own pilots, so no need for a bridge.

With that in mind, look at the raider side view, and think of a superhero flying to the left, head up, each arm straight ahead with palm down. The head blends aft into the torso. Nothing behind the waist.

That's how I see the raiders now, but it took a while to get there.

[Jeremy McCreary]

Video showing principal axis orientation in pure couple unbalance, which preseves static  balance...