A finger top is one that can be spun up to good effect with a simple twirl of the fingers. This page just scratches the surface of the finger tops waiting to be built in the LEGOŽ realm. Since posting this page, I've made dozens more with no end in sight.
The 19 LEGOŽ tops in the video above and group shots below have 2 important things in common: (i) All qualify as finger tops, though some are easier to twirl than others. (ii) All stay up at least 3 sec, and all but 2 spin longer than 12 sec.
∧ Of the 19 finger tops shown above, 1 spins longer than 100 sec, 3 longer than 60 sec, 6 longer than 40 sec, and 9 longer than 30 sec.
Close-ups of 17 of these tops follow -- roughly in order of decreasing best run times. The 2 tops included in the group shots but not featured here are (i) the DGB 3-arm top (12 sec) at far upper right in the overhead group shot, and (ii) the orange and black 3-arm top (5 sec) near top center in the same photo.
For completeness, this page also has a bit to say about my Asteroid top, which had to be cannibalized temporarily to make the Centrifuge top shown below.
The best run times reported here were obtained on polished fine-grained granite, a nearly ideal supporting surface. They beat best times on the porcelain tile floor in the video by a good 10-30%.
Ninjago: 102 sec, 0.043 kg
∨ My longest-running finger top by far -- and the only one to break the 100-second barrier when this page was first posted -- is based on a Ninjago spinner.
∧ The spinner's well-balanced built-in weight boosts run times by (i) lowering the top's center of mass (CM), and (ii) adding just the right amount of axial rotational inertia (aka moment of inertia).
∧ The superstructure is just there to provide a stable stem, as the spinner itself lacks a central axle hole.
∧ The infrastructure is just a mount for one of top's most important components -- the custom tip.
Modifications made after these photos were taken took spin time to 158 sec -- mainly via (i) a lighter superstructure and (ii) a new tip cut from the end of a round-tipped 4L antenna.
∨ The photo below shows the new tip in use in one of my Klingon tops. In fact, all of my tops now use this tip. Most use the 2x2 dome mount shown below as well, but that mount is too high for a Ninjago spinner-based top.
∨ Aerodynamics count for a lot in the top biz. The 2nd longest-running finger top in this early collection owes much of its endurance to streamlining. High axial rotational inertia and a lower than average center of mass also contribute.
∧ Stack-of-Dishes runs so smoothly and quietly that it sometimes appears to be frozen in time rather than spinning. My best sleeper, it stays bolt upright until the bitter end.
X-pod: 74 sec, 0.027 kg
∨ This simple, long-running top is just an X-pod container, and axle, and a tip.
∧ X-pod sleeps occasionally but, like Down Under, strongly prefers to precess when twirled.
Fabuland: 48 sec, 0.044 kg
∨ The big yellow top below is built around a pair of Fabuland merry-go-round bases (4750) joined base-to-base. It also likes to precess.
∨ Racing Stripe is the B&W top with the racing stripe in the right foreground below. It has a very nice feel as it spins up. The shimmering wagon-wheel illusions it triggers when spinning are the best in this collection.
Tank top: 32 sec, 0.110 kg
∨ At ~0.1 kg each, Tank top, Centrifuge, and Asteroid are by far the heaviest tops here. All 3 take muscle and practice to twirl -- especially Tank top, as it has the highest axial rotational inertia of all. The good news: Tank top has the lowest topple speed of all by a wide margin.
∧ Most of Tank top's mass and therefore axial rotational inertia resides in the pre-stressed outer ring of inverted large tread links, as desired. The spokes are strong but light.
Motorcycle Wheel 2: 28 sec, 0.057 kg
∨ The rotor on this top consists of pair of white motorcycle wheels clamped between a pair of clear 10x10 dishes
∧ The 4x4x6 B&W cylinder above the rotor was originally just a fancy timing mark for my laser tachometer. Now it's just there for looks. The top would run a good bit longer with a lower center of mass.
Lotus: 23 sec, 0.037 kg
∨ Lotus is the B&W top with 6 "petals" in the left foreground below. Like Racing Stripe on its right, it generates excellent wagon-wheel illusions when spinning.
∨ Square is the litte white and DBG top with the square rotor at upper center in the photo below. Like Racing Stripe and Lotus in the foreground, it has a very satisfying feel when twirled.
∧ Run times suffer from (i) a relatively high CM, (ii) so-so aerodynamics, and (iii) low rotational inertia ratio.
The rotational inertia ratio of a top is given by Iaxial / Itransverse, where Iaxial is the rotational inertia of the top about its spin axis, and Itransverse is the maximum rotational inertia about an axis perpendicular to the spin axis and through the CM. For maximum stability and run time, this ratio should be much greater than 1.
∨ What better place to demonstrate centrigual force than on top of a spinning top?
∧ The very soft bronze centrifuge return spring peeking out from between the white wheels of the centrifuge is the only non-LEGOŽ part used in all 20 tops.
∧ This large, heavy top uses the same ring and hub as Asteroid.
Glow: 16 sec, 0.026 kg
∧ The black and white 4L light saber blades sticking up from the corners of Glow's rotor (right) induce dandy wagon-wheel illusions when the lights are on. (That's Down Under on the left.)
∧ Things get even more interesting when the lights go out.
Sawtooth: 15 sec, 0.016
∨ This very lightweight top is usually well-behaved -- until it lands, anyway. Would've been well-behaved in the video, too, if I'd remembered to put its tip back on.
∧ There's no simple way to fix a saw blade like this to an axle -- hence the Technic rubber bushes serving as friction clutches.
Lime: 15 sec, mass not available
∨ The lime green top at upper left in the photo below benefits from a very low CM but suffers even more from excessive air resistance. The hissing sound it makes when spinning is second only to that made by Honeycomb.
∨ Lime is better seen in the video and the group shot below.
Honeycomb: 14 sec on granite, 0.041 kg
∨ Honeycomb is of course the red and gray top on the left. As with Lime, excessive air resistance is its only real flaw. (That's Motorcycle Wheel 1 on its right.)
∧ Stud-generated aerodynamic drag is a braking force to be reckoned with in a fast-spinning LEGOŽ top -- especially when the studs are far from the spin axis. Large rotor perforations are even worse in this regard. The loud hiss Honeycomb emits when spinning is the sound of drag braking.
Flop: 3 sec, 0.031 kg
∧ This floppy top, made from ancient Technic suspension arms, may be the shortest-running top on this page, but it's still a lot of fun.