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[Jeremy McCreary]

Finally snagged a pair of these very rare large green LEGO wheels for testing.



The bare top on the left has a maximum radius of 80 mm, a mass of 63 g, a very low center of mass just 27 mm above the table, and a relatively large axial moment of inertia (AMI) due to the favorable mass distribution.

Should be a recipe for long spin times via low critical speed and high resistance to braking torques. But the large aerodynamic braking torque generated by the many small plastic fins still limits spin time to ~40 s -- and that's with a powerful wind-up starter!

On the right is the same top with a stretchy white cloth fairing over the fins. Despite the open mesh, the fairing boosts spin time by 50% with the same starter! Granted, the 1.3 g fairing adds 1.9% to the bare top's mass and a little more to its AMI. But these changes in mass properties are much too small to account for a 50% spin time gain.

Sometimes I envy you guys for the low-drag tops you usually deal with.

[Jeremy McCreary]

When life gives you lime department: Frustrating that the price for such a big, beautiful (lime) mass distribution in a LEGO top would be all those #@$%^&* little fins! A spin time that could have been well over 200 s with a powerful wind-up starter reduced to a mere 40 by drag. Tragic, really. Granted, covering the fins with that stretchy white cloth fairing above did bump spin time to 60 s -- a gain of 50%. But still disappointing.

Then my wife's bad-ass new blow dryer rode into town...



The hollow body makes it easy to aim for maximum speed, and jet height's just about right with the dryer on its side.





Best spin time's still only 60 s. But man, oh man, that turbine wail! And from the top, not the dryer.

I'll post the release speed and some sound and video when it's safe to ask for help.* Meanwhile, guessing well over 2,000 RPM from the sound alone. And now I'm embracing the drag.

* My wife has no idea that her precious hair dryer's being used in the name of science. And we're going to keep it that way till I've tried all the attachments. Aren't we?

[the Earl of Whirl]

As Sargent Schultz used to say......"I know nothing.  I am not here.  I did not even get up this morning."

[Jeremy McCreary]

As Sargent Schultz used to say......"I know nothing.  I am not here.  I did not even get up this morning."

One of my favorite TV characters of all time! If you ask me, our dear Sargeant should have shared a Nobel Peace Prize with the guy who invented "Yes, dear!"

[Jeremy McCreary]

But wait, there's more! department: Being able to really hear the speed can make up for a lot of sins in a top. But with great aerodynamic driving torque about the spin axis comes great perpendicular torque (when the vanes are orientated like these). Attitude control with the original coaxial wind-up starter was easy and precise -- and good thing with that measly 4° scrape angle. But you can't avoid cutting into flywheel top speed when your fingers are struggling to keep the stem vertical in a gale. At least not with the flywheel keyed to the stem.

So now there's a sliding dog clutch between the flywheel and the stem-to-tip central axle. With the clutch engaged (down), you have a normal (rigid) top you can start with a twirl of the fingers or a mechanical starter on the stem...



To disengage the clutch for blow dryer starts, you just stand the top on its tip after pushing of the stem home in that direction. Gravity will drop the red receiver cup below the light gray clutch dogs, and the stem will be free of the flywheel...





Result: Fewer scrapes during and after spin-up, slightly longer blow dryer spin times, and even sweeter turbine whines.

But wait, there's even more! More play value, that is. With the clutch disengaged, you're free to handle the top by the stem as you please. Which means that you can change the tilt precisely at speed and see how the top responds without slowing the spin. Or wave the stem around with the flywheel going and really feel the gyroscopic rigidity that comes with so much rotational inertia. Then you can re-engage the clutch to twirl and brake the stem with your fingers and really feel that inertia resisting any change in spin rate. These are interesting sensations with or without the science.

So just add blow dryer and clutch, and a disappointing top's now a fun spinological experience to see, hear, and feel. And it takes all of 2 seconds to switch between free and locked flywheel modes. I really like this top now!