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[Jeremy McCreary]

This final Parapluie attempt needs a starter and stays up only 5 s even then. Moreover, the core tends to precess relative to the canopy, with the two axes coming into alignment only at the very end.



Nonetheless, it has its redeeming qualities. My favorite is the oddly satisfying 1:1 relationship between stay angle and spin rate. Here, "stay angle" β is just the average angle between the frame stays and the top's spin axis.

With the right elastic band (see below) and the manual 1:4 planetary starter shown, you can easily reach any desired stay angle from β_min ~ 50° at rest to β_max ~ 90°. Better yet, the starter complements the visual feedback provided by the stays with a pleasing tactile feedback of its own.



Also like the orange/black color scheme and the mechanical design.



Apex-down mode: This is the Parapluie's intended mode of play. Centrifugal force then opens the canopy against the restoring elastic band with gravity's help. The lower photo here shows the top fully opened at β_max.




Apex-up mode: If there were a good way to start the Parapluie with its apex up, CM-contact distance could in theory be even smaller than with the apex down, and the top might stay up a bit longer. Too bad it's not a viable option in practice. Why? Well, to realize this reduction in CM-contact distance, the contact still has to be fairly close to the hub. And that puts it way up inside the canopy when the top's resting on the ground at β_min.

Only 2 ways around this, neither good: (1) Scrape the stays on the ground till they finally lift up above the tip at β > 70°, or (2), start the top on a tall pedestal to keep the stays off the ground at rest. Problem is, the friction in method (1) puts too much strain on the starter, and the top's just too big and wobbly for method (2) — at least with the pedestals available to me. For all these reasons and several more, I've lost interest in apex-up mode.


It's all about the band
To provide an entertaining range of stay angles without letting the canopy open too far, the elastic band needs the right combination of stiffness and circumference. The flat black band with the glued knot below is just about ideal. (Only took a week of testing to find it!) The two rubber bands behind it are too stiff for their circumferences.



In order to reduce the band's interference with the canopy's natural self-balancing tendency, I hooked it to the stays with rollers designed to give its tension a chance to even out around the frame while in operation. Doesn't work perfectly, but it definitely helps: Abruptly starting and stopping the top in both directions a few times before the final spin-up makes the canopy open more evenly.

[ta0]

I looks nice! Can we see a video in operation? Maybe in slow motion as it only lasts 5 seconds?

The color and folding are reminiscent of the Clown Top

[Jeremy McCreary]

I looks nice! Can we see a video in operation? Maybe in slow motion as it only lasts 5 seconds?
The color and folding are reminiscent of the Clown Top

Thanks! I'll try to make you a video. Love that clown top -- especially the way the collar tucks itself back in at the very end.

[Jeremy McCreary]

This video covers both of the parachute-based tops in this thread but primarily the folding Parapluie. Slow motion of the latter at 6:34. Credit to ta0 for the umbrella top idea at 10:03.



The Parapluie turns out to be a rather interesting mechanical system. Details in video captions and description.

A closely related system...



@ortwin: The metal washer and return spring in the centrifugal tachometer (close-up at 1:34) are non-LEGO. So are the elastic bands in the Parapluie.

[ta0]

Nice video.
The Paratoupie is a convincing demonstration of the usefulness of fairings.
The Parapluie looks very nice. It's unfortunate that it doesn't spin longer.

The prefix para in parachute and parapluie, means stops: stops fall, stops rain. Therefore, "para" is not a great prefix for a top that you want to spin long!

PS: It could also be argued that it comes from a common meaning of para as "associated with", but in Spanish para is stops and paracaídas and paraguas, literally mean stops-falls and stops-waters, without any direct use of Latin, so I think I'm right.

[Jeremy McCreary]

@ta0: Wiktionary roughly agrees with you on parapluie and parachute but puts the meaning of the "para-" prefix in these words more as "protection against" than "stops"...

https://en.m.wiktionary.org/wiki/para-

As for the Parapluie's miserable spin time, perhaps "parastayingup" would be a better name.

Of course, "para-" confers many other meanings as well. For example, "In the nightmare, Jorge found himself standing in front of the classroom without a parapants."

I'll let myself out.

[ta0]

I stand corrected. As a Spanish native speaker the meaning of para as stops in those (and similar) compound words comes so natural that it never occurred to me that it was not the case. Although a shield/protection must stop something, so it's not far off.

[Jeremy McCreary]

I stand corrected.... Although a shield/protection must stop something, so it's not far off.

I'd say you were closely parallel.