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Author Topic: Top Nr.13 (23 min)  (Read 618 times)

Jeremy McCreary

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Re: Top Nr.13 (23 min)
« Reply #15 on: April 14, 2019, 11:16:33 AM »

Nearly all of my LEGO tops have stems ending at 4.8 mm. The high-AMI cases add a 6.8 mm step to get them started. Works beautifully for single twirls, and I never even notice the step-off.
Yes, from 6.8 to 4.8 diameters there is only 1 mm step, I understand that in this case the step-off is barely noticed by the fingers.

What the fingers do notice -- even with such a small step -- is how much easier it is to get a high-AMI top started when you begin the twirl on the thicker part of the stem.

Since muscle and tilt control are always somewhat antithetical during a twirl, even with practice, the ability to start a top with less muscle translates into better tilt control. And in a broad, low-slung high-AMI top like James', with very little wiggle room to avoid scraping on a flat table, that means a big gain in play value when you don't have a pedestal.

Subtleties like these keep finger top-making interesting.
« Last Edit: April 14, 2019, 02:26:35 PM by Jeremy McCreary »
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Playing with the physical world through LEGO

Iacopo

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Re: Top Nr.13 (23 min)
« Reply #16 on: April 15, 2019, 03:51:14 PM »

What the fingers do notice -- even with such a small step -- is how much easier it is to get a high-AMI top started when you begin the twirl on the thicker part of the stem.

I agree...
Things then are a bit complicated; not necessarily more narrow knurls are more unconfortable or more difficult to use.
The top is accelerated more slowly with a more narrow knurl, but the spinning action lasts longer, so it is not certain that with a larger knurl the top will be started at higher speed, at parity of muscle, even for single twirl tops.
The narrow knurls allow for a good starting speed, not because they have to be twirled harder, but because the spinning action lasts longer.
So each one of us should test what works better for himself.
Even control is not necessarily better with a larger knurl. In my experience the slower acceleration of more narrow knurls can allow for more control.
 
Spinning an almost 1 kilogram top with a 4 mm knurl is not comfortable, but this was just a test I made.
The original stem of that huge AMI top is 8-12 mm, which are fine diameters.
Anyway the test revealed that a more narrow knurl works better for to achieve a higher starting speed, when twirling the top more times, in spite of the high AMI.
I didn't spin the top with the more narrow knurl harder.
The result of this test was not so obvious and I found it interesting.
Based on this test I designed the stem of my huge AMI top Nr. 22 which is large at the base but quite narrow at the top, and this was an improvement of the design, because I can start comfortably that top with the larger part of the knurl, and, if I want, I can accelerate it to an higher speed, thanks to the quite narrow part of the knurl.
     
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Jeremy McCreary

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Re: Top Nr.13 (23 min)
« Reply #17 on: April 17, 2019, 06:08:35 PM »

So each one of us should test what works better for himself.

Yes, that's the take-home lesson here.

I think all finger tops benefit from knurled stems. And higher-AMI tops generally benefit from tapered or stepped stems. We've discussed some of the reasons above. Here's another: Since the optimal stem for a single-twirl top may differ significantly from the optimum for one allowing multiple twirls, tapering or stepping the stem may give you a top that plays well both ways.

For the actual stem diameters to be included in the taper or steps, however, there's just no substitute for careful testing.

Even control is not necessarily better with a larger knurl. In my experience the slower acceleration of more narrow knurls can allow for more control.

I've had the same experience with high-AMI, low-drag tops allowing multiple twirls. But most of my tops have smaller AMIs and a lot more drag than yours and hence aren't amenable to multiple twirls. For these single-twirl tops, the trade-off between applied torque and tilt control seems hard to escape.

This trade-off may even be baked into the biomechanics of twirling. Generally, the more strenuous the twirl, the larger the muscles recruited. Crank hard enough, and even the shoulder muscles come into play. Problem is, the larger the muscles driving a motion, the less fine control you tend to have. (This is golf's central challenge.) And finger top twirling is a fine-control task if ever there was one.

A multi-twirl top allows you build up speed slowly with a series of low-torque twirls recruiting only the small muscles of the hand and forearm. You can then go to a much narrower stem than in the single-twirl case without sacrificing control.

Twirl duration adds another layer of complexity that I'm still trying to understand.
« Last Edit: April 17, 2019, 07:11:09 PM by Jeremy McCreary »
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