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Author Topic: offset top  (Read 23386 times)

ortwin

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Re: offset top
« Reply #60 on: May 26, 2021, 12:14:58 PM »

What I also did sometimes, is to convert short videos to .gif format.
Then the rest of the process is as fast as loading up a "quick photo".

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In the broader world of tops, nothing's everything!  —  Jeremy McCreary

Jeremy McCreary

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Re: offset top
« Reply #61 on: May 26, 2021, 01:10:23 PM »

Duh! Every one of the 100+ videos I've put on YouTube had to be designated "Public", "Unlisted", or "Private" before it could be published. And never once did I wonder what use I could make of "Unlisted".

This is revolutionary! Not to mention liberating!

Some of the tops I've shown here have already been scrapped. But one Q&D (quick-and-dirty) wobblefest coming up with the rest. I'll still have to add titles or captions indicating how I judge the wobble shown. But I'll do it for the team.
« Last Edit: May 26, 2021, 03:28:52 PM by Jeremy McCreary »
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ortwin

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Re: offset top
« Reply #62 on: May 26, 2021, 01:41:02 PM »

...had to be designated "Public", "Unlisted", or "Private" before it could be published. And never once did I wonder what use I could make of "Unlisted".
...
You may have asked yourself  why you were never notified of new videos that I posted in the forum, although you subscribed to my channel.
This is the explanation, I designated them unlisted. So you don't have to worry that your subscribers will get notifications of videos that make not much sense without the accompanying text you write in the forum.
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Jeremy McCreary

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Re: offset top
« Reply #63 on: May 26, 2021, 02:01:09 PM »

The number of things I should have asked myself grew fastest in my teens but seems to be on the rise again. :o
« Last Edit: May 26, 2021, 02:03:37 PM by Jeremy McCreary »
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Iacopo

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Re: offset top
« Reply #64 on: May 26, 2021, 02:38:09 PM »

Duh! Every one of the 100+ videos I've put on YouTube had to be designated "Public", "Unlisted", or "Private" before it could be published. And never once did I wonder what use I could make of "Unlisted".

The same for me, I didn't know it. 
Otherwise probably I would have avoided to open a second YouTube channel for to publish my "quick and dirty" videos and leave the main channel clean.
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Jeremy McCreary

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Re: offset top
« Reply #65 on: May 27, 2021, 06:42:38 AM »

Well, showing and rating different degrees of wobble in 6 of my offset tops took a lot of clips and titles and captions. So quick-and-dirty wasn't really an option for this particular video.

https://youtu.be/sIbKwPYFpXY

Several hours of work, in fact — though it would have taken even longer if it weren't unlisted. This will be my last offset top project for a while.
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ortwin

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Re: offset top
« Reply #66 on: May 27, 2021, 09:14:12 AM »

Jeremy, it seems you still need to practice a lot to be able and willing to do "quick and dirty"!  >:D
As you said yourself it took several hours, you can't call it quick, and by my standards I did not find any dirt anywhere!

Thank you for making this requested video! Now I think we have a good reference and we can understand each other better on the topic of wobble.

The most impressive behavior to me, is the one top Nr.1 is showing. But as you say, all do pretty good! I think my best behaved  LEGO offset (circular) top has phases in its best runs where you would rate the wobble "tolerable", at best. 
But I do not understand yet why its best phase is not at its highest speed. It is rather at the other end. Maybe I should make another quick and dirty video, also to teach you  >:D .
Eh, what do you mean actually by "couple unbalances"? Is that dynamic unbalance?






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Jeremy McCreary

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Re: offset top
« Reply #67 on: May 27, 2021, 11:52:55 AM »

Eh, what do you mean actually by "couple unbalances"? Is that dynamic unbalance?

For static balance, a rotating body's CM must lie exactly on its spin axis. And for couple balance, the spin axis must exactly parallel one of the body's 3 principal axes of inertia.

Having one kind of balance here does not guarantee the other. And for dynamic balance, you must have both. Since pricipal axes always go through the CM, that means a spin axis that exactly coincides with a principal axis. Otherwise, wobble-free spins will be impossible.

Wikipedia's article on rotating unbalance will get you started here, but expect to do some reading and experimenting (with LEGO, for example) to get what the statements in this reply really mean.

For a top to spin perfectly smoothly, it must have dynamic balance. And per the tennis racket or intermediate axis theorem, for its spin axis to be stable in direction, the pricipal axis the spin axis must coincide with has to be either the greatest or least principal axis, not the intermediate one. Again, lots of homework for you here.

Practically speaking, in a LEGO top made up of several layers of parts arrayed along the intended spin axis at various levels, the best way to insure couple balance is to force static balance on every layer separately. It's not enough for one layer's static unbalace to cancel another's at a different level.

Top 1 clearly doesn't meet this criterion. However, the couple unbalance created by its upper white plate cancels that created by the lower white plate, while both contribute to the top's overall static balance. So dynamic balance holds. Top 5 has a slight residual couple unbalance, but it doesn't produce much wobble in this case.

Couple unbalace also arises when the contact point on a spike tip is off the pricipal axis established by the rest of the top. Iacopo works hard on his replaceable tip alignments to avoid this.

Wobble-wise, couple unbalance is often way worse than static. It generally takes a severe static unbalance to make the tip of a wobbling top scrub audibly on the ground. When you hear that, think couple unbalace first.

PS: You're right in thinking that quick-and-dirty kind of goes against my nature. So it's gonna take some practice. But I should have more success with subjects that don't need multiple examples to pin down what I mean.
« Last Edit: May 27, 2021, 02:11:06 PM by Jeremy McCreary »
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ortwin

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Re: offset top
« Reply #68 on: May 27, 2021, 04:17:48 PM »

.. And for couple balance, the spin axis must exactly parallel one of the body's 3 principal axes of inertia....

...

Wobble-wise, couple unbalance is often way worse than static. It generally takes a severe static unbalance to make the tip of a wobbling top scrub audibly on the ground. When you hear that, think couple unbalace first.
...
In fact I know about the 3 principal axes of inertia and all that. That Is why I planned originally also three vertical grub screws in the flywheel of an endurance top.
What I did not know was the term "couple balance" and I thought "dynamic unbalance" means that what you call "couple unbalance". So basically it was a confusion because of language. So mostly homework in "technical English language" really.
 But what you say about "couple unbalance" with regards to its role in spinning tops is interesting and valuable. I will consider that more attentively in future.





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Jeremy McCreary

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Re: offset top
« Reply #69 on: May 27, 2021, 07:07:50 PM »

In fact I know about the 3 principal axes of inertia and all that.... So mostly homework in "technical English language" really.

Well, needed some practice making Q&D videos anyway, so I made this one this morning...

https://youtu.be/-OB4GDQ_cUM

Think I'm starting to get the hang of it.

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ortwin

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Re: offset top
« Reply #70 on: May 28, 2021, 01:56:54 AM »

I am glad that you seem past the phase where it physically hurts to do Q@D videos!
Not putting music in the background was an important step.
That camera shake you introduced at some points seemed a bit affected, but you get over that too!
Hopefully time wise you also got into the direction of "Q"?
Introducing unbalance was presented very clearly, I think people can learn from that video.
 
But that was the easy part, the hard question is how to see how one has to change the weight distribution to achieve good balance in a spinning top!
I mean a practical and easy way that can be done at home (still it should be enlightening to look up what principles are used to balance your car wheels in those garages) . Even with the laser balancing method it is not directly possible to distinguish static from couple unbalance. And often you have a mixture of both.
Something like filming tip and stem movement in slow motion and good spatial resolution simultaneously, could work. You would have to correlate both motions and analyze them to find where to change weight. But at the moment that does not really sound feasible. If one has all the setscrews one needs, trial and error approach is probably faster most of the times.
« Last Edit: May 28, 2021, 03:02:09 AM by ortwin »
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ortwin

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Re: offset top
« Reply #71 on: May 28, 2021, 03:13:44 AM »

Aside for @ortwin: The octagonal half-and-half top above isn't a keeper. But no end to the fun (non-offset) LEGO tops you can build on these octagonal plates. ...
Can't stop thinking about the S-TOP (Stop Top) when I see those octagonal plates. But LEGO has (of course ) a real stop sign already:


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Jeremy McCreary

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Re: offset top
« Reply #72 on: May 28, 2021, 06:20:34 AM »

That camera shake was setting the phone down on the counter (on a short angled selfie stick) to free up both hands and then picking it it again. Totally legit.

Pretty handy for doing single continuous takes actually, and the tilted background while the phone was down didn't seem to detract that much. Q&D serendipity!

I've not delved into balancing methods to the extent you have, as they're generally not needed in LEGO tops. Have adapted the paintbrush and laser methods to LEGO construction to good effect -- mainly to address static unbalance in asymmetric tops like this space Ferrari...

https://youtu.be/DOjTg9pH__4

In the end, there was still a good bit of trial and error, as you say -- mainly because of the inherent couple unbalance in this particular design. Lots of cursing involved with this one, too.
« Last Edit: May 28, 2021, 06:22:40 AM by Jeremy McCreary »
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ta0

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Re: offset top
« Reply #73 on: May 29, 2021, 10:05:44 AM »

I have not have time to look past reply #65 (thanks ortwin for starting to reference the reply numbers on a thread: I had never paid attention to them).
Top number 1 on that video is incredibly well balanced with a large offset. It's eerie. I would like to have that top in my collection: what are the LEGO parts I should get?

Sometimes I upgrade an unlisted video to public. I think this video has enough quality and interest to do that.
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Jeremy McCreary

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Re: offset top
« Reply #74 on: May 29, 2021, 12:43:02 PM »

I have not have time to look past reply #65 (thanks ortwin for starting to reference the reply numbers on a thread: I had never paid attention to them).
Top number 1 on that video is incredibly well balanced with a large offset. It's eerie. I would like to have that top in my collection: what are the LEGO parts I should get?

Sometimes I upgrade an unlisted video to public. I think this video has enough quality and interest to do that.

Agree, those Reply # references are very handy.

Wow, it's a red-letter day for LEGO topmaking when a collector of ta0's caliber wants one, not just to play with, but for his collection!  Also a tribute to ortwin for leading us to the offset top concept, which I've not seen elsewhere. Via beer no less!

Top 1 is my favorite, too, both mechanically and visually. You'll need 6 different parts -- none expensive, and most with many colors to choose from. I recommend trying the high-contrast B&W color scheme shown for the visual effects. But you might also want to try a color-mixing scheme while you're at it. In LEGO, the most striking mix is still 50% orange + 50% lime at rest -> yellow at speed.

I'll provide direct BrickLink links to the parts you'll need in an addendum Reply #79 below.

Kind words about the video. Planning a public version with title cards and captions focused on the tops rather than on the wobble -- which many viewers won't even notice in most of the tops if I don't point it out. Not that there will be many viewers.
« Last Edit: June 03, 2021, 03:15:08 AM by Jeremy McCreary »
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