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Author Topic: 2020 Giant Top 2.0 Philippines  (Read 647 times)

JMauk

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Re: 2020 Giant Top 2.0 Philippines
« Reply #15 on: May 12, 2020, 10:01:59 AM »

BTW, ta0, I should be a full ITSA member.  I paid my dues!  Oh, maybe I just caught up with this year's dues today!
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JMauk

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Re: 2020 Giant Top 2.0 Philippines
« Reply #16 on: May 12, 2020, 10:09:04 AM »

BTW, the manual pull test (as corrected by ta0) has a good close up of the top sitting on the bearing. Sorry I had the wrong one for those of you who viewed earlier.
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ta0

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Re: 2020 Giant Top 2.0 Philippines
« Reply #17 on: May 12, 2020, 10:32:35 AM »

BTW, ta0, I should be a full ITSA member.  I paid my dues!  Oh, maybe I just caught up with this year's dues today!
Thanks for renewing your membership, Joe! ITSA is proud to have you as a member!
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Texture

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Re: 2020 Giant Top 2.0 Philippines
« Reply #18 on: May 12, 2020, 10:52:44 AM »

I've seen big tops before, but this is AMAZING! Can't believe how much work went into it. Keep it up!
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Split that top!

Jeremy McCreary

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Re: 2020 Giant Top 2.0 Philippines
« Reply #19 on: May 12, 2020, 01:06:53 PM »

Agree with ta0 (1) that the frame's air resistance contibutes significantly to the total braking torque acting on the skinless top at speed, and (2) that a smooth skin should be a big improvement on that front. Hopefully enough of a torque reduction to offset the increase in bearing torque from the added skin weight.

However, drag by itself would never cause the halting bumblebee descent observed. And neither would simple sliding friction at the tip.

So something in the system must be binding intermittently. If not in the cable run or the bumblebee wheels, I'm with you in pointing the finger at your tip pivot bearing.

Assuming you want the resting top to at least hint of its willingness to fall without the tether at the crown. If so, your pivot bearing has to support a shifting 800+ kg load while allowing at least a few degrees of tilt below critical speed. Yikes!

Have you considered a ball tip resting in a shallow socket supported by a roller bearing?  Might reduce tip resistance without keeping the top from falling over. Works well in LEGO tops and might scale up to your case.
« Last Edit: May 12, 2020, 02:07:33 PM by Jeremy McCreary »
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Playing with the physical world through LEGO

ta0

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Re: 2020 Giant Top 2.0 Philippines
« Reply #20 on: May 12, 2020, 02:33:18 PM »

Agree with ta0 (1) that the frame's air resistance contributes significantly to the total braking torque acting on the skinless top at speed, and (2) that a smooth skin should be a big improvement on that front. Hopefully enough of a torque reduction to offset the increase in bearing torque from the added skin weight.
Oops! I actually believe the reverse! I think the drag of the open frame is much less than it would have with a continuous skin.
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the Earl of Whirl

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Re: 2020 Giant Top 2.0 Philippines
« Reply #21 on: May 12, 2020, 04:27:16 PM »

I love the video with the guys inside the giant spinning top.  I think they have great stories to tell their friends and families!  By the way, great work on that giant whirler.  It looks really solid.  What a terrific spinner!!!
« Last Edit: May 12, 2020, 11:59:54 PM by the Earl of Whirl »
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Jeremy McCreary

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Re: 2020 Giant Top 2.0 Philippines
« Reply #22 on: May 12, 2020, 08:05:29 PM »

Agree with ta0 (1) that the frame's air resistance contributes significantly to the total braking torque acting on the skinless top at speed, and (2) that a smooth skin should be a big improvement on that front. Hopefully enough of a torque reduction to offset the increase in bearing torque from the added skin weight.
Oops! I actually believe the reverse! I think the drag of the open frame is much less than it would have with a continuous skin.

Ah yes, I misread. Space frames tend to generate lots of drag, but there aren't many longitudinal frame members here, so maybe you're right.
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JMauk

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Re: 2020 Giant Top 2.0 Philippines
« Reply #23 on: May 12, 2020, 09:36:19 PM »



Have you considered a ball tip resting in a shallow socket supported by a roller bearing?  Might reduce tip resistance without keeping the top from falling over. Works well in LEGO tops and might scale up to your case.

Yes, I took apart the ball bearing of my large Chinese whipping top and showed them.  They thought such a device would not stand the weight of the top.









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jim in paris

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Re: 2020 Giant Top 2.0 Philippines
« Reply #24 on: May 14, 2020, 12:15:47 AM »

thanks for the report , Joe !
it's good to hear from you and your team

jim
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Mermouy

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Re: 2020 Giant Top 2.0 Philippines
« Reply #25 on: May 21, 2020, 06:40:13 AM »

Simply WOW!
This is project!
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Kirk

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Re: 2020 Giant Top 2.0 Philippines
« Reply #26 on: May 22, 2020, 10:03:48 AM »

When dealing with small bearing points the stresses are way more than one might guess.  The smaller the point is the worse things get (really fast).  Heinrich Hertz did the math for us in the late 1800s.
https://amesweb.info/HertzianContact/HertzianContact.aspx
This nice web calculator will let your crew determine how blunt the point needs to be.  You will wish to be well under the allowable stress for the materials.  You want 2 materials with significantly different hardness to prevent friction welding.  If possible to get , special materials like Nitronic60 are ideal for such an application and would allow a less dull point.


Ah yes, I misread. Space frames tend to generate lots of drag, but there aren't many longitudinal frame members here, so maybe you're right.
Jumping into this conversation. (a topic I know less about)  I suspect that the smoothness of the skin will play an important role. A faceted top will have more drag than a round one. (think cometa spider)  Perhaps some light weight (wood?) intermediate hoops would help.  I doubt I would go to the trouble though.
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JMauk

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Re: 2020 Giant Top 2.0 Philippines
« Reply #27 on: May 23, 2020, 06:02:16 AM »




When dealing with small bearing points the stresses are way more than one might guess.  The smaller the point is the worse things get (really fast).  Heinrich Hertz did the math for us in the late 1800s.
https://amesweb.info/HertzianContact/HertzianContact.aspx
This nice web calculator will let your crew determine how blunt the point needs to be.  You will wish to be well under the allowable stress for the materials.  You want 2 materials with significantly different hardness to prevent friction welding.  If possible to get , special materials like Nitronic60 are ideal for such an application and would allow a less dull point.


Ah yes, I misread. Space frames tend to generate lots of drag, but there aren't many longitudinal frame members here, so maybe you're right.
Jumping into this conversation. (a topic I know less about)  I suspect that the smoothness of the skin will play an important role. A faceted top will have more drag than a round one. (think cometa spider)  Perhaps some light weight (wood?) intermediate hoops would help.  I doubt I would go to the trouble though.


Thanks for the input. Will pass it on to manufacturing team.  Thanks.
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ta0

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Re: 2020 Giant Top 2.0 Philippines
« Reply #28 on: May 23, 2020, 10:10:55 PM »

Great information Kirk!
I'm not a mechanical engineer, but I'm guessing the stresses given by the online calculator will let you see if the tip will dent the surface just by it's weight. In addition, there is the milling effect when it rotates.
I think it's worth making the tip less pointy and see if the damage can be minimized without a big penalty in friction.
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Jeremy McCreary

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Re: 2020 Giant Top 2.0 Philippines
« Reply #29 on: May 23, 2020, 11:49:16 PM »

When dealing with small bearing points the stresses are way more than one might guess.  The smaller the point is the worse things get (really fast).  Heinrich Hertz did the math for us in the late 1800s.
https://amesweb.info/HertzianContact/HertzianContact.aspx

Thanks for bringing up Hertzian contacts. We talk a lot about "tip friction" around here but not enough about [i=https://en.wikipedia.org/wiki/Contact_mechanics]contact mechanics[/i] -- even in finger tops.

Tip resistance" (total tip-related braking torque) is more complicated than simple sliding friction in any top, and Hertzian sinkage at the contact is one reason why. The sinkage is microscopic in tops of normal size but still there -- especially with spike tips but even with ball tips. The rolling resistance encountered by a tip rolling without slip on its supporting surface is partly due to dynamic sinkage.
« Last Edit: May 23, 2020, 11:52:53 PM by Jeremy McCreary »
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