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Author Topic: Earth-powered top starters  (Read 1072 times)

ortwin

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Re: Earth-powered top starters
« Reply #60 on: May 12, 2021, 12:12:01 PM »

...
You may want to look at this thread Re-thinking spin dynamics for world's largest top
Thank you for pointing me to that thread. A quick view yielded that with the "Giant Top 2.0" we are at a starting height in the range of about 10 m if it is using only its own mass? Yeah, totally different game.  There were probably reasons why CM is so high up giving high critical speed.........
 
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Jeremy McCreary

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Re: Earth-powered top starters
« Reply #61 on: May 12, 2021, 01:05:11 PM »

A quick view yielded that with the "Giant Top 2.0" we are at a starting height in the range of about 10 m if it is using only its own mass? Yeah, totally different game.  There were probably reasons why CM is so high up giving high critical speed.........

Pretty sure they're going for the peg top look in a top-like display that spins long enough to please Joe, his visitors, and the Guiness rules.

Could have added internal mass near the tip (as in Relampago peg tops) to draw the CM downward if necessary. But the top is contrained above to near-zero tilt for safety and various mechanical reasons.

So not sure how important lowering critical speed really is in this case. Since the top can't fall, all time spent spinning counts as apparent spin time -- at least as far as the crowd's concerned.
« Last Edit: May 12, 2021, 01:09:36 PM by Jeremy McCreary »
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Playing with the physical world through LEGO

ortwin

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Re: Earth-powered top starters
« Reply #62 on: May 12, 2021, 02:33:35 PM »

....as in Relampago peg tops...
A search, to tell me what that actually is, mainly gave results where a certain "McCreary" is involved somehow. Yes and something in Spanish.
... So not sure how important lowering critical speed really is in this case. ...
Well from what I read in that thread it is not so easy to reach appropriate speed. Sso going for lower critical speed would have made things easier, lighter bumblebees at least.
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Jeremy McCreary

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Re: Earth-powered top starters
« Reply #63 on: May 12, 2021, 03:48:21 PM »

....as in Relampago peg tops...
A search, to tell me what that actually is, mainly gave results where a certain "McCreary" is involved somehow. Yes and something in Spanish.

Relampago (lightning in Spanish) tops are highly sought-after 3D-printed throwing tops designed and made in limited quantities by forum member Jose Madrigal, who won a recent world championship with them.

Searching the entire forum should turn up many hits, the vast majority of which should have nothing to do with me. I'm just a proud owner.
« Last Edit: May 12, 2021, 04:06:48 PM by Jeremy McCreary »
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ta0

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Re: Earth-powered top starters
« Reply #64 on: May 12, 2021, 11:23:25 PM »

I believe one reason the original Guinness World Record application wasn't accepted was that the top didn't spin free enough. Lowering the center of mass could be a good idea in that respect and not something we considered at the time.
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Jeremy McCreary

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Re: Earth-powered top starters
« Reply #65 on: May 12, 2021, 11:51:32 PM »

I believe one reason the original Guinness World Record application wasn't accepted was that the top didn't spin free enough. Lowering the center of mass could be a good idea in that respect and not something we considered at the time.

Just how much leeway in tilt does the top have?
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JMauk

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Re: Earth-powered top starters
« Reply #66 on: May 13, 2021, 01:44:30 AM »

Okay, I figured out last year how to get those little quote snippets posted to give answers but can't figure it out this year (no memory comments please).

Just did some measuring to confirm.

Height of rails at top of top launcher- 7.3M above ground.
Height of rails at bottom of ramp- 0.2M above ground
Note: We haven't determined level of ground from the two points but, by eyeballing, the slight downward slope from platform to end point would certainly compensate for the 0.2M and maybe more.

The length of rail from start of slope to end of slope is 24.4M

Bumblebee weighed in at 1,550 Kg.  The cart it is sitting on is estimated at 200-250 Kg.  So perhaps a combined weight of 1,800 Kg.
In prior tests of Giant Top 1.0 we successfully added another 500 Kg to cart by use of sand bags (to reach 200 rpm).

The bearing that controls top shaft wiggle is 27 cm. inside diameter. The central shaft is a 3" (7.6 cm) diameter steel round bar. (Giant Top 1.0 had a 2" shaft)

In our manual pull the other day, the guys had 60M of rope wound around it.  When we use Bumblebee we use pulleys attached to cart and platform to enable a 40M length of wind for the 20M fall. (which I now see is actually 24.4M). When we haul up Bumblebee we add another pulley to a nearby coconut tree so it takes 60M of rope to bring the cart up to the top of ramp platform.

The weight of frame itself was about 800 Kg from factory.  We don't think the tarpaulin cover weighs more than 50 Kg.

You are correct that Guinness wanted evidence it was spinning without leaning on the controlling bearing.  We actually videoed the evidence but have never sent it in.  It would bang back and forth but was obviously not dependent on leaning on the ring.

Yes the goal is also to have it look like a peg top.

Thanks!

« Last Edit: May 13, 2021, 01:51:22 AM by JMauk »
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ortwin

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Re: Earth-powered top starters
« Reply #67 on: May 13, 2021, 06:55:19 AM »

...
Just did some measuring to confirm.
...

Yes the goal is also to have it look like a peg top.
...
Thank you for providing those details here in a condensed version. Even if they are given before in another thread it is tedious to find them, especially if one did not follow that thread at the time.
Since you like to have the (upright) peg top look, you can safely ignore the rest  of this post Joe!
.... Lowering the center of mass could be a good idea in that respect and not something we considered at the time.
Maybe one could still bring the center of mass down considerably!Imagine mounting the top upside down! (Except for the tip of course)CM would go down from 3/4 of its height to 1/4 of the height. From the formula critical speed would decrease by a factor of sqrt(3) . That means you would need only one third of the energy to get to critical speed! You could split what you win in between safety considerations (braking of the bumblebee, or its mass and speed), ease of start (manual start possible) and spin time.But I guess you would find an upside down peg top looks strange. To me a peg top looks strange to start with. For me with my cultural background the archetypal spinning top would look somewhat like this:







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