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 1 
 on: Today at 05:42:08 AM 
Started by the Earl of Whirl - Last post by MarkLeithead
WOW!!!  Good luck with all your travels, Mark.  I look forward to hearing your stories.

We are on with the 22nd.  I just got word from the city of Miamisburg and we are all on the same page.  If you can, please put us on your schedule.  It will be another great spinning time in the Burg on that fourth Saturday in August in the year 2020!!!


Nice! Thanks for the kind words. Good to know the dates as well. Looking forward to it! :)

Quote from: ta0

 :o I'll see you in Budapest, Mark, but I cannot make Miamisburg the following weekend.

I added Miamisburg to the calendar, and it appears to be also Jim Neff's birthday  :)

Cool! Sounds like a plan. Should be fun. I'm so grateful the World came to my backyard in 2019. Budapest should be great, the venue looks pretty slick. :D

 2 
 on: Today at 04:10:12 AM 
Started by Iacopo - Last post by Iacopo
Pure couple unbalance occurs when the top is constrained to spin about an axis passing through the CM but not one of the top's principal axes.

I was thinking only about unbalanced tops supported at the center of mass, so the only source of imbalance was the direction of the principal moment axis aligned in a direction different than the stem. In that case the only pure imbalance would be the false imbalance. But I can see that if the center of mass is away from the support the top, the top cannot have a stable spin. At this time I cannot tell if there can be "pure imbalance" with no (or much smaller) torque-free precession.  :-\

To say it in different words, if a top can spin in sleeping position, with the principal moment axis staying vertical, and passing through both the center of mass and the tip, I would say that the top is balanced; if such a top had the stem bended, the stem would wobble, but the imbalance would be apparent, not real.

The imbalance is real when the center of mass is away from the support of the top. 
I saw high CM tops to spin unbalanced and with some torque-free precession, I am not sure whether these tops can spin unbalanced without the torque-free precession.
But I can tell that my tops with low CM, when unbalanced, (I mean real imbalance), can spin without torque-free precession, and they trace a simple circular trajectory. I call this "pure imbalance wobble".


 3 
 on: Today at 02:35:17 AM 
Started by Iacopo - Last post by Iacopo
You got them mixed up. In the left side (prolate case) the precession and spin are in the same direction while on the right side (oblate case) they are in opposite direction.

You are right... but there must be an error somewhere..
My oblate tops have the spin and the inertial precession in the same direction, not opposite.

 4 
 on: Today at 12:25:15 AM 
Started by Dick Stohr - Last post by the Earl of Whirl
Sure!  Bring them to Miamisburg and I could most certainly use them!!!

 5 
 on: Today at 12:23:14 AM 
Started by paxl13 - Last post by the Earl of Whirl
It came through tonight.  Good job.  I enjoyed the video!!!

 6 
 on: January 27, 2020, 11:55:09 PM 
Started by paxl13 - Last post by jim in paris
great flow , Xav ! you have tamed this soda with flare/flair ;)

as you say
"keep spinning!!"

jim

 7 
 on: January 27, 2020, 11:38:18 PM 
Started by Dick Stohr - Last post by Dick Stohr
We are trying to reduce our foot print in the storage unit, which is expensive. I have 4 display racks which I think were originally designed for shot glasses or thimbles or something small. Interesting the holes can hold tops or yo-yos. The overall dimensions are 25"h, 13"w and 1 3/4"deep. Each hole is 2 3/4" x 2 3/4" x 1 5/8" deep. These have become excess now that I have no place to hang them. I have 6 others that are a bit larger but I have not removed the yo-yos at this time. I would like to sell them. Doing a little research I have found that in one configuration UPS will pack them for #33.XX and ship for $125.XX. That I thought was too much so I reconfigured them and he said $20.XX to pack and $65.XX to ship.I still think that is a lot. I am open to other options if there is interest. Would anyone be interested in free shipping if I brought them to Miamisburg this year.


 



 8 
 on: January 27, 2020, 10:13:14 PM 
Started by Iacopo - Last post by ta0

If the top spins like a balanced top with just a bended stem, I think that I could call it "false unbalance".

I see the real unbalanced top as the top with the tip and the center of mass vertically misaligned.
The behaviour is different, the real unbalanced top may appear nearly well balanced at high speed, but then it makes a circular trajectory with the stem which becomes wider and wider by the time, until toppling down. The spin time is reduced.

The "false unbalanced top" instead, (just the stem bended), would have the stem wobbling since from the start, and its circular trajectory would not become wider and wider by the time, at least until towards the end of the spin; it would move like a balanced top, (hence "false unbalance").   
I was thinking only about unbalanced tops supported at the center of mass, so the only source of imbalance was the direction of the principal moment axis aligned in a direction different than the stem. In that case the only pure imbalance would be the false imbalance. But I can see that if the center of mass is away from the support the top, the top cannot have a stable spin. At this time I cannot tell if there can be "pure imbalance" with no (or much smaller) torque-free precession.  :-\

 9 
 on: January 27, 2020, 10:01:12 PM 
Started by Iacopo - Last post by ta0
It took me some time to understand why the cones were drawn in that way, flanked at the left and one inside the other at the right.
They both produce the same kind of motion.
Then I realized that in the first case the spin motion and the inertial precession motion have opposite direction in the first case, and the same direction in the second case.

It means that oblate tops which spin clockwise, have inertial precession clockwise.
Prolate tops instead, when spinning clockwise, have inertial precession counterclockwise.
You got them mixed up. In the left side (prolate case) the precession and spin are in the same direction while on the right side (oblate case) they are in opposite direction.
The oblate case is hard to visualize.

 10 
 on: January 27, 2020, 06:34:28 PM 
Started by Iacopo - Last post by Jeremy McCreary
I guess you can correctly call it pure unbalance, although the top is spinning perfectly stable: it's just the stem that it's in the wrong place!  :D
If the top spins like a balanced top with just a bended stem, I think that I could call it "false unbalance".

There's already a name for that -- "couple unbalance". Or maybe "dynamic unbalance" if the bend also causes some static unbalance. In any case, no false unbalace here.

Pure couple unbalance occurs when the top is constrained to spin about an axis passing through the CM but not one of the top's principal axes. More than one way to end up there.

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