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[Pulpowsky]

I'm starting to have fun with my new lathe and I happened to take the gap left by the bearing tip within the body of Saturn Roller top to add some more weight.

>Estoy empezando a divertirme con mi nuevo torno y se me ha ocurrido aprovechar el hueco que deja la punta de rodamiento dentro del ápice del cuerpo de trompo Saturno Roller para añadir algo más de peso.

Ese hueco deja la puerta muy abierta a tuneos que mejoran y mucho las prestaciones. En principio le he puesto una punta que estaba preparando para un Saturno.<

That gap leaves the door wide open to let tune that improve performance. In principle I have given a tip that he was preparing for a Saturn.

>Al ser pieza torneada y tener el agujero en el plástico mucha profundidad, la pieza queda perfectamente centrada. Se nota especial mejora en trucos difíciles en el que ayuda que el trompo de rodamiento tenga más peso en la punta en vez de en la corona, como los grandes lazos.<

As machined part and have the hole in the plastic much depth, the part is perfectly centered. Improvement is especially noticeable in the difficult tricks that helps has more weight a bearing top on the end instead of the crown, such as large loops.

[ta0]

Glad that you are starting to use your new metal lathe and making useful things.

You like tops that are tip-heavy, don't you?  Mass on the tip doesn't add to the rotational inertia ("moment of inertia") of the top around it axis, so it doesn't affect the spin. Neither it adds gravitational torque so it should not affect the precession of the top. So you get a top that is heavier without affecting it rotational properties.

[poptop]

What Ta0 said!  This seems especially relevent for fixed tip play and design.

Thanks for the photo Pulp!

[ROTA 66]

I am very impressed by the technical reply of Tao about the add weight in Saturno Roller maked by Pulp.
Tao: you are very sure about the several forces working in the case described by Pulp (large loops or lassos). Really, in this trick, the weight does´not add anything to make easy the lasso?
Pulp: I am glad that you are using your lathe.

[ta0]

Tao: you are very sure about the several forces working in the case described by Pulp (large loops or lassos). Really, in this trick, the weight does not add anything to make easy the lasso?

Although the extra weight will not help you hitting the top with the lasso, it probably helps you keep it on the string: he top will remain more stationary when you push it with the string and it will give you more time to snag it.

[Pulpowsky]

It is posible to modify the spinning properties of a top adding or removing weight of different parts.

- In the outer edge of the tip. (centered).
- In the inner part of the tip. (centered).
- In the widest part of the body.
- In the center of the crown. (centered).

Adding weight in the inner part of the tip don't modify the inertia but helps the tip o stay onto the string. The cost is a very lightly raise of the precesion speed. (Little, as the weight being placed near the groove). And the center of gravity be placed a bit near the tip.

[ROTA 66]

OK. Very good explanations, TaO, Pulp. I think I am perfectly understand the description of the forces in action and the consequences with the modification of the weight proposed by Pulp. Thanks.

[poptop]

I've heard some recent news commentary that the Earth's rotational speed increased following the earthquake in Chile.  This was explained as a result of subducting crustal mass shifting inward toward Earth's axis of rotation.  The analogy was been made with a spinning ice skater accelerating as the skater's body's mass is pulled inward.

The story made me think of this post and previous discussion of tops that might feature the capability to shift mass mid-spin.  Interesting stuff to think about...

Anyone willing to provide a basic description of moment of inertia?  Keep it simple, I'm not so smart...

This is what I could find, it seems pretty good: http://en.wikipedia.org/wiki/Moment_of_inertia

"The moment of inertia of an object about a given axis describes how difficult it is to change its angular motion about that axis. Therefore, it encompasses not just how much mass the object has overall, but how far each bit of mass is from the axis. The farther out the object's mass is, the more rotational inertia the object has, and the more force is required to change its rotation rate. For example, consider two hoops, A and B, made of the same material and of equal mass. Hoop A is larger in diameter but thinner than B. It requires more effort to accelerate hoop A (change its angular velocity) because its mass is distributed farther from its axis of rotation: mass that is farther out from that axis must, for a given angular velocity, move more quickly than mass closer in. So in this case, hoop A has a larger moment of inertia than hoop B.

 
The moment of inertia of an object can change if its shape changes. A figure skater who begins a spin with arms outstretched provides a striking example. By pulling in her arms, she reduces her moment of inertia, causing her to spin faster (by the conservation of angular momentum)."

[Neff]

My wife brought that up one evening; the idea of a top with arms like an ice scater... she asked if something similar to the clutch mechanism in the Yomega Brain would increase the spin of the top as the weights moved inward.  I intentionally don't think about this, because it makes my brain hurt.

[Spinningray]

Dave and Seth once made a battle top from a BK and a Yomega brain. When it was spinning, spikes would extend out of the body and then retract as it slowed down. The spikes were fully retracted when you threw it. It was deadly and wicked cool.

[MatiasStuntMan]

Hmmmmmm.....

[ta0]

if something similar to the clutch mechanism in the Yomega Brain would increase the spin of the top as the weights moved inward.

As it moves inward the spin speed (RPMs) will increase, but not necessarily the total spin duration, as now the moment of inertia is smaller. The total rotational energy does not change because there is no external torque. This is a consequence of the law of conservation of angular momentum. The only change in spin duration would come with changes in friction (air and ground): the result could actually be a shorter spin duration 

Anyone willing to provide a basic description of moment of inertia?

Normal (linear) inertia is given by the amount of force you have to apply to an object to start it moving or to stop it when it is already moving. In the same way, the moment of inertia is given by the amount of torque you have to apply to an object to start it rotating or to stop it when it is already spinning.  Normal inertia is given by its mass. The moment of inertia not only depends on its mass but also on its "average" distance to the center of rotation.

Dave and Seth once made a battle top from a BK and a Yomega brain. When it was spinning, spikes would extend out of the body and then retract as it slowed down. The spikes were fully retracted when you threw it. It was deadly and wicked cool.

Wow! 

[SpinQueen]

Ta0, I thought this thread was the perfect time to whip out one of your top patents.  I'm sure you have a top design somewhere that would fit right into this topic.

Pops, I don't know about your hoops but with our hula hoops at school (small and large made of the same material)...the larger "rounder" folks always have a way harder time getting the big hoops to stay up and get the momentum going....forget the little hoops...they don't even stand a chance with those.   I can spin both sizes, but have to work my butt off to keep the little hoops going...I need to spin it WAY faster and when I stop moving, it practically just falls straight down off me, unlike the big hoop that gradually stops spinning and slows down to a stop.   I would say that the larger of these two hoops is heavier though, since there is more of it.  Our K teacher is of the softer body type and she works really hard to keep the big hoop going...I'm thinking of adding some duct tape to one of the hoops to add some extra weight for her.  I'm pretty sure it will help.    I'm thinking that the hoops also lose less energy against a harder body not just a smaller frame.   If I tighten up my abbs I can spin the little hoop more easily, and longer.....not sure how/if this last part applies at all to tops?? 

I just play.   I'll save all of the heavy thinking for you science geeks 

[the Earl of Whirl]

Your hula-hoop comments made me think of this video I saw....

http://www.5min.com/Video/What-the-Worlds-Largest-Hula-Hoop-Looks-Like-63913736

[ta0]

Ashrita Furman . . . this is your old friend who has the world Guinness record of more world Guinness records . . ., including the longest duration whipping a top!

Mmm, I think this hula hoop record is something I would have fun trying to break, contrary to most of them which are closer to torture.  It looks feasible, even though my largest homemade hula is only 5 feet wide. Actually, I have an idea of how it could be done . . .