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[johnm]

Looks great!  I always think your brightly colored bearing collars provides great contrast to aid visualizing the target for lasso catches etc.

Do you think hollowing the cap and inserting the solid delrin collar plus bearings and bolt adds a useful amount of weight to give it a less top-heavy feel?

[the Earl of Whirl]

This is all mind blowing stuff for my little pea brain.  Thanks for sharing all of it, though.  I will continue to try to digest it.

Great work, everyone!!!

[Eric]

Do you think hollowing the cap and inserting the solid delrin collar plus bearings and bolt adds a useful amount of weight to give it a less top-heavy feel?

The Delrin is heavier than the HDPE and my bearing tip section is not hollowed out, so Decapitated Rototop #2 is 294 grams almost the stock weight....so about 14 grams of additional weight is right down by the tip.  My guess is that helps with the stability.

[cecil]

The Top is looking great. Tops this size love the great outdoors. And long line.

[MarkHayward]

Yup.

[MarkHayward]

Hey John,
Eric and I have been having a discussion today about balancing these tops on the lathe. If you were to chuck up a top with an open crown, and pour in some liquid (like epoxy or melted plastic) and then run the lathe until it solidifies, would that balance the top? Eric and I are in fairly strong disagreement whether this would make it better or worse. I feel like the liquid would settle into the low/thin spots in the widest part of the top and make it more balanced overall. Eric thinks that the liquid would spread basically evenly because of the centrifugal force and would not help the situation.

What do you think?

[ta0]

I feel like the liquid would settle into the low/thin spots in the widest part of the top and make it more balanced overall. Eric thinks that the liquid would spread basically evenly because of the centrifugal force and would not help the situation.

There is a third possibility, that it makes it worse . . . I think any of the outcomes is possible depending on the situation.

Here is a mini freestyle testing my roto top:



I don't know if I got lucky with my color selections or if I am too accustomed to playing with unbalance tops, but I wouldn't touch mine. I love them!

[Jack]

I feel like the liquid would settle into the low/thin spots in the widest part of the top and make it more balanced overall. Eric thinks that the liquid would spread basically evenly because of the centrifugal force and would not help the situation.

There is a third possibility, that it makes it worse . . . I think any of the outcomes is possible depending on the situation.

Here is a mini freestyle testing my roto top:

I don't know if I got lucky with my color selections or if I am too accustomed to playing with unbalance tops, but I wouldn't touch mine. I love them!

next lvl skilled @-@

[ta0]

next lvl skilled @-@

Thanks, but the top does play well. This was the lightest of the two tops I have. And that is good because I tried a boomerang pirouette and it hit my shoulder: ouch!

There is a third possibility, that it makes it worse . . . I think any of the outcomes is possible depending on the situation.

I think I recall some (dubious) commercial products that claim to be able to balance a tire in a similar way.
Imagine two cases.
In the first case you have ring shaped like the outer race of a ball bearing. It would be perfectly balanced. Now you drill pits around the inside surface and get it unbalanced. I think Mark's proposal would work: the epoxy would fill the pits first and any left over would form a uniform coating. If the epoxy has the same density as the ring material, it would become perfectly balanced.
In the second case you have a ring that has a bulge somewhere but the wall thickness there is thinner so it happens to compensate for it and it is perfectly balanced. The epoxy would accumulate there and make it unbalanced.
In the case of the roto tops, the epoxy would accumulate at the widest section. If balancing could not be achieve by adding putty at that height, the epoxy method won't be able to balance it either.

[jim in paris]

hi all
this discussion goes so fast i haven't got time to catch up !

Eric : excellent mod as usual
i'm sure this Rototop begged to get a bearing

Jorge : cool freestyle , in the wind ..
""This was the lightest of the two tops
same  here : the heavy one wobbles and the light one almost doesn't

jim

[cecil]

I would try the method I use. I drill the 3/16 holes on the top of top and put the rope lead in. All my tops have came out great. Black Walnut and Cedar are the the worst to balance. And I will never make a top out of that kind of wood again.

[johnm]

Fluid dynamics is certainly not my thing and with all sorts of issues at play like non-symmetrical surfaces, rotation perpendicular to gravity, changing viscosity of the epoxy, etc. etc. this is probably a complicated issue.  To a first approximation, I would guess that a fluid enough filler material of enough volume would flow to the largest diameter and form a uniformly round inner diameter, heavily coating thin spots and thinly coating thicker spots.  At any given height along the rotation axis I would expect a constant radius to the inner surface, but I would expect the radius of that surface to change as the height along the axis changed but not necessarily follow the contour of the outside of the top.  By that I mean I expect the final wall thickness to be uniform around the top (provided the outside was symmetrical) where adequate filler was supplied but I do not expect the final wall thickness to be uniform along the rotational axis.

I found a photo sequence of a Hydro Gyro toy (a fluid filled top/gyroscope launched by a ripcord) used horizontally in a gravitational field.  Without rotation the liquid rests in the lower half, with some rotation the liquid is more uniformly distributed but not perfectly, with high speed the liquid is uniformly out to the largest perimeter of the allowed volume.   Although this volume is symmetrical, I would expect the same uniformity of the fluid’s inner diameter for a non-uniform shell.



Does this mean the top will be balanced?  Not necessarily because the non-uniformity of the wall thickness is over all the body of the top and to get the uniform filler surface everywhere, one would have to basically fill the entire volume.  Of course there may be some middle ground because the tip section is very close to the rotational axis and plays a more minor role.

Perhaps a different approach would be to again use a filler of similar density to the HDPE but with a very high viscosity and short work life and apply it like butter on toast or frosting on a cake while the top is spinning.  This would be applying material to a fixed diameter at each height along the axis of rotation thus creating the symmetrically thick wall.
I think putty is still looking pretty good.

[Neff]

I have tried the silly putty thing several times.  It does seem to distribute a little and it smooths out a little but it never helps as much as the sticky tack method.