awesome video and very informative I never though of adjusting the the CG with screws like that... Im trying to fix a large wobble top and I think I will do this with some tungsten weights
+Engineering Science , the idea of the screws comes from the dynamical top of Maxwell. Whoever is interested in the physics of the spinning top, will find interesting that Maxwell top. Three horizontal screws are enough for the static balance. Then other three ones, horizontal, are necessary for adjusting the inertia of the axes of the top, (not for balance). Other three ones, vertical, are for the dynamic balance. It is interesting the use of a coloured disk for studying oscillations ( I suppose nutation) of the top. Maxwell describes his top here, from page 248: books.google.it/books?id=Jrzq_7NhGRkC&pg=PA262&lpg=PA262&dq=dynamical+top+maxwell&source=bl&ots=DvfbGGs_P_&sig=whB-CUxE5QBbYzNLXXHhFOeL9f0&hl=it&sa=X&ved=0ahUKEwiV8L6xiKPMAhWDEywKHSvhBg8Q6AEIJzAC#v=onepage&q=dynamical%20top%20maxwell&f=false
UPDATE: Referred to the part of this video starting from 9'37"; The spinning surface is important in this test, because if it is slippery (glass, steel, carbide) the unbalanced top spinning especially at high speed makes the tip to wobble slipping sideways and the marks on the top become randomly distributed around the stem. This is what has happened in the top in the video. If the top is spinned on a too soft surface, (cardboard, wood), the tip will not wobble but it digs a hole in it and then the top wobbles in a more unpredictable way, and again the marks become misleading. I found a compromise with a soft plastic material, and I have been careful not to make the top to spin too fast, to avoid the tip slipping and wobbling on the base. So I have been able to observe that there is a particular behaviour of the top in this situation: in fact the marks left by the brush on the stem have been always about 90 degrees after the heavy side of the top, (the top was spinned in clockwise direction). It doesn't matter if weight is added at the center of the flywheel, or above, or below it; marks are always about 90 degrees after the heavy side. If the top is spinned counterclockwise instead, then the marks appear in the opposite side. Also shifting the added weight in different sectors of the top has changed nothing, each time I shifted the weight in a different sector of the top also the leaning direction of the top changed, staying always at about 90 degrees after the shifted added weight. Rotational speed (400 - 900 RPMs) has some effect (not strong) on the position of the marks, and that at higher speed the top leans a bit more towards the heavy side and at lower speed a bit more towards the light side. All this has been tested with the barycenter height of the top setted at about mm 16. (The diameter of the top is mm 72). At about mm 14.5 or less the marks are always in the heavy side of the top. At about mm 18 or more instead the marks are always in the light side of the top. Then there are halfway positions for the marks depending on the height of the barycenter; at about mm 17 the marks are 135 degrees after the added weight, and at about mm 15 the marks are 45 degrees after the added weight. That's all. I thought to what could be the reasons of this behaviour but still I don't understand them. It doesn't seem precession, because I expect precession to take place when there is a steady force applied to one side of a spinning wheel. If instead the force (the added weight) spins together with the wheel, (being the weight attached to it), as in this case, I would expect unbalance, with the top staying leaned towards the heavy side (or the light side), and not at other different angles.
Hello again. Still not getting the wobble out of the brass top but it's better. So if I install 3 grub screws and adjust them the wobble would magically disappear... I just want a descent spin out of it. Like I said I'm just buying a 1/4" steel rod from hardware store and using a file and sandpaper to make a point. The point could be off to. I don't have a lathe. Might pick up a smaller diameter steel rod and try another one. I think 1/4 steel rod is to big for the size of the top.
Hello, Steve. To adjust the balance with the screws is easier than filing the sides of the tip. Anyway it is not totally sure that the three screws alone will make the wobble to disappear completely, because these screws are for adjusting the static balance alone, and do not correct the dynamic balance. It is possible to add other three screws, vertical, to the top, for adjusting specifically the dynamic balance, (so there would be six screws, three horizontal ones for the static balance and three vertical ones for the dynamic balance); with these six screws it is possible to adjust the balance of the top completely, and to achieve a really perfect balance of the top. You can see a top made in this way by Maxwell, (he put six horizontal screws, but three are enough, then you can see the three vertical ones): commons.wikimedia.org/wiki/File:NSRW_Top_-_Maxwell%27s_dynamical_top.jpg If you prefer to stay simpler, you can put only the three horizontal screws, and ignore the dynamic balance. This is what I usually do with my tops, but I use a lathe for making my tops, so the simmetry of the top is accurate and I don't really need to correct the dynamic balance. Making tops without a lathe is different; if the simmetry of the top is not accurate, there is the possibility that dynamic balance too would need to be checked, if very good overall balance is wanted. I agree with you that 1/4 steel rod is a bit too big, I think 1/16 or 1/8 would be more than enough.
Interesting video. I got into tops a few months ago. Of course now I want to make my own. I'm working on a brass. Top. A 1/4 " thick brass stock.....1 3/4" circle. Just got a 1/4" steel rod.. filed it to a point on my portable drill press. I'm trying to file the outer edge so it spins descent. I'm getting there. When I spin it fast it's pretty stable once it starts slowing down here comes the wobble. Pretty bad wobble but it still spins for a good while. I like that grub screw idea. Is that the rule to put grub screws at 3 points? . I don't know, any ideas on how to get this top spinning better? I know I still have filing to do. Made one out of plexiglass. Spins pretty well , but it's weird as it gets really slow I get a revolution or 2 where it wobbles a little then the next 2 revolution it's smooth. Then the next 2 it wobbles then the next 2 it's smooth etc. Then it stops. Any way. Love the video I think it will be very helpful. Any ideas would be greatly appreciated. Thanks. Steve from mass.
Thank you, Steve. Stability at fast speed with wobbling which increases at the slowing of the spin speed is a fingerprint of unbalance. There are three causes of wobbling in a top, the other two being nutation and precession, but what you see is unbalance. You recognize unbalance from the other two kinds of wobbling also from the top spinning staying leaned always towards the same side of itself, so that the marks of the brush appear always on the same side of the stem, and this observation tells you that this is indeed unbalance. With nutation and precession instead, the marks appear randomly around the stem. See also this video, (what I call "oscillation" in this video is nutation): th-cam.com/video/DprVi-_dVAk/w-d-xo.html When the top alternates wobbling and spinning smoothly phases, this means that there are at least two different causes of wobbling at the same time, (usually unbalance and nutation, if the top has very low center of mass, otherwise unbalance and precession, in high center of mass tops at relatively slow speed). One of the two wobbles is slightly faster than the other one, when they are in phase the wobbling is given by the sum of them and it is evident, when after a while they become in counterphase they tend to cancel each other out and the wobble is temporarily reduced or cancelled. Some more information about compound movements in this video: th-cam.com/video/m9Bq0FfCi-g/w-d-xo.html You can put how many grub screws as you like more. The minimum is two grub screws, at 90 degrees angle the first from the second. I prefer three screws for aesthetics, for simmetry. Three are enough, and I don't feel the need to put more. The screws work well for fine tuning the balance of the top, just put them at the same height of the center of mass of the top, otherwise you introduce a bit of couple unbalance when you use them to compensate some static unbalance in the top.
awesome video and very informative
I never though of adjusting the the CG with screws like that... Im trying to fix a large wobble top and I think I will do this with some tungsten weights
+Engineering Science , the idea of the screws comes from the dynamical top of Maxwell. Whoever is interested in the physics of the spinning top, will find interesting that Maxwell top. Three horizontal screws are enough for the static balance. Then other three ones, horizontal, are necessary for adjusting the inertia of the axes of the top, (not for balance). Other three ones, vertical, are for the dynamic balance. It is interesting the use of a coloured disk for studying oscillations ( I suppose nutation) of the top. Maxwell describes his top here, from page 248:
books.google.it/books?id=Jrzq_7NhGRkC&pg=PA262&lpg=PA262&dq=dynamical+top+maxwell&source=bl&ots=DvfbGGs_P_&sig=whB-CUxE5QBbYzNLXXHhFOeL9f0&hl=it&sa=X&ved=0ahUKEwiV8L6xiKPMAhWDEywKHSvhBg8Q6AEIJzAC#v=onepage&q=dynamical%20top%20maxwell&f=false
Thank you for all the detailed infomation. It is really helpful
You are welcome, Jeff.
Great video, thank you!
You're welcome, David.
UPDATE:
Referred to the part of this video starting from 9'37";
The spinning surface is important in this test, because if it is slippery (glass, steel, carbide) the unbalanced top spinning especially at high speed makes the tip to wobble slipping sideways and the marks on the top become randomly distributed around the stem.
This is what has happened in the top in the video.
If the top is spinned on a too soft surface, (cardboard, wood), the tip will not wobble but it digs a hole in it and then the top wobbles in a more unpredictable way, and again the marks become misleading. I found a compromise with a soft plastic material, and I have been careful not to make the top to spin too fast, to avoid the tip slipping and wobbling on the base.
So I have been able to observe that there is a particular behaviour of the top in this situation:
in fact the marks left by the brush on the stem have been always about 90 degrees after the heavy side of the top, (the top was spinned in clockwise direction).
It doesn't matter if weight is added at the center of the flywheel, or above, or below it;
marks are always about 90 degrees after the heavy side.
If the top is spinned counterclockwise instead, then the marks appear in the opposite side.
Also shifting the added weight in different sectors of the top has changed nothing, each time I shifted the weight in a different sector of the top also the leaning direction of the top changed, staying always at about 90 degrees after the shifted added weight.
Rotational speed (400 - 900 RPMs) has some effect (not strong) on the position of the marks, and that at higher speed the top leans a bit more towards the heavy side and at lower speed a bit more towards the light side.
All this has been tested with the barycenter height of the top setted at about mm 16.
(The diameter of the top is mm 72).
At about mm 14.5 or less the marks are always in the heavy side of the top.
At about mm 18 or more instead the marks are always in the light side of the top.
Then there are halfway positions for the marks depending on the height of the barycenter;
at about mm 17 the marks are 135 degrees after the added weight, and at about mm 15 the marks are 45 degrees after the added weight.
That's all. I thought to what could be the reasons of this behaviour but still I don't understand them.
It doesn't seem precession, because I expect precession to take place when there is a steady force applied to one side of a spinning wheel. If instead the force (the added weight) spins together with the wheel, (being the weight attached to it), as in this case, I would expect unbalance, with the top staying leaned towards the heavy side (or the light side), and not at other different angles.
I put the shaft in my drill press and use a file and sandpaper to make a point.
Hello again. Still not getting the wobble out of the brass top but it's better. So if I install 3 grub screws and adjust them the wobble would magically disappear... I just want a descent spin out of it. Like I said I'm just buying a 1/4" steel rod from hardware store and using a file and sandpaper to make a point. The point could be off to. I don't have a lathe. Might pick up a smaller diameter steel
rod and try another one. I think 1/4 steel rod is to big for the size of the top.
Hello, Steve. To adjust the balance with the screws is easier than filing the sides of the tip. Anyway it is not totally sure that the three screws alone will make the wobble to disappear completely, because these screws are for adjusting the static balance alone, and do not correct the dynamic balance. It is possible to add other three screws, vertical, to the top, for adjusting specifically the dynamic balance, (so there would be six screws, three horizontal ones for the static balance and three vertical ones for the dynamic balance); with these six screws it is possible to adjust the balance of the top completely, and to achieve a really perfect balance of the top. You can see a top made in this way by Maxwell, (he put six horizontal screws, but three are enough, then you can see the three vertical ones):
commons.wikimedia.org/wiki/File:NSRW_Top_-_Maxwell%27s_dynamical_top.jpg
If you prefer to stay simpler, you can put only the three horizontal screws, and ignore the dynamic balance.
This is what I usually do with my tops, but I use a lathe for making my tops, so the simmetry of the top is accurate and I don't really need to correct the dynamic balance.
Making tops without a lathe is different; if the simmetry of the top is not accurate, there is the possibility that dynamic balance too would need to be checked, if very good overall balance is wanted.
I agree with you that 1/4 steel rod is a bit too big, I think 1/16 or 1/8 would be more than enough.
Interesting video. I got into tops a few months ago. Of course now I want to make my own. I'm working on a brass. Top. A 1/4 " thick brass stock.....1 3/4" circle. Just got a 1/4" steel rod.. filed it to a point on my portable drill press. I'm trying to file the outer edge so it spins descent. I'm getting there. When I spin it fast it's pretty stable once it starts slowing down here comes the wobble. Pretty bad wobble but it still spins for a good while. I like that grub screw idea. Is that the rule to put grub screws at 3 points? . I don't know, any ideas on how to get this top spinning better? I know I still have filing to do. Made one out of plexiglass. Spins pretty well , but it's weird as it gets really slow I get a revolution or 2 where it wobbles a little then the next 2 revolution it's smooth. Then the next 2 it wobbles then the next 2 it's smooth etc. Then it stops. Any way. Love the video I think it will be very helpful. Any ideas would be greatly appreciated. Thanks. Steve from mass.
Thank you, Steve. Stability at fast speed with wobbling which increases at the slowing of the spin speed is a fingerprint of unbalance.
There are three causes of wobbling in a top, the other two being nutation and precession, but what you see is unbalance.
You recognize unbalance from the other two kinds of wobbling also from the top spinning staying leaned always towards the same side of itself, so that the marks of the brush appear always on the same side of the stem, and this observation tells you that this is indeed unbalance. With nutation and precession instead, the marks appear randomly around the stem.
See also this video, (what I call "oscillation" in this video is nutation):
th-cam.com/video/DprVi-_dVAk/w-d-xo.html
When the top alternates wobbling and spinning smoothly phases, this means that there are at least two different causes of wobbling at the same time, (usually unbalance and nutation, if the top has very low center of mass, otherwise unbalance and precession, in high center of mass tops at relatively slow speed).
One of the two wobbles is slightly faster than the other one, when they are in phase the wobbling is given by the sum of them and it is evident, when after a while they become in counterphase they tend to cancel each other out and the wobble is temporarily reduced or cancelled.
Some more information about compound movements in this video:
th-cam.com/video/m9Bq0FfCi-g/w-d-xo.html
You can put how many grub screws as you like more. The minimum is two grub screws, at 90 degrees angle the first from the second. I prefer three screws for aesthetics, for simmetry.
Three are enough, and I don't feel the need to put more. The screws work well for fine tuning the balance of the top, just put them at the same height of the center of mass of the top, otherwise you introduce a bit of couple unbalance when you use them to compensate some static unbalance in the top.