Dyna Beads - Do they work? If so, how?

[Fred W]

Well, it seems that the folks who hang out in "Physics Forums" can't come to an agreement on how these things work (or if they really do) either. But there is one hypothesis presented here which may have merit:

If you consider a rigid circular unbalanced wheel, not in contact with the ground, with the axle mounted on equal stiffness springs horizontally and vertically (i.e. a wheel on a balance machine, not on a car), the mass of the wheel and the stiffness of the springs have a natural vibration frequency. If you spin the wheel at a speed below that frequency, it will rotate so it moves with "heavy side out" (i.e.the heavy side is furthest from the point near the axle that doesn't vibrate) and the amplitude of the unbalance force will increase as the RPM increases. When the RPM equals the spring-and-mass vibration frequency, the ampllitude of the out of balance motion will be a maximum. If you increase the speed above this point, the amplitude reduces and the wheel now moves with the light side out. That may not seem intuitive, but it's a straightforward deduction from the equations of motion, and easy to confirm by experiment. One way to understand it is that a very hgih RPMs, the inertia of the wheel means the "easiest" thing for it to do is rotate about its own center of mass, not about the axle position).

If the bolded statement is true, then I can see how the beads would gravitate to that light side, it being the furthest from the axle.

I've also now found some new explanations that liken an out of balance wheel to an out of balance Frisbee. I'm sure that you've all done this experiment before: Put a glob of mud under the edge of one side of a Frisbee and throw it. The Frisbee precesses in an elliptical pattern with the mud cake towards the center because the center of mass has shifted towards the mud. So, in that instance at least, the light side will be pushed further out from the physical center where an axle would be.

Maybe this is the bit we've been missing. We have all assumed that the heavier side would pull itself further away from the axle by centrifugal force, but maybe the opposite is true of the fast spinning wheel due to its center of mass?

Some high speed photography would prove or disprove if that is what is happening.

 

[wheatonFJR]

I'm still waiting for a definitive answer on the conveyor belt thread.

 

[Fred W]

I'm still waiting for a definitive answer on the conveyor belt thread.

 

[ionbeam]

Headache material below, if you are prone to crossed eyes, sudden sleep attacks or get dizzy and fall out of chairs DO NOT READ THIS.

The beads go to the light weight spot on the tire. Lets get past this right now as far as beads go.

When your motorcycle is stopped all the little beads sit on the bottom of the tire. As you start to pull away friction will cause the beads to start to follow the tire around. As the tire speed gets faster lateral acceleration -- street name centrifugal force -- will hold the beads against the tire. In a perfect world the beads would try to disperse and make a uniform ring. But, the world isn't perfect and neither are the tires. The out of balance tire will create vibrations which are annoying enough to make people balance the tires. Just as sound waves will make ripples on water the spacing of the ripples change with the frequency the tires. The tire vibrations will get stronger with speed.

At very low speed the vibrations are low enough that you don't notice them. In fact the vibrations don't become noticeable until the bike is traveling at significant speed causing the vibrations to become stronger. Now the beads that are trying to be orderly in a ring start to be subject to the vibrations in the tire and start to separate in waves like the harmonic ripples on water. It is the vibration harmonics that cause the beads to arrange themselves and vary wave spacing with the frequency of the vibration.

Because of the strong forces on the tire and the mass of the tire it is unlikely that a 1/2 cup of beads will be able to damp all the vibrations (energy). Then every time the tire goes over an regularity that makes a concussive strike on the tire there are secondary vibrations created. The conventional external weights would not damp this but the beads will have their harmonics disrupted. If there was a sufficient weight of beads in the tire to damp the energy of the tire vibrations the tire would feel balanced because the vibrations have been damped. Also, for this to work the ripples in the beads would have to have a fairly long wave length creating gaps big enough for the beads to have an effect.

-- Or not, it's just a guess.

 

[rushes]

Yeah, that's what I meant...

 

[A41Billy]

 

[beemerdons]

Yeah, that's what I meant...

I know exactly what you mean Brother Russ, I just hate it when Alan Ionbeam just barely beats us to the damned answer! jes' sayin' and nuff said!

 

[ionbeam]

I know exactly what you mean Russ, I just hate it when Alan beats us to the damn answer! jes' sayin' and nuff said!

You have no idea how much scotch it takes to make up shit like that

 

[rushes]

Yeah, that's what I meant...

I know exactly what you mean Brother Russ, I just hate it when Alan Ionbeam just barely beats us to the damned answer! jes' sayin' and nuff said!

No, I had it.

Sometimes my brevity goes right over peoples heads....

 

[Fred W]

I do believe the Professor is spoofing. If that was how the phenomenon worked it would not work like this when there is no contact with the road to generate all the groovy ripples.



NEPRT = Never Ending or Pointlessly Recurring. This one is two pages and I do not recall this particular question (the how does it work question) occurring before.

 

[wheatonFJR]

I know exactly what you mean Russ, I just hate it when Alan beats us to the damn answer! jes' sayin' and nuff said!

You have no idea how much scotch it takes to make up shit like that

Damn, now we have to guess how much scotch it takes!!???

Life is too hard.

 

[ionbeam]

I do believe the Professor is spoofing. If that was how the phenomenon worked it would not work like this when there is no contact with the road to generate all the groovy ripples.

Ok Captain, are you saying that the free air wobbling of an object (tire, coke bottle video) is not a vibration? Since it's Friday, when does a wobble stop being a wobble and become a vibration? Looking at the way the guy's hand with the drill shook with the bottle it sure looked like a vibration to me.

 

[Fred W]

Define vibration.

That orbital precession caused by the imbalance is at such a (relatively) low frequency I don't think we are getting standing waves and damping inside the tube with the fluid and steel balls in it.

NB - I am assuming the Centramatic works on the same principle as the DynaBeads.

 

[Bustanut joker]

Vibrations,Beads, Harmonicas, Scotch, and a shaking hand..

This sounds more like a penthouse forum thing.

 

[PhilJet09]

I'm still waiting for a definitive answer on the conveyor belt thread.

[img=[URL="https://thetruthaboutplas.com/wp-content/uploads/2011/08/busted.jpg%5D"]https://thetruthaboutplas.com/wp-content/uploads/2011/08/busted.jpg][/URL]

https://www.youtube.com/watch?v=YORCk1BN7QY

Seriously? The dumbass pilot didn't know he'd get off the ground? Wow.

 

[Fred W]

Mythbusters didn't do an accurate recreation of the myth, at least as I understood it.

The way it was supposed to go is that the plane only propels forward enough to stay stationary, and the conveyor belt goes back fast underneath at take off speed.

But you are right, why the pilot thought he wouldn't take off when he gunned it is a mystery.

edit - I wonder if I could convince MythBusters to do a piece on "Balancing Beads?" They probably would shy away to avoid legal proceedings initiated by the bead companies...

 

[beemerdons]

Vibrations, Beads, Harmonicas, Scotch, and a shaking hand..
This sounds more like a penthouse forum thing.

Don't stop them Barry, Fred and Alan are on a roll!

 

[ionbeam]

Seriously? The dumbass pilot didn't know he'd get off the ground? Wow.

+1 to that. Once there is sufficient air flow over the wings it's gonna be able to lift. Heck, even if the air frame is restricted from moving, get a wind storm to blow 60 knots (70 mph) down the length of the aircraft and a 172 could still be able to lift off with the air frame at 0 mph in relation to the ground

Mythbusters didn't do an accurate recreation of the myth, at least as I understood it....

Since this thread starter is also going to be a thread hijacker too...

That is the mother of all poorly worded and framed questions/conundrums. To get a good answer you have to ask a good question.

Don't stop them Barry, Fred and Alan are on a roll!

And with that, it's time to go see about that scotch. In a few minutes I may not understand better but I'll care a WHOLE LOT LESS.

 

[Fred W]

That is the mother of all poorly worded and framed questions/conundrums. To get a good answer you have to ask a good question.

Truer words was never spoke.

Mythbusters both entertains and infuriates me. Perhaps the latter is part of the former.

So... how about those Patriots?

signed Fred (Hijack is my middle name) W

 

[jmgrif]

The wheels on the plane will be rotating at the speed of the conveyor belt plus the speed the propeller is pulling the plane along! I think?