Toy with magnetic levitation 2

[quark]

Gentlemen!

Recently I saw a toy (may be it is new to me) of this shape <>=<> but with rounded edges.Below that there is a U shaped base (with less deep groove) and a glass is attached to that base. When you see from the front view the above shape seems to be cantilevered on the glass, but it is absolutely floating in the air. When you spin the shape it rotates without falling down and without sliding.

Whenever I try to keep magnets one on top of another, the top one is always thrown away. But here it stands.

I jus want to know the working principle and the equations. any ideas?

Thanks in advance

Note: I posted this also in Electric Motors & Controls Engineering Forum

 

[FrenchCAD]

heh, looks like it is a funny toy. wish I could see it.

FrenchCAD
Goodrich Actuation Systems France
Airbus A380 group
cyril.guichard@goodrich.com

 

[Metalguy]

Sounds like they use magnetic repulsion instead of attraction.

 

[diamondjim]

My wife bought something similar in China
and metal guy is right it is magnetic
repulsion principle that keeps it hovering
above the bed. What I have is rectangular
with a top that spins and is suspended in
air above the base. It has an 0-ring allowing
different weight to be added depending on the
magnetic fields in different areas. I cannot
read the instructions as they are in Chinese.
G + F = 0
G gravity
F repell forces
It also must be very near level for it to work.
It is neat and circus barkers would have a ball
with this at fairs etc. I assume it has four
magnets at each corner of the base, and the
gyroscopic force of the top keeps the magnet
in the top repelled equally about the magnets.

 

[quark]

This is a Chinese Toy available at my place.As I feel I got good responses so far, it is better to word my concerns.

By placing magnets either side, you can equate the vertical components of force to gravity and cancel out horizontal components. But when we keep two bar magnets one on top of another (with same magnetic intensity) with oppsite poles facing, the top one will be thrown away.

The height at which the toy floats is about 11/2&quot;. My question is can a sphere be magnetized to one pole?

No responses from Electrical Forum so far.

The postage charges will be atleast 6 times the cost of the toy.

 

[Scipio]

Actually I've got one of those sitting on my desk here in my office. It's not entirely balanced on the magnetic field though, that vertical glass plate on one end keeps the rotor from 'sliding down' the magnetic field on that end. Without that glass plate, the rotor shoots off the stator just the way you suspect it would. The glass plate doesn't exert any vertical force on the rotor, just a horizontal force to counteract the horizontal component of the magnetic field. Also, it only works a certain way, because of the polarity of bar magnets. Put the rotor on backwards (end-for-end) and it sits right down on the base. Not particularly well balanced, but what can you expect from a $10 gizmo bought at a 'science for kids' type store, and I've still been able to get it to spin by itself for 10 or 15 minutes.

I'll tell you though, you want to see someone forget why they came into your office, put that in front of any engineer, mechanic or millright, and it'll buy you an extra few minutes of peace and quiet while they figure out how it works

 

[FrenchCAD]

hehe

Quark : I'm not sure it is possible to magnetize only half of any body, because of the magnetic radiations it produces, those should spray all along the body, magnetizing it. If the bar is half metal/half plastic (or any other non-magnetic material, then you could do so.

And yeah, I bet shipping would be more expensive than toy itself ;-) I gonna look if I can fount it somewhere in a store here

FrenchCAD
Goodrich Actuation Systems France
Airbus A380 group
cyril.guichard@goodrich.com

 

[Metalguy]

Scipio,

The toy I like best is the one that has a bunch of steel balls hanging by strings--all in a line.

You swing one ball into the stationary line and one ball flies off the other end. But when you swing 2 of them, it doesn't make the ball on the far end swing away higher/faster; instead 2 balls fly off.

The reason why is simple, but I've won money from &quot;engineers&quot; who didn't understand it!

 

[ivymike]

My question is can a sphere be magnetized to one pole?

My answer is no. If I remember my beginning physics correctly, there is no such thing as a magnetic monopole, except on Valentine's day.

 

[IRstuff]

While a monopole is not possible, a spherical object with only one pole showing is not necessarily the same thing.

If the sphere were hollow and you plastered the surface with sheet magnets where poles are on opposite sides, then you might be able to build one that had only one pole showing.

The caveat is the almost all commercial sheet magnets are actually striped with alternating poles.

TTFN

 

[ivymike]

Wouldn't the magnetic flux lines have to travel through the surface of the sphere to get from one pole to the other? It seems like the effect of creating such a sphere would be similar to creating one that's not magnetized at all, but I'm just guessing.

 

[quark]

Thanks Guys for your inputs.What I summarized so far from your ideas and my thoughts is

1. Weight of the shape is balanced by the magnetic force. (Can I calculate this if I know the mass of the two magnets and the distance between them using the classical equation for magnetic force?)

2. I agree with Scipio regarding axial movement.

3. I think the circular cross section of the shape maintains its CG to always fall in its Base.

4. Though IRStuff has given a beautiful idea to maintain single pole for the magnet, I doubt because that toy is costing less than 4 USD (in my monetary units). But then if that has two magnetic poles, then how is it balanced even when it is rotated?

Thanks once again, somehow I am feeling restless with this puzzle and that is why I am troubling you people (and I know it is against the principles of this forum)

Note: Now I have a good souvenir incase any of you people happen to drop down at my place.

Best Regards,

 

[MrBeebs]

This is an example of a fully passive magnetic bearing system. A guy called Earnshaw showed that with any system of charged particles (monopoles or dipoles) or equivalently magnetic particles (only dipoles, so far as we know), it is impossible to make an arrangement that is stable in every degree of freedom.
Typically spindles with passive magnetic bearings may be arranged with k_x = k_y (= k_r radial stiffness) and a negative axial stiffness k_z = -(k_x+k_y) = -2*k_r.
Such a bearing, being unstable in the axial direction, needs to be combined with something like a ball bearing, or an active (servo-controlled) magnetic bearing to make a workable spindle.

http://www.mathpages.com/home/kmath240/kmath240.htm

http://scienceworld.wolfram.com/physics/EarnshawsTheorem.html

http://www.chem.yale.edu/~chem125/125/history99/7BondTheory/LewisOctet/Earnshawproof.html

Also read a guy called J.P.Yonnet who wrote several key papers on passive magnetic bearings and couplings
&quot;Analytical Calculation of Magnetic Bearings&quot; 5th Int. Workshop on Rare Earth Cobalt Perm. Magnets and their Appl. 1981 p.199-251.

Hope this Helps

Barrie Brewster