Copper pipe/ magnet experiment....

[mike89]

if anyone is familiar with the experiment, of which you take a copper pipe and you drop a spherical or cylindrical magnet through it, and it then falls at a lesser rate than it would outside of the pipe...... would anyone know how strong this force is.... would you be able to hold the pipe horizontal and still have the magnet "levitate" within the pipe? or maybe at the most 45 degree angle or something? i am sure there are many factors to persuede the results one way or another but any ideas on the experiment would be a lot of help, thanks

[GAHD]

I'm not familliar with the experiment, please explain the actuall setup a bit better.

[CraigD]

if anyone is familiar with the experiment, of which you take a copper pipe and you drop a spherical or cylindrical magnet through it, and it then falls at a lesser rate than it would outside of the pipe...... would anyone know how strong this force is.... would you be able to hold the pipe horizontal and still have the magnet "levitate" within the pipe? or maybe at the most 45 degree angle or something?

I can’t readily provide formulae for this, but can informally describe it.

 

A permanent magnet moving near a conductor that forms a circuit induces a current. The current produces a magnetic field, which repels the permanent magnet. A tube of copper, aluminum – any non-magnetic conductor – can be pictured as a wide ribbon – that is, a conductor forming a circuit, so will produce this effect. It can also be produced with a conductive disks – aluminum washers, for instance – in the outline of a tube, spaced closer than the magnet is long, or with gaps cut in the tube. 2 or more conductive tubes or arrays of washers placed parallel to each other and closer together than the width of the magnet will support a moving magnet nestled between, not inside, the tubes. The tube shape can be flattened, rectangular, or many other shapes.

 

Note that the “levitating” force depends on the speed of the magnet. The arrangement can work with the tube(s) horizontal, provided the magnet moves fast enough. The effect results in a slight drag on the magnet, so unless it’s given a slight driving force, it will eventually slow and settle until it touches the tube(s). The speed at which the magnet levitation enough to safely avoid touching the tube(s) is usually called its “takeoff speed”.

 

A mature, patented implementation of this effect is the Halbach array, which has applications in magnetically levitating (maglev) trains, high-speed launching systems, and low-friction bearings. Halbach arrays have the neat effect of only having a strong magnet field on one side, with their poles pointed outward, making them levitate at a much lower speed than a simple poles-on-the-end cylindrical or rectangular permanent magnet.

 

:hyper: For years, I’ve wanted to build a toy Halbach array maglev train – I think it could be done with ceramic coated wire wrapped around hot-wheels track, some wood, glue, and 5 hobby magnets like these – but haven’t had time to try. (curse my busy professional life!) So, if you work out some useful formulae to predict takeoff speed, etc., I’d love to see them. :hyper:

[Jay-qu]

I beleive they are called 'eddy currents' and no dont think you could calculate it - even if you had a formula how could you get the value of the current?

[mike89]

thanks for the info guys, the reason i am asking about this is because of a project i am planning on working on, i am mostly trying to figure out right now if it would actually be efficient enough to bother with but here it is..... i have always been interested in cars and magnetics so i was just thinking of a way to make the turbo more efficient, spool up more quickly, reach greater rpms with even bigger turbos. i was thinking maybe replacing the shaft on a turbo charger with one of ferrous composition, and by some means produce a force to make the shaft and its components to levitate therefore ridding it of the bearing systems that are used presently.... whether it be a layer of oil, or a ball-bearing system or other wise. I am thinking that this concept could eliminate a good deal of resisting forces. Now the thing i am not sure of what to use right now is the surrounding of the shaft, the part that is going to actually make it happen. i had a couple ideas, an electomagnetic surround of the same charge to repel it from all directions which could possibly be run off the alternator, or i came across the experiment with the copper pipe and the magnet and it kind of made me wonder if this was possible to utilize this concept for the project. if anyone is not familiar with a turbo charger and how it works

http://auto.howstuffworks.com/turbo.htm 

this link will show you... any interest in and/or help on any ideas or help will be much appreciated thanks everyone

[mike89]

actually come to think of it gahd i descussed the project with you back when i first thought of it when i first became a member... now that i have a lathe i can use it seemed like the perfect time to try and figure out exactly what i should be trying to do

[CraigD]

… i was just thinking of a way to make the turbo more efficient, spool up more quickly, reach greater rpms with even bigger turbos. i was thinking maybe replacing the shaft on a turbo charger with one of ferrous composition, and by some means produce a force to make the shaft and its components to levitate therefore ridding it of the bearing systems that are used presently …

I suspect you could probably get some magnetic bearings commercial-off-the-shelf – this Wikipedia article “Halbach cylinder” says they’re used now in brushless electric motors and generators.

 

I don’t know if magnetic bearing would provide much practical improvement over current commercial sleeve or ball bearing turbochargers, though. My personal take on how to make “the ultimate supercharger” is to drive the compressor off of an electric motor powered by a high-voltage battery charged by a generator off of the crankshaft – essentially an electric version of a belt-driven supercharger. As with a belt-driven supercharger, lag could be nearly 0, boost limited only by the fuel used – with gasoline, there’s a danger of “diesel” compression detonation at very high fuel-air mixture compression, putting a practical upper limit on how big a supercharger a given displacement engine can have.

 

My personal take on car powerplants in general is that the ultimate is to be had in something like the Chrysler Patriot WSC race car, keeping the gas turbine generator but replacing with the troubled flywheel energy storage system replaced with either a high (~ 400 V) voltage battery, or maybe something very exotic, like an large aerogell capacitor. The idea of having a 750 HP water-cooled electric motor under the hood stirs my long-dormant gearhead soul.

[mike89]

yeah thanks for the input

[UncleAl]

Lenz' Law. The magnetic field must be moving vs. the conductive walls to create eddy currents. An N45 Fe-Nd-B magnet reasonably close fit in a copper or aluminum tube will very slowly descend, like goosedown floating to earth.

[GAHD]

hmm, if it's based offthe earlyer discussion, whu not continue it there?

On a side-note, it would have to be run off the timing belt/chain, or off of an electric motor, as exaust gets hot enough to corrupt magnets.

[mike89]

the whole heat is a good point.... although you could just run it somehow so that it is spun by an electromagnet throgh propulsion or attraction... using the elctromagnet like you said the charge could be determined by the pully or belt or whatever drives the electromagnet to spin it faster and faster

[cwes99_03]

I don't think anyone has said it yet, but it was probably implied. You can not just drop the magnet through the tube and get it to eventually levitate. The magnet has to be moving to create the eddy currents, and if the magnet slows down then the eddy currents will get smaller.

 

We actually measured the effects of eddy currents with a driven oscillator (aluminum) passing through a magnetic field. Slowed the combed pendulum down a lot less than the solid pendulum, because smaller eddy currents fromed in the combed one (not to mention less surface area total of the pendulum passing through the magnetic field.

[labview1958]

Does a thicker copper pipe slows the magnet more than a thin one?

[CraigD]

Does a thicker copper pipe slows the magnet more than a thin one?

I think so, but only by a small, perhaps unmeasurable amount.

 

The increased thickness would result in reduced electrical resistance to the induced “eddy” currents that produce the magnetic field that slows the magnet, but I think the effect would be very small.

 

Replacing the copper pipe with one made of a super-conducting material would, I think, have a dramatic effect. It’s actually possible to “levitate” a magnet on the magnetic fields it induces in a small superconducting plate placed beneath it. How it would superconductivity would effect the magnet and pipe apparatus, I don’t with confidence know.