Newbie question about maglev

[njeffers]

Hello all. I'm new to the forum, so please don't call me an idiot just yet. I have some questions about how to build a miniature maglev train. I don't want to use any electricity (ie no electo-magnets). So is it possible to to set up a guide rail and appropriate magnet configuration to float the car AND keep it stable? Also, I curious to know if you accelerate the car does the change in flux (one magnet passing by another) create an opposing EMF in the magnets and actually try to slow the car down. The reason I ask is due to an experiment in physics class where you drop a bar magnet through a tube and the magnet induces a current in the tube which creates an opposing emf and actually slows the magnet as it passes. I assume (maybe incorrectly) that magnets conduct electricity so I am curious to know what would happen.

Thank you for your help,

Nick

 

[UKpete]

Nick, I've never seen any personal abuse on this forum! it isn't like that. In answer to your question I'm afraid it isn't quite possible to do as you propose using only permanent magnets, you will need some active or mechanical bearing in at least one axis. There is a complex mathematical proof of this - Earnshaw's theorem (you can search on this, one example below).

http://www.wikinfo.org/wiki.php?title=Magnetic_levitation

What this means is that with say a rotary magnetic bearing you can support a shaft radially with passive bearings (i.e. fixed magnetic field such as from a permanent magnet) but it is not possible to control it passively in the axial direction at the same time; or vice versa.

With regard to the braking effect, yes indeed this will happen, it's referred to as eddy current braking and occurs whenever you have a magnetic field moving within a conductor. This is Faraday's law of electromagnetic induction and Lenz's law indicates that that the effect will be to oppose motion i.e. to brake.

 

[UKpete]

One small correction to your final assumption, the eddy currents are in the tube (not in the magnet as the flux isn't changing and is stationary within the magnet). So your tube must be an electrical conductor; thick walled copper will give the best braking action as the electrical resistance will be lowest - ignoring silver that is!

 

[njeffers]

Thanks for the info. I just found something really cool. Check out Halbach arrays and how they are using them to make passive maglev trains!!

http://www.llnl.gov/str/Post.html

Again thanks for the help.

 

[UKpete]

I hadn't heard of that, it will be interesting to see what develops.