×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

(OP)
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.

Nick

### RE: Newbie question about maglev

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.

### RE: Newbie question about maglev

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!

### RE: Newbie question about maglev

(OP)
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.

### RE: Newbie question about maglev

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

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!