small electromagnets

[buzzrocket]

could i get some suggestions for a place in which i can find small electromagnets? i dont want to build them because i want to use a computer to alternate their polarities as i put them in sequence. everywhere i look seems to not have electromagnets of a small enough size and high enough power.

[hotwaterwizard]

Buy a bunch of solenoids real cheep.

This one looks like a Door Bell solenoid 
http://www.allelectronics.com/cgi-bin/category.cgi?category=575&item=SOL-89&type=store
MINI SPRING-RETURN SOLENOID
CAT# SOL-89
    $ 1.35 each
100 or more  $ 1.00 each
In stock
Ships within 24-48 hours
   

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http://www.allelectronics.com/cgi-bin/category.cgi?category=575&item=SOL-85&type=store
24VDC SOLENOID
CAT# SOL-85
    $ 1.25 each
10 or more  $ 1.00 each
In stock
Ships within 24-48 hours

[Guest Alun]

If you remove the spring from the solenoid and fixe the core in the coil with a suitable adhesive you have and electromagnet.

I would strongly reccomend making your own and using a switched mode constant current regulator to dirve it, this will lead to the highest possible efficency as you could alter the current to find the point where it just saturates. To get a strong magnet you need a core with a high saturation flux, hysteresis and edy current loss shouldn't be a problem as long as the polarity reversal frequency is fairly low. For DC to a few Hz, I'd use a soft iron nail for higher frequencies a laminated core would be needed and even higher ferrite would have to be used.

What frequency to you plan to reverse the polarity?

[buzzrocket]

the problem with rolling my own magnets is that i find it to be tedious, time consuming, and usually less effective. every time i have attempted this it doesn't work out right. i prefer machine-coiled. i like the idea of using the solenoids, but what do you think would be a good adhesive? i want it to be stable, but i'm not sure about super glue. i know it won't mess with the field, but it is sort of expensive and easy to mess up with. with regards to frequency, i was hoping to network a track of electromagnets and experiment with the frequency. i wanted to use the japanese eds (electrodynamic suspension) maglev system with superconductors, which require a minimum speed to attain levitation (about 62 mph or 100 kph). i wanted to test that concept scaled down and develop models for this sort of suspension and take my ideas from there.
                                                                                          thanx 4 the posts.
p.s. i'm thinking like a max of 10 Hz. any more might be too fast for what i want to do. soft iron nail still cool?