Homopolar Motor


Slow day at the office?  Here’s a trick that’ll make your coworkers smile. Dangerously Fun has a guide to build a homopolar motor from a battery, copper wire, and magnet. A homopolor motor doesn’t rely on electromagnets in an armature changing their polarity to force a rotation movement compared to stationary magnets. Instead, they use an electrical current’s orientation to a magnetic field to provide a repulsive or rotational force.  In this implementation, the current moves through a loops of copper wire from one pole of a battery to the other.  A rare-earth magnet on one pole of the battery provides the magnetic field.

After the break we’ve embedded video of this simple example as well as a few more complex homopolar examples such as a five speed version.  The motor in action certainly brings a smile to our faces and places this firmly in the useless machines family of hacks.

Oops, this next one’s NOT a homopolar motor.  Thanks Fallen.

[Thanks Paine]

36 thoughts on “Homopolar Motor

  1. @Fallen

    Yes, it is a homopolar motor, there’s no commutation.

    Use the right-hand rule for Lorentz force. Lay your palm out, with your thumb at a 90 deg angle to your fingers. Put your fingers in the direction of the magnetic field, thumb in direction of current, and your palm pushes the direction of the force.

    In the last video we can assume (for example) that the current is flowing clockwise and the magnetic field is pointing up. Using the Lorentz force you see that the bottom of the ring is pushed away from the camera, while the top of the ring is pulled towards the camera. This force continues as the ring begins to rotate.

  2. Mere seconds after seeing this I grabbed a AAA battery, some magnets from the back of some LED flashy things, a coat hanger and a piece of solder and surprised my wife when I showed her my own working homopolar motor!

    Now, of course I have to make a nice one to sit on my desk!

    THANK YOU HACK A DAY and the creators for bringing this to me!

    Delight! Delight I say! :D

  3. It is far from new, but still cool. I thought the first time I read about this a long while back that it was b.s., then I tried it. I only had square neodymium magnets so it did not work right but it showed very clearly that the concept worked. It rotated poorly, still worked tho! Square wheels do suck after all. An example of one of these motors doing work (something useful other than education.) would be awesome. Probably hard to do with a motor that appears to have slightly more than zero torque.

  4. its NdFeB, some peope call em NIB for neodymium iron boron. i wish i had one lying around that had the poles arranged correctly. i dont wana break my hard drive magnets in half, and the other ones i have are way too small.

  5. looks like the magnet has to conduct electricity, so i might try wrapping a round black magnet with aluminum foil or something when i find one. sure it wont be as fast cuz it wont be neo, but this is cool nontheless

  6. @jeditalian: if you magnet doesn’t conduct electricity, just put a washer or coin on top of it and touch the wire to that. It is not critical that the current goes through the magnet, it just has to be flowing.

  7. you just found this ? So tell me why did you chose to live in the cave most of you life, since you escape from basement you was locked in by child molester for 10 years ?

    Posted at 2:38 pm on Nov 10th, 2009 by therian



  8. I just got my mind blown because I’ve spent my entire life knowing that magnets don’t stick to pennies (I remember from experimenting with magnetism as a kid)

    Turns out our (Canadian) pennies have been able to stick to magnets since 2007…

  9. @v.dog: Amen! Firefox/Adblock Plus have made the net a nice place to visit.

    Also, as a cave dweller I had never seen such a motor before and I think this post is great. Can’t wait to impress the nephews with it!

  10. This Blows
    .. my mind! lol.
    right hand rule: say the electrons are going up to + terminal. stick yo right thumb up. your fingers are pointing in the direction of the newly created spinning magnetic field. if u could point your right thumb up 4 the other wire, and see the magnetic fields like wheels, both rotating ccw, put a wheel in the middle, it will go clockwise. the magnet is so strong that it makes the battery a big str8 magnet, but where those fields interact is where i get lost, because up and down are n and s, rgw wire mag field is like a wheel one side n one side s, spinning 90degrees to the updown n s battery, and the magnetic fields r acting like invisible gears turning. the 5 speed rig is just mindblowing. anyway that 90degree magnetic field interaction cuts down on magnetic drag/ lockup/pull/ friction.. but i believe also reduces the ability to do real, useful, harnessable w0rk. if you had 2 or more normal 2polar mags spinning where N attracts S attracts N, you could transfer mechanical energy, without the problem of worn out gear teeth, since the gear teeth are magnetic instead of material. but try putting those magnets like spinning [N-s] o [s-N] spinning, where o is a coil. monitor the electrical signals coming from the coil. i’d like to know what happen. or where o is an up-down magnet like the battery magnet combo. im pretty sure it would resonate trying to seek equilibrium. . as long as the[ns] [sn] magnets are spinning, you’ve built a 3 magnet vibrator! but it can be much more useful than a vibrator, if you put your mind to it.

  11. @ jeditalian i dont think you need to break your hard drive magnets (you shouldnt break these magnets because of the sharp edges and pinch factors).

    it looks like the aa battery is being held up by the magnets and is being charged by the magnet.

    i think you should be able to use a dead watch battery lr44 http://en.wikipedia.org/wiki/LR44_battery

    wrap it in foil so you short the battery to prevent the power from the aa battery from going through the lr44 battery.

    the lr44 battery just like a stack of small washers would be used to elevate the aa battery and would magnetically charge the aa battery then you can set it on the drive magnet.

    also if your town has an electronics recycling center that does not have any data privacy policies and will allow you to take electronics from the bins you could take an old computer for it’s hard drive.

    also dumpsters are a good source of old computers too as long as your state or the federal does not have any electronics disposal laws that bans the disposal of electronics via the garbage.

    if you have a computer repair shop you may be able to ask them they may give you some broken hard drives.

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