Introduction: Pair of Hearts Homopolar Motor
Make a pair of rotating copper heart motors...that unite to become one!
In this Instructable, I show how to make a special 2-piece homopolar motor with a bass speaker, some coins, a battery and two pieces of copper wire.
A neodymium magnet can be used instead of the bass speaker and coins.
This is a great display for Valentines Day...or any day of the year!
The homopolar motor is the simplest form of electric motor. It consists of a battery, a conductor, and a magnetic field.
Unlike other electric motors, the homopolar design doesn't require changing magnetic fields to work. It is a demonstration of the Lorentz Force.
For detailed info, see Wikipedia under "Homopolar Motor" and "Homopolar Generator".
The flat Heart shape is the most basic of homopolar motors. The Heart with legs is the next most simple shape. With a little ingenuity, the two shapes can be combined into one spinning body!
The above movie shows a bass speaker as the source of the magnetic field for the Heart homopolar motor. Pennies are used as a commutator.
Note: No neodymium magnet is needed in this case!
Song is "Be Excellent To Each Other", courtesy EJ Gold, from the album "California Dreams" .
The above movie shows a traditional neodymium magnet used as the magnetic field for the Heart motors.
Background music is a non-traditional band called Wolf Parade from Montreal, with "This Heart's On Fire". (Used with band permission)
Note: Unfortunately, mere permission from the band was adequate for Warner Music, and the music of this video has been stripped from it by them.
Here is a YouTube video with the "This Heart's On Fire" song, so that you can try playing it at the same time as the above movie...http://www.youtube.com/watch?v=0Xq4o-kE-j8
Step 1: Materials and Tools
- 3 foot (1 metre) of AWG 10 gage (preferred), or up to 18 gage, solid copper wire.
- AA battery (I recommend the Duracell AA NiMHrechargeable battery with 2650 MAh rating)
- 10 inch or better bass speaker (or use a good sized neodymium magnet)
- 7 Canadian magnetic pennies, or other coins as a commutator
- (optional) Neodymium magnet 1/2 inch x 1 inch minimum (such as # DX08 from K&J Magnetics )
- Soldering iron
- Wire stripper
- D cell size battery or tube of same size (for forming wire)
- nail or centre-punch
Step 2: Strip, Cut, and Straighten the Wire
Strip the wire with an appropriate wire stripper such that the bare copper wire is exposed.
Cut off 12 inches of wire for the flat Heart. Cut off 18 inches for the other bent-legged Heart.
Take out the bumps in the wire as much as possible before continuing. Use your fingers and thumbs if you have strong hands. Or try using a pliers or vice, with plastic tape wrapped around the jaws to prevent scoring of the wire.
Step 3: First Wire Bends
Find the midpoint of each of the wires by balance or measure.
Bend the wires at that point back onto themselves flat.
A vice is handy to make the final crimping as shown. Or use pliers.
Carefully straighten and flatten the wire again when done.
It's also a good time to grind, file and polish the crimped end contact point, so it will rotate well on the battery + terminal.
Step 4: Make the Flat Heart Shape
Make the Heart shape either by using a D-Cell battery, or a piece of pipe, as a form. Put it in the vice and wrap the wire over it. The idea is to wrap the wire most of the way around the form to give a rounded look.
For the flat heart, the two straight ends become joined by soldering, so they must meet together. Also, the total height of the heart must be correct (about 8.5 cm works well) for it to sit on the battery, touch the coins or magnet commutator, and not touch the speaker or table. The distance from battery + terminal to the magnet contact point should be about 6.0 cm.
The second Heart shape requires a complex bend into two flat-bottomed legs that encircle, but don't touch, the magnet. Have a close look at the pictures and use fingers (and a pliers if necessary) to make the bends.
It is tough work requiring strong fingers if 10 gage wire is used!
The total height of the second Heart should be about the same as the first Heart ( 8.5 cm). It uses the same 6 cm distance from + terminal of the battery to the magnet contact point.
Step 5: Make the Legged Heart Shape
This procedure is similar to the Flat heart shape, but the legs require special twists and curves to work and be balanced.
The idea is to end up with bottom legs that encircle the commutator coins or magnet, without causing any drag. There should be a gap of up to 1/8 inch where the copper wire of the leg meets the commutator.
Step 6: Dimple the Battery
Make a small dimple on the battery + terminal to help in centering the Hearts as they rotate.
Use a light tap with a blunt nail or centre-punch to gently dimple the + terminal of the battery while holding it carefully in a vice.
Step 7: Final Tweaking and Trouble-Shooting
1.) Using The Homopolar Motor With A Bass Speaker:
I used a 10 inch speaker. I used 7 magnetic Canadian pennies as a commutator for best magnetic effect. Other conductive coins may work too.
Place the stack of coins in the very centre of the back of the speaker, with the speaker face-down on a table or floor. Place the fully-charged AA battery on top of the coin stack.
Put the single flat heart onto the + terminal of the battery. It should go around.
Then try the two-legged Heart.
Adjust the legs so that there is a loose gap between the legs and the coins.
2). Using The Homopolar Motor With A Neodymium Magnet:
Place the fully-charged AA battery on top of the neo magnet. Then put the first flat Heart shape on to the battery + terminal. The Heart should start spinning as soon as it makes contact with the magnet.
If it doesn't spin, then it is not making contact, or the battery is too weak, or the magnet is not big enough.
Try the second Heart (with legs). It should spin right away, but sometimes may need a push to get it started. Adjust the legs so they nearly touch the sides of the magnet or pennies.
If both the legs touch the commutator at once then they are too tight, and the Heart will not rotate. If the legs are too loose around the magnet or coins, the Heart will tend to fly off.
Finally, place the flat Heart, inverted, on top of the second legged Heart. The shapes may have to be altered slightly to mate with each other. Give that combo a spin!
Balance is critical for successfully making the combined shapes spin at speed!
Step 8: Final Polishing...and Make a Movie!
For best looks, sanding and polishing can be done with various grades of sandpaper from 150 to 600 if the scratches are deep, or use a ScotchGard-type pad if there are no deep scratches. Metal polish can be used for a shiny look. A Dremel tool is nice for buffing.
Make sure that the copper wire contact surfaces, at the battery and commutator, are as smooth as possible.
A cool final touch is to find a nice box to fit the parts of the Homopolar Hearts, so they won't get out of adjustment or lost...and to present to your loved one as a gift!
Finally, make a movie for the rest of the world to see...then have me post it here!
Step 9: Addendum: Some Safety Precautions
Homopolar motors are generally safe. However, there are a couple of things to remember.
1.) Neodymium is poisonous. Magnets are covered by a nickel plating that keeps the neodymium inside. Try to avoid handling chipped or worn-out plated magnets.
2.) Don't eat magnets, and keep them away from young children who might do so. It can be fatal for children to ingest 2 or more magnets because of possible pinching of the intestine.
3.) When playing with multiple neodymium magnets, always use eye protection. Two or more neos on a table will inevitably collide, and often they chip when that happens.
4.) A point to consider is that the wire, battery and magnet can get very hot. Especially so when the Heart is not turning efficiently, or is stalled out. Be careful with your fingers until you understand about this.
5.) Don't allow the Hearts to rotate very long, as the battery will get over-heated and have a short life. If the battery feels too hot to touch, it has gone too far.
Have fun and play safe out there!