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MOD: Air hockey


cooper
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I don't know why, but for some reason I started thinking about Air Hockey today.

I always liked playing that in arcades and stuff, and it seems relatively straightforward to build your own. Get a table, drill some small holes, add a leafblower, some edges and you're 99% done. The problem with this setup is that it's really, really noisy.

So I started thinking about other means of levitation, which yielded the following idea:

Levitation through magnetic repellance.

Buy a bunch of screws.

Take a wood en sheet, 2mx1m in size, and drill small holes in it, with a wider recess at the top to accomodate the head of the screw. Space the holes evenly. Say, 1.5 cm apart.

Screw the screws into the holes. The sharp part of the screw should stick out under the wood for some distance, and the top of all the screws should be as even as possible with the rest of the wood.

Take a standard 12-volt power brick. The more amps the better, and put a potentiometer (one of those fan-control dials you've got collecting dust on a shelf somewhere) in between so you can play the power a bit.

I should note that since the magnetic field is determined by the amount of amps going through the coiled wire, this might not be any good.

Get a good length of telephone wire. Strip it so you only have the 4 insulated inner wires.

Wrap the wire around each part screw that's sticking out of the bottom of the wood with the wire, always going in the same direction (say, clockwise, bottom to top). The idea is that when you pass current through the wire, the screw becomes an electro magnet, and all screws will have the same polarity.

Get a sheet of plexiglas, the thinner the better. Paint the field on one side, then glue the painted side onto the wooden sheet.

Create an edge around the table to keep the puck in.

For the puck:

Get a number of magnets. The stronger the better, the flatter the better (like those used on those magnet board with memos and stuff).

Get a sheet of plexiglas that's as thick or thicker than the magnets, 7x7 cm in size, and another sheet of plexiglas that's as thin as possible, 10x5 cm.

From the 7x7 cm plate of plexi, saw out a circle. the rounder the better, that is 6.35 cm in diameter (2 1/2 inches).

Drill evenly spaced holes in it to make room for the magnets, in a circular pattern that's 5 cm in diameter. Test-fit the magnets to make sure all is well.

Cut the 10x5 plate in half, and then saw out a circle from the two halves. To keep the weight of the puck down, it would be a good idea to also drill, saw or dremel out the inside of these circles so you end up with rings that completely cover the magnet holes on the larger sheet.

Figure out what the polarity of your magnets is, then place them inside their designated holes of the larger circle, all having the same pole up.

Glue the two circles on top of it. As always, try to keep things even.

Whatever you use as a mallet, be sure to stick some form of durable cloth onto the bottom so that it will allow swift motion and maybe more importantly prevent excessive scratching of the table's plexiglass surface.

Put the puck onto the table and power up the power brick. Hopefully the puck levitates (if not, try flipping it over :wink:).

If it doesn't levitate, try using more or stronger magnets in the puck, thinner material for the surface of the table and the rings on the puck, more amps on the power supply, or more coils around the screws.

Assuming it works, you'd wind up with your very own Air Hockey table that won't wake up the neighbors when in use. Well, assuming you and your apponent can keep your voices down.

I should add that it's probably not a good idea to keep things that don't react well to magnetism (backup tapes, bank cards, harddisks, radios, etc) in too close proximity to the table, especially while in use.

Price-wise, the plexiglas alone is about 60 euros in 2mm thickness. You can get it in 1mm thickness which would be better for this and probably cheaper. The power brick will be in the 40-60 dollar range for a new one depending on the amount of amps. You can probably get a used one for a LOT less on eBay.

You can get those board magnets cheap. Like, 10 for a buck or something.

No idea what the wood would cost. It needs to be thick/sturdy enough so as not to flex too much. You might want to add a second sheet to cover the bottom once you're done there.

A couple of legs would be nice, but of course some milk crates would do the trick just as nicely.

So I'm guessing somewhere in the 150-200 dollar range with all-new parts.

Any thoughts? I'm a coder rather than an electrical engineer, so I might just be talking out of my ass on this one, but so far most people I've told this idea to wondered why this isn't around already.

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One problem I see is that each screen would need at least 10 turns of the wire to produce an effective electro-magnet and you have nearly nine thousand screws in your set up.

Thats alot of long boring work. Might work if you could be bothered, but I personally wouldnt.

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Could you explain the math on that one to me? Why 10 turns or more? I've got a power brick here that (claims that it) can spit out 9 amps.

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Not really, you would need to put about 1 500 holes in the table. Here is a much easier way to do it.

1. Attach a metal plate to a piece of plexiglass.

2. Attach magnets to the metal plate all going in the same direction, I would go 10 by 15 = 150 magnets.

3. get a air hocket puck and attach a magnet to the top of it.

There a powerless magent hockey table.

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They claim high-power, yet they're the more standard type of magnet.

I still think getting a set of board magnets will be way cheaper.

Alternatively, you can open up a dead harddisk and take out the NIB (rare earth) magnets they use in there. Those are the most high-powered magnets around, though rather brittle. The big problem would probably be to get the magnetic field even across the board. It would take a rather large amount of near-identical dead harddisks.

Anybody got a bunch of old deathstars left? :)

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I've found a magnet manufacturer here in .nl that sells magnets in ALL shapes and sizes. I'm going to pitch this idea to that company. Maybe they'll send me some samples so I can see how many I need. There should be a way to compute this, but now's not the time for me to get into that. (Wacken tomorrow!)

The puck will probably weigh about 20-25 grams. About 10 grams for the plexi plus 10-15 for the weight of the magnets you tuck in there. I'm unsure if you'd need 4 or 8 for the best result, but if you want to use 8 and have them in a ring that is no more than 5cm in diameter the magnets should be about 1cm or less in diameter (round of course). There's absolutely no reason you couldn't use those exact same magnets for the table, so buying bulk is an interesting option.

Unfortunately the metal sheet might bring the overall price up a bit. I still need to look into that. Currently I view metal as expensive, but that's because I've primarily worked with aliminium (yes, that's what it's called. Aluminum doesn't exist) which tends to be pricy.

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Neodymium is incredible, I once made a petty rail gun using Nd magnets. If you choose to use Nd, make sure that they are securely fastened in place, because they are strong and wil attract eachother, and if they are allowed to fly freely at eachother, shatterage is guaranteed.

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i would get a small piece of aluminum and 2 magnets glue one magnet to the aluminum and make sure that the aluminum actually widens the magnetic field and is able to repel the other magnet a good distance from the glued on magnet just so you dont waste any money if it doesnt work.

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get two magnets try to push them to gether one trys to flip over, the force at which it is pushing it away is enough for the thing to fully flip. what i would do is instead of using a normal puck make it a ball, and have to magnets that inside the ball the will allways make the ball "float" so it doesnt matter if it starts to flip over, or in this case spin.

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Guest zacharygriggs

^^^^^ exactly but then you have problems with the scoring into a small flat area and hitting the "ball" with a little handle

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I would assume that in order to get any stability in the puck you would need 3 or more magnets in a circular alignment. And because they would be embedded in a 6.5cm flat shape, they would need to have a TON of power at comparatively large distances before the puck would even consider flipping.

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I would assume that in order to get any stability in the puck you would need 3 or more magnets in a circular alignment. And because they would be embedded in a 6.5cm flat shape, they would need to have a TON of power at comparatively large distances before the puck would even consider flipping.

But the puck no matter what is going to be lifted up high enough for it to flip, try it with two magnets.

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