Project Hulk - Magnet Tutorial

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Introduction

Since one of the most commonly asked questions concerning Project Hulk is, "How did you do the magnets?"; I figured I'd put together a bit of a tutorial to explain the whole process with visuals to help provide clarity.

My system isn't by any means the only (or "best") way to do this, but for the guidelines I set down and this project it worked remarkably well.


Part I: Understanding the Magnetics

The key behind making terrain tiles that will "lock" to each other magnetically lies in the basics of magnetism as it relates to bar magnets.

For those who slept through science class, every fixed magnet projects a magnetic field that has "polarity." That means that the field jutting out of one side will have one polarity (usually referred to as "North") and the field coming from the opposite side will have the opposite polarity ("South.")

Magnetic fields of like polarity will repel each other (North pushes away North, South pushes away South), whereas fields of opposite polarity will attract each other (North pulls South and vice versa.) Not surprisingly, the key to making pieces join together is getting the polarities lined up so that no matter which way you connect them, they always mate North with South or South with North.

Luckily, with terrain tiles like those in Project Hulk, we can solve this problem by thinking exclusively of the "joining" points, which are always openings of corridors, rooms, etc. and are always the same size. You will need two magnets at each opening on each piece to make this work.

As you can see from the diagrams below, if we decide that two particular blocks are going to house the magnets (the two pieces in the lower corners, for example), and we always position the magnets so that one is the North polarity and the opposite is the South polarity, and we keep this orientation throughout all the pieces (i.e. the block on the "right" as you're looking out from the piece is always "North" and the one on the left is always "South", then any other piece that will connect to us with the same polarity will have North-South and South-North connections.

It's this trick of positioning that allows you to create a generic system whereby all the terrain pieces can potentially interlock.


Part II: Building your First Blocks

With block-casting projects you actually have a tremendous amount of freedom with magnetics and the ability to actually cast the magnets inside the blocks you're making. Since magnetic fields are not blocked by resin or plaster, you can make some amazing pieces and have a fantastic level of control over "magically" joining your pieces together.

The first step is deciding which blocks will need to be cast with magnets inside. This is usually done well after your basic design is solidified, as you need to know the block in the best position for connecting your pieces. The block you want to use should be one that's positioned at the right spot, and ideally should be all the same block and/or a very commonly used block in the project (as well as for future projects.) With Project Hulk the choice was obvious. The only good candidate at both corners of the openings was the 1/2" square "sloped edge" block from Starship Wall Mold #301.

You're going to need an equal number of North-facing and South-facing magnetic blocks, and you'll need one of each (two blocks total) for each opening you want to connect. In the case of my block, it was slightly more complicated because the North blocks had to point outward from the "leftward" side whereas the South blocks had to come out the "rightward."

You also need to decide what magnets to obtain. I actually recommend getting two different magnets, one smaller one which will act as a "spacer" and the other larger magnet which will provide the bulk of the magnetic force.

For this block, I chose 1/8" diameter, 1/16" thick magnets to use as spacers, and 1/4" diameter, 1/4" long cylinder magnets for the main pulling force. These didn't take up too much room inside the block while giving a good strong field. I bought mine from K&J Magnetics, but there are several good sources online.

Making your first couple blocks can be somewhat tricky using the original molds. You can make castings straight out of the Hirst Arts molds with the magnets inside, or drill holes in pre-cast blocks to insert the magnets. Eventually, if you're doing these in any quantity, you'll want to use Silicon RTV to make a special mold just for building your magnets.

To start with, make at least one pair of magnets. If you look at the mold your brick comes from, you can probably figure out an orientation where you can place a magnet inside the brick slot and hold it in place by putting another magnet (poles facing the same direction) against an adjacent brick slot (see below.) Holding it in place in this fashion will position the magnet properly inside the mold, aligned with the block. You might need some trial and error to get your first few blocks, but eventually you should be able to make enough master blocks to make a magnetic mold.

Note the spacer magnet and how it's placed. This spacer serves a very important function. When the plaster is poured in and around the magnets, there will be a small "donut like" ring around the small magnet which will harden and hold the main magnet in place. What I found in the early stages of the project was that the main magnet would often be strong enough that it would pull free from the block (especially with the magnets cast in the RTV molds.) By placing this spacer, even if the small magnet comes free, the main magnetic will remain inside the block (short of the block tearing apart, that is.) If this happens, the smaller magnet can either be replaced with glue or a little putty can fill the hole left behind.

You can continue to make blocks in this fashion if you only need a few of them for your project, but I highly recommend going the rest of the way and making an RTV mold. It's really much quicker.

You'll probably want to cast up about 3-4 blocks of each polarity to make a mold with 6-8 total (or more if you're going to need a very large number of magnetized bricks.) Once you have these, you can begin creating the RTV mold for mass production.

Position your master blocks on your surface in a way that allows an even number of blocks with opposite polarity on each side. You'll need to do so in a configuration that prevents the magnetic fields from conflicting and moving the blocks around (this may take a while to get stable if you put the blocks too close together.) Then, on the surface of the block where the magnet shows, place one 1/8" spacer magnet (it should line up in the center), and on the other side place one of the 1/4" magnets.

Pour and finish your mold. You should see the small spacers, but nothing else on the inside of the mold, the magnets being trapped inside the RTV.

The spacing technique will prevent the large magnet from pulling free of the mold when you de-mold your bricks as in my example mold above.

Now, whenever you go to pour more bricks, you can simply take a spacer and a large magnet, pop them into each block slot, and when you pour plaster into the mold you'll end up with exactly the blocks you need with the polarities you want.


Part III: Construction

Construction becomes relatively simple, but you always have to be aware of what polarity you're putting on what corner, especially with blocks that can be flipped over without seeing an obvious orientation difference.

To help with this, one of the first things I constructed was a "test bed" where I glued down two magnets of different polarity in the same position as they would end up on the final model.

Before putting any of the pieces together, I could pop the pre-cast magnet blocks in place and visually see that they were lined up correctly and that the polarity was right.

Then, after everything had been put together and was mostly dry, I'd double-check one final time against my test bed that everything lined up. Out of almost 100 pieces and well over 250 magnets, I never once had to pull out and re-orient a magnet block using this method.


Part IV: Conclusion

Using these same sorts of techniques, you can cast magnets into nearly any custom mold, and make incredibly easy and quick blocks to line up terrain tiles. I've even used this to put magnets into towers and walls so that they would stay together better on the table. Depending on the scale you're using, the magnets can get expensive, but foresight and planning will go a long way toward understanding (and potentially deferring) your costs. Experiment and have fun ... it's well worth it in the long run.



Please send any comments/criticisms/corrections to webmeisterzeke@att.net


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This page was last updated on July 2nd, 2010 at 06:20 PM