Making a railgun (thing)

A more realistic homemade railgun

Short of obtaining a Nuclear power station, UV lasers, and a supply of superconducting materials, there actually is a way to make a home-made Railgun with just a few compromises. It will not (usually) kill or maim people, and isn't good for self-defense. There are better ways to defend yourself. This simple railgun, however, if we allow for the use of static magnets, rather than electromagnets, can be made mostly with materials you might find in your garage or around the house.

Materials:

• Three to five small but strong magnets - preferably cylinders, flat-ended rods, or cubes. Rare-earth Neodymium magnets work great!
• Steel ball-bearings, about the same diameter as the magnets. Two to three per magnet.
• A non-ferromagnetic flat object with a straight groove - an everyday wooden ruler works well.
• Tape

Construction:

• Space the magnets (M) about 5-7 cm / 2-3 inches along the ruler in the groove with a space at both ends, and tape them in place. Make sure the magnetic poles are oriented all in the same direction along the axis of the ruler

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             M         M         M         M          M

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• Place two ball bearings (O) on one side of each magnet. (The first ball-bearing spaces the second away from the magnet so that the magnet doesn't simply overcome the forces involved by holding on to the ball bearing)

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            MOO       MOO       MOO       MOO        MOO

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Now you have a simple but working railgun! To fire it, roll a ball-bearing toward the first magnet (on the opposite side from the other ball bearings), and don't stand in front. Reloading is as simple as replacing the ball bearings back in their original positions (you supply the potential energy here that is converted into kinetic energy.) Here's how the railgun works:

1. The first ball-bearing rolls toward the first magnet, is accelerated by the magnet, and hits with velocity V₁.
2. The force of the impact is transmitted through the magnet and two ball bearings, causing the second one to shoot at the second magnet. It is also accelerated, and hits with a higher velocity V₂.
3. The cascade continues, each ball-bearing hitting with a higher velocity, transmitting greater energy through the magnet and first ball bearing, and imparting it to the second, until the last ball bearing shoots off the end of the railgun.

You are now ready to go out and attack some tissue paper or bananas. The effect at this point may or may not be underwhelming... so let's tune the sucker!

Tuning your Railgun

There are a couple of ways of tuning the railgun, so let's discuss each one.

Bigger and longer
Our military knows that the way to make weapons better is to make them bigger. In this case, you can use bigger magnets, and/or a longer base. Using bigger magnets works great, but remeber that with strong magnets you can wipe out you credit card, ruin your wristwatch, or pinch the living snot out of your finger (It takes two), so be careful!

Balancing distances
You can improve the performance of your railgun by increasing two distances: The distance of the ball bearing being "kicked" from the magnet, and the distance that ball bearing has to be accelerated by the following magnet.

You can increase the first space by inserting more ball bearings, or by using an iron rod (which transmits the force well and will hold the ball bearing magnetically).

The second space can be increased just by... well... increasing it. There are rapidly diminishing returns to both methods as the magnetic field falls off proportional to the cube of the distance, and friction begins to eat away at your railgun's efficiency.

The best method is, on a level surface, to increase the first distance by enough that the ball bearing is barely held in place by the magnet, then to gradually move the second magnet closer and closer until the ball bearing is pulled off, then back it up just slightly.

Other Considerations
There are very strong magnets to be had, and tuning the railgun correctly can result in some pretty significant velocities. This can result in damage to your magnets by chipping or even exploding, and the fragments can put out your eye. Depending on the magnet strength and your tuning prowess, you may wish to invest in leather gloves, wear eye protection, and refrain from pointing the business end of the railgun at breakable objects or people that you like. A great source for magnets and more information is www.wondermagnet.com. If you can convince them you are an industrial concern, they may even show you The Good Stuff!

Thanks to Wingbat for showing me his prototype railgun, and for the cool cube magnets!