Intro: Magnet Cannon
In this article, we'll look at a few ways to shoot magnets across a room! This isn't a thing we normally recommend doing with magnets--it's not their primary use!
Not only will we discuss a couple ways to shoot magnets across the room, but we'll get a little nerdy and talk about how these things actually work!
Step 1: Not a Coilgun or Railgun!
First, let's start off by saying what we're NOT making: we're not making a coil gun or rail gun. These types of guns, also called "Gauss guns" use some type of electromagnets and metal object.
A coil gun consists of a series of electromagnets wrapped around a tube. By switching them on and off at just the right time, the electromagnets can attract a steel projectile, accelerating it down the tube. It’s a really neat project, made with electromagnets and some electronics wizardry.
We will be using only permanent, neodymium magnets!
Step 2: Permanent Magnets Only!
Here's one take on a "magnet cannon" that uses a bunch of angled block magnets and some other magnets moving through them. A row of angled block magnets is arranged on either side of a wooden slot. They are set so that all the north poles are facing downrange, down the barrel.
The forces felt by the projectile changes direction as it progresses along the barrel. Here, we break this down into four stages:
1. When the projectile is placed in the barrel from behind, it is pulled into a stable position just before the blocks on the sides. It is attracted to this position, and finds its stable resting place there. In the graph below, this stable position is where the force curve crosses the x-axis for the first time.
2. Next, we push the projectile down the barrel. There’s magnetic force resisting this, so it takes some force to keep pushing, slowly sliding the magnet down the barrel. The resisting force rises, and then decreases back to zero. This force is shown as negative numbers on the graph.
3. Once you pass this point of zero force, the magnetic forces start pushing the projectile magnet in the opposite direction. The forces start propelling the projectile down the barrel. It gains speed rapidly, and shoots away!
4. Once clear of the block magnets, there is a small amount of pull force trying to pull the projectile back towards the barrel. This force slows the projectile a little, but isn’t strong enough to prevent it from leaving. Since magnetic forces drop quickly with distance, it isn’t able to slow the projectile down enough to matter much. (On the graph below, this return to force in negative numbers is cut off on the right hand side of the graph.)
Step 3: Ring and Cylinder Setup
Since the straight blocks work well, why not surround the barrel with a whole ring? If we consider a cross-sectional slice through the center of a ring magnet, we find the magnetic field looks just like the setup with blocks on either side. The advantage of a ring is that we get even more magnet material surrounding the barrel.
Not every cylinder magnet will shoot well through every ring. Some combinations are downright duds. Here are a few we settled on that worked well:
We used the plastic coated magnet because it is a much more durable projectile. We could use plain magnets, but wanted to avoid breaking a lot of magnets when they slam into our steel targets. Brittle neodymium magnets won’t hold up to repeated abuse like this!
Step 4: Magnet Cannon
With a little creativity and design, we created a "magnet cannon", equipped with an RX8CC magnet and the same plastic coated magnet.
We used a hole saw to get the perfect wheels to make this cannon mobile and portable!
Step 5: Bigger Is Better?
It's our duty to try this same trick with the biggest magnets we could find. We made a 3/4" thick ring magnet by stacking some thinner magnet together, forming a 3" OD x 1.5" ID x 3/4" thick ring. We used a large 1" x 3/4" magnet as the projectile!
While these bigger magnets did shoot, there are dangerously powerful! Not to mention, the bigger projectile creates more damage if it hits a wall (not showed in the video).
Don't try big ones like this at home! Big magnets are dangerous!