We love LEGOs at our house! Er, I mean, of course, that my kids love LEGOs at our house and that I am merely a disinterested observer... Over the years, we (they) have quickly discovered that any model that moves is fun, but a model that shoots is the best!

Among the many models we've come up with, one of our favorites is the LEGO canon! It's gone through a couple of revisions, and will probably be refined further, but the one documented here works well and is capable of firing projectiles up to about five or six feet. It's fairly easy to build and mostly uses common LEGO blocks, as well as a few less common ones, and two springs.

I've avoided describing the detailed placement of each brick because that would be dull and unnecessary. Just follow the pictures and try to keep the model strong by overlapping your bricks, and you'll do fine. If any step needs clarification, please let me know in the comments and I'll try to make improvements.

How to build a LEGO canon
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Step 1: Collect Your Pieces

Most of the LEGO pieces involved in the LEGO canon are common pieces that any decent LEGO collection should have; mainly normal blocks and plates. A few smooth-topped pieces will be required, but they shouldn't be difficult to obtain either.

The more exotic pieces required are shown below. They may be difficult to find, I'm not sure, and I'll describe ways to work around them, if necessary.

You'll also need a few rods to use for the launcher and projectiles. LEGO technic sets should be a good source for these.

Finally, you'll need a couple of springs. One should be fairly stiff and will provide the power for the launcher. The other should be looser and will be used in the trigger. I found a good pack of assorted springs at Home Depot for a decent price (Try this one: http://www.homedepot.com/p/Everbilt-Spring-Assortment-Kit-84-Pack-15642/202045461#.UggnQ9K1GSo).

Step 2: Build the Base

The base is easy. You'll want enough plates to create an 8x10 base on which to build the canon.

Step 3: Build the First Level

Build up a single layer of blocks on top of the base. You'll need to leave a 2x2 section empty for the trigger. See the photos below for the location.

Step 4: Build the Launcher Base

Add plates to the center of the first level, leaving a border of one stud at the front and back of the canon and two studs on either side. Leave the 2x2 trigger opening clear.

Add enough smooth pieces to cover the launcher base. The launcher will slide across these pieces when the canon is fired.

Step 5: Build the Second Layer

Add another layer of blocks to form the second layer, still leaving the 2x2 trigger area clear. At this point, you can drop the trigger spring into the trigger area.

Step 6: Build the Trigger (ideal Version)

Build the trigger using the pieces shown.

In this version of the trigger, the funky triangle-shaped piece works great because, as the launcher is pushed back, the trigger is forced down and out of the way automatically, making loading pretty slick. In this version, the L-shaped piece is vital to keeping the trigger mechanism from falling apart.

Don't worry if you're missing either the funky triangle-shaped piece or the L-shaped piece. The next step describes a different trigger mechanism that is made of more common pieces, and will work just fine.

Step 7: Build the Trigger (alternative Version)

An alternative version of the trigger can easily be built using a 2x1 and 1x1 block in place of the two rare pieces (okay, I don't actually know how rare they are, but I assume they're not particularly common) used in the previous step. The trigger will still work fine, but loading isn't as slick.

Step 8: Build the Third Level

Add blocks to create the third level. Leave a 4x1 space empty at the front of the canon, and a 2x1 area at the back. Leave the 2x2 trigger slot empty as well.

Go ahead and insert the trigger into the trigger slot now. You should be able to push it down easily and it should spring back up.

Step 9: Build the Launcher

The launcher is where the action happens. When you load the canon, the launcher will be pushed back, and will be stopped by the bottom of the trigger. When the trigger is pushed down, the launcher will spring forward, ejecting the projectiles!

Assemble the launcher as shown below. After thinking about things, the smooth pieces at the front of the launcher are not really needed, but I like them. Use them or not. It's really your choice...

Step 10: Attach the Launcher

To attach the launcher to the canon, slip the rod through the brick with one hole and attach as shown. Attach the brick with three holes to the front of the canon.

Okay, so that's not necessarily clear. Just look at the photo. You'll get there...

Step 11: Build the Fourth and Fifth Levels

Add more bricks to make the next two levels. Pretty simple stuff.

Step 12: Cap It Off

Add plates to the top to cover the canon up. The trigger should be left peaking out the top.

And you're done! To load it, push a projectile into the center hole at the front of the canon. You may need to hold the trigger down while pushing, and release it to lock the launcher in place. Load two more projectiles, if you want, find a target (don't shoot out anyone's eyes, please), and fire!

There's obviously a lot of ways this can be adapted and improved, so go crazy with it and have fun!