Create a Recoiling Cannon for an Interactive Halloween Display

Each year, we try to something new for Halloween.  These displays are grounds-up builds each year and meet this criteria: fun, exciting, interactive for the kids, involve gameplay, and offer a chance for me to get electricuted.  Check out our display for last year, the MUTEX Lab Tour: http://www.youtube.com/watch?v=LVnGLCG9Nzg

This Halloween, trick-or-treaters were conscripted into service on a pirate ship.  Their mission, which they would avoid at their peril, was to send their enemy's ships to Davey Jones' Locker.  Two kids would compete against each other and try to sink each other's ships.

I created a game in C#.net that would allow the kids to play against each other on two different screens and shoot each other's ships.  As they fired their cannons on-screen, "real" cannons that we made out of wood and canvas, would recoil.  The cannons had 1/2 horsepower electric motors in them that we would send charges to make them bounce back, as if being fired.

The computers on which the game was run would communicate via wireless network and would send scoring and other information to each other.  Attached to each computer were circuitboards from Phidgets, to which we connected joysticks, pressure sensors, and 120v circuits. 

The kids had fun playing the game (as you can see in the video) and we had a blast creating the game.  Hope you enjoy it too!

NOTE: this instructable is for the cannons only. 

Step 1: Build the Base

First, we built the base out of 2x2s and OSB boards.  We did some research on how pirate cannons were typically shaped and designed them to match those as best possible. 

Note that we were trying to go for as light a base as possible.  We wanted the cannon to real move when a charge was applied to the motor.

Step 2: Cut Out the Rings for the Barrels

Using a router and a jig, I cut out a bunch of rings for the barrels.  I used OSB boards since they tend to be cheapest.  I ended up cutting two boards for each ring and then glued them together so that I would have a good thickness.

Do some research on the shape of cannon barrels.  Most barrels are larger at the base and smaller at the end where the cannonball exits.  I made rings of three different shapes for my barrels.

Step 3: Attach Your Rings Together Into a Frame

Using 2x2s, we attached the rings together into a frame.  Note that the 2x2s go on the inside of the rings.  You want to do that so that the tarp will not lean against the 2x2s.

Step 4: Attach Canvas to the Frames

I bought some canvas tarps from Home Depot (in the paint aisle).  Using a staple gun with 3/8" staples, I attached the tarps to the rings.  I chose to attach the tarps on the inside of the rings, about a half inch from the outside (a bit hard to describe this; hopefully the picture will show you what I mean).

You can see that I attached some PVC plumbing to the frame before connecting the tarp.  This holds it to the frame.

Step 5: Attach Your Motor

I borrowed a couple of 1/2 horsepower motors from my brother.  We rigged them up so that they would spool some rope.  This rope would be run out of a hole in the base and would be attached to some heavy object.  Once power was applied to the motor, the cannon would recoil.

You can also see in this shot that we used the canisters from canister lights as the ends of the cannon barrels.

Step 6: Attach Your Wheels

We attached doweling to the base of the cannons using the metal tape that plumbers use to attaching plumbing to wall frames.  We then attached wheels that we had cut out of OSB using a router and jig. 

Cut a hole in the wheels that is slightly larger than the doweling.  While this step is obvious, I tried to make it a little bit larger than expected so that the cannon would roll a bit clunky when it recoiled.  I wanted to have a loud, rattle-y cannon!

Use a drill bit to cut a hole for a smaller doweling in the larger ones.  These will hold your wheels in place.

Step 7: Paint the Barrel and Base

We used a metallic silver paint on the barrels.  Since they are canvas, the don't look as metal as other material would, but from a distance, they look pretty cool.

To paint the bases, we spray painted them brown and then applied detail work using darker and lighter browns.  Use a brush for this step.  Add some knot holes and nails using this approach too.

In the first picture, you can see the barrels after they were painted, but the base has not been painted yet.  The second picture shows the cannons in action and fully painted.

Step 8: Attach the Barrel to the Base

Using the same metal tape that we used to attach the axles to the base, we attached the barrels to the bases.  Loop the tape around the plumbing that is sticking out of the sides and then attach it to the base using wood screws.

Step 9: Hook It Up to a Power Source & Final Thoughts

I used my cannons as part of an interactive game that trick-or-treaters played in our driveway.  I wrote the game in C#.net and attached a circuit board from Phidgets.com that allowed me to apply a quick jolt of 110v to the motor, in sync with a sound effect and cannonball on screen.

You could easily hook your cannons up to a powerstrip to get the recoil.  The sound effects will have to be up to you. 

Another thought is the addition of fog via some sort of pneumatic device.  I toyed with the idea, but determined that it would be cost and time prohibitive (watch the video - the fog wasn't needed anyway).

Shout outs:
Thanks go to my awesome wife Kristi, for putting up with a new build each year.  Thanks to Sarah, Scott, Kay, Karen, and Erich for helping with painting and whatnot.  Special thanks to my fellow gearhead bro Mike, for the electric motors.  

Extra special thanks go to Jerry Jodloski, an awesome designer and gearhead who keeps upping his game (forcing me to as well).  Check out his Instructable for this year:
https://www.instructables.com/id/Make-a-life-sized-Batmobile-Tumbler-and-Batman-The/

Extra, extra specials thanks go to Zack, my son (and future programmer) who helps design and build some of this stuff.