I saw a short 4 second youtube video last year on a giant mousetrap scare and wanted to try my own hand at building one. In the original, a PVC air cannon with a sprinkler valve shoots out the front under the candy bowl and extra air exits through a PVC Tee on the exhaust that moves a cylinder slightly that pushes up the arm of the trap a hair.
When I set out to build one similar it needed to accomplish a few things. First it needed to last. I go camping for a weekend at a Halloween Campout at a state park and the trap will be set off at least 1000 times over the 3 days. I also wanted to get two individual scares. The first is a large loud blast of air at your ankles vs under the candy bucket. This way no little kid gets hit in the face with it. The second is the trap actually moving about 4 inches like it is going to snap closed. This needed to be fast and hit hard so the noise of it hitting scared as much as the movement did.
I designed it so I can trigger either one separately or both together depending on what I need or want it to do.This is helpful when you get a group of kids. The first kid nothing happens. The second the air cannon goes off, and now they know the gag, but the third kid gets the movement of the trap and they all jump again. Full control with a push button vs automated is needed to make this scare effective and safe.
Step 1: Tools and Supplies
*** for the mousetrap
Screws or nails
paint - red and black
silver spray paint
2 large eye bolts
Wooden dowels to fit in conduit
metal tapping screws - secure dowels to conduit
metal pan for candy
short metal tubing for candy pan stand
used rubber air hose - for the spring
*** for the air cannon/ cylinder/ electronics
**** Air cannon
Deltrol EV25A2 dump valve
pipe thread tape/ dope
3/8th push connect fittings
3/8th push connect tubing
3/8th 3 way solenoid - 12 volt
NC (normally closed) push button momentary switch
3/8th push to connect to compressor
1/4" push to connect fittings
1/4" push to connect tubing
1/4" 3 way solenoid 12 volt
single acting cylinder - 4 inch throw
bolt to framing
NO (Normally Open) push button momentary switch
NO (Normally Open) push button momentary switch screw terminal
Wire to trigger - 3 strand
NC (normally closed) push button momentary switch screw terminal
18 gauge wire
shrink crimp connections
soldering torch - to shrink connectors - no soldering involved
RC jack connectors
12 volt power supply
Step 2: Building the Frame
The framing was made out of reused 2x6 lumber. It was reclaimed from a bathroom remodel and worked great as it is already aged for that rustic look. The trap is about 32 x 60. I cut the corners for a butt joint not mitered. The top piece is 1/2 plywood. I used a left over piece from a previous project as well so the top is actually 2 pieces vs 1 whole piece. I put screws in around the top and made them line up with where I wanted my painted stripe to help hide them a bit.
Step 3: Paint the Top
I used a small mousetrap to base my paint design off of. The whole thing was hand eyeballed and laid out in painters tape. Then I just painted in the area and removed the tape. It isn't perfect but it works for what I wanted it to do.
You do need to paint the top before the spring is put on or everything is just in the way.
Step 4: Make a Spring/ Snap Arm
The spring was made from a used air hose off my compressor that sprung a leak. The hose was the rubber type not plastic so it is flexible. Each spring wrap was screwed in through the plywood to hold it in place. The spring was then masked off with some paper and sprayed with a silver spray paint to make it look metallic.
The snap arm is next. I used some scrap pieces of already bent 3/4 conduit that they put in the scrap bin at work. I cut them down with a copper pipe cutter and seamed them together with some wooden dowels inside. The dowels would be easier to just buy new but I used a broken rake handle and sanded them down a bit to fit inside. Plus this way I didn't need to run back to the hardware store. The snap arm is basically a square and is only held tight at the top with the spring release arm to the air cylinder.
Step 5: Air Cylinder to Jump the Snap Arm
A hole was drilled through the top of the trap to connect to the spring arm. This connection is actually an air cylinder vs just a piece of conduit. It has a 4 inch shaft that extends when activated with air. When powered it will shoot up 4 inches and look like the spring is getting ready to snap on the unsuspecting trick or treater.
The cylinder is bolted to the frame underneath and a 1/4 inch air line run out of it.
Step 6: Air Cannon to Startle
There are a bunch of air cannon videos on youtube for how to build a variety of styles. Here is a short and sweet how to build this one.
Get an air cylinder to hold the air. I had a machinist friend re-tap an old aluminum escape bottle for me to fit 1/2" threaded pipe. You can also use an out of hydro test CO2 cylinder. I reduced that to 3/8th to fit my dump valve. The dump valve connects to the cylinder, the exhaust pipe (end that shoots the air) and the 3/8th solenoid. The air from the compressor is split with a Tee to the cylinder and the solenoid. When the solenoid is powered it pushes air into the back of the dump valve which presses a rubber seal up against the valve opening. This makes the cylinder hold air. When you turn off the solenoid, it allows the air between the solenoid and the dump valve to escape through the exhaust port on the solenoid. This lets the rubber seal go and all the air is instantly dumped out of the cylinder. Air still flows into the cylinder all the time so if you hold the button down it will just hiss air out forever. Let go of the button, the rubber seal re-engages due to the air pressure being back on it and the cylinder refills in a few seconds.
You need a NC or normally closed push button momentary switch. This means that the item you are powering is always on. When you push the button it turns it off. In this case the solenoid is what is being powered. It needs to be on at all times to keep the air against the rubber seal until you want it to fire. Then you push the button for a quick second and it fires the air. You can fire it about once every 5 seconds as it takes that long to refill fully.
I used a flush mounting plate to mount the air cannon to the trap and worked to make the whole thing stable so the force of the air wouldn't move it. The electronics were put in a project box as described in a few steps.
Here is a quick tip. You will need about 100 psi to keep the rubber seal in place and fill the tank. Otherwise the air will just leak through as the cylinder can't keep pressure. I spent an hour tearing apart my build trying to figure out what I did wrong when I had the air compressor set at 60psi from a previous pin nail gun need.
Step 7: Pneumatics (air Power)
The air compressor needs to be set at 100 psi. This is overkill for the cylinder but needed for the air cannon. I didn't get my parts in for Halloween to have an inline air flow reducer but the cylinder should be down to about 40 psi max. As of Halloween it is too violent due to the high air flow, although the flying candy is entertaining.
The air cannon is fed by a 3/8th solenoid and the air cylinder is fed by a 1/4" solenoid. One main 3/8th line feeds into the trap and is split to the 2 solenoids. This psi should be 100 to 120.
The air is further split to the 3/8th solenoid and the air cannon cylinder.
When building and then testing I had a small air leak. I couldn't figure out if it was the fitting part that went into the solenoid or the push connect fitting. A little bit of soapy water will show you the bubbles of where it is leaking. I didn't have it tight enough into the solenoid.
I got most of my fittings from www.halloweenfx.com
They sell a variety of fittings, solenoids, tubing, etc. I did get some items from Amazon but you have to know what you are ordering or you get something that is not designed for air but water instead.
The cylinder was from Ebay and left over from a project 10 years ago.
The air tank was from a scrap bin at work. Any air tank will work as long as it can hold 120 psi. I have one from a previous purchased air cannon that was made from welded tube steel. I also have pictured a re-tapped CO2 cylinder for 1/2" thread. This will work too.
Step 8: Electronics
Both solenoids run on 12 volt power. You can get them to be 110 volt if you want but I wanted the lower power level for both safety reason and because most of my props already run on that.
Each solenoid has 2 wires - red and black. Put power to both and the solenoid turns on. To make it power up just when I want it to, I split the black wire to a hand held push button first. The red wire is wired directly into the power supply.
I made my power supply to be able to be unplugged as well as powered by my LED lighting with RCA jacks. The 12 volt supply was fitted with an RCA jack adapter so they are interchangeable. This give me the ability to put the prop almost anywhere as long as I can get it to one of my power supplies and to an air line.
Everything was built into a project box for protection from the weather and abuse from moving the prop.
The hand held control has 2 push buttons on it. I used a 3 strand wire to feed it. 1 common strand goes from the power supply to each switch. The other two run to my solenoids. The solenoids need two different power feeds. One needs to always be on and the other needs always off. So an NC and NO switch was needed in the controller. They were wired up and secured into a piece of PVC with about a 50 foot lead. Getting two push buttons into the pvc and wired was way more time consuming than I would have liked but it worked out ok. This lets me control the prop from up to 50 feet away.
Just to clarify again.
The solenoid to the air cannon needs to always be on so a NC (normally closed) switch is needed.
The solenoid to the spring snap arm needs to be always off so a NO (normally open ) switch is needed.
Step 9: Finishing Up
Once wired up, the prop needs plugged in before you put air pressure to it. Remember the solenoid needs powered at the air cannon or air just rushes out.
Test out the cannon and put some candy on it for Halloween.
We ran the trap at a State Park Halloween campout and scared a few hundred kids. At my home we handed out some full size candy bars on it to the trick or treaters. We probably only had about 25 kids.