Monster in a Box, Haunted House Halloween Prop

When I built this project, I wasn't originally planning on making an instructable with it, so please forgive me for the lack of photos early on in the building process. However, with the exception of the mechanicals, the construction is pretty much straightforward.

Being one of the volunteers and planners for our community’s annual haunted forest, I wanted to build an automated startle prop that would sit along the side of a trail and as unfortunate patrons passed by, the box would appear to come alive with lights, scary monster sounds and the loud banging of the heavy wood lid.

I had three main goals in mind when designing this project:

1. I didn’t have a lot of money to work with so the parts and material cost had to be inexpensive.
2. It had to be durable enough to at least make it through 4 busy nights of our haunted forest.
3. Most importantly, it had to be very scary and startling.

Step 1: Box Construction

The box and lid are both constructed of old wood pallets. I disassembled the pallets, cut the planks to size and screwed them to wood corner supports, leaving a ½” gap between boards for the interior lights (to be added later) to shine through.

Many grocery or department stores are happy to give away their old wood pallets, or at least sell them very cheap. I picked up mine for free from a local tractor supply store.

I looked for pallets that were in good condition yet would still give the box a good weathered appearance.

If you decide to take on this project, and have never surgically disassembled wood pallets before then you are in for a real treat. Use a pry bar, large screwdriver, hammer, saws-all, whatever it takes to remove all the nails and staples. Be sure to wear safety glasses and gloves and keep small children away to protect them from expletives.

Step 2: Electrical

For this project, I chose to use all 120VAC electrical components, mainly because I just happened to already have the perfect AC gear motor in my collection of miscellaneous parts. I knew my hoarding would come in handy sooner or later.

The red rope lights were robbed from last year’s Christmas decorations and they make an excellent effect when shining through the slats on the box. A strobe light or red light bulb mounted inside the box would work equally well.

The motion sensing is handled with a replacement PIR sensor for an outdoor security light, mounted to an electrical box. The sensor’s "ON" timer is set to the demo setting so the "monster" is only active for a few seconds.

Inside the box I mounted an electrical outlet. I configured the outlet so one receptacle is switched with the motion sensor. The other receptacle is always live.

I also mounted a power strip inside the box that supplies power to the components that are switched on when motion is sensed (motor, lights, powered computer speakers, MP3 player, fog machine, etc).

Step 3: The Lifting Mechanism

When I first designed this contraption, I wanted the motor to do two things: First, I wanted the lid to lift up an inch or two and slam down, which it does very well. I also wanted the entire box to lift up ½" on one corner. This would cause the box to shake and give an illusion that there is actually something in there trying to escape.

Using my band saw and a homemade jig, I cut two cams out of 3/4" plywood (one for the lid, and one for the lifting of the box. After experimenting with many different cam sizes and designs, I finally found one that worked. I discovered that a cam with 2 irregularly spaced cogs provided pretty good timing for the speed of my motor. The required size of the cam will also vary greatly based on the motor’s torque and RPM. My cams ended up with a 3" radius at its widest point and a 2" radius at its narrowest point. It’s very important to make the slope of the cam as gradual as possible to limit unnecessary torque on the motor and gearbox.

One of the most challenging parts of this project was trying to figure out how to attach the cams to the motor shaft. I tried gluing a wood setscrew insert into a hole drilled in the side of the cam, but the soft wood was no match for the motor’s torque and this lasted only a few minutes.

After several unsuccessful attempts, I finally drilled and tapped a hole through the motor’s driveshaft and threaded a small bolt through it. I then cut a slot in the cam for the bolt to rest in. I’m sure there is a much better way to do this but it worked.

After carefully measuring, I then added a mount for the motor and the linkage for the lifting mechanisms. I also attached rollers to the bottom of the lifting arms that ride on the cams to help reduce friction.

Although both lifting mechanisms worked great, I decided I needed to take some steps to reduce the load on the motor. After all, the box was rather heavy and the motor gearbox had plastic gears. I ended up disabling the entire box lifting mechanism by cutting ½" off the bottom of the lifting board. It was a neat feature but I felt the overall effect was not worth the risk of damage to the motor.

I also lowered the lid lifting arm and added a stiff spring to the end that contacts the bottom of the lid. The purpose of the spring is to protect the motor and gearbox if the lid were to be forced closed. This way if some punk kid jumped on the box while it’s running, the spring would compress with each pass of the cam but the motor would still continue to run.

Step 4: The Sound System

The sound effects are what really give this prop a sense of realism. The movement and banging of the lid and the red lights are one thing, but add a loud scary monster scream or roar and you have something right out of a Hollywood horror movie.

For my sound system I used a set of powered computer speakers and subwoofer donated by a good friend and the MP3 player from an old out of service cell phone (more freebies). Conveniently the speaker audio jack was a match for the phone. Some phones use a smaller headphone jack which would have required an adapter.

I did a Google search for MP3 monster sounds and found many to choose from. I downloaded several of my favorites and transferred them to the phone. The "always live" electrical outlet is perfect for a phone charger to ensure the phone’s battery doesn’t die early in the night.

Conveniently the inside of the box is plenty big enough to house the speakers. I set mine on the ground, but they could be mounted easy enough to the inside of the box if desired.

The effect is pretty cool when the powered speakers are plugged into the switched power strip and the monster sound is set for looping play on the MP3 player. The box will be completely still and quiet until someone trips the motion sensor, then the sleeping monster awakes with lights, loud growling/screaming and the banging of the heavy wood lid. "Eat your heart out Stephen King."

Step 5: The Finer Details

For the finishing touches of this prop, I thought an old rusty chain and padlock would give some extra creepy visual appeal as well as add to the noise of the banging lid. Unfortunately, I did not have an old chain or padlock that gave the rusted look I was after.

Using a new chain, I first cut it to the proper length making sure there would still be enough slack for the lid to open. I then spray painted the chain with a brown primer basecoat followed by a very light, uneven coat of silver paint to give the rusted look.

In the spirit of keeping a low budget, the padlock was fabricated from a scrap piece of wood and a "J" bolt I had on hand. I used the same spray paint weathering techniques on the padlock as I did the chain.

To attach the chain and padlock to the box, I pounded nails in the back corners of the lid and the front bottom corners of the box. I then bent the nails into hooks and loosely attached the chain in the four corners. If I need access to the inside of the box, I simply unhook the chains from the nail hooks on the lid.

I also thought it would be neat to include some signs on the box warning patrons of "dangerous live animals" or "do not to feed" the monster.

Using a stencil font in my word processor, I typed the sign text, cut out the letters with an exacto knife and spray painted the text onto the box. Although this text cannot really be seen in the dark, it does give the prop a sense of realism and if you are anything like me, then you have a difficult time ignoring small details like this.

The final thing I did was add a couple rope handles to make the heavy box easier to carry, as well as contribute to the prop’s overall visual effect.

Step 6: Conclusion

Overall, I had a lot of fun designing and building this prop and the finished result turned out to be very impressive.

Here are a few key takeaways in case you decide to build your own version of the Monster in a Box:

• Don’t overcomplicate the design. My idea of wanting to lift both the box and the lid using the same motor and dual cams ended up costing quite a bit of wasted time and effort since the box lifting mechanism was eventually disabled.
• One person’s junk is another’s treasure. Don’t be afraid to ask friends, relatives or co-workers if they can help you find the parts you need. Due to equipment and parts donations from friends and acquaintances I was able to build this prop for under $40. The only things I bought new were the PIR sensor, electrical boxes, chain and some miscellaneous hardware.
• Don’t get frustrated and quit halfway through removing the staples and disassembling the first wood pallet. This can be a very tedious job, but just remember, it will be well worth it the first time you hear a grown man scream like a 12 year old girl.

If you liked this project, be sure to visit my YouTube channel (http://www.youtube.com/diyhauntedprops) and check out some of my other prop builds.