Monster-In-A-Box Halloween Prop (Part 2, the Guts)




About: Father, husband, drummer, fledgling guitarist, small business owner, Halloween fanatic that loves working with my hands.

This is the 2nd part of a 2 part instructable on building this prop. See my other instructable "Monster-In-A-Box Halloween Prop (Part 1, The Box) or just a good pallet box" for instructions on building the box.

In this part I'll go into detail on how I went about applying pneumatics, a prop controller, a fog machine, lights and sound to create and choreograph the movements of the prop. This is my first Halloween prop and I have to admit I was learning as I went along on this part. There may be better or cheaper methods of doing this. This is just what I ended up with. I will provide a parts list of the inner workings in step 1.

Step 1: Parts List

I have tried my best to get all of the parts listed here. There were many and I might have missed something. If you see something I missed, let me know.

Brains / Prop Controller

BooBox Flex with 4 outputs

(1) PIR Motion Detector

BooBox Director Software

(1) 1GB SD Card

(1) Power Strip

(1) 12V 5A AC Adapter

Muscles / Pneumatics

Air Cylinders:

  1. (Bottom) Bimba SR-092-DQ: 1-1/16 Bore, 2" Stroke
  2. (Top) SMC NCME106-0150: 1-1/16 Bore, 1-1/2" Stroke

Solenoids: (2) Airtac 4V210-08 12 Volt 4 Way, 5 Port

(2) 1/4" Flow Control Valves

1/4" tubing, approx. 7'

(4) sintered bronze mufflers (used on solenoid exhaust valves to muffle sound of air escaping)

(6) 1/4" male connector push-on fittings (used on A, B and supply line valves of solenoids)

(1) swivel branch tee (used to branch the single incoming air supply line into 2 lines, one for each solenoid)

(1) female thread quick connect (used to connect the swivel branch tee to the air supply line coming from compressor)

(4) 1/4" male swivel elbow push-on fittings (used on the ports of the air cylinders)

(2) cylinder foot brackets

(1) cylinder flange mount

(2) cylinder rod bumpers

Breath / Fog

Chauvet Hurricane 901 Fog Machine with wired remote

12V single relay board

1-1/2" PVC straight pipe, approx. 6"

(2) 1-1/2 PVC 90 degree elbows

(1) 1-1/2 galvanized pipe strap

(1) can flat black spray paint

Growl / Speaker

Fender Guitar Amp

10' Speaker Cable


(2) Red Nano-spot miniature spot lights

heavy chain, approx. 15'

old padlock

(9) u-bolts

(4) eye bolts

(6) chain quick links

black felt

18 gauge wire, approx. 20'

2" furniture hole cover

3/4" Plywood 4'x2'

Step 2: Adding Muscle (Pneumatic Cylinders)

I wanted my box to pitch forward as if a monster was inside pushing against the front wall of the box and I wanted the box lid to bang up and down. I've seen different methods of accomplishing this. The cheapest and easiest seemed to be to using a small windshield wiper motor and a stepper gear. I didn't really like this method though because the movements did not seem natural or real. I wanted something erratic, forceful and convincing. I settled on using air cylinders. That decision ultimately required more equipment (air compressor or air tank, hose, tubing, cylinders, solenoid valves, fittings, flow controls, etc - none of which I knew anything about) and more expense. Youtube was a great resource for learning about pneumatics. I also gathered information from the resource section on I purchased some of my parts from frightprops as well. I sourced my parts according to price so I ended up buying my parts all over the internet at the cheapest places I could find.

I used 2 pneumatic cylinders I purchased on eBay to create the movement in the box. Both cylinders are double acting; which means you can apply air pressure to forcefully move the piston in both directions (in and out). I felt like the movements from these cylinders could be more controlled and also be made to appear more erratic than single acting cylinders.

I planned to use a larger bore (inside diameter of the cylinder) size for the cylinder that lifts the box off of the ground since it would be lifting the weight of the box and a smaller bore size for the cylinder that bangs the lid up/down since it would only be lifting the weight of the lid. However, I found a deal on two that were both larger bore sizes so I ended up with a little heavier duty bore size than I needed on the top.

I applied teflon tape to 1/4" male swivel elbow push-on fittings and attached them to the air cylinders. I attached cylinder rod bumpers to the ends of the cylinder shafts.

I drilled a 1" diameter hole in the middle of the floor at the rear. I cut a small square of plywood and drilled a 1" diameter hole in the middle as well. This piece was to serve as a spacer and to provide additional strength to the floor where the cylinder would attach. I placed the spacer piece on the floor so that the 1" holes lined up. I attached a cylinder flange mount to the air cylinder. I lined up the cylinder so that the cylinder shaft extended down through the center of the spacer and the floor. I marked the 4 mounting hole locations and drilled 4 holes through the spacer and the floor. I used 4 bolts, 4 bolts, 4 washers and 4 locking washers to fasten the cylinder flange mount to the spacer and floor.

I attached 2 cylinder foot brackets to the second cylinder. I lined up the second cylinder on the inside right wall of the box towards the front. I marked and drilled the holes. I mounted the cylinder with bolts, nuts, washers and locking washers.

Step 3: Adding Brains (Controller and Solenoids)

I drilled a 2" diameter hole in the back of the box near the bottom to route my power cable, air hose and PIR sensor cable through. I popped a 2" furniture hole cover into the hole to protect the hoses and cables from the sharp edges of the wood. I had to trim the bottom of the hole cover because I drilled the hole too close to the 1x2 frame.

I opted to go with 12V components (solenoids and relays). You can also use 24V components. I used a BooBox Flex as the prop controller. I mounted the Boobox on the rear wall inside the box towards the top. I mounted the solenoids on either side of the Flex. I mounted a black power strip to the floor for all of my powered devices and routed the cable out the hole in the back.

Step 4: Adding Air Tubing and Blacking Out

Since all of the power devices inside the box have some sort of external light on them, I wanted to black out the areas that they might shine through. I cut 2 pieces of black felt and placed one over the front jail bar opening and the other on the underside of the top lid. I secured them with a staple gun. I also added some cable supports to stop the lid from opening too far.

At this point I began routing the 1/4" air tubing. I attached a swivel branch tee to female threaded quick connect using teflon tape at the joint. The quick connect will be the attachment point of my air cylinder/air compressor hose. The swivel branch tee will connect to each solenoid. I cut two lengths of 1/4" tubing. I inserted one end of each section of tubing into the "P" port of each solenoid and ran the other ends to the each side of the swivel branch tee. This will supply air to each solenoid.

Here's how I attached the air tube: It's the same for each solenoid and cylinder. I cut one length of tube and inserted one end into the "B" port and placed the other end in a 1/4" flow control valve. I cut another length of tube and ran it out of the flow control valve to the port on the air cylinder that extends the piston (in this case it is the port opposite the end that the piston comes out of). I wanted a flow control valve here so I could control how much force is used to open the box and push it off of the ground. I cut one more length of tube and inserted it into the "A" port of the solenoid and placed the other end in the other port of the cylinder (this port pushes the piston back down inside the cylinder). I didn't feel like I needed to have a flow control valve on this connection but you could adjust how quickly the lid closes and the box drops back to the ground if you had a flow control valve here. Again, this tube routing is the same for both so just repeat for the second set of solenoid/cylinder. See photo for example. Note that the first time I ran the hoses I did it wrong. I had to take another photo later which shows more things done to the box that I have not yet covered.

I added the ac adapter for the Boobox Flex and zip tied it to the floor of the box.

Step 5: Chaining the Beast

I used chains to loosely hold the lid closed and to hold the box in place. I attached 2 long chains to the box at the rear with u-bolts. These will drape over the top of the box and connect to another u-bolt I placed on the front of the box via a padlock. I kept these two chains loose with some slack so the lid could open a couple of inches. I left them too long so that I could shorten them up if needed once I had the box working.

I added a small section of chain on the front of the box at the bottom merely for appearance.

I used a 3/4" thick piece of 4' x 2' plywood for the base. I drilled holes in the 4 corners of the plywood and attached a u-bolt at each corner with a piece of chain. I drilled a hole on the outside top corners of the box and attached an eye bolt. I attached the other end of the chains from the base to the eye bolts with a chain quick link. I wanted the chains that attached the box to the base to be long enough that the box could move around a bit but not walk off the platform. I had to play around with the length a bit. Give yourself too much chain because you can always shorten it later.

I bought an impressive looking lock off of eBay. The lock shaft proved to be too large to pass through my chain links so I had to add a couple of larger quick links to the end of the chain that drapes over the box.

Step 6: Nerves (wiring) and Breath (fog)

Take appropriate safety precautions when wiring. I'm not going to go too in depth on wiring. Whatever prop controller you use will provide instructions on wiring. Each prop controller may differ and I'm hardly qualified to give electrical instruction.

The BooBox I used has 4 outputs. Since I'm triggering 2 cylinders, a fog machine and a pair of lights (eyes) I will be using all 4 outputs. I placed one solenoid on output 1, the other on output 2, the fog machine on 3 and the spot light nano led lights on 4.

In order to trigger the fog machine with the BooBox I had to hack the fog machine's remote and wire it to a relay. The BooBox documentation had some instructions on how to do this. I also found a document on that provided additional instruction. After wiring the remote, I ran those wires out to the relay. Then I ran another set of wires from the relay to the BooBox output 3.

I attached the AC adapter to the BooBox.

I'm triggering the prop with a PIR sensor that is placed outside of the box. I connected the PIR sensor wires to the Boobox trigger input and ran the wire out of the rear of the box to the PIR sensor. I mounted the PIR sensor on a sign that says "Turn Back Now".

I mounted a small section of straight 1 1/2" pvc pipe to the front of the box with pipe strap. I attached a 90 degree elbow at the bottom. This will be the fog intake and will direct the fog out the front jail bars.. The fog machine was then mounted to the floor of the box. I placed the fog machine so that the nozzle was an inch away from the pvc intake opening. If you place the nozzle inside the pvc pipe it interferes with the fog machines ability to properly produce fog. You won't like the result so make sure you leave an inch or two gap between the nozzle and pipe. I painted another 90 degree elbow black and once it was dry I attached it at the top of my straight pvc pipe to direct the fog out the front jail bar opening. I cut a circular hole in the black felt and placed the other end of the elbow through it.

Once that was done I secured the fog machine remote and cabling to the interior side of the box with zip ties. I ran a power cord from the fog machine to the power strip.

I ran long wires from the BooBox output 4 around the front of the box and connected the 2 red spot light nano led lights. I mounted these to a piece of 1x2 just behind the jail bar opening above the pvc pipe. These will serve as red eyes for the beast. I cut a small hole in the black felt for each light so it would shine through.

Step 7: Sound and Animation

Sound and animation is controlled by the BooBox. I programmed the Boobox with the Boobox Director Software. It took me a while to find a soundtrack I liked for the growling. Once I did I had to cut it up with a .wav editor to get it where I wanted it. Once I had my sound track, I then animated the box by turning on and off outputs 1 - 4 relevant to the audio track.

The Boobox will play ambient sounds or music when the prop is not triggered. I added some eerie Halloween sounds to play when the prop was not triggered.

The Boobox has a stereo line out that I plugged a long audio cable into and ran it out of the box to an external small guitar amplifier. I tried to find a good way to place a speaker inside the box but I could not get a satisfactory volume level and I was concerned about how much the box bounces around so I went with the guitar amp that I hid in a nearby bush.

I used a beer keg Co2 tank to supply air to the prop. Originally I planned to use an air compressor but it was too loud even from inside my garage. I didn't want that to distract from the prop so I went with an air canister. I ran a long air hose from the air tank to the prop. I hid the tank in the bushes with the guitar amp.

Step 8: Finishing Touches

I painted the base flat black so it wouldn't stand out so much. I added some fake blood around the top opening and down the sides. I found that red puff paint works great for this. I added some stencils on the sides and top to finish it off.

This box was a huge success on Halloween night. It literally scared everyone; including the parents. It just sat quietly on the path to our front door until people were almost in front of it then it started jumping and growling and we sent them all running and screaming. It drew a nice crowd.

If you like this project please comment. Feel free to ask questions. Let me know if you attempt this build and how it works out. This is my first instructable and I hope you enjoyed it. Thanks for viewing.

Step 9: Video in Action!

Here is the video. Enjoy!



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    73 Discussions


    Reply 1 year ago

    Kara me,

    I'm building your Monster in a box prop this year and it is coming along fine. I'm looking for a good growl audio fille. Can you tell me where you found yours or possibly share it with me?


    Reply 1 year ago

    I got the audio from a Halloween compilation called "666 Scary Halloween Sounds". The track is called "Monster in the pit, No. 1". I edited it a little. I got it off of iTunes several years a ago.


    8 months ago

    Awesome build! Was try looking for parts to build this when I found that FrightProps made a kit based off of this design. It's just the (guts) part of it with the controllers, pneumatics, and


    Link to the Animatronic Kit (wood and other hardware sold separately)


    1 year ago

    Outstanding tutoria!

    Did using the CO2 Beer Keg container affect the props run time? I assume the small volume of air needed to activate the pistons didn't dramatically affect he run time.

    1 reply

    Reply 1 year ago

    I usually only run my props on Halloween day. It'll run it all day.


    1 year ago

    This is awesome, does anyone have any thoughts about putting hinges connecting the bottom of the box and the front of the box ( opposite the cylinder that lifts the back )? That way the back of the box still goes up but the inside remains stationary. I’m concerned about shaking all the components . I would love to hear some opinions


    1 year ago

    Thank you!!!! That helps a lot for sure.


    2 years ago

    This is an awesome project! I've had a similar idea of a trash can jack in the box that I'm building for Halloween. The only difference is it only needs one cylinder and I programmed an AVR microcontroller to be the brains behind it. I'll post an instructable once the project is complete.

    1 reply

    Reply 1 year ago

    Would love to see it. I'm working on a Jack in the Box this year as well.


    2 years ago

    Wow! I have been away from Instructables over the past year and missed all of these awesome comments and direct messages! Thank you to everyone for your input and I'm so sorry I never replied. I'll keep a better watch on this site. Should probably do a few more Instructables...


    3 years ago

    Where did you purchase the pneumatic cylinders from?

    NaVNrs dotwprod

    Reply 3 years ago

    Yes it is!! Did get my parts and pieces.. sides of the box built.. coming together.. thanks for the motivational video post! It will be interesting to compare builds.

    Happy Halloween!


    Reply 3 years ago

    I would also recommend picking up one of these to use in addition to the motion detector (which may not be appropriate depending on the setting). I can trigger 8 different scenes, open the lid, raise the box up, control the eyes and smoke, and trigger the aaoooooga horn. Very simple to incorporate.

    NaVNrs dotwprod

    Reply 3 years ago

    I am envious of your hands coming up.. So today I start putting things together. will try to do some step by step and materials. I will be happy if it turns out half as good as yours!


    Reply 3 years ago

    It was pretty easy. I made silicone castings of my hands and set threaded rods to cure in the silicone so I could easily attach them to the cylinder.

    dotwprod dotwprod

    Reply 3 years ago

    here is what I rigged up to make the eyes move down when the box lifts up.