A Modular Halloween with Grid Beam


I love Halloween, but don’t like the clutter it creates afterwards. I recently discovered grid beam which is basically an adult Erector set.

After putting together a basic set of sticks and components, I was able to replicate a set of classic Halloween electrically operated animatronic props in a fraction of the time it might take otherwise. More importantly, the modular nature of grid beam encouraged prototyping, allowing me to experiment with a wide variety of structures and motor placements. Grid beam is a set of wood or metal sticks drilled at intervals equal to their width. This site by the inventors of grid beam provides the key introduction. The key concept behind what gives grid beam its strength is the concept of a ‘tri-joint’ which is a three way joint that forces a perfect rectilinear self-reinforcing structure.

If you decide to go forward in drilling your own sticks, I strongly suggest you acquire this book which is densely packed with practical examples and instructions.


I’ve also added a few notes the appendix about getting started I’ve found useful.

Once animatronic Halloween props get beyond the size you might find at Target or Party City, they tend to be constructed with custom made metal and wood components. Countless examples of the resourcefulness of prop builders can be found on the Monster list of Halloween Props, which I used as the source of inspiration. If you’re building from an exact plan, you can benefit from measurements provided on well thought out websites or books. However, as it most often the case, if you’re building from a brief Youtube video, or a photo, or have a different mix of parts than the author, you are on your own.  Your motor may have different torque or speed, which requires a different lever arm or your pneumatics in hand may be of different length.

This is where grid beam Halloween prop construction shines. Since the grid beam can be connected in many ways, you can experiment with placements until the motion is exactly right. The penalty for a mistake is not a miscut piece or a trip back to the drill press. Just move the carriage bolt (the standard connector piece for grid beam) to another hole and try again.
a grid-beam ‘tri’ joint (from gridbeamers.com)

a grid-beam ‘tri’ joint (from gridbeamers.com)

The second significant bonus is that the ridiculous contraptions you build for Halloween can be broken down, back to the base sticks if you desire, to meet any storage goals. If you absolutely love what you built, go ahead and store it intact. If it was less than perfect or you want to recover the sticks, break it down. The grid beam is more than strong enough to act as the final structure (especially because Halloween props generally only need stand for a few nights), but it’s easy enough to turn them into permanent structures by mapping the exactly stick length and subset of holes used into a fresh set of sticks (or changing out the wooden sticks for lighter and stronger aluminum).

There’s nothing inherent in the grid beam that makes it only suitable for moving props. The grid beam inventors have tended to recommend wood for ‘furniture’ and interior structure builds and (the far more expensive) aluminum for vehicles and mechanics. For my use, I’ve used wood, but am starting to experiment with aluminum. I’ve produced three classic Halloween props this year using this technique. In most cases, I’m showing the final iteration that worked well with my props and motors, but there was experimenting before hand. In all cases, I have no doubt that these props went together quicker and easier than multiple iterations on custom sticks or metal.

I’m not going to into a lot of detail on these builds as each of these projects is documented on literally dozens of sites. What’s novel is only the classic prop idea and the modular use of grid beam.

The Projects

The Kicking Legs

The kicker is inspired by this page from the highly recommended Scary Terry (who claims inspiration of his own). There’s nothing particularly novel about my mechanism, but what I had on hand was set of grid beam, PVC tubes, a different motor, with a different mount. With less than an hours work, my kicking legs were ready to use. The legs are intended to stick out from a prop lawn-mower or monster mouth and gruesomely kick!
kicking legs halloween prop using wiper motor and grid beam

kicking legs halloween prop using wiper motor and grid beam

covered kicking legs prop using grid beam, pvc, and a wiper motor

covered kicking legs prop using grid beam, pvc, and a wiper motor

The Tombstone Peeker or “Head Popper”

tombstone peeker

Too many references to cite, mine was inspired by this head popper.  His design is more economical than mine, but I wanted to keep the tombstone separate, and create a reusable mount for the wiper motor. I’m not a purist – I was happy to incorporate non-grid beam plates and elements to secure the motor.
head popper wiper mount mount using grid beam

head popper wiper mount mount using grid beam
head popper wiper mount mount using grid beam

head popper wiper mount mount using grid beam

Freestanding Flying Crank Ghost (FCG)

The grand effect of home haunts, I’ve wanted to build this forever. The classic reference is Phastasmechanics, which has a wonderfully detailed build. As usual, I had a different motor and no desire to hang it from my ceiling. I used grid beam not only to build the rig, built to build a freestanding moveable ‘cage’ around the rig so I could avoid hanging it and experiment with placement in or outside the house. As you can see from the structure (which is invisible when the blacklit ghost is operating), this isn’t a structure I’m keen to store.
freestanding flying crank ghost using grid beam

freestanding flying crank ghost using grid beam

I’d also like to point out that my first pass, illustrated below, used a ice-cream maker motor. While accessible and cheap (try Goodwill), they are noisy and make for a challenging crank connection.
fcg original ice-cream motor mount using grid beam

fcg original ice-cream motor mount using grid beam

Once I incorporated the wiper motors from Monsterguts.com, my upgraded FCG was incredibly smooth and quiet. In this example, this particular motor was mounted in the bottom of a dead power supply case, into which I drilled holes 1 1/2″ apart, making it compatible with the grid beam spacing. The change out from the ice-cream maker motor/mount to the wiper motor/mount, once the new crank was finished, was minutes of work and is illustrated below. Try doing that with a custom built wood or metal rig!
fcg improved mount with wiper motor

fcg improved mount with wiper motor

Static Props

Grid beam makes an ideal stands and structures for more substantial static props than for which 1/2″ PVC might ordinarily be used. Since it connects with bolts and not glue, you can change things out or dismantle it.

Safety Considerations

Although the grid beam and joints can be structurally strong, there’s a potential for elements to work loose if the grid beam is used in movable joints, as I did on the kicking legs project in particular. The default ‘carriage bolts’ mentioned in the appendix are not locking. The problem is easily addressed by using appropriate washers and locking nuts.

The motors discussed, although fairly small, produce a surprising amount of torque, and when combined with a thin crank shaft, could produce a nasty surprise. Work on elements with the power off and use appropriate caution around these motors. Around pneumatic projects, in particular, you need to exercise particular caution in ensuring that they are secure before operation and thereafter.


My inclination at this time to break down the structures post-Halloween. I’m not going to kid you – drilling the sticks is a bit tedious and needs to be done with some accuracy. So recovering them for future projects (and future Halloweens) is appropriate. Ready-made sticks are available and if anyone sets up CNC drilling please let me know!

Grid beam projects have an inherent ’self-documenting’ property. By looking at a picture of a grid beam project, you can reconstruct it by ‘counting the holes’ between joints. This web page acts as documentation for future builds should I want to recreate exactly the same projects.

Send me your pictures (admin at creatrope.com) of your grid-beam Halloween pictures and I’ll post them or link to them.

If you liked this project, you might enjoy my other Halloween projects:

General Grievous animated costume

Rocking Gravestone using K’Nex

PVC Halloween Mannequin

AVR Robot Halloween Costume

Alien Costume


Getting Started With Grid Beam

I found it a bit challenging to actually get started with grid beam. Here’s a few notes, most of which are in the grid beam book, but not consolidated in a way that I found accessible. If you drill 1 1/2″ fir sticks, your first hole is 3/4″ from the end and 1 1/2″ thereafter. The bolts you probably want to use to join these sticks are McMaster parts:

2 0 10.03


4 0 9.77


My hesitation in being particular was probably misplaced, as although it turned out although getting these nice bolts at the local Lowes wasn’t an option, pretty much any 1/4″ threaded bolt and a few fender washers come in handy during the above builds. So buy some wood or aluminum and start drilling!

Wiper Motors

Using wiper motors made the difference. They are easy to mount and use and are inexpensive. This is the best resource I found on how to use them.  Although he recommends the post mount, I found the semi-circular fence post mount worked better and had holes just the right distance for the grid beam!