It's a quest of sorts, to build something unique and unexpected.
The amazing talent among the home haunting community is a seemingly endless source
of inspiration. Creativity, dedication, and ingenuity overflow the pages of personal websites
and forum posts. The sharing of knowledge within this community keeps it alive and well, and
we're truly honored to play our small role in this constantly evolving group.
With so much to see, how does one decide where to start?
I think some projects choose the builder.
Okay, Eric, enough with the blah, blah, blah ... show me the prop already .
Brent Ross is the key individual behind Devious Concoctions.
His personal haunt, the DC Cemetery is filled with his creations.
He was wise in deciding to capture this annual event on video,
because there simply aren't words to describe the show.
(Copies are available through his site.)
After numerous viewings of the DC Cemetery videos,
we came to the conclusion that Mr. Ross was really onto something.
The specific "cemetery" theme, if approached cautiously,
could include a much wider spectrum of props than our current
haunting endeavor.
Even though we're primarily focused on prop design and construction,
adopting and maintaining a theme would certainly improve our collection.
(...not to mention the "quality" of the haunt itself.)
Thanks to Brent, our first dedicated "cemetery" prop
will be a pneumatic grave marker prop.
Having some newly fueled motivation ...
What better place to start then the oldest local cemetery?
You'll have opportunity to familiarize yourself with tangible objects. Grave marker styles have
changed over time, and surely vary with geographical location.
From simple flat head stones to elaborate statues, monuments, blankets, etc.,
there are dozens of marker types.
While snapping a few photos of textures, colors, etc.,
one feature, which was at first overlooked, dominated the overall appearance of several stones.
Cracks.
Mostly superficial, probably weather or age related, but occasionally
obvious, deep fractures.
The quest for our next prop basically introduced itself to us.
A combination of structural and artistic features from these markers
are the main sources of inspiration for the animated obelisk prop.
An unfortunate act of vandalism to the tall thin spire of one monument
inspired us to "open" our grave marker prop.
The more compact, stout proportions of the second obelisk could be used to
provide ample room for a concealed body prop ...
Knowing what the finished product should do, and what it should resemble,
it was time to begin the research and development phase of the project.
An Internet search for "obelisk" produced interesting results for this "less-than historically-versed" prop maker.
The Obelisk has a long history, as described here. While this information may help define the nature
of the structure, we need something a little closer to home. A second Internet search for "obelisk as Halloween prop"
delivered more relevant sites of interest.
Photos above are links to corresponding builder's pages.
The plan is to build a structure using steel tube stock. A hinge near the top of the prop will
allow one full wall of the obelisk to swing upward, bringing to view a prop body.
The base is constructed of 11 gauge 1 X 2" tube stock.
The rear wall (at left of each photo) and lower box use 11 gauge 1" tube.
The extra wall thickness provides additional strength and adds weight to stationary portions
of the frame. This prop, when finished, will likely be quite top heavy.
The front wall, pyramid top, and all diagonal braces are cut from 16 gauge 3/4" tube stock.
Given the generally short lengths between supported points, this will be more than strong enough,
but as light (weight) as possible.
The "V" shaped intersection at the bottom of the front wall serves two purposes.
First, it provides an additional four inches of headroom for the prop body.
Second, it guarantees proper alignment when the lid closes.
Overall structure dimensions;
18" X 18" at the base
14" X 14" at the top
48" tall, closed
85" tall, extended
We decided on these measurements after estimating the dimensions of the prop body to be installed.
It'll be a tight fit, but the plan is to keep the obelisk as small as possible when closed.
It might be a dangerous assumption, but hopefully nobody will expect this prop to open.
The lid's pivot point is made using a pair of heavy duty door hinges welded directly to the frame members.
The hinge linkage is made from 3/4" tube stock and 3/16" X 1" flat stock.
Each joint consists of three identical fingers, 1" wide by 2" long.
A 1/4" bolt, centered in width, 1/2" from one end will become the pivot point for each joint.
By adding this hinge linkage, we'll be able to lift the obelisk lid using a shorter cylinder stroke
and keep the mechanical components neatly tucked away at the rear of the prop.
We'll need all the room we can get a little later in the project.
The final (open) position of the lid would make it difficult to lift using only a linear actuator.
There's a good chance the cylinder would bind at or near full extension.
This linkage will offset the "effort" point, taking advantage of favorable leverage.
Once the frame is blocked out, it's time to begin fabrication of the prop body armature.
With more welding tasks in store, it would be foolish to begin detailing the structure.
We'll use a foam backed latex prop body.
We need a steel armature to support this prop body, attach the
body to the structure, and permit any additional movement.
The goal is to create a set of secondary motions.
After the Obelisk opens, the prop body will drop down/forward.
At the same time, the arms will unfold slightly, and the head will tilt upward.
Naturally, the armature will be built to the specifications of the skin(s).
We'll experiment with secondary animations
using a combination of pneumatic and cable control.
Above are early photos of the arm and neck linkage components.
Both of these motions will be produced via cable control.
One lever of each joint will use a coil spring (return), while the opposing
lever is pulled (actuate) using a steel cable.
In these photos, the armature is beginning to take shape.
Arm and head linkage components are bolted in place (for easy assembly inside the latex prop skins)
Spring returns are added and fine-tuned. 1/2" washers are welded to the frame
to perform the honorable duty of cable sleeve anchor points.
After a brief test fit within the skins, the armature is removed and disassembled.
In the second photo, the small four-bar linkage is added to the spine.
This linkage will be pneumatically powered, and will simultaneously
actuate the control cables for the arm and head motions.
With the majority of the frame and body armature fabrication complete, it's time to add the pneumatic cylinders.
The lid lift is accomplished using a pair of 1.25" X 8" Atlas dual-acting cylinders.
Stops have been welded to the frame to limit how far the lid can be lifted.
Without these, the stresses placed on the cylinders and frame members would have destructive potential.
These stops are positioned so the entire load at full extension is just short of balanced above the pivot point.
The body armature cylinder is an 1.5" X 2" Clippard dual-acting cylinder.
This motion will occur after the lid lift is complete, creating the effect of a quick "lunge."
The placement won't introduce any possibility of cylinder over-extension.
(stops aren't required here.)
Above photos show the prop (minus arm and leg linkages) up to this point.
As mentioned, we'd like to experiment with cable control.
Essentially, the cable will be anchored to the crank or follower bar of a four bar linkage.
As the linkage extends, the cable is pulled the same distance the linkage travels.
The "loose" end of the cable will be attached to joints in need of animation.
Maybe this isn't the industry standard, but it accomplished the task.
By encasing the cable in a sheath, and anchoring this sheath to specific locations,
you'll be able to pull from *any* direction, which opens up a lot of possibilities.
Keeping as much of the mechanical workings inside the prop body as possible might add a touch of
craftsmanship to this project ... you know ... class the joint up a little bit ...
Parts list:
(McMaster-Carr Part Number where applicable)
(# 50375 K412) Rigid Polyethylene Tubing ... 1/8" ID, 1/4" OD.
( # 5532 K422) Polypropylene Low P.S.I. Compression fitting, male pipe adapter, 1/4" tube OD, 1/4" n.p.t.
1/2" flat washer, welded to frame.
9/16" 18 t.p.i. nut ... not very easy to find, but the salesman at a local hardware store
is amazingly efficient at his job.
A standard 9/16" fine thread nut will work for this application, and is much easier to find.
( # 3458 T16) Type 302 Stainless Steel Wire Rope 1X7 strand, 3/32" diameter.
Swivel Anchor Bolt Contraption (more information below.)
... Necessity, the mother of invention ...
Here's our dilemma:
We have a 3/32" cable and a lever measuring 7/16" in width.
Unfortunately, we're not able to drill a 1/8" hole, insert the cable, and clamp it as a loop.
The cable is too rigid, and there is not enough room to accommodate the extra travel length.
Here's our version of the solution:
Drill a 1/4" hole in the lever. Weld a short length of 3/8" all-thread to the hex end of a 1/4" 20 t.p.i. bolt.
After drilling an eighth-inch hole in the 3/8" all-thread portion, the cable easily passes through.
The 1/4" bolt portion is secured through the lever with a nylon locking nut, which allows the whole contraption to swivel.
The cable is locked in position between the washer and the weld.
This will permit adjustments to the cable length during the testing phase.
Above photos show the body armature fitted with control cables for head and shoulder/arm linkages.
Front view of the shoulder/arm linkage.
Why three coil springs?
The design incorporates two motions per arm assembly.
When the cable is pulled, the prop's elbows will travel away from the torso roughly five inches.
The pivot point for this motion is a 1/4" bolt at the shoulder. When this joint reaches maximum travel,
the cable continues pulling the lever, which rotates a rod running through the (upper arm) square stock.
This action will cause the forearms/hands to rotate on the elbow approx. 90 degrees away from the body.
Above is a rough drawing of the shoulder joint components.
Photos of the obelisk prop including body armature and control cables.
(Photo above/right is a link to a GIF animated version)