Compressed Air Made Simple - Part 3

To Part 1 To Part 2

Building a Pneumatic Pop-Up Device: The Grave Popper

Shown below is the completed pop-up, with all the parts and sizes shown. As usual with our props, the material is 1/8" thick aluminum in flat and 90-degree angled 1" width. It cuts with a hacksaw and drills easily with a hand drill. If you haven't read part two of this feature, please do so before you begin.

If you've ever shopped for a completed prop like this one, you know that most examples are made of welded steel and are not at all inexpensive. So, how can we get away with using light weight aluminum? By controlling the violence of the action using flow restrictors (Grainger part # 4A788). You will need two, as you will see below. DO NOT OPERATE THIS PROP WITHOUT FLOW RESTRICTORS AND A REGULATOR or you will damage it and/or yourself! We're not kidding. If you're still with us on this, let's continue...

In the above photo, We've identified the key parts you'll need from Grainger, and will do so whenever the need arises in following illustrations. (The Stanley brackets shown come from Home Depot.) Begin by cutting the frame parts as shown, and deilling the holes for the hardware. The holes should be in the center of the face of the aluminum stock, in other words, the hole centers are 1/2" in from the edge. All holes are 1/4" diameter. The holes for the corner brackets are most easily drilled by clamping the brackets in place with a C-clamp, and then drilling right through the holes - you can't miss this way! (Note that there are all sorts of extra holes in the pieces I used, but just ignore the empties! We re-used stock from previous experiments.) That hole for the pneumatic cylinder's clevis end is drilled within 1/16" of the edge of the arm, so be careful with this one. Note that when you install the pin through the clevis, you'll need to insert the included cotter pin and expand it to secure the device in place. Also, when you isntall the cylinder, arrange the pivot brackets on the base so that the cylinder stands perpendicular to the base (it will tilt a bit as it moves the arm, but not much.) The pivot brackets are separate, one for each side of the pivot.
Here's how the completed base should look with the upright and corner brackets installed. You can see the pivot brackets screwed to the base in the left photo.
If you've built our Hitcher or CamDrive Floater kits, you alreeady know about these pivots. A 1/4" coarse threaded bolt goes through the hole in the upright and is snugged down with a single nut and lockwasher, as shown. To make the pivoting element, a flat washer is placed on each side of the arm that moves, and is snugged down with a pair of nuts locked together. In this device, we've added a lock washer to the pivot stack to apply some side thrust to eliminate as much wobble as possible. Before assembling each pivot, apply some automotive grease to the bolt and flat washers.The top pivot shown here uses the single nut already secure on the upright as one stationary surface, and a pair of locked nuts as the other surface. To lock these nuts together, snug down the first one until the arm can still pivot but is quite snug, then, while holding the first nut stationary with a wrench, use a second wrench to lock the second against the first firmly. When done, the nuts should not move when you pivot the arm. Be sure they are quite tight, or they may work loose as the prop breaks itself in. You should check for this as you test the prop - before putting it in a display situation.

The lower joint, formed on a 2" bolt as shown, must allow the flat arm to clear the side of the pneumatic cylender as shown. Its pivot is locked with a double pair of nuts, as the photo makes clear. Once again, apply grease before assembling.

The opposite end with its 13" riser arm is completed exactly as this end. The riser is tall enough for you to mount a wig stand on it, over which a halloween mask or other custom face may be placed. There is also room for a pair of wire shoulder forms (as with the shoulders of an FCG marionette) and the 22 inch throw will allow for the average head and shoulders (about 18" high) to be completely hidden behind a tombstone.

Now it's time to talk about applying air to the device, and triggering it. We described the components shown below in part two, so they should be familiar to you:

Assemble your chain as shown in the images. Tubing length may vary as needed, but try to keep your flow restrictors as close to the pneumatic cylender as possible, while still leaving room for tube flexing and adjustment of the restrictors. Note that the restrictors are arranged with their flow arrows in reverse to each other. The one with the arrow pointing to the cylender controls ascent, and the other restricts speed of descent. As mentioned in part two, they don't regulate pressure, but only control speed of flow.

Once you have your air chain assembled, you need to install the event timer as shown at the right. Make sure it is operating and that the valve is cycling before you apply air to the Popper.

More about the chain: The regulator is the first active component. The Popper will operate properly with 40 pounds of air or less, so don't go beyond that pressure. We'll come back to this in a bit, but it's good to know it in advance.

Pay attention to the flow arrows on the regulator when hooking it up. The arrow(s) should point toward the pneumatic cylender on the Popper. To begin testing, adjust your regulator before connecting it to your compressor's master regulator, to make sure that no air will flow initially. (Turn the adjusting knob counterclockwise until it stops. This shuts it off.)

The solenoid valve is also directional. On the aluminum block with the fittings are some numbers: 1, 2, and 3. The inlet - which connects to your regulator - is #1. #3 is the outlet, which is normally closed when power is off, and goes to the first flow restrictor. (For the record, #2 refers to the tiny hole in the top of the solenoid assembly (black case) which exhausts the air when the valve turns off.)

Begin your testing with no load on the Popper. You'll add weight and repeat the test with your final working load later.

First, go to your flow restrictors and screw them fully clockwise. Position the Popper so that it will not hit you or anything else - so no one gets hurt, and nothing gets damaged. Remember, using air under pressure is serious business! Adjust your compressor's master regulator to deliver about 45 PSI. Now, connect your Popper regulator, and, after making sure thet the timer is not firing, dial up about 20 PSI by turning it clockwise slowly. Now, set the timer to give you about 5 seconds of on time and trigger it. While it is triggered, slowly open the Pop-up flow restrictor just until the arm begins to rise. Do not let it slam upward! When the valve shuts, carefully open the reset restrictor so that the arm falls slowly back down. Again, don't let it flop down hard.

Repeat your test until you are satisfied with the results. If it is still too violent, screw the restrictors down some. If it's too slow, do the reverse. The Popper should rise to its full height in about 1/2 second or longer. Much faster than this and wear becomes an issue over a long period. It should fall back to rest even more slowly - allow 3 or so seconds for a full reset. (If you've even been in Haunted Mansion, Orlando, you know that the attic pop-ups take their own good time in popping and resetting - with good reason.) If your pop-up rises within 1 second, you still get the startle without undue wear on your pneumatic device.

Now it's time to add your prop head and shoulders for a full working test. Begin the test with your current settings. If necessary, begin by adding slightly more regulator pressure, not by opening the rising action restrictor. Remember, do not exceed 40 PSI. (Watch that weight!) A pressure between 20 and 30 PSI should work. If the speed is still too slow, then open the restrictor very slightly. By all means avoid slamming the arm on the upstroke. You will probably also need to further restrict the fall as well. Keep testing until you get consistent safe action.

Now, some advice on safety: If you put this prop in a public area, the public must not be allowed close to it, or worse, allowed to tamper wih it. What this means, practically, is that you must rope off the display and have a staffer on duty to observe crowd behavior. As this is an unusual sight in a home haunt, curiosity may draw the older visitors to snoop the mechanism, so be on the lookout. The best method of triggering a pop up is to do it yourself, watching for the best opportunity for a scare. This allows for the ultimate control of safety.

If you must use a passive IR switch (some event timers we know of offer this option) then make sure the prop is out of harm's way, and that the 'Off Time' knob has at least 10 or so seconds set on it, to keep your prop from constantly bashing itself like a tire pump in action. This also keeps the effect from becoming a bore, and failing to scare anyone.

Have fun building and using your Grave Popper!

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