# Gas chamber prop mechanism



## grismcdonald (Aug 23, 2011)

Hey
Does anybody have a plan for a mechanism that will rotate from left to right and also move up and down. Looking for something as in this prop


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## GhoulishCop (Sep 25, 2009)

grismcdonald,

I'm good friends with Dave and I've had the chance to see the inner workings of the prop up close and personal and I can tell you it's not just one thing that makes that prop move, but quite a few. My head nearly exploded when he showed me all the mechanisms, cylinders, and supply lines that went into making that awesome prop (and if you ever get a chance to talk with Dave, make sure you call it an electric chair and not a gas chamber because it really sends him over the edge!).

But I'll be talking with him later on today and I'll ask him if he has any recommendations on how you should pursue this.

Cheers,
Rich


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## halstaff (Nov 18, 2009)

I'd start with 2 cylinders arranged something like this -










By using a wheel assembly like this one with the wheel removed, you get a place to mount your post for the upper part of the body as well as the swivel mechanism needed for the side to side motion.


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## GhoulishCop (Sep 25, 2009)

So I spoke with Dave and as Halstaff says, it is just two cylinders doing all the work. Well, one doing the side-to-side motion and the other doing the up and down. But Dave also said the prop is obviously much more complicated than just two cylinders, and I can tell you there are counterweights, guy-wires, and a bunch of other things going on to get that motion.

But on the most basic level, it is indeed just one cylinder going one way and another going the other.

Cheers,
Rich


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## hauntedyards (Mar 24, 2005)

Easiest route I can see would be a cylinder with a sturdy 4-Bar linkage to lift and on top use a rotary cylinder to turn the body (which you can adjust the degrees of turn to your liking). Love the violent movement on that...


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## bfjou812 (Aug 15, 2008)

Another option, though it can get expensive ,is to use a rotating cylinder that has linear movement also. They are used quite frequently in pick and place operations in assembly machines.


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## grismcdonald (Aug 23, 2011)

Ok been brainstorming and reading all day. First, I have to say this will be my first pneumatic prop. I have a good idea of how I will build it but I have a couple of questions. I thought I would first build the frame/mechanism out of PVC because I have a good source for all of the parts and pieces. This will allow me to adjust lengths of arms,etc easily. Also, do you first build a frame and then figure out what length cylinders you would need depending on the range of motion and where is the best place to buy valves and cylinders ? Once I get it to operate the way I like, I can build it out of tube steel but do I really need to? Are the pneumatics too mutch for a PVC frame? I typically only use my props for two nights. A party and halloween night.


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## hauntedyards (Mar 24, 2005)

If you are looking for that kind of motion I'd go with steel I can't think PVC would stand up to that... I've had 1/4" bolts break on violent motions.

Pneumatic parts I'd look on Ebay... If you have time. If you HAVE to have it running now then frightprops and DCprops have stuff for sale.


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## niblique71 (Dec 2, 2009)

You can use any material for almost any propose. the question is..... how many times will it be required to cycle before failure/rebuilding?? Heck, you can now "Print" a plastic gun which will fire at least once reliably.

If you have 3 TOT's a year, use PVC. If you have 800??? You'd better use steel.


Now, with that said. PVC is also great to add a piece of, to a metal frame...which will allow a Head or arm to flex a bit more than steel to give it more movement.

In short, use the right material to achieve the motion you desire and keep the safety factor high.


Another thing to consider is... How much time will you invest in building this prop??? and how much time are you willing to invest in constant repairs and possible liability??? Building a complicated prop is time consuming and I'd go with the MOST reliable materials to insure that my creation would last at least 5 seasons if not 10 or 20.


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## grismcdonald (Aug 23, 2011)

What is the cost of a rotary cylinder? Where is a good source? Figured I would use Halstaff's recommendation an use a beefy wheel assembly. Attach a base that I could build the upper torso off of and attach a cylinder to the base to get the left/right motion but if I can get a rotary cylinder at a reasonable cost, that seems to be the easiest.


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## Hippofeet (Nov 26, 2012)

I didn't even look at the prices, but we get cylinders from them sometimes, in an emergency. http://www.smcusa.com/top-navigation/products/actuators-air-cylinders.aspx

Expensive though, even for linear.

Ebay might be a good bet, if you can wait for the right one.


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