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Discussion Starter #1
I'm going to use pneumatic cylinders to create pretty basic tombstone pop-ups. I made a very rough contraption to start learning how pneumatics work but am running into a problem. As the video shows, to get the board (future tombstone) to pop up, I have to give the board a nudge upward with my hand to get it moving. There is enough air pressure, but the piston initially pushes straight forward without transitioning into an upward motion. Do I need to put the cylinder at a steeper angle to the bottom of the board? Should I make a different sort of attachment for the underside of the board? Would appreciate some suggestions from those of you familiar with pneumatic props. Thanks. Jay

 

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Yeah, it's the lack of angle when collapsed. The easiest fix might be some spring loaded hinges. The air pressure will keep it fully retracted but when activated, the springs should be enough to get it moving.
 

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Just an FYI, a much shorter stroke cylinder would have probably been a better choice for this. The short stroke would allow the cylinder to be mounted at more of an angle and still be able to lift the stone 90 degrees.
 

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Discussion Starter #4
I need to make five of them and haven't purchased the other cylinders yet; so I'll go with shorter rods. Thanks for a commonsense (though not apparent to me) suggestion. I'll also check on spring loaded hinges.
 

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I need to make five of them and haven't purchased the other cylinders yet; so I'll go with shorter rods. Thanks for a commonsense (though not apparent to me) suggestion. I'll also check on spring loaded hinges.
Another option to consider along with shorter cylinders is single acting spring return. This type of prop doesn't need double acting, single acting will be cheaper and easier to rig up.
 

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Discussion Starter #6
Maybe I'll get one of the single acting to try it. My display is going to be Christmas versus Halloween, with the house alternating between Halloween and Christmas decorations (Halloween doesn't like Christmas decorations in the stores before Oct. 31). Mostly it's a synchronized competition of lights, but I thought I'd add the timed popping up of tombstones, but as the tombstones fall backwards, up will rise a tombstone-size Christmas package (just a wooden or foam cutout). They'll be connected at the base in an "L" shape. One goes up, the other goes down. I like the idea of being able to control the speed of the rods with needle valves (?).
 

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You can still control the speed up and down with a single acting cylinder using a 3-way solenoid and a speed control on the supply port and another on the exhaust port.
 

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Discussion Starter #8
Do you have any suggestions about where to buy cylinders? I ordered one from Frightprops.com. I'm wondering if there are decent but less expensive ones elsewhere, although Frightprops isn't outrageous.
 

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There's usually a good selection on ebay for cheap and most of them are new. For your short throw stone application I would go with 1" or 1-1/16" bore.
 

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While I think Fright Props is an amazing company and recommend them, you may want to check out Automation Direct (https://www.automationdirect.com) for the cylinders and fittings. They likely will be a bit cheaper. One of the great things about Fright Props though is that if you need assistance or have questions they will help you out.
 

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Another tip I thought I'd pass along is that it's best to mount your cylinders so the rod extends and not the cylinder. That way your air lines have minimal movement.
 

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I design pneumatic driven equipment for conveyors and material handling systems. I use that exact cylinder style all the time. I want to help you out here.

First and foremost, you need to look at the triangle you've formed. You have three points: The hinge, the cylinder base clevis, and the cylinder rod clevis. Your cylinder's force is directed from the base clevis, through the rod clevis, to create a torque moment upon the hinge. To get more torque, you need the cylinder to push next to the hinge, perpendicularly. Your hinge in the video looks like the cylinder is aiming its force directly INTO your hinge. Your cylinder in the down position (cylinder retracted) is simply pushing, without any torque occurring.

Imagine trying to get your bicycle to move forward, when the pedal is at the top. You can't get moving forward. But as soon as that pedal is rotated forward all the way, your bike really starts to move.

I sketched up an example of how to fix this setup. Simply put, lower your rear clevis, by making your box taller.
 

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You're very welcome, Ghostland. You just gotta remember that kinematics and physics can play a hefty part of even a Halloween display. So you have to learn as much about your ideas and applications as you can.

And I've also learned, it's harder to learn this stuff in a classroom, than when you need to learn about something when you actually care about it. Kinda like a necessity. You study harder, and learn more, when you have an immediate application for the stuff you study. So feel no shame when asking about stuff! It means you're learning! And a life without continued learning, is a life less interesting. I learned that philosophy long ago, and always remind myself of it. Motivation to keep improving your life!
 
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