# Scissor hinge question



## Hauntactor (Nov 27, 2016)

I've been looking into building a scissor hinge, and the one thing I can't seem to figure out is whether or not to use a single acting or double acting cylinder. Any tips would be appreciated!


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## diamonddave_k (Nov 9, 2016)

Depends on the retracting speed you would like. If you're doing something vertical the mechanism with a single acting should drop fairly quickly on it's own via gravity depending on the weight of your prop and the amount of air released if you are going to control that at all. 

Double acting you can control the extension and retraction speed of the cylinder making for a swift motion both ways if that's what you prefer. 

I have props with single acting and props with double acting, just depends on what you're going for.

What are the planning on doing with the scissor mechanism?


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## Hauntactor (Nov 27, 2016)

I'm thinking of building a prop of a person in a chair. The person then extends out a few feet.(sorry if I did a bad job at explaining). Also do you know the difference between a nose mount and a universal mount, and which one you would suggest? Thank you!


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## diamonddave_k (Nov 9, 2016)

Oh ok cool. I would do a universal mount just to give yourself more mounting options and more stability. Are you planning on building the scissor out of aluminum? Steel? Just curious. I've thought of doing something similar but never got around to it. Let us know on your progress as you move along we would all love to see!


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## BillyVanpire (Apr 22, 2015)

i would suggest a dbl action cylinder for a horizontal dummy extension.
much more control.

here's one i made


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## Hauntactor (Nov 27, 2016)

Ok thanks guys, I really appreciate the suggestions! I hope to start building this soon(and hope that this isn't another project I never get around to). Thanks again guys!


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## Screaming Demons (Jul 12, 2009)

You pretty much have to go with double acting since it probably won't retract by itself, depending on how you mount the cylinder.


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## Hauntactor (Nov 27, 2016)

I know it's been over a year since this was originally posted, but I thought id update everyone on the mech. The video ill post below was taken in December of 2017. I'm now farther into the process. The main problem right now is the rig over extending itself. I probably should have went with a cylinder an inch shorter. As you can see, once its extended to the full length, it cant support enough weight at the end of the hinge. Im currently planning on adding a few more beams to the mech, then ill program the controller so it doesn't extend out to its full length.


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## corey872 (Jan 10, 2010)

[oops - posted reply to the wrong thread - please feel free to delete]


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## DarkOne (Oct 16, 2012)

Depending on your valve, you may not be able to program a stop before full extension. You could however put a mechanical stop that would only allow your cylinder to push out so far. That's probably the easiest way to go.


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## Hauntactor (Nov 27, 2016)

I’ve just been experimenting with the controller for the cylinder. Since I can control the psi at all times, I’m just allowing the cylinder to get air until it’s about 3/4 of the way extended. Lol it’s hard to explain, the video might show this a bit more clearly, but I’m having trouble uploading it.


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## DarkOne (Oct 16, 2012)

Does that mean when it's 3/4 full, you are immediately retracting it? So the prop goes out then in, no resting in the out position? That should work just fine but I would think you would need the psi low so the cylinder doesn't move very fast to be able to stop giving it air at that moment. If you want a faster moving prop, either use a physical stop or replace the cylinder with a shorter one, you can always use your original cylinder on a new prop!


The stop I'm thinking about could just be a short piece of angle iron bolted in between the two arms of your scissor so the moving side of it would hit the stop when you've reached your desired reach.


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## Hauntactor (Nov 27, 2016)

Yeah, I agree I’ll probably need to buy a shorter cylinder at some point. I just really don’t want to buy anything else before this Halloween 😂. With all the weight on the scissor, I’d say it takes almost 2 seconds for full extension. So when I programmed it, I only allowed the solenoid to get power for about 1.5 seconds. It seems to be working for now.


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## Batbuddy (Sep 3, 2014)

I made one of these as well, I ended up supporting the middle of the first scissor on a bearing/roller tied to the upright steel. Kind of hard to explain. The first year the prop shot out so quickly that it would break the scissor bars, so next year I beefed them up and added some valving to the air line inputs which helps to slow things down a bit. this is the third year and I have removed some of the scissor sections (used to fly about 7 feet). It seems more tame with fewer sections, probably because it doen't get inertia built up. I'll Have to see if I can get a video of it.


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