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I am trying to find instructions on how to build a spring bridge and can't find anything. We saw one in the display at spirit Halloween and are first on the waiting list for it but they said it would be around $500 and I'm sure we could make one for much less than that! I saw something about using some sort of thin metal attached to wood planks but I'm confused as to what it kind of metal that would be and how to assemble!
 

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Okay. Gonna do a bit of reverse engineering here off these videos.

You've got a box frame, with a few cross braces. In between the braces, the bridge boards flex down. It looks to me the braces have the flexible connecting material between them, and the boards attached on top.

Now, the goal isn't to suspend this up in the air, but just to create the uneasy feeling of the floor boards giving out from underneath you. So here's how I would try to replicate this.

2x6 frame and 2x4 braces, with garden hoses running the length, attached on the top of each brace. Then the boards attached to the hose. The boards sag until you touch the ground/driveway/pavement/earth beneath it, so the sag is limited in its drop.

Now if the garden hose can allow sag, but doesn't recover and pull tight again, then you need to change the hose to some lengths of chain. BUT.... the chains are not hard anchored to the braces, but instead have springs anchored to the braces and the chain attached. I think you could go as simple as the springs used at the top of a storm door. Each brace then has four springs, attaching two per bolted connection, then chains between to bolt the boards.

Time to see what happens. And remember, take plenty of pictures!
 

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Here is what I posted in the thread I attached above.

Come to think of it i am pretty sure how this works. We have a park with one of those large wooden play centers on it and they have a bridge That is just a piece of stretched food belting that has a pipe or board across it every few feet so between the pipes the belting flexes witch (lol notice the spelling) would give the exact effect of what you are seeing in the video. But you would also have a little side to side flex as well as length wise. You dont see any side to side in the video. Like the one below. One issue is that say 10 ft. of conveyor belting would run you about $100. But when you look at the cost of what they have it is considerably cheaper. So using Bryans frame suggestion and belting i am betting less than $250 for it compared to over $1500 for the one in the video. Also note that this belting is use in the ag industry and can be stretched tight but will still flex as you see in the spring bridge video.

 

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I have made a version of this on two different occasions. I used foam pool noodles put in wooden tracks on both sides with 2x4s placed over top (imagine planks). There was another 2x4 running along both side to hold the planks in and to keep anyone from getting pinched by the moving boards. Worked great both years. I will look for some pics.
 

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I'm considering building this as well. Made a mock version 2 weeks ago after picking the brain of a Spirit manager.

Going to give this concept a try over the weekend.

Section will be 5'x3' frame (black lines). Constructed of 2"x6". Planks will be 2"x4"x30" (brown lines). I will run 3 bungee lines (blue lines) under the planks, attached to the boards with fence staples and then tightened.

Bungee has a 250lb load, so with three runs and managing the occupants it should suffice.

I may add a 2x4 underneath running the length of the frame and on center to prevent excessive droop. (Not shown)

Crude drawing attached.
 

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I made one of these last year. I made mine similar to HauntBrothers above, but mine was 8' long and 4' wide.
I kind of over-engineered it by running 1/8" cable along the length (where HauntBrothers has his blue lines). This year I will be rebuilding it and plan to try out either seat belt material o something similar I found on ebay/amazon.

The problem I found was that the way it was built, no matter how tight I pulled the cables, it wasn't springy enough. I then realized what it needed.
If you take a third piece of wood and put it under the bridge halfway between the ends (a third 3' piece in HauntBrothers case), it woks great. Especially when there is a light person on one side and a heavier person stepping on the other.

I do remember last year thinking that I needed to work on the lengths of the spans. I think I was thinking I might need to shorten up the spans (which would mean making the whole thing longer and adding a second intermediate piece. Essentially having three springy sections. Not sure yet if having a 3d section will make things more springy, or diffuse the spring. I'm thinking the latter, but I guess I'll see.

I'm working on other projects at the moment, but plan to revisit this before October to make it a lot better.

Another issue I found.... One bridge was not enough. I funneled people through the bridge to get their treats, but didn't realize it would be getting two way traffic. So next year there will be a flow of traffic with one in bridge, and one out bridge.

Edit: Found a picture from last year. Someones flash went off at the same time so it's somewhat lit up. I was really dark and I was a little afraid of people tipping on it, so I thew a light rope underneath it. Turned out good for last minute fix. Also for a last minute prop. It's going to be a lot better this year.

Also looking at the picture, maybe I cut it down to 6' not 8'. Can't remember. Lol
 

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