Counterweight Elevator/Trapdoor


Active Member
Has anyone had any experience making one of these? For an upcoming show I had an idea of using a trapdoor for a scene or two to move some things on and off stage with.

We have an apron in our theatre that has the panels that come out (either all of them or just the individual ones) as an orchestra pit. The pit, is a bit deeper than a "normal" orchestra pit, which gives us lots of room.

I was thinking that we could take out a panel or two and then build a platform that fits in where the original panels were (which would be fairly easy b/c they're all almost squared) and then under the stage have the elevator part.

I really don't know how to start such a project; I could build a platform, but I've never built anything like an elevator :)

If there is any online documentation that anyone knows of, or if you got any suggestions let me know. If there is a book that's worth reading that has some documentation, give me the name too.

I'd like this thing to opperate smoothly (duh - nobody suddenly propelled into the air from the orchestra pit :) ) and tips and suggestions on that would be good too.

Anyone made one?

Well as much far as i can go is to say use some extra pulleys and try to build a "mock flyrail" or if you have access use a hydrulic lift (might be more exspesive, but defintly faster and easier)
I worked on a show about 4 years ago at the University of Illinois, this is the trap elevator we made. The PVC pipes where the guides for it, and the ladders would be pulled away when the load we on the "elevator". It worked and was cheap to build but was in no way perfect.


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What sort of material besides PVC did you use as far as cabling and weights, and how did you put it together? It's kinda hard to tell from that picture.

Looks neat though!
If you have access to a library, you may have better luck browsing through stagecraft books. You might find some pictures and photos.

You are really going to have to do some careful design drafting work with this. As they say, the devil is in the details, and you’ll want to stumble on them while on paper, not necessarily in the work shop or when you build it.

A few things to consider: When the trap is not operating, it will probably have to be flush with the existing stage floor. Will removal/replacement of the panels permit this?

Will any of the panel attachment hardware/joists/structure be in the way of operation? (I guess I picture floor pieces being support from underneath, even if its just along the edges.)

When not operating, the trap will need some sort of positive latches so that it doesn’t accidentally open or give way.

I may be mistaken, but the frame in the photo posted by Footer4321 looks like bolted or welded steel channel or structural tubing. (Not that lumber couldn’t be used.) From a practical standpoint, you’ll probably need to lift at least 200 lb, maybe even 250 lb.

Consider how far your vertical travel actually needs to be. Will you need, say 6 feet for someone standing, or could you manage with say 4 feet?

I suspect that keeping the trap platform on track and level (and not binding) may be the most difficult detail.

Watch the pinch points between the trap door and door frame as it closes. Your movement mechanism will be unforgiving.

Also consider crew safety below when the trap moves down.

While some sort of counterweight-driven or -assisted system will help the lift, it will limit your vertical lift for the pulleys and support. (That is, you won’t necessarily have the full subfloor to bottom of stage distance to travel.)

And if it is counterweight-driven, remember that the system will sometimes behave just like an unbalanced pipe in a stage’s fly system – if nothing is on the trap platform, and the ropes/cables are unlocked, the trap door will fly up out of control, propelled by the ~200+ lb of counterweight. Now that I think about it, bringing the platform into the down-position may take some effort, if the platform is empty.

You might consider a hand cranked winch. I’ve seen that depicted in stage sketches in books. (And I think that’s what the stagehand is doing in the opening number in the movie Chicago. Though that crank could be a fake for the movie with a real powered lift…)

The main thing in building any thing that lifts and lowers things is Make sure it is safe because you never know what could happen.
"Theater Engineering and Stage Machinery" by Toshiro Ogawa, Entertainment Technology Press; Cambridge G.B., 2000 ISBN: 1 904031 02 1

This book does not go into a lot of details of specifically how to rig it but does show a lot of ways of doing this amongst various types of motors, hydriodic and pneumatic and I believe also counter weight. Lots of info on elevators that would be useful to look at. Lots of alternate ideas on how to rig it even if counter weighted, could spring into your head. I would recommend at least giving a read thru of it.

"Stage Scenery: its construction and rigging" by A.S. Gillette, Harper & Row; N.Y. 1959 Library of Congress #59-13576 pp 250-252

This book is golden - I did not see the formula in anything from Scenery for the Theater to many other books old and new, other than in this one. Good reason to collect and read not just new texts but search out used book stores and E-Bay for older texts. The references cited in texts you have read and liked would be those the author was using to learn from. Good way of finding good texts is to search out what references the author cites.

"The Disappearance Trap and Elevator" is the chapter and it goes into very specific detail of how to do it - a mechanism I have not seen since like freshmen year in high school - about 24 years ago.

Find this book by way of inter-library loan or perhaps the book is already on the net by way of the library.

If you can't find a more modern book on the subject, nor it in the library, I can probably fax the pages.

A word of caution, there is a reason you won't find this method used much. First it's obsolete given a number of other methods available that are both more compact and easy to use and much more safe to be using. Renting say a hydraulic lift from a scenery company such as say Texas Scenic, Tiffen or Chicago Scenic amongst others might be cost effective by way of R&D time spent otherwise and liability should it fail. When I got out of college my first 9 months was spent at Chicago Scenic Studios as an assistant in the metal working/rigging shop. Part of what I was learning to do was use was the constant installation of both pneumatic and hydraulic lifts in a theater in the round. Primary thing I learned I think was how easy they were to master.
Jwl868 has some good points to follow

Tolerances in your elevator verses raised decking and how they are attached together could not just be a problem in the making with the lift failing but could cause the entire orchestra pit to fail - realistically. It must be impossible for your lift to first come un-done while not in use by way of being pinned or braced so it won’t lower while not in use. You must have a safety pin in place that is removed just before operation. You also must ensure that it’s impossible for your platform and all other moving parts in raising or lowering - much less being abused won’t hit or come out of alignment and touch a component of the orchestra pit platforms. This especially if they are for part of their support interdependent in locking with each other. Should the elevator hit something that locks with another platform as a means of support, it being bumped by the elevator could be catastrophic.

On the other hand, you don’t want a large enough hole between platform and elevator that someone could get a heel caught or trip. No more than a at most 3/4" gap between elevator and deck or change in height between them.
Me and some friends just built a counterweight elevator for a magic show we performed for our Stagecraft Class. It was our "disappearance" trick. It took a lot of work but when you get down to the basics, you just need to remember that your counterweight is:

a) heavier than the platform the actor is to stand on, and
b) lighter than the platform + the actor

After that all it takes is a couple of drifts, some pulleys, a track, platoform and a lot of hard work. You don't necessarily have to work everything out on paper beforehand, but you might have to do some experimenting with different aspects once the system is set up.
Me and some friends just built a counterweight elevator for a magic show we performed for our Stagecraft Class. It was our "disappearance" trick. It took a lot of work but when you get down to the basics, you just need to remember that your counterweight is:
a) heavier than the platform the actor is to stand on, and
b) lighter than the platform + the actor
After that all it takes is a couple of drifts, some pulleys, a track, platoform and a lot of hard work. You don't necessarily have to work everything out on paper beforehand, but you might have to do some experimenting with different aspects once the system is set up.
At the risk of being booted, I'm going to say something that needs to be said:
Sir, are you a complete idiot? The mis-information you spout on this website is absurd! Now, before I go any further, let me remind folks that you have posted the following:
1.the only publicly verified lip syncing I've heard of was with Britney Spears
*Have you been paying any attention at all? Or don't you know your history?
2. You used a YOUTUBE video of David Copperfield as your source material for trying to construct a flying rig for the lifting of human(s). This is your OWN admission.
Your oversimplification of concepts, ideas and fabrication shows that you have absolutely no idea what you are talking about. I pray to every deity I can think of that I never cross your path onstage, or on the street for that matter. I can only imagine the danger I might be in if I did.
These drifts you're using- what's the WLL on them? Did you get the D/d ratio correct? Do you know what a D/d ratio is?
How about those pulleys? You failed to mention if you used wire rope sheaves, or not. Big problem there if you got that wrong. Were they rated for the load?
YES YOU DO HAVE TO WORK IT OUT ON PAPER BEFOREHAND!!! You have a moral-if not legal- obligation to perform due diligence and make sure you have a mechanically and structurally sound design before you put anyone or anything on something you build!
You go around here with a "oh, it's no big deal" type of attitude about things, and all it takes is one person to decide they're going to listen to you and the probability of injury goes through the roof.
You're a student, and I've got 18 years of real world gigs and experience with zero injuries and zero failures.
I am certified in rope access by SPRAT, fall protection by OSHA, and work under some of the most knowledgable riggers in the US. Your knowledge seems to come from an incomplete undergraduate "education".
Before you post any other sage advice around here, do us all a favor and please don't.
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Hey Rigger's a little hot under the collar and probably needs a time out... and don't all riggers when you think about it... but his point is valid.

If you screw up lights it gets dark. If you screw up sound it gets quiet. If you screw up rigging people die.

I highly encourage you to stop messing around with what you haven't been trained in and encourage others to NOT follow your lead. There's a lot more to rigging than just a couple pulley's and ropes. Even a simple device like you described can be very dangerous, if you don't know what you are doing.

Finally for you young folks the ultimate Lip Sync scandal was Milli Vanilli... they lip synced their way to 3 #1 hits and a Grammy for Best New Artist in 1990 before we found out they didn't even sing the original tracks on the albums.
Gaff's right....I am hot under the collar. Got my knickers in a twist. Somebody put a quarter in me, and pulled the handle.
It is the nature of what I do. I trust MY LIFE to the people I work with. We all have a responsibility to one another, and people that represent themselves as knowledgable-when facts prove they are not-must be dismantled. Figuratively, that is.
But hey, when I was in college, I thought I knew something too. ****, was I ever wrong.
So now I will go and meditate on a quiet corner of a self-climbing truss, and enhance my calm. For now.
No apologies.
Remember kidz, this is the internet. DO YOUR OWN LEGITIMATE RESEARCH and don't take anything you see at face value.
Milli Vanilli! H3LL YES! That was an awesome debacle.
Ashley Simpson got what she deserved.
Hehe... riggers... points... hehe... stage humor...

Hehe... riggers... points... hehe... stage humor...

Jewish carpenter on the cross, how did I miss that?

That's it...time to start a new thread.

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