Otis Again
April 17, 2009 11:31 PM   Subscribe

How to make a theatrical version of the Star Trek doors that can be operated by one person using only one rope. Must be able to both open and close.

A link to a diagram or a drawn diagram will most assuredly hit the spot. We can mount pulleys and eyelets and whatever else necessary to the ceiling, wall and/or ground. Simplest plan is most desired. Here's an example of the type of door we desire.

Thanks for assistance and ideas.
posted by cloeburner to Grab Bag (16 answers total) 5 users marked this as a favorite
How about this? (Excuse the childish crayon drawing - I'm using a touchpad here. Also, I'm trying to share a Google doc for the first time, so fingers crossed.)

You'll need some decent carpenters to pull off the construction, but the rigging shouldn't be that difficult. The doors need to be as frictionless as possible, to minimize the weight of the bricks you need.
posted by ctmf at 12:39 AM on April 18, 2009

This is what I'd do.
  • The red outline is your flat/wall with door hole.
  • The blue is your two doors. Note the projections on the top.
  • The green are two long springs.
  • The two red circles are your pulleys.
  • The purple line is the cable which is controlled on the right.
The doors are mounted on a sliding track of your choice. The springs attach to the flat at one end and to the door at the other. They don't have to be all that strong, just enough to return the doors to the closed position.

The cable is attached to both doors. The right door at the top of the projection and the left door at the bottom of the projection. From the actuation point on the right the cable runs over the right hand pulley, connects to the right hand door on the way to the left hand pulley, makes a 180 turn around the left hand pulley and finally connects to the left hand door.

To open pull down on the cable. The doors will open the same distance in opposite directions directly proportional to the amount the cable is pulled down.

To close let the springs pull the cable up.

A ring attached to the end of the cable could be hooked over a knob to keep the doors open if that is required.

You can also skip the springs and instead use two more pulleys and loop the free end of the cable back to the doors from the other direction. The doors would open or close depending on which way you moved the cable. The problem with this is it is a bugger keeping proper tension on the cable so it doesn't come off the pulleys.
posted by Mitheral at 1:23 AM on April 18, 2009

On a funny side note, Gene Roddenberry (the creator of Star Trek) was once asked by automatic door company executive what device he used on the original series to make the doors open and close so smoothly. Gene Roddenberry looked confused for a second, laughed, and then said that they just have two guys physically lift the doors to open and close them each time.

I know this doesn't do a good job of answering your question, but I just figure I would throw this out there.

PS Please pardon me if I accidentally butchered the story.
posted by AZNsupermarket at 2:55 AM on April 18, 2009

You can do what aznsupermarket staed. Just have us backstage techies open and close them . Why use some fancy pully system that could possibly break in the middle of the performance.
posted by majortom1981 at 4:47 AM on April 18, 2009

You can do what aznsupermarket staed. Just have us backstage techies open and close them . Why use some fancy pully system that could possibly break in the middle of the performance.

OP however wants a singular techie to be able to open both doors (presumably at the same time) which would necessitate some some of mechanical affordance.
posted by mmascolino at 5:36 AM on April 18, 2009

If you just want to figure out the arrangement of pulleys and ropes, just inspect a standard center draw traverse curtain rod like here.
posted by JackFlash at 9:58 AM on April 18, 2009

Look into pocket door construction. Your budget might be big enough for a kit?
posted by EnsignLunchmeat at 6:37 PM on April 18, 2009

Maybe make one door the "master" and the other a "slave," and attach some kind of push-pull tab to the 'master' and have some kind of hidden (transverse curtain rod assembly-esque) machinery moving the 'slave' door in the opposite direction?

On smoothness: skate bearings, angle iron and gas pipe have worked famously well for home-grown CNC machines' axes for years. Or maybe bearing drawer slides mounted to 2x4s? Or on preview, pocket door kits, but then I suppose your main problem is still transverse movement...

We have supermarket-style doors at work in a few places that do this. They use a single gear on a motor and a toothed belt to open both doors in opposite directions. The gear spins, and the 'top' side of the belt moves one way while the 'bottom' side of the belt moves the other way.

But you have stagehands instead of motors who can push and pull on cue. So maybe if you mounted a taut loop of rope between two pulleys and attached the loop to strategic points on the (now-smoothly moving, bearing-equipped!) doors, that would work - moving one door east would cause the other to move west and vice versa, without weights or grommeting. I've seen toys that do something similar.

Come to think of it, I think I just described the basis of the transverse curtain/blind assembly mechanism.
posted by ostranenie at 7:14 PM on April 18, 2009

I drew it. I couldn't resist. What do you think?
posted by ostranenie at 8:35 PM on April 18, 2009

Wow, nice drawing, ostranenie.

I was thinking that the weight of the bricks would give the whole thing some extra inertia, which might make it operate more smoothly. At the same time though, that would make it operate more slowly, or require the operator to put a little more effort into moving it. Also, if this is being put in an existing theater stage, the operating line could go to the existing fly rail, which would be a bonus.
posted by ctmf at 9:32 PM on April 18, 2009

Thanks! Inkscape is teh rulex0rx. For great justice. Anyway...

Gravity is good for inertia for sure, but if it was on smooth enough bearings and made out of heavy enough material (plywood versus cardboard), it might still have the right amount of 'wooosh.' Although if you were really going for cheap, you could make the whole thing out of cardboard and glue some slippery vinyl to the top/bottom of the moving doors, and the lightness combined with the slipperiness might be enough for convincing movement.

For operating on a line, I guess you could combine the weights and pulley/lines idea with the 'master' door - meaning the master door operates on a weight principle, and carries the slave door with it because of its attachment to the taut loop. (I would think a door would be normally closed, too, not normally open, so gravity would automatically close the doors rather than open them - that would be a momentary thing). I'd draw it, but... I'm tired.

Oh, if only there were a way to get photos of the finished product! (hint, hint!)
posted by ostranenie at 10:26 PM on April 18, 2009

With weights added. "Slave" and "Master" don't really apply here either, since they're both slaves of the loop now.

Mmmmmm...slaves of the loop. Drool.
posted by ostranenie at 6:19 AM on April 19, 2009

Hey, damn, ostraenie, that schematic is great, I just showed it to the guy designing the doors and he slapped his forehead, more or less, as a result of the simplicity. As it happens, after I posted the question the tech dude developed his own system and executed it, it works pretty perfectly. If I can find a digital camera I will take some pictures/video of it in action.

Cheers everyone and thanks for your time and tttinput, hopefully this will serve as a resource for future theatrical Star Trek performances.
posted by cloeburner at 9:49 PM on April 20, 2009

Heh. I just noticed the page title on your second diagram.
posted by ctmf at 11:20 PM on April 20, 2009

Strange things happen when you're drawing early in the morning. (And hey, that album even has its own Wikipedia entry!)

Glad to help and I can't wait to see pictures (video, maybe, can I has?) of it.
posted by ostranenie at 9:37 AM on April 22, 2009

There will be video, the performance was filmed. I don't know when editing will be completed, but when it is, I will probably make a projects post and/or send you a PM.
posted by cloeburner at 11:56 AM on April 27, 2009 [1 favorite]

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