Brail, motorized curtain

[kenact]

I'll be setting up a show in a 65 seat black box theater, for a 5 week run, 6 performances per week.

The show calls for a curtain, but the theater doesn't have one, and I can't install a permanent curtain.

I'm currently thinking of a curtain comprised of two, flat, 8 foot wide by 10 foot high pieces, that would have to be lifted twice per performance.

My plan is to use light weight scrim material, rigged as a brail curtain, using 3 lengths of fishing line per curtain, each wound on its own spool on a single axle. I've purchased a high torque, low rpm, reversing, dc motor.

I'm planning to purchase a 120vac DPDT relay, to allow me to reverse the current to the motor, thus changing the direction.

The grid will only allow me to lift the curtain 10', and I've insured that it will not throw shadows on the stage.

I haven't done this before, but I'm comfortable with my electrical and DMX skills, to make this work, and I'm comfortable that I can rig it safely.

I'm feeling that, as long as I keep the lift lines taught, I shouldn't have any problem with the lines fouling.

Does anyone have experience with this type of setup? Is there anything I need to be careful of. Does anyone have any ideas to make this easier? I will have several months to play, before I have to hang the curtain.

Thanks

 

[DrewE]

Typical relay-based reversing for DC motors (at least one typical system) is to use a pair of SPDT relays, with the common terminal of the relays connected to the motor's wires and the two other contacts connected to the power supply busses. That way, when neither is energized, both motor leads are at the same voltage rail, and energizing one or the other will let it go forward or backwards. Energizing both simultaneously will stop the motor with no harm or short circuit or anything. This also makes it quite easy to put in a limit switch or two (in series with the normally open contacts of the appropriate relay) to prevent overtravel, assuming you can find a way to operate the switch itself reliably. You could also have the limit switch operate on the coil circuit for the relay, which means the limit switch doesn't need to switch the full motor load...but also doesn't protect from overtravel in the case of faulty or sticky relay.

Something like this, if you excuse the rather poor drawing:

(Of course, if you can spare a body, it may be simpler and pretty well foolproof to have someone yank on a rope manually someplace offstage rather than constructing a motor drive.)

 

[kenact]

Typical relay-based reversing for DC motors (at least one typical system) is to use a pair of SPDT relays, with the common terminal of the relays connected to the motor's wires and the two other contacts connected to the power supply busses. That way, when neither is energized, both motor leads are at the same voltage rail, and energizing one or the other will let it go forward or backwards. Energizing both simultaneously will stop the motor with no harm or short circuit or anything. This also makes it quite easy to put in a limit switch or two (in series with the normally open contacts of the appropriate relay) to prevent overtravel, assuming you can find a way to operate the switch itself reliably. You could also have the limit switch operate on the coil circuit for the relay, which means the limit switch doesn't need to switch the full motor load...but also doesn't protect from overtravel in the case of faulty or sticky relay.

Thanks for that. My thought was that a DPDT, which is NC/NO, would do the trick. When not energized, one side is NC and the other is NO. Three sets of pins, Common, NO, NC. Power runs to NC, Positive on 1 and Negative on 2. NC Positive feeds NO Negative, and NC Negative feeds NO Positive.

Passive, Common is Positive/Negative. Energized, Common is Negative/Positive.

Power to the relay and motor would be controlled separately via DMX. To raise the curtain, supply power to the motor. To lower the curtain, supply power to the relay, than to the curtain.

I'm also planning to have a set of cut offs, to ensure the motor stops at full-up and full down.

 

[JChenault]

I would be worried about the choice of scrim as your curtain material. ( Assuming you mean sharkstooth scrim, mot just a thin fabric).

First of all, it would not really be opaque. ( Not sure if this is an issue or not)
Secondly, the point load of a ring would likely pull the material - make it pucker, etc.
To solve this you might be able to put a vertical piece of fabric / webbing and attach your rings to that - but again you have the problem of how to sew scrim. My fear would be puckers, etc. And you would have opaque vertical stripes in the curtain.

Just my two cents.

 

[kenact]

I would be worried about the choice of scrim as your curtain material. ( Assuming you mean sharkstooth scrim, mot just a thin fabric).

First of all, it would not really be opaque. ( Not sure if this is an issue or not)
Secondly, the point load of a ring would likely pull the material - make it pucker, etc.
To solve this you might be able to put a vertical piece of fabric / webbing and attach your rings to that - but again you have the problem of how to sew scrim. My fear would be puckers, etc. And you would have opaque vertical stripes in the curtain.

Just my two cents.

Thanks John,

I'm not too concerned about it being opaque. Lighted from the front, it should look pretty solid. Lighted from the back, should allow the audience to see through it, to some extent.

I plan to have the bottom weighted, with a pair of eyelets every 12 inches, so I'm expecting something of a fanfold, as it's raised.

Thanks for the 2 cents. If everyone else puts in their 2 cents, I might make $5 by the time this thread is done.

 

[RonHebbard]

Thanks John,

I'm not too concerned about it being opaque. Lighted from the front, it should look pretty solid. Lighted from the back, should allow the audience to see through it, to some extent.

I plan to have the bottom weighted, with a pair of eyelets every 12 inches, so I'm expecting something of a fanfold, as it's raised.

Thanks for the 2 cents. If everyone else puts in their 2 cents, I might make $5 by the time this thread is done.

@kenact Lighting across the front face with the beam spilling across stage between legs and disappearing out of site lines into the opposite wing ought to be your best option for not lighting / revealing U/S of your cloth before you want to. That's my devalued 3 cents for your collection.
Toodleoo from north of Donald's walls.
Ron Hebbard

 

[kenact]

Thanks Ron

 

[BillConnerFASTC]

Are you hanging weights over people's head on fishline? I sure hope not. A continuous pocket with a light jack chain might be a little safer - at least avoiding the single point failure of one line dropping a weight on someones head or into their eye. From just a few feet even a light washer could be trouble.

 

[kenact]

A continuous pocket with a light jack chain might be a little safer

This is my plan, while also sewing the chain in place, at several points. I'm only looking for enough weight to make sure the curtain comes down.

No barbells or dumbbells will be used in the construction of this curtain.

 

[Van]

When you say 'fishing line' I assume you mean Braided Dacron Line? Something with a 100lbs test or so?

 

[DrewE]

Have you given any thought to an olio curtain rather than the brail? I'm assuming there's some sort of side masking you can work behind...if not, the olio is probably not going to look "finished" enough. It seems to me an olio would be easier to rig up and get operating properly.

 

[kenact]

When you say 'fishing line' I assume you mean Braided Dacron Line? Something with a 100lbs test or so?

I'm planning to use 100 lbs test, but I wasn't thinking about braided. I estimate that each curtain, with a jack chain, would be less than 10 lbs. Remember, each curtain will only be 8' x 10', and plan to lift each with 3 lines. I think 3 lengths of 100 lbs test, to lift 10 lbs of curtain, should be safe.

If I'm missing something, please feel free to enlighten me. Like everyone else in the world, there's no way I can know everything.

 

[kenact]

Have you given any thought to an olio curtain rather than the brail? I'm assuming there's some sort of side masking you can work behind...if not, the olio is probably not going to look "finished" enough. It seems to me an olio would be easier to rig up and get operating properly.

I have no side masking at all. All 4 side edges, as well as top and bottom, will be in full view of the audience at all times.

 

[Van]

I'm planning to use 100 lbs test, but I wasn't thinking about braided. I estimate that each curtain, with a jack chain, would be less than 10 lbs. Remember, each curtain will only be 8' x 10', and plan to lift each with 3 lines. I think 3 lengths of 100 lbs test, to lift 10 lbs of curtain, should be safe.

If I'm missing something, please feel free to enlighten me. Like everyone else in the world, there's no way I can know everything.

Do not use Mono-filament for rigging. If you are looking for a good, small diameter trick-line, you want to use a braided Dacron. It has a much higher abrasion resistance and it's much more static. It is also slightly more resistant to heat than mono-filament. You can find it at almost any fishing supply or you can order it from Ebay. You can get colors to match your curtain or simply get it in black. Here's an example.

 

[kenact]

Do not use Mono-filament for rigging. If you are looking for a good, small diameter trick-line, you want to use a braided Dacron. It has a much higher abrasion resistance and it's much more static. It is also slightly more resistant to heat than mono-filament. You can find it at almost any fishing supply or you can order it from Ebay. You can get colors to match your curtain or simply get it in black. Here's an example.

Thanks

 

[RonHebbard]

I'm planning to use 100 lbs test, but I wasn't thinking about braided. I estimate that each curtain, with a jack chain, would be less than 10 lbs. Remember, each curtain will only be 8' x 10', and plan to lift each with 3 lines. I think 3 lengths of 100 lbs test, to lift 10 lbs of curtain, should be safe.

If I'm missing something, please feel free to enlighten me. Like everyone else in the world, there's no way I can know everything.

@kenact I'd NEVER purport to be rigger. That said; I believe braided is often considered preferable to any manner of mono-filament and matte black often hides better than anything glossy and light-reflective.
@egilson1 @What Rigger? @derekleffew Care to comment???
Toodleoo!
Ron Hebbard

 

[kicknargel]

Other options for the line would be 1/16" black aircraft cable (wire rope), or tech-12. Definitely not mono-filament.

 

[What Rigger?]

@kenact I'd NEVER purport to be rigger. That said; I believe braided is often considered preferable to any manner of mono-filament and matte black often hides better than anything glossy and light-reflective.
@egilson1 @What Rigger? @derekleffew Care to comment???
Toodleoo!
Ron Hebbard

No mono-filament. Ever.
Seriously, save your sanity because trying to tie any kind of knot in that stuff is just "agony city" to quote Bob Ross. Go with the braided. I'd still recommend finding an actual rigger to team with on this as well.

 

[What Rigger?]

Other options for the line would be 1/16" black aircraft cable (wire rope), or tech-12. Definitely not mono-filament.

Let's not forget that most T-12 manufacturers will tell you that you have to splice terminations in it, and that knots are forbidden because that stuff is so darn slippery.

 

[Jay Ashworth]

Rewinding to that schematic sketch, I approve of the design that grounds both sides of the motor because, as I understand the thing, that setup tends (depending on the type of motor; I'm assuming PM) to keep the motor shaft (mostly) locked until you try to move it.