Rigging lights over scenary via 16 feet long bar

[belford]

Hi guys and girls,

I need your help.

For a film production in mid september, I need to rig three lights (each about 2.5 kg, i.e. 5.5 lbs) above three tables standing in a row. I can't rig from the ceiling (this is a room 10 Meters (33 feet) high from the 19th century!), so I need to rig from a balcony right next to the tables.

The balcony is 2.5 meters (8 feet) in depth.

I've attached a drawn view of this. For safety and easy of calculation, I will assume a single 8 kg (17.5 lbs) weight at the end of the extension bar, rather than the three lights spread across the open width of 5 meters (16 ft).

Now this is all dandy and well, and the counter weight is easily calculated as minimum 16 kg / 35 lbs (not considering the weight of the bar itself yet which must be counterweighted).

Now I did some experiments at a local metal equipment supplyer: when keeping the diameter of the bar under about 5 cm (necessary for being able to grip the lights to it), it will bend too much. Tried this with a steel bar, I guess aluminium will bend even more.

Now one solution would be to add a vertical bar to the extension bar at the edge of the balcony and run a steel wire over it for taking some weight off the end of the bar, taking away some of the bending. This part (vertical bar and steel wire) is drawn green. This is very similar to how a construction crane is built.

The problem is that with that "crane" solution, new problems arise: now the center of weight might end up below the bar, so it has to be stabilized against rolling to its side etc etc.... not sure if this is worth the "engineering muscle"..

Are there any other solutions that you can suggest? Can a lightweight 2-point or 3-point aluminum truss be somehow extended over the balcony edge into the set? As far as I know that are no trusses larger than 6 meters... and usually those are flown at two ends, not at one...

Thanks...
belford.

 

[DuckJordan]

this is getting into more of a rigging category than a lighting category, the only thing i could suggest since, it would violate CB Rules, is to talk to a certified pro about getting custom built Truss, yeah the stuff you can buy as a consumer is about 6m in length but the stuff they use in large touring gigs is about 20' it would also help if there is a balcony on the opposite side so you can have two anchor points, any more specific than that and i would probably get into some trouble.

 

[fredthe]

You really need to find a way to support the far end of the bar. In order to get something strong enough to cantilever, you will need a LOT of weight...

Can anyone tell me what he forgot about in his drawing?

-Fred

 

[belford]

fredthe, that's the problem: no way to use a support at the other side. Otherwise it'd be really easy... without that stand it turns into a hard problem.

Curious as to what I forgot in that drawing... though please note it's a very simplified drawing just to give a rough idea.

belford.

 

[fredthe]

Curious as to what I forgot in that drawing...

You forgot to account for the weight of the bar. (Though I just noticed that you did mention it in the text.)

Trusses are generally designed to be supported at at least two points... your design puts all of the force at one point, 1/3 of the way from one end. Not a good idea without something specifically designed for this.

Your idea of strengthening it with steel wire might have some merit, but that really falls into the area of "consult an expert". Do you really want to be liable for the injuries caused when it fails?

How long a pipe/truss would you need to use in order to allow you to support the far end? I presume the issue is keeping any vertical support out of the shot?

-Fred

 

[belford]

For a truss supported at both ends, the truss would need to be about 19 meters (62 feet) in length. It also would need to be flown just under the celing (height about 8 to 10 Meters (33 feet) height). From there I'd need to somehow lower down the lamps so they are in about 4 meters (13 ft) height over the table; hanging them freely is not good because it's fresnel units that will need to be tilted etc to some minimal degreee for the final tweaks, difficult if they "swing" freely.
I may get around the problem of the truss being visible, though one shot shows a subjective view pointing upwards. But the truss possibly would need to be blackened, because we bounce a large HMI into the ceiling, which may (or may not) reflect from the truss..

 

[Chris15]

People have been cantilevering balconies off the sides of buildings for years...
The floppiness of the pipe would largely be overcome by using a truss of some description so long as it's not flat truss run horizontally.

The project needs some competent engineering assistance in working out the moments and how much counterweight will be needed as well as the material strengths needed to carry the respective forces but I see no conceptual barrier to what you are thinking about...

 

[mstaylor]

Not being familar with your space, is it possible to attach your counterweight to the floor and atttach a truss to that. You still need to get a consultant to verify local conditions but it could take away some of the over engineering needed.

 

[MNicolai]

People have been cantilevering balconies off the sides of buildings for years...
The floppiness of the pipe would largely be overcome by using a truss of some description so long as it's not flat truss run horizontally.

I would think this would be a situation where triangle truss would be most suitable. (...based on my basic engineering knowledge -- don't quote me on this or take this as a good idea. As always, consult a professional, which in this situation, I most certainly am not.)

 

[kicknargel]

I gotta say: of course it's important to be cautious and hiring a pro is always the best choice. However, in this situation you're in a very controlled environment on a closed set doing a static rig that will be used in exactly one way under supervision and taken down. I'd think you could test a method experimentally in a shop. Get some truss, the lights (or the equivalent weight) and a bunch of counterweight and see if it works 1' off the floor. If it does (and can some extra force), I'd trust it for this application.