Drop Down Booms on Truss

[Sam_Lowers]

Hi All

 

I'm looking for some help and suggestions for an idea that some of you may have used before.

 

I have been toying with an idea for creating some drop down booms from a main truss point. I got the idea from some TV work that I have done before.

I am looking in a way to create how they do their FOH lighting on drop down rigging points direct from their grid.

 

My idea is to have 5 drop down booms coming down from my back truss. The centre boom to be 1m drop, next two at 2.5m and the end pair at 3m creating a triangular effect. Now at the base of each of these booms will be placed either a 575 or 700 moving light (weight 32-35kg). I have a couple of concerns about how to do this. My original idea was to place all the booms on the front of the truss and then all the rest of the rig onto the back. I have some reservations about this though as I think the truss may then lean because of the distance the units are hanging below it.

My second idea was to clamp a short scaff bar between the top two bars of the box truss and the same on the bottom two. I could then clamp the drop bar in the centre of these points so as the bar would hang directly central to the truss. At the bottom of these booms I would then clamp a horizontal piece of scaff (1/2m) to create an upside down "T" so the unit would hang horizontal.

I am wondering though if these scaff bars will need to have a back up on them and the best way to do this. A coupler to rigging eye and a steel cable? Also the best way to attach the safety of the unit itself?

 

Does anyone have any feedback on how to do this? I have seen it done before but am not sure how. The only other solution I can see it to use the traditional vertical truss with a unit mounted on top of it - but again then the tallest will be 3m in the air and will have to have a fairly heavy base ballast to stop the wobble.

 

I look forward to hearing some of you ideas. Maybe someone knows of an actual "T" shape boom that could suffice?

 

Thanks

Sam

[son of lx dad]

I have done precisely as you describe in your first idea with safeties as mentioned, on a UK Tour and had no problems. PRG (and probably many others) do a manufactured inverted T in black of various lengths. I had all of my lights and scaff on the front cord and starcloth on the back. I did have to bias the basket towards the rear of the truss very slightly to allow it to hang level but again this did not create any problems.

 

Obviously the above is just in my experience - the usual Blueroom terms apply. A forum is no substitute for having an experienced rigger checking over your work.

[Sam_Lowers]

Thanks for that. Just out of interest did you have much more on the front bar of your truss? How did you attatch the safety to the unit? Steel cable again?

 

Lastly what did you find was the best way to attatch it to the truss itself? Did you connect the drop T to both the top and base bars on the truss with couplers or just the base?

 

If anybody else whant to add more comments please do!

 

Sam

[dunk_1984]

Just a point, Doughty make just what you're after, save you playing jiggery pokery with scaff clamps.

 

http://www.doughty-engineering.co.uk/shop/7/61/index.htm

[gareth]

You say you got the idea from a TV job you've done, so on the assumption that you have some experience with film/TV lighting I'm rather surprised you didn't think about bog-standard drop arms - either with a spigot plate for the units you're using inserted directly into the bottom end, or with a T-bar to clamp the mover onto.

[niclights]

Usually you would hang the drop bars off the back with fixtures on the front of the truss. This makes both the truss fixtures more usable along with keeping the dropped fixtures out of the way. Alternatively you can drop some front and some back.

 

Normally coupler to just one rail & safety direct to truss if possible.

[son of lx dad]

That particular truss had 9 studio colors and 7 VL2000 Spots plus the 9m drop RGB starcloth.

 

I would always use 2 couplers as you describe, one on the top chord one on the bottom. I would not consider a single coupler as 'normal'. The scaff would be able to slip around the chord with the shifting momentums or simply pulled with the weight if only one clamp was used. Not exactly sure what you mean by "attach the safety to the unit". I would safety my moving light to the halfcoupler to eye with your normal light safety, then steel safety the coupler to the truss - easy.

 

I suspect that the price of a TV drop arm versus a 'T' scaff from PRG would make the drop arm untenable on a non TV budget or package.

[knotted]

if you're going to build your own drop arms from scaff (quite feasible) it can be usefull to drill a hole and put a bolt through the top end of the vertical arms to stop it sliding through the top couplers.

At least one company I know of does this with their pre made doughty drop arms anyway.

as for safetying a ML on long drop arms a common option can be a standard steel dropped down from the truss which you can then attach the ML safety to.