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[Robert Piascik]

After talking to the guys at Applied, I think the solution is to keep the truss on the lifts, but keep the front (audience facing) leg up, and ballast the back leg. Applied thought a couple hundred pounds ought to be plenty to keep the whole thing from falling forward, and we can also likelylash it to the stage.

That seems like a really bad idea, I'm surprised that the Applied guys would suggest that. I've done hundreds of events with all four legs on the ground and never had anyone 'bowl into the lift.' Is the dancing at your events really that crowded and rowdy that you would consider this? I'd mark the front leg with some highly conspicuous colored tape, or put cones around it, or block it with the subs or do nothing at all before I'd consider not having all four legs on the ground.

[Mark Ellis]

I would go with the 90lb base + ballast before I would do this. At the very least the structure has to stand on it's own, which the stands wouldn't do if someone bowled into the front base with one leg raised.

That seems like a really bad idea, I'm surprised that the Applied guys would suggest that. I've done hundreds of events with all four legs on the ground and never had anyone 'bowl into the lift.' Is the dancing at your events really that crowded and rowdy that you would consider this? I'd mark the front leg with some highly conspicuous colored tape, or put cones around it, or block it with the subs or do nothing at all before I'd consider not having all four legs on the ground.

Well, that's interesting. Yes, having the front leg stick out onto the dance floor is an absolute deal breaker. No event coordinator we work with would allow that for aesthetics or safety.

Is a vertical column of truss and on a 36" steel base plate with some ballast really more stable than a Lift with one leg raised and ballast on the opposing leg? There's only 3 sq. ft. of surface area to put ballast on the back of the steel plate. Meanwhile, I could put a couple hundred pounds of amp racks on top of the back leg of the lift.

Is there someone who's considered an expert I can ask/hire to do the math on this? 

[Jay Barracato]

Just back the whole truss up until the front of the leg is even with the front of the stage.

[Marlow Wilson]

That seems like a really bad idea,

Some of the stuff in your pic doesn't strike me as being a really good idea either.  Specifically the method of attachment to the truss and the cantilevered truss segment.  A city engineer for a weekly event also wanted additional ballast for using L16's outdoors - whether or not we agreed didn't matter (plus, these days it feels good to have an engineer conceive of and approve anything that could possibly be blown over).  All this to say that if you have the subs in a L/R cluster for aesthetic reasons and/or to block the legs, make something so that the weight of the subs is acting as a ballast. 

[kristianjohnsen]

Just back the whole truss up until the front of the leg is even with the front of the stage.

+1.

Also, if one gets the rotating type of truss adapter up top, the lift can be rotated 45 degrees.  That way two legs protude underneath the stage and two away from it.  In this manner one doesn't have to push the lifts so far back to be clear of the dance floor. 

Also one can lay down a small sheet of ply on the front two legs and put subs across them AND put down a sheet of ply on the back two legs and put the amp rack across those.

Sound guys tend to think in straight angles 

EDIT:  WARNING:  Turning the base 45 degrees to one side will also make it less stable front-to-back, but considering the manufacturer suggested lifting one leg, it's still a lot better!

[Mark Ellis]

The stages we typically see are 16' deep and 24' wide. The legs on the L16M stick out 36". Rotating the lift 45 degrees they would still stick forward about 28". Either option would put our front lights shining straight down on the performers. Also, while I don't think it would be much of a problem if they're high enough, the speakers would be slightly behind the front line mics.

Global Truss was emphatic that a 14' X 30' goal post would be completely safe on a 36" steel base (no ballast). I decided to email them for clarification, and they replied that the whole thing would need water or concrete block ballast. (I suspect having these sort of safety issues 'in writing' changes their mindset a bit.)

I emailed the same guy at Applied Electronics that I had spoken to as well. I reminded him of our phone conversation (he'd suggested leaving 3 legs of the L16M lift down, and ballast with a couple hundred pounds the back leg). I asked if they had done any safety tests on this. His response was that it ought to work fine, but they don't test for this sort of thing, and they're not guaranteed in any other arrangement than all 4 legs down. Fair enough, and I very much appreciate the straightforward and honest answer.

Which brings me back full circle to my original idea: Connecting the front truss to our truss at the back of the stage. Currently our back truss remains on the L16 lifts during the show. It seems to me that if the front truss was on vertical truss with steel plate bottom, or 3 legged lift with ballast then connecting the front truss to the back with a stick of truss would make the whole thing very stable, right?

[kristianjohnsen]

The stages we typically see are 16' deep and 24' wide. The legs on the L16M stick out 36". Rotating the lift 45 degrees they would still stick forward about 28". Either option would put our front lights shining straight down on the performers.

Easy one:  This is what you need: 

http://www.brisound.com.au/Retail_Catalogue/7524_item.html

Just make sure the boom is attached to the innermost tube of the truss so that it's "resting" on the outermost one, that way it won't "sag".

Also, while I don't think it would be much of a problem if they're high enough, the speakers would be slightly behind the front line mics.

 

Considering the levels I have run PAs at with the performers running out in front of the main speakers...I'd say your're probably OK.

[Mac Kerr]

Easy one:  This is what you need: 

http://www.brisound.com.au/Retail_Catalogue/7524_item.html

Just make sure the boom is attached to the innermost tube of the truss so that it's "resting" on the outermost one, that way it won't "sag".

Using a sidearm will move the center of gravity of the whole rig farther away from the tower, seriously derating the load capacity of the lift.

Band lighting is all about side light and back light anyway. 

Mac

[kristianjohnsen]

Using a sidearm will move the center of gravity of the whole rig farther away from the tower, seriously derating the load capacity of the lift.
Mac

Like anything it's about how much.

It's not an uncommon approach for a few front fresnels in my corner of the world, which I was kinda assuming this was about.

I'm absolutely certain that using the rig with one leg raised is a lot worse!

Band lighting is all about side light and back light anyway. 
Mac

Yeah, haha.

[Mark Ellis]

So, it looks like the only way to have a front truss directly above the front lip of the stage (and not 3' back is:


I would think this setup wouldn't need anything in the way of ballast, or even very large base plates. As long as the truss that links the two goal posts is well attached, could this thing possibly fall over?