Freestanding Truss "Pillar"

[OGGY]

I want to use a 2 metre length of Astralite as a "pillar" to support a single MAC 250 at the top. My question is how big a "foot" would it need to have to cope with:

 

(a) the forces created by the Mac 250 whilst in full flow?

 

and

 

(b) to reasonably withstand being bumped into by a member of the public or band member?

 

My plan is to use a normal base plate which would then be secured to a larger "foot" to give the extra stability. Given the height and the high centre of gravity caused by the Mac 250 is there a minimum angle it has to be able to recover from if knocked in to?

 

Physically securing these to the floor isn't an option as they aren't going to be permanently installed. I know having a heavy base would help but as these need to be portable I want to try and keep the overall weight as low as possible.

 

My theory is that if the foot is low profile I can use a guitar cab, etc to help weigh it down, however if that isn't possible I want them to be safe in their own right.

 

I intend having four of these so want to get it right first time.

 

Alternatively is this just a bad idea?

 

 

Thanks

 

 

Mark

[Suzette]

IMHO - it's a bad idea .... however is there any way you can secure from above if you can't fix to floor?

 

Just standing on their own with no fixing and no safeties sounds like a recipe for an accident, especially as it sounds like public are going to be walking past them.

 

Or if you are having 4 - are they in a square formation that you can use truss or similar to fix them altogther at the top?

[adamharman]

I assumed they were on stage, as guitar cabs were mentioned, so more out of the way of the public.

The base would still need to be fairly large and heavy to make it stable enough. A base radius of 1/3 to 1/2 of the height would be the sort of proportion to look at, and it needs to be stiff enough not to bend if the truss moves.

[mac.calder]

Provided you use a proper M250 truss adapter, a 1m diameter barby plate will be fine. Did this sort of thing in corporate events all the time, 250's don't generate too much force, so you are pretty safe, for extra stability though, sandbags are always a good thing.

[djw1981]

Having Guitar cabs in an area with public around is just asking one of them to move it, and when they do, whatever stability you thought it was giving has gone.

[OGGY]

Thanks for the responses.

 

The venues where these would be used is going to range from hotel conference rooms through to theatres. When on a stage the general public issue reduces to practically zero however it's the hotels, etc where I see the problem, there would be a designated "performance" area but nothing to form any kind of physical barrier to the dancefloor when being used for things like Wedding parties.

 

Like everything I think it will come down to only using them where the risk of a problem can be mitigated. If not they'll stay in the truck.

 

Thanks

 

 

Mark

[Ynot]

This was discussed to death some while back.

Opinions varied, but mine was that it is NOT a good idea at all.

 

It is done on occasion I know, and several people will say that they have done so. But as with everything else, whether it's successful or not depends on the circumstances. How you can secure/weight the base, whether you can tie-off to a solid structure...

2 metres is quite a high plinth on which to put a mover - All due respects to Mac, but at that height I believe the turning forces (or more properly the change of direction turning) can be quite harsh, so can easily unbalance a poorly set up support.

 

And unfortunately, no matter what barriers you erect, at events like weddings there's ALWAYS a good chance of some very merry punter getting too close for various reasons and bumping the truss!

 

My opinion.

[mac.calder]

2 metres is quite a high plinth on which to put a mover - All due respects to Mac, but at that height I believe the turning forces (or more properly the change of direction turning) can be quite harsh, so can easily unbalance a poorly set up support.

 

True, the forces can be high in certain circumstances, however it is a case of being sensible with what you do. A proper bbq plate, 1m in diameter made out of 8mm steel provides a very sturdy (and heavy) base - weighs over 40kg from memory. This puts the center of gravity pretty far down (if not actually within the base plate) - 21kg of mac250, truss is <10kg + 1kg for adapter plates etc. If memory serves, the truss needs to tilt >45 degrees before it will start to fall under it's own power.

 

I have seen much heavier and much more violently moving units sat higher. Obviously if you do not feel comfortable doing it, and you cannot assure yourself that the setup is safe, you should not do it. All I can say is that I have done it before, and I will probably do it many times in the future, and whilst there are things that need to be considered, if you have the correct equipment available and you can assure yourself it is safe, then there are very few reasons why you should not do it. If you have never done it before though, try talking to a local 'large-ish' hire place - see if they have the gear there and see if you can visit to see it set up. As an aside - gym weights or fly weights fit nicely inside tri-truss as extra ballast too.

 

I cannot stress it enough though - if you are not confident in it's safety (and that you can defend the rig should it cause someone injury) then you are better off not to do it.

[Andrew C]

And unfortunately, no matter what barriers you erect, at events like weddings there's ALWAYS a good chance of some very merry punter getting too close for various reasons and bumping the truss!

Don't forget that your punter, if he is close enough to bump the truss, will be standing on the plate (given the 1m dia). This will prevent any tipping.

[Ynot]

And unfortunately, no matter what barriers you erect, at events like weddings there's ALWAYS a good chance of some very merry punter getting too close for various reasons and bumping the truss!

Don't forget that your punter, if he is close enough to bump the truss, will be standing on the plate (given the 1m dia). This will prevent any tipping.

Hmm...

Yeah...

OK........

:huh:

[MarkPAman]

Remember that sooner or later a small child (or drunk adult) will mistake your truss for a climbing frame. :)

[Jivemaster]

I have seen and heard of these plates before. Mentions of 1m square 1m diameter or 2m diameter come to mind Yes heavy in their own right and big enough for punters to stand on.

 

They need careful usage to handle rhe weight without damaging the venue decor. AND someone needs to make a suitable truss to plate adaptor.

 

Designe and risk assessment is up to you!

[johnhuson]

Like many others I've done this myself many times and doubtless will do it many times in the future. As mac suggests a 1m square steel plate with the truss suitably attached to provides plenty of stability, it takes a lot to pull one over even with a mover(s) on a 3m stick of truss. It certainly requires more force than someone just bumping into it at floor level and the forces generated by the head moving itself don't even come close to making it unstable.

 

This is a common practice in the live events industry and provided that the truss is attached to a suitably sized and weighty base plate it's a perfectly safe activity.

 

What I do have a problem with is A-Type/Pre-Rig/Medium Duty size truss being stood on end to be used as towers without any base plates, a practice I've seen on more than one occasion and in my opinion the stability of this is highly questionable.

[gingertom]

The other option is to use the X - style bases that are around for A-type / 500mm GP. The legs of which come out from the chords at 45 degs to the truss box as it were. They are incredibly stable and significantly lighter to drag around than the large solid plate bases.

[Jivemaster]

Call it a scaled up version of a "Taank Trap"

 

In a dark club chequer plate is OK but in a hotel venue you may need carpet to cover the base.