Chain Hoists

[DSA]

Please help with something that I have never really understood....

 

...Chain hoists.

 

I understand why they are used etc, but how are implemented??

 

By this I mean which bit is attached to the truss?? Is the assembly of the motor attached close to the truss by means of a sling, or is the motor itself right by the ceiling and a chain drops to the truss???

 

Sorry if this is pedantic, but I just wondered.

 

Oh and if say you have a medium sized rig, say with 4 hoists on it, how do you make sure that they all move at the same rate i.e. that the rig is level?? or is it trial and error?

 

And how are the hoists rigged in the first place??

 

Perhaps a picture could explain this easily if anyone has one?

 

I cant find anyting on the internet re this!!

 

Thanks,

David

[Ben]

as far as what is attached to the truss, it depends on the motors, some will work either way, some will only work chain down I can't think of any that work only motor down but there probably are one or two.

 

all moving together is about the motors matching and the control used, a good control will have something like switches where you will choose the motors and move them together up or down.

 

how the motors are rigged depends a lot on the venue, most common is probably to have a rigger in the grid and have either the motors hoisted up to hight and then secured depending on where it is, some will have hook clamps and will attach to a bar or to truss, it may just be placed above the grid and fed through holes depending on the grid. if it is motor down then the motors are attached to the truss with either slings (or similar) or with built in hook clamps or shackles, the rigger then will drop a line and will hoist up the chain and attach it to the grid however is appropriate.

 

hope this all makes sense, and answers what you wanted to know.

Ben

[Rob]

As Ben says, hoists are available that will work with the motor up or down.

 

Motor's are often used in the 'motor down' configuration as this means that only the weight of the chain has to be hauled into the air, rather than the whole motor which may well be very heavy. This may not be appropriate visually in many applications, where you do not want to see an ugly motor on the top of your flown scenic piece.

 

Most of the motor systems commonly used in the entertainment industry are operated by control systems whereby you select which motors you wan't to take control over and then move the selected hoists together. Of course this means that you need to use hoists which all run at the same speed on each flown item.

 

Despite this, hoists sometimes don't run quite as similarly as they should, and the operator will have to watch this by eye carefully. If for example you had a truss with two motors supporting it, you might attach a tape measure to both ends of the truss to measure the height from the floor at both ends. Often trusses have to be levelled 'by eye' though.

 

Motor's are usually attached with varying combinations of proprietary rigging gear - Attachments are usually made to trusses with either soft slings or truss steels which are steel cables covered in a plastic sleeve to protect the truss.

 

I can highly recommend Chris Higgs' book "An introduction to rigging in the entertainment industry" as a good read.

 

HTH

 

Rob

[gareth]

I can highly recommend Chris Higgs' book "An introduction to rigging in the entertainment industry" as a good read.

I was about to do exactly the same thing! Chris is also a member of this forum, so if you have any specific questions and he happens to pop in you might be lucky enough to get an answer from the man himself.

[gareth]

if it is motor down then the motors are attached to the truss with either slings (or similar) or with built in hook clamps or shackles, the rigger then will drop a line and will hoist up the chain and attach it to the grid however is appropriate.

As the great Mr. Morecambe once said, "You're playing all the right notes, but not necessarily in the right order" ....

 

The chain (and the relevant equipment to create a point - strops, steels, shackles, burlap, etc.) are usually hoisted up to the grid first, and the point attached. At this point, the motor (which is still in its case) is run to draw the surplus chain through and lift the motor out of its box. Then the motor is attached to the truss with either strops (spansets) or PVC-coated steels. Repeat for all points, float the truss just of the deck, level it, and away you go.

[Kevin Robertson]

I agree with all points here.

If you are using just one hoist you can control it with a pickle

2 hoists can be controlled with a double pickle.

Any more than that and a special distro is needed to control all hoists at once and individually.

Just to raise a point that Gareth raised. PVC coated steels are not generally used as they do not conform to loler as the drift can not be easily inspected. unless the plastic is see through (normally garden hose).

You can also buy clamps that attach onto the truss that you are using.

As said before Chris Higgs is the man if you need anymore information.

[gareth]

Just to raise a point that Gareth raised. PVC coated steels are not generally used as they do not conform to loler as the drift can not be easily inspected. unless the plastic is see through

Yeah, that's the kind I meant - large diameter steels with a loose sleeve of clear PVC. The other kind, steels with a close-fitting sheath of black PVC - don't seem to be appearing much these days, presumably for the LOLER reasons outlined by Kevin. Now that people like Rope Assemblies and Flints will happily sell you drifts made from black SWR, I guess there's no longer a need for coated ones.

[DSA]

Thanks so far...

 

so would a 'square' rig be happily flown with 2 hoists, or would it need at least 4? I presume there would be a tendancy for the truss to tilt diagonally...

 

Also in a similar vain, can a ground supported truss just comprise of a single plane vertically? What I mean by this is a sort of goalpost design (e.g rugby), without any additional support.

 

Or would it need to be constructed like a cube??

 

Thanks,

David

[robloxley]

You can make a goalpost but you need 2 out-riggers per leg (look like scaff tower or tallescope outriggers) to stop it falling over sideways.

[trussmonkey]

There are too many variables in rigging to explain it all safely and adequately in the confines of this forum but all the points above certainly feature in the list. If in any doubt pay the money and get a rigger. Accidents can be very expensive and certainly career ending and potentially life threatening.

[Bryson]

I think he was just interested - not planning to do anything rash...

 

A square truss would normally go up on four (or more, depending on the size) motors - two would give you something very unstable and with a single point of failure - if just one point were to fail the whole thing would fall rather dramatically - on four points, if you lose one, the other three will probably hold it (as long as they were sufficently rated, the cantilever weren't too big etc etc). The Chris Higgs book is very good - extremely readable as well as useful. And not too expensive, either.

[DSA]

Yes very much only interested in the chain hoists side of things! To be honest, certainly on the first time I would always seek professional help!

 

Anyway, with the 'goalpost' truss, I may well invest in some trilite or similar in the future to build a little rig to take around, to act as a frame for a projection screen, and also for lighting purposes etc. etc.

 

David

[Guest lightnix]

If in any doubt pay the money and get a rigger. Accidents can be very expensive and certainly career ending and potentially life threatening.

Well said. Don't forget that any rigging equipment you buy will have to be used and maintained according to the LOLER regs (just for starters), so it's probably worth hiring the kit in, for the short to medium term, along with a competent rigger to put it up.

 

Goalpost trusses can be safely built and used, but are generally not the ideal solution, need to be kept well away from punters and very well safety-bonded to something solid. Most people seem to build them too long and / or overload them.

[smeggie]

I am a lampie meself, (so take what I say with a pinch of salt) but,

 

I have always been taught to rig with the motors close to the truss with the chain going into the roof.

 

we have at least four motors on our trusses with any weight on them - for decorative bits, a spanset attaches it with a bridle to one motor.

the raised truss is taken up and locked on with a few lines of steel.

 

they are controlled with switches that are filp flop types with power isolators on each motor line. - the power acts as the switch.

 

on to the other thing. we usually use a cube type structure with four drop legs, we then have bracing to each corner from the truss with trilite.

 

cheers

andrew

[Bryson]

I have always been taught to rig with the motors close to the truss with the chain going into the roof.

 

That's the norm for touring and temporary jobs - it's lighter and easier to lift the chain rather than the whole motor by hand to the point. My install is (semi)permanent (the semi is for the benefit of english heritage....) and so we have the motors in the roof space instead - it's neater that way, and means you don't have to take the load off all of them to work on them.