Issues in public assembly facility design, operation and maintenance.

So…I spent some time recently troubleshooting a balky motor and control system at a client’s site–and learning a lesson in overthinking things!  A little background:

This is a system that is about 18 years old.  It’s a high-speed lineset (top speed is about 200 feet per minute) controlled by a PLC.  This client was never given a copy of the PLC’s program, the original contractor does not have a copy and neither has complete documentation of the system.  This is a counterweight assisted motorized set that CAN be disengaged from the motor.  It also has ultimate up and down limits, “normal” up and down limits and the ability to set soft trims.

We started the process by assuming that the PLC was fine, that the problem was elsewhere in the system–mostly because neither they nor we have the software to connect to the PLC nor the program to restore it if a problem had occurred there–and because it is more likely that the problem was somewhere else.  A review of the schematic and the installed wiring turned up some oddities in the stage-level controls.  Relays that should have been open were closed and some were closed that should have been open.  So up to the grid (a long climb up a straight ladder) to examine the motor control cabinet.

Through all of this, we were rechecking the diagnostic work already done by the client–a routine technique to verify that, for example, none of the 21 fuses in the overall system have been missed.  The relays in the MCC checked out normal–none were stuck.  More checking (and rechecking), we found a set of fuses that had not yet been checked.  Bingo!  One bad.

Two days later, after installing the new fuse, the system ran for a moment in one direction, then stopped…here’s where the over thinking part comes in.  After rechecking the fuse and then checking the limit switches, relays, cycling power and finding nothing else obviously wrong, we started to be concerned that maybe there really was an issue with the controls.

Until we went back down to the floor and the main control panel.

Since the arbor can be decoupled from the motor, the system has a built-in resynchronization procedure.  This basically involves taking the lineset to its normal high limit–which is about two inches from the ultimate up limit–and then running the motor until the system thinks the motor and lineset are in the same place.  The clutch that allows manual operation is an electromagnetic device.  What happened, that we finally caught, was that during the “running the motor” step, there was enough residual friction to drift the lineset another 3-4 inches–putting it firmly on the ultimate limits.  On top of that, the system believed that it was actually past the soft trim set in the system–another fault condition.

Putting the lineset back within its limits and resetting the zero allowed clearing the trims–and, finally, normal operation of the system.

The clues were all there (one of the faults was an “Ultimate” fault) but we thought the problem was more complex than it actually was and jumped to a different, and wrong, conclusion about the reason for the issues.  Sometimes, it pays to look at the obvious: a blown fuse was the root cause; human error was the rest.

This was a good show for us!

Here are the answers to the questions we submitted (the organizers of the show chose to use the light source technologies question).

Four options to support and access performance lighting in front of the proscenium include catwalks, tension grids, dead-hung battens and battens (pipes) on some type of hoist or lowering system.

• A catwalk (or lighting platform–this is NOT your classic catwalk as the railings are intended and spaced to support lighting functions) allows easy access to fixtures but must be carefully placed to be effective.  Too close and the light will be aiming almost straight down, causing heavy shadows particularly in the eyes.  Too far, and the lighting becomes very flat and uninteresting.
• Tension grid, which is a woven steel cable mesh, provides the greatest flexibility.  Lights are above the mesh and shine through onto the stage below.  The mesh does not affect lighting (or sound) going through it with one exception: PAR fixtures.  The beam of light is parallel enough to project the image of the mesh to the surface below.  Lights can be used anywhere above the surface as needed.  The cost is about the same, per square foot, as catwalk while weighing less.  It is also possible to rig through tension grid.
• Dead-hung battens are surprisingly common and about as inconvenient as possible.  This is also the least expensive, initially, of the available options, as it is nothing but a pipe suspended from chain, cable or threaded rod directly from the structure above.  Like catwalks, these must be carefully placed to be effective.  Access for maintenance and focusing is ideally from a lift (although seats frequently interfere) or from a ladder, if low enough.
• Hoists for this application come in many flavors, each of which has its strengths and weaknesses.  Lineshaft winches, dead-haul drum winches, package hoists, self-climbing trusses, trusses with chain motors, counterweight assisted winches are just some of the options.  There are also manually-cranked winches and other variations.  The major weakness, other than placement, is that focus (aiming) of the lights will take extra time as the hoist has to be raised and lowered repeatedly to focus the lights by trial and error.

Next up are the three most common stage rigging technologies being installed in current theaters, churches and auditoriums.  Those are manual counterweight, powered hoists and dead-hung.  What is appropriate for a given stage and application varies with the space, the users and the intended uses of the system.

• Manual counterweight systems operate by balancing the load (lighting or scenery, typically) with steel counterweights.  There are variations even within this type of system (single purchase, double purchase, motor assisted, etc.)
• Powered rigging systems are most commonly seen in the form of package hoist systems.  These are standardized zero fleet-angle winches that operate on a common backbone (power and control) and usually have a common control point that often allows grouping and presets.  Other types include lineshaft winches and dead-haul winches.
• Dead hung rigging includes any rigging suspended in a static manner from the structure above.  Some examples are studio pipe grids and curtain tracks that do not fly.

The two dominant lighting source technologies at the present in the theater world are tungsten-halogen and LED.  Fluorescent is used heavily in TV studio applications.  LED technology is rapidly evolving and quickly gaining ground on traditional halogen sources.  Already, LED cyclorama lighting fixtures outperform their conventional counterparts–at least when the rich colors typically used on a cyc are involved.

Finally, the role of a theater design consultant.  Primarily, the design consultant’s role is to provide options to the design team.  Once the function of the facility and its primary program functions have been determined, HOW to accomplish those goals becomes the next puzzle.  In presentation environments, there are many ways to accomplish the same end–and each has its own strengths and weaknesses.  What is right for one user may not be appropriate at all for another.

This is probably the oldest, and simplest, style of stage rigging technology.  This label for overhead rigging generally includes:

• spotline rigging (one or two lines placed temporarily to raise and lower or otherwise manipulate a single scenic piece)
• 3 or 5 line linesets
• head blocks (with multiple sheaves) and loft blocks
• rope used as the lifting material
• one or more pinrails

Flipping this list around, an essential piece of this technology is the pinrail.  On a sailing ship, which is the source of much of this technology, this would be either the fife rail (around the base of the mast) or the pin rails at the bulwarks.  In the theatre, this is either a timber or pipe, typically with holes punched every 12-18 inches for the belaying pins.  Traditionally, the belaying pins are removable for the simple reason that you can release a line very quickly by simply pulling the pin out (preferably while holding the rope!).  Modern pin rails are sometimes fabricated with pins welded into place.  Like so much theatre technology, pin rails have not disappeared with the advent of newer systems; many new theatres are still built with this device.

The rope, on the other hand, has changed.  Natural fiber (hemp or manila) has been nearly universally replaced with synthetics.  The simple reasons are strength and longevity.  Natural fibers are sensitive to moisture and will deteriorate over time.  This is not an issue with synthetic fibers.  There are trade-offs, however.  The synthetic fibers can be more slippery and can me more costly.

Like many things, there are advantages and disadvantages to this style of rigging.  Some advantages:

• Flexible–especially in a stage with a gridiron, setting a spot block and running a spot line is a very quick, simple process.
• Nearly silent–if the equipment is in good repair, the only noise from a rope system is the rope whispering over the blocks.
• Trimmable–it is very simple to adjust for trim (level) across any given lineset.
• It is possible to add counterweight, with either a Sunday or trim clamp.

There are also some drawbacks:

• It takes a very high level of skill to set up and use a rope system.
• Much of the time, the linesets are unbalanced.  This is an inherently unsafe scenario and has to be handled thoughtfully and with caution.
• It is very easy for a lineset to get out of trim (level).

The type of facility you would typically see a full-blown rope system would be in a smaller facility that most frequently utilizes painted fabric scenery–essentially, the average theatre from the 1930′s and earlier.

Spot line rigging, on the other hand, is common in many theatres and most especially in those with a gridiron, as the gridiron makes it very easy to rig.  This includes theatres currently in various stages of design or construction.

A technician working with a rope rigging system needs:

• to be able to estimate weights
• to be able to handle the amount of weight hanging on the other end of the rope
• a basic knowledge of knots

Like any rigging system, a rope rigging system should be regularly inspected, including having a periodic professional review (we recommend annually with all rigging systems).  The other major maintenance items are keeping the lines coiled and neat–off the floor, away from dirt–checking the condition of the rope and ensuring all knots are securely tied.

This is the kind of rigging system usually visible in movies showing a theatre.  It is far more “theatrical” and interesting visually than counterweight sets or winched sets–in the case of the last, there might not be anything to look at except the controller!  Watch for sandbags and coils of rope on the screen.

All stage rigging systems have essentially one goal: to hold material (scenery, lighting, masking drapery) in the air–safely.  There are many similarities between the various systems that have been devised to do that job.  There are also significant differences, mostly dependent on exactly what you want to do with the scenery and how you want to do it.  Here’s an overview of each type of system.  Later articles will look at each type in detail and discuss the strengths and weaknesses.

Dead-hung.  This refers to rigging systems that cannot be moved vertically.  Typically, this consists of pipes or tracks suspended directly from the building structure with chain or cable.

Hemp.  These are the systems we see frequently in old movies with 3-5 ropes and sandbags.  The name comes from a frequently-used rope fiber–although it is interesting that the majority of natural-fiber ropes used in the modern theatre building are spun from manila rather than hemp.  But that’s a different discussion!  The equipment is able to be moved vertically.  The sandbags are used to balance the load applied.

Counterweight.  It is probably a safe guess that this is the most common type of rigging system installed in theatres in the United States.  There are many variations within this category.  two big ones include how the arbors are guided and if the system operates in single or double purchase.

Manually winched.  The most common example of this type of system has one or two hauling lines from the winch to a clew, then multiple lift lines out from the clew to the batten.  These are typically used on equipment that needs to be accessed relatively easily but not rapidly or frequently.

Powered winches.  This is easily the most diverse category.  Hydraulics, packaged hoists, counterweight assist, dead-haul…the list goes on!

As I noted above, later articles will discuss each category in more depth and touch on the options, strengths and weaknesses.  In the meantime, regardless of the type of system, remember that it is suspending thousands of pounds of weight over people’s heads.  These systems should be inspected on a regular basis.  We recommend annually!

Last year, one of our projects featured examples of four of these–on the same stage, at the same time.  There were dead-hung line sets, some hemp sets (with one really old sandbag that basically disintegrated when it was touched), two different versions of counterweight and even a manually-winched set.  There were a lot of interesting “features” to that system.  One of these was the access system devised to allow relatively easy re-rigging of the hemp sets.  One of the down sides to a rope system is that if you accidentally let go of the rope, there is a distinct possibility that the rope will snake its way right out, over the block and into a nice pile–at the floor.  Since this particular auditorium did not have a gridiron, the designed solution from the 20s or 30s was this.  A center catwalk was installed running from stage left to stage right.  It was long enough to reach all three of the primary rigging beams.  At the far downstage and upstage ends of the rigging beams, there were squared steel “loops,” about 12 inches wide, hanging down to approximately the elevation of the catwalk.  We could not figure out what they were until we noted the 2×12 plank laying on the floor.  We finally made the connection.  The intent was that you’d carefully extend the plank out from the catwalk into the loop.  One end of the plank rested in the loop, the other on the edge of the catwalk.  That allowed a worker to walk out, balancing on the plank,to re-reeve the offending line into the block.