Steel weights in an arbor match whatever hangs on the bar. Balanced, the load moves by hand.
Guide · Rigging
Updated 17 Aug 2026
Rigging
Fly systems
Theatre fly systems, explained. Counterweight, purchase and the lock.
A counterweight system lets one person move half a tonne of scenery by hand. How the balance works, how a line set is run, what to demand of powered flying gear before you buy it, and what the annual inspection grades.
Single purchase: arbor travels the same as the bar. Double purchase: half the travel, twice the arbor weight, wing space back.
Grip both lines, release the rope lock slowly, pause and confirm balance before you move anything.
Ask for 8:1, two independent brakes and a manual brake release. The load rating is the part everyone gets right.
A fly system almost never hurts anyone because it is heavy. It hurts someone because it is out of balance and nobody said so.
One bar, one arbor, and a balance you can feel.
A counterweight fly system is a balance, not a lift. Steel weights are stacked in a cradle until they match whatever is hanging on the bar. Once the two sides agree, a single operator can move several hundred kilograms of scenery, drapes or lighting through the full height of the fly tower with one hand on a rope.
Everything else in the system exists to make that balance safe, repeatable and controllable. Understanding the parts in order is the fastest way to understand the whole.
Follow one line set from the stage upward. The batten is the horizontal pipe the load hangs from. Several lift lines rise from evenly spaced points along it to the grid, where each one passes over a loft block that turns it from vertical to horizontal. The lines then run across the grid to the head block at the top of the tower, a single multi-groove sheave that gathers the whole set and turns it back down toward the offstage wall. There they terminate at the top of the arbor.
The arbor is a steel cradle running in vertical tracks alongside the wall, and it is where the counterweight stack lives. In some lower-capacity systems guide wires do the job of tracks, limiting how much the arbor can swing as it travels. A continuous operating line runs from the top of the arbor, up over the head block, down the wall past the operator and around a tension block at floor level, then back up to the bottom of the arbor. Pulling one side of that loop drives the whole set. A rope lock at the operating position clamps the line and holds a balanced set exactly where it was left.
| Part | What it does | What goes wrong |
|---|---|---|
| Batten | The pipe the load attaches to, spanning most of the stage width. | Bowing, damaged splices, overloaded past the set's rated limit. |
| Lift lines | Steel wire ropes carrying the batten up to the grid. | Broken wires, corrosion, worn or incorrect terminations. |
| Loft blocks | Grid sheaves turning each lift line from vertical to horizontal. | Worn grooves, seized bearings, poor fleet angle into the block. |
| Head block | Multi-groove sheave gathering the set and turning it down to the arbor. | Groove wear, rope jumping a groove, loose mounting steel. |
| Arbor (cradle) | Carries the counterweight stack and travels in guides beside the wall. | Missing or loose spreader plates, bent rods, worn guide shoes. |
| Operating line | The continuous rope the operator hauls on to drive the set. | Fraying, glazing, hard spots, damage from knots and ribbon marks. |
| Rope lock | Clamps the operating line and holds a balanced set in position. | Worn jaws, poor adjustment, used to hold an unbalanced set. |
| Tension block | Keeps the operating line under tension at the bottom of its run. | Seized sheave, lost tension, guard or capture missing. |
Some venues run all of this without a counterweight in sight. A pile hoist or a motorised set drives the bar on wire ropes from a winch, and an automated fly system runs it on cue. Most Australian venues run a mix: manual counterweight sets for the bars that rarely change, motorised sets for the ones that move every show. All four approaches are covered on the fly systems page.
Single or double purchase. The trade is travel against space.
Purchase describes how the lines are reeved between the arbor and the batten, and it decides two things: how far the arbor has to travel, and how much weight it has to carry. It is the first thing to establish about any tower you are asked to work in.
In a single purchase system the arbor travels the same distance as the batten and carries the same weight. It is the arrangement most towers are built with, and the most direct to load and read. The trade is space: the arbor run needs as much height as the batten travel, so the counterweight tracks occupy the full offstage wall from the fly floor to the deck.
In a double purchase system the lines are reeved through a moving block so the batten travels twice the distance of the arbor. For every metre the arbor moves, the bar moves two. That halves the arbor travel, but it also doubles the weight the arbor must carry to balance the same load, because the mechanical advantage cuts both ways. The pay-off is that the arbor stays high in the tower and the wing space underneath stays usable for cast, crew and scenery.
Double purchase buys wing space and pays for it in arbor weight.
That trade drives the practical difference. A double-purchase set takes twice as much steel in the cradle to balance the same bar, so loading takes longer and the loading gallery carries more weight. It is chosen where the building forces it: limited fly height, limited wing space, or a tower retrofitted into a room that was never designed for one.
| Property | Single purchase | Double purchase |
|---|---|---|
| Batten travel per metre of arbor travel | 1 m | 2 m |
| Arbor weight to balance the same load | Equal to the load | Twice the load |
| Arbor run height needed | Full batten travel | Half the batten travel |
| Wing space below the arbor | Occupied by the counterweight run | Stays usable |
| Loading effort | Lower - fewer weights per set | Higher - twice the steel to move |
| Typically chosen when | The tower has the height and the wall run | Fly height or wing space is limited |
Two hands on the rope before the lock comes off.
Operating a balanced line set is a short, fixed sequence. It looks routine, which is exactly why it gets skipped, and skipping it is how an unbalanced set gets discovered the hard way.
- Clear the path. Look up and check nothing is in the way of the batten or its load - cables, lamps, set pieces, another bar's dead-hung gear.
- Call it. Warn the stage before anything moves, and keep calling while it moves. Every fly cue is a shared-space cue.
- Take both lines. Approach the set and grip the front line and the back line together in one hand before touching the lock.
- Release the lock slowly. Easing the rope lock off rather than snapping it open means an unevenly weighted set is felt in your hand instead of taking off on its own.
- Pause and confirm. With the lock off and both lines held, feel whether the set is balanced and whether you have full control of it. If it wants to run, stop here.
- Fly it. Pull the desired line and take the bar to its mark. On a conventional system the front line brings the bar in and the back line takes it out.
- Slow it with friction. Grip both lines together to create friction and bring the set down to walking pace before it arrives, rather than stopping it with the lock.
- Lock off. Set the rope lock once the bar is at its mark and the set is at rest.
A well-maintained system is quiet. Squeaks, knocks and grabbing are early evidence of wear or a developing defect, and they are worth reporting the day you hear them rather than at the next inspection. Left alone they become the larger problem, and the larger problem always arrives during a bump-in.
A counterweight system looks straightforward and can be genuinely dangerous, so it should be operated only by people trained on it. Where the work moves beyond operating an existing system into hanging, installing or altering one, it stops being operation and becomes rigging with its own licensing requirements - the line between the two is set out in rigging competency levels.
Loading is the dangerous part. Treat it that way.
Every time the load on a bar changes, the arbor has to change to match it. That transaction - two people, two levels, steel moving in a cradle above an open floor - is where counterweight systems do their damage. It is also completely controllable with a fixed protocol.
Know the weight first. Before anything goes in the cradle, know what has gone onto the bar. Guessing at the loading gallery means discovering the error through the rope lock.
Lock it, then lock it again. The line is locked off and a secondary hand lock added before loading starts. The rope lock alone is a position-holding device, not a device for holding a deliberately unbalanced set.
Talk, both ways. The fly operator and the loader confirm the line number, the number of weights going in or coming out, and that the line is clear to load. When the loader is finished they call the line number back, the number of weights placed, and that the cradle is clear.
Keep the area clear. Nobody under or around the arbor while it is being loaded. Counterweights are dropped, not thrown, and they are dropped onto a cradle above people's heads.
Weight goes on the bar first, then in the arbor. Never the other way round.
That sequence matters. Loading the arbor before the bar is loaded leaves the set heavily arbor-side, and an arbor-heavy set runs up, taking the bar out at speed with nothing on it to slow it down.
Two hoists, same rating. Only one you'd stand under.
Every hoist on the market will quote you a working load limit, and most of them will meet it. The number on the plate is the least of it. What separates a system you trust for twenty years from one you tolerate is everything the datasheet does not lead with - and it is all askable.
These are the questions worth putting to any supplier, including us. If the answer is vague, that is the answer.
| Ask about | The bar to hold to | Why it decides the outcome |
|---|---|---|
| Safety factor | 8:1 | 5:1 is a common floor in lifting gear. Over a stage, with people below, the extra margin is the point. |
| Brakes | Two independent spring-applied brakes - primary on the motor, secondary on the drum | A single brake is one component away from a dropped load. Two, on separate parts of the drive train, are not. |
| Failure behaviour | Gearbox efficiency under 50% at low speed | A non-backdriving gearbox will not free-fall if a brake ever does let go. It is a mechanical answer, not an electronic one. |
| Position feedback | Dual encoders - absolute and incremental | An absolute encoder still knows where the bar is after a power cut. Incremental alone means re-datuming before you can move. |
| Wire monitoring | Cross-wire detection as standard; slack-wire detection available | A fouled or slack line is how a bar comes in crooked or a rope jumps a groove. Detect it in the machine, not from the deck. |
| Limits | Rotary cam limits, mechanically set | Travel limits that do not depend on software staying healthy. |
| Certification | Independently certified to AS 1418.1 and AS 1418.2 | "Compliant" asserted by the manufacturer and "certified by a third party" are different claims. Ask which one you are being sold. |
| Recovery | Manual brake release, so a load or a performer can be lowered during a power outage | The plan for when the power goes out mid-cue should not be "wait". |
| Support life | Made and supported in Australia, parts held locally | A hoist is a 20-year asset. Ask who will have the parts and the drawings in year 15, and what the lead time looks like. |
The rating tells you what it lifts. The rest tells you what happens on the day something goes wrong.
That list is not a wish list. It is the specification the flying equipment we build is designed to, because it is what a room full of people underneath a moving bar actually requires. The next chapter is what that looks like as real equipment.
When manual stops being enough. What replaces it.
A counterweight tower is a good answer to a hard problem, and plenty of venues will run one happily for another thirty years. But it asks for a trained operator, a loading gallery and a bump-in every time the rig changes. When any of those three stops being realistic, the bar gets driven instead of balanced.
TSA designs and manufactures that equipment in Australia rather than reselling it, which is why the specification in the previous chapter is the specification we build to. Three routes for driving the bar, then what hangs on it.
Pile hoist
An electric pile-wind hoist on wire rope, permanently fixed to the wall or roof structure to fly a lighting or stage bar. Built for rooms where whoever presses the button is not a rigger.
Rated
500 kg, up to 14 m drift, 3 to 7 lines.
Behaviour
Ramped start and stop, roughly 8 m/min, very quiet. Up/Down push-button with E-Stop.
Best for
School halls, community and civic venues, theatres and PACs.
Not for
Point loads or show cues - that is a chain hoist or a drum hoist.
Hercules Junior
A drum hoist designed and built in Australia for theatre, not adapted from industrial lifting. This is the chapter-05 specification as a product.
Rated
500 kg, up to 15 m drift on six lines, variable to 0.5 m/s.
Carries
8:1 safety factor, two independent brakes, dual encoders, cross-wire detection, SIL 3 capable.
Best for
Small to medium venues, and any bar that moves on a cue.
Hercules Performer
A high-speed drum hoist designed from scratch for performer flying - not adapted from stage, industrial or climbing equipment.
Rated
150 kg at 50 Hz, up to 30 m drift, variable to 3 m/s.
Carries
Dual brakes that cannot actuate together, absolute and incremental encoders, manual brake release for lowering during a power outage.
Best for
Flying people, on cue, repeatably.
And the bar itself
Driving the bar is half the job. What hangs on it is the other half. The ILX theatrical lighting bar is a structural aluminium I-beam batten rated to 250 kg per 3 m section with power and DMX built in, so a lighting bar arrives as one item instead of a pipe plus a loom plus a splitter. For drapes, the curtain winch is a track-mounted capstan that opens and closes house tabs up to 60 m wide, virtually silently, and flies with the bar it sits on.
All of it runs on Atlas control, from a single up/down station to a networked rig. Hoists, motors and controllers are rigging equipment, and they are specified together - see the fly systems page for how a full system comes together, or size a chain hoist directly with the Hoist Selector.
Whatever you fly it with, it gets inspected.
Manual or motorised, a flying system should be inspected annually by a competent person, in line with manufacturer guidance and the relevant Australian Standards. Done properly it is not a walk-through with a clipboard: every component of every set is examined against published discard criteria and given a result you can act on.
The method is visual, tactile and functional. Visual against discard criteria; hands-on for wear, looseness, deformation, alignment and corrosion; functional on brakes, limits and stops where the set is powered. Significant defects are photographed, and minor corrective maintenance - lubrication, tightening, small adjustments - is carried out during the visit and recorded.
The standards behind it include the AS 1418 cranes, hoists and winches series, AS 2089 for sheave blocks, AS 2759 and AS 3569 for steel wire rope, and AS 4991 for lifting devices - part of the 50-plus standards a TSA inspection is assessed against.
Every component gets a compliance result, then a condition grade. That grading is what makes a report usable: it turns "the tower needs work" into a dated, prioritised list you can budget against.
| Grade | Result | Plain meaning | Action timeframe |
|---|---|---|---|
| A | Pass | Good working condition, well within limits | Routine |
| B | Pass | Good condition with signs of wear | Monitor |
| C | Pass | Worn but still serviceable | Monitor / adjust |
| Low | Fail | High wear or minor defects | 6-12 months |
| Medium | Fail | Exceeds discard criteria - replace or repair | 3-6 months |
| High | Fail | Condemned - remove from service | 0-3 months |
Each asset also carries a persistent Asset ID, so the same block, rope or cradle is tracked year on year and the report shows condition history rather than a fresh snapshot. The report ends with a Maintenance Priority List grouping assets by urgency, and the whole document stands as due-diligence evidence that the venue has met its obligations.
The scoped version of this for a tower is a fly system inspection. The whole-of-venue version, covering every stage system rather than the flying alone, is the Venue Systems Health Check. Terms used through this guide are defined in the TSA glossary.
We make it. So we can still support it in year fifteen.
Most suppliers of stage flying equipment in Australia import it. TSA designs and manufactures the hoists, the bars and the control here, which changes what we can promise after the invoice is paid.
It means the specification in chapter 05 is a design brief rather than a shopping list - the 8:1 factor, the second brake, the absolute encoder and the manual brake release are in there because we decided they should be. It means an unusual drift, an odd line count or a bracket that has to clear a heritage truss is a build variation, not a "no". And it means when a part is needed in year fifteen, the drawings and the tooling are here rather than on a container.
Around the equipment sit the in-house teams that install it, integrate it and come back to inspect it - one point of accountability from the first drawing to the annual report, Australia wide. If your tower is manual and the same three bars move every show, motorising those sets is usually the shortest route to a safer bump. If you inherited a tower and do not know what state it is in, start with an inspection and work from the priority list.
FAQ
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A batten hangs on lift lines that run up to loft blocks on the grid, across to a head block at the top of the tower, then down to a counterweight arbor. Steel weights are loaded into the arbor to match whatever is on the batten. Once the two sides balance, one operator can move several hundred kilograms by hand on the operating line, and a rope lock holds the set where it is left.
In single purchase the arbor travels the same distance as the batten and carries the same weight. In double purchase the batten travels twice the arbor distance, so the arbor carries twice the weight but only travels half as far - which keeps it high in the tower and leaves the wing space below usable. Double purchase is chosen where fly height or wing space is limited.
One where the weight in the arbor does not match the load on the batten, so the set wants to run on its own. It is the most common hazard on a counterweight system. Rebalance it at the loading gallery, and flag and lock the set off until you have.
Look past the load rating - most hoists meet the number they quote. Ask for an 8:1 safety factor, two independent brakes on separate parts of the drive train, a gearbox that will not backdrive if one fails, dual absolute and incremental encoders, cross-wire detection, mechanically set limits, independent certification to AS 1418, a manual brake release for power outages, and a manufacturer who will still hold parts in year fifteen. Chapter 05 is the full list.
Annually, by a competent person, in line with manufacturer guidance and the relevant Australian Standards. TSA carries out fly system inspections in-house with Competent Inspection Officers, grading every component and issuing a report that stands as due-diligence evidence.
Yes. A line set can be converted, or you can run a mixed rig - motorised on the bars that move every show, manual on the rest. TSA manufactures the equipment in Australia: pile hoists for fixed hall and PAC installs, Hercules Junior for bars that move on a cue, Hercules Performer for flying people. See fly systems for how a full system comes together.
Operating an existing, proprietary system using its standard method is generally not rigging as defined under WHS regulations - but it does require training on that system, site supervision and the venue's own procedures. Installing, altering or hanging from the system is a different matter. The line between the two is set out in rigging competency levels, and licensing differs by state.
Specifying a system, or working out what you already have?
Start here
Specifying powered flying
Book a Venue Systems Health Check.
One visit, one technician, a clear picture of every stage system you have and what to plan for. If the flying is the part you are worried about, a scoped fly system inspection goes deeper on the tower alone.
Book a Health CheckSee the flying gear we build.
Pile hoists, Hercules drum hoists, ILX bars and Atlas control - designed and manufactured in Australia to the specification in chapter 05.
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