Reprinted from PROTOCOL, the Journal of the Entertainment Services and Technology Association (www.esta.org) Fall 2003 issue. 2003 ESTA.

Electrical Winch Controlsby Tom Young

T he form of motor control we all know best is thes imple manua l s ta t ion wi th up and downpushbuttons. While these stations may still be the perfectchoice for certain applications, a dizzying array of moresophisticated controls is also available. This article ad-dresses the basic electrical requirements of the motorsand user interface issues you will need to address beforespecifying, building or buying winch controls.

To begin with, the manual control stations should beof the hold-to-run type, so that if you take your fingeroff of the button the winch stops. Additionally, everycontrol station needs an emergency stop (E-stop) thatkills all power to the winch, not just the control cir-cuit. Think about itif the winch isnt stopping whenit should, you really need a failsafe way to kill the linepower. Its also a great idea to have a key operatedswitch on control stations, especially where access tothe stations is not controlled.

due to an electrical or mechanical problem, the winchruns past the normal limit. If you hit an overtravel limitthe line contactor opens so there is no way to drive off ofthe limits. If this occurs, a competent technician needs tofix the problem that resulted in hitting the overtravellimit. Then, you can override the overtravels using thespring return toggle switch inside the starteras op-posed to using jumpers or hand shooting the contactors.

Variable Speed RequirementsOf course, the simple fixed speed starter gets replacedwith a variable speed drive. Heres where things start toget interesting! At the very least you need to add a speedpot to the control station. A joystick is a better operatorinterface, as it gives you a more intuitive control of themoving piece.

Unfortunately, you cant just order any old variablespeed drive from your local supplier and expect it toraise and lower equipment safely and reliably over kidson stage. Most variable speed drives wont, as they arentdesigned for lifting. The drive needs to be set up so thattorque is developed at the motor before the brake is re-leased, and (when stopping) the brake is set beforetorque is taken away.

For many years DC motors and drives provided apopular solution as they allowed for good torque at allspeeds. The large DC motors required for most winchesare expensive, costing many times what a comparable ACmotor costs. However, the early AC drives were not veryuseful, as they had a very limited speed range and pro-duced low torque at low speeds. More recently, as the ACdrives improved, the low cost and plentiful availability ofAC motors resulted in a transition to AC drives.

There are two families of variable speed AC drives.Variable frequency inverters are well known and readilyavailable. These drives convert AC to DC, then convert itback to AC with a different frequency. If the drive pro-duces 30 Hz, a normal 60 Hz motor will run at half speed.In theory this is great, but in reality there are a couple ofproblems. First, a typical 60 Hz motor gets confused at aline frequency below 2 or 3 Hz, and starts to cog (jerkand sputter), or just stops. This limits you to a speed rangeof as low as 20:1hardly suitable for subtle effects onstage! Second, many lower cost inverters are also inca-pable of providing full torque at low speeds. Employingsuch drives can result in jerky moves, or a complete fail-ure to lift the pieceexactly what you dont want to seewhen you are trying to start smoothly lifting a scenic ele-ment. Some of the newer inverters are closed loop (ob-tain feedback from the motor to provide more accuratespeed control) and will work quite well.

The other family of AC drives is flux vector drives.These units require an encoder mounted on the motorshaft allowing the drive to precisely monitor the rotation

Safe operation by authorizedpersonnel must be considered

when designing even thesimplest manual controls.

Controlling Fixed Speed MotorsThe actual controlling device for a fixed speed winch is athree phase reversing starter. The motor is reversed bysimply switching the phase sequence from ABC to CBA.This is accomplished by two three-pole contactors, inter-locked, so they cant both be closed at the same time. TheNEC requires both overload and short circuit protection.To protect the motor from overheating due to mechani-cal overloads a thermal overload relay is built into thestarter. This has bi-metallic strips that match the heatingpattern of the motor and trips contacts when they over-heat. Alternatively, a thermistor can be mounted in themotor winding to monitor the motor temperature. Shortcircuit protection is generally provided by fuses rated foruse with motors.

A separate line contactor should be provided aheadof the reversing contactor for redundancy. This contactoris controlled by the safety circuits: E-stop and overtravellimits.

This brings us to limit switches. When you get to thenormal end of travel limit the winch stops and you canonly move it in the opposite direction (away from thelimit). There also needs to be an overtravel limit in case,

Reprinted from PROTOCOL, the Journal of the Entertainment Services and Technology Association (www.esta.org) Fall 2003 issue. 2003 ESTA.

Cutting-edge portable consoles allow multiple operators to controlthe action from the best vantage points and provide 3D displays.

of the armature. A processor determines the exact vectorof magnetic flux (thus flux vector drive) required to ro-tate the armature the next few degrees at a given speed.These drives allow an infinite speed range, as you can ac-tually produce full torque at zero speed. The precisespeed and position control offered by these drives makethem a favorite in high performance applications.

cuit). When multiple winches are used to carry a singlepiece, the winches must be perfectly synchronized, orthe load can shift so that an individual winch can becomedangerously overloaded. The control system must be ableto keep selected winches in synch or provide a rapid, co-ordinated stop if a winch is unable to stay in synch withthe others. With a typical top speed of 240 fpm and a re-quirement to keep the winches within a 1/8 of eachother, you have less than three milliseconds to recognizea problem, attempt to correct the errant winchs speed,determine that youve failed and initiate a coordinatedstop of all the winches in the group. This takes a lot ofcomputing, fast I/O, and well-written software.

There are two very different approaches to large rig-ging control systems. Originally, a single console was used,with the usual problem of where it should be located forthe operators optimum view. Unfortunately this can changenot only from show to show, but also from one cue to thenext. This dilemma has been partially addressed by usingvideo cameras at different locations in conjunction with3D screen graphics that allow the operator to view theexpected rigging motion three dimensionally from anyviewpoint. This allows the operator to view the on screenmovement of the rigging from a viewpoint that matcheshis actual view of the stage, or the actual view of a closedcircuit camera. For complex moves with inter-relatedpieces this makes the control and understanding of whatis happening much simpler.

The other approach is a distributed system, with sev-eral portable consoles. This allows different operators tocontrol different aspects of the rigging, in the same man-ner we have done with manual sets. A dramatic exampleof this approach is used by the Royal Opera at CoventGarden, where there are ten consoles controlling a totalof 240 motors. Each console has five playbacks, and is setup so that each motor is assigned to a single console. Oneoperator and console could control everything, but fre-quently one console may be running stage lifts, anotherthe onstage rigging, and a third is being used backstage tomove stored drops.

PLC-based controls provide system status as well as control options. This screen givethe operator full access to Carnegie Halls nine stage floor lifts.

PLC Based SystemsA PLC is a programmable logic controller. First developedto replace the relay based industrial control systems ofthe 50s and 60s, these controls are at home in rugged,industrial environments. These are modular systems witha great variety of I/O modules allowing semi-customhardware configurations to be assembled easily at a rea-sonable price. These include position control modules,counters, A/D and D/A converters and all sorts of solidstate or hard contact closure outputs. The great variety ofI/O components and the modular nature of the PLC makethis an effective way to build custom and semi-customcontrol systems.

The greatest drawback to PLC systems is the lack ofreally great displays to tell you what they are doing or tohelp you program them. Monochrome and medium reso-lution color displays are the norm, as the primary use forthese components in on a factory floor.

One of the first major PLC systems used in a large en-tertainment venue is the complex lift and wagon systemat the original MGM Grand (now Ballys) in Las Vegas. Sev-eral manufacturers offer standard PLC-based systems anda host of semi-custom acoustic banner, shell, and lift con-trol systems is also available. The ability to build customsystems from standard building blocks is the greateststrength of PLC-based controls.

High End ControllersThe most sophisticated rigging controllers go well be-yond speed, time, and position control. They include theability to write complex cues, record profiled moves, andmanage multiple cues running at once.

Many of the larger opera houses are moving towardpoint hoist systems, where there is a separate winch foreach lift line (the rigging equivalent of dimmer per cir-

Reprinted from PROTOCOL, the Journal of the Entertainment Services and Technology Association (www.esta.org) Fall 2003 issue. 2003 ESTA.

ConclusionThe tremendous variety of rigging control systems cur-rently available ranges from the pushbutton station tocomplex multi-user computerized control system. Whenshopping for rigging control systems you generally getwhat you pay for. The most important features are safetyand reliability. These are features with real value, and youshould expect to pay a fair price for this security. Workwith an established manufacturer who can show youworking installations and who will put you in contactwith users who have requirements similar to yours.

Tom Young is Vice President of Sales and Marketing for J. R. Clancy,and also serves at the ESTA Manufacturer Vice President and co-chairof the E1.6 Powered Rigging Systems Task Group. He has been work-ing with powered rigging system for theatres and opera houses in theU.S. and overseas for over 15 years.