How You Can Use It
Being an arena rigger by trade , I always thought in terms of chain hoists when I first started training in automated rigging . “ What could I do with all of those hoists ?” was what I was thinking . What I wasn ’ t thinking about was the bigger picture . While hoists typically cover movement along the Z-axis , let ’ s focus our attention towards other practical applications .
Winches are a popular tool for faster or more powerful moves but they are most often used for Z-axis movement , as are chain hoists . There are lots of different capacities of winches and some are capable of creating much more force or power than a standard entertainment chain hoist . Being able to generate incredible speeds and high torque , they can be used in a wide variety of applications to provide accurate , smooth pulls along one axis . This can be seen in many formats , from architectural installs to theatres to high-speed camera movements in film to actually flying performers .
Trolleys are a practical way to accomplish movement along the X and Y axes – specifically upstage / downstage and stage left / stage right . This is often accomplished via an electric motor that is mounted to a track . The motorized trolley has a rigging point that can be moved along this track by applying power to the drive .
Furthermore , you can compound your axis by rigging a hoist to the bottom of your trolley . As your trolley tracks along an X or Y axis , the secondary system can move up and down along the Z axis , giving you a compounded axis with many more options for movement .
The last axis of movement is rotation . This is accomplished via rotators , devices that spin , tilt , or rotate an object around an axis . This could be a simple rotator on a point that allows it to spin , such as a mirror ball , or it could be as large as a circular section of staging that spins inside the outer staging . There are even examples of large-format stages with an inner rotating circle that has a ground-supported structure in the middle . This centre section rotates , changing the position of the downstage point of reference of the stage itself . This is an awe-inspiring effect when used in a 360-degree environment , or in a more familiar term , “ playing in the round .”
OPTICAL ENCODERS
There are many types of encoders , but let ’ s focus on a commonly used variety in stage automation : the optical encoder .
This is a common electro-mechanical component that houses a glass disc with opaque and clear sections around it , like a bicycle wheel or a pie missing every other slice . As it spins , light passes through the glass disc and a sensor sends electronic pulses when it sees changes in the light . The software then interprets these pulses .
Because we are able to count the number of pulses per revolution , we are able to tell how many times the encoder has turned and associate that value with a measurement in physical space . The more pulses that you can read per revolution , the more accurate your encoder will be . This is called encoder resolution .
The reasoning behind this is that you can divide one revolution of your mechanical turn , or physical distance traveled , into a larger number of pulses per full revolution , resulting in more data and better accuracy . We also need to establish how many pulses are read for each measurement of physical distance ( chain processed ). This is called scaling and can be done with a measuring system and some calculations .
There are two basic forms of automated rigging equipment : fixed speed and variable speed systems . Both have their practical applications , but the key word here is speed . Speed is what determines how the force is applied by a motor that is energized as it starts , runs , and stops .
In physics , this is described by Newton ’ s second law of motion and the formula F = ma , which can be translated to : force in Newtons is equal to the weight in kg , times acceleration in m / s2 . Or , 1 Newton = 1 kg times m / s2 .
Let ’ s look at this in a practical sense . The heavier your object is and the faster you move it , the more force you generate . If you take a heavy video wall and move it with a highspeed motor , you will put a lot of force on your rigging when it changes speed . Heavier objects should be moved at slower speeds unless the systems and supporting structures are capable of safely dealing with the forces they can generate .
Now , taking this full circle , fixed speed automated motors are an economical way to provide show moves . Variable speed motors enable faster and smoother movements . This is accomplished by ramping the acceleration and deceleration of the motor providing the movement . By curving the rate of the beginning and end of the move , you are able to better control the force applied . This ramping reduces the shock load on your rigging by starting slow , accelerating to speed , making the move at speed , and then slowing down gradually before the brake is applied to stop the movement .
It ’ s just like adjusting the amount of pressure you apply to the accelerator of your car as you take off , or before you apply the brakes . If you have the pedal to the metal right up until you hit the brakes , the deceleration will be harder than if you slowly let off it before applying the brakes . You can also apply the brakes gradually to slow down before coming to a stop . This initial braking is done electrically in show automation , which reduces the velocity of an object before the machinery ’ s brakes stop the movement . Keeping these simple physics in mind can make a huge difference in the safety of your system . Bear in mind that even if a system can provide a smooth ramp , the emergency stop or a loss of main power supply will engage the brakes immediately , causing an instantaneous stop and high dynamic load .
MUSE ’ S CONCENTRIC PYRAMID VIDEO SCREEN AUTOMATED ON VARIABLE SPEED HOISTS WITH LINK TO MEDIA SERVERS , ENABLING IMAGE MAPPING ACCORDING TO SCREEN POSITION .
24 • PROFESSIONAL LIGHTING & PRODUCTION