With the disadvantage of the electric batten becoming apparent, theatre architects soon sought another way to automate the stage rigging systems in new theatres.

The principals of the hemp and sandbag systems and the counterweight fly system had changed little since the ancient Greeks introduced the first deus ex machinaseveral thousand years ago. Though the electric batten was a first step away from these ancient methods, it was the motor driven spotline fly system that proved to be the first successful automated fly system.

The system is based on the double purchase counterweight fly system. But rather than a rope purchase line a chain is used to connect to the arbor. This chain is controlled by a variable speed 3/4 horsepower DC motor. An important step up from the earlier electric batten was the use of a variable speed motor, as well as having a combination of dynamic and electromechanical braking.

Unlike other sytems though, the top of the arbor is not connected to fixed sheaves on the grid but to a series of ball-bearing pulleys mounted on a track. By moving the pulleys in the track, the rigger can fly battens at many different, incrementally adjustable angles. This is a signifcant advantage over traditional fly systems, in which the battens are permanently hung parrallel to the proscenium arch.

However, the system has several disadvantages compared to manual fly systems. The first disadvantage is of course the great expense. Secondly, motor driven systems can be very loud. This makes an upstage scene change impossible in all but the loudest fight scenes or musical numbers.

Another major disadvantage is that the rigging of a motor driven spotline system creates a 2:1 mechanical disadvantage. This means that the rigger must load twice the amount of counterweight when balancing the system. Of course, this also means that the top speeds of the batten are doubled, but the danger of moving heavily loaded battens on a full stage means that it is very rare to ever run the lineset at full speed.

Part of the Stage Rigging Metanode

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