Generally, moving lights are attached to a truss structure that is flown as a grounds support or a larger rig. The truss construction is so stable that rotational accelerations, such as those generated by a moving light during pan and tilt, have no effect whatsoever.
Dynamic flywheel system for motion smoothing of moving light
If, on the other hand, a crosshead or load bar is suspended with only two ropes, the reaction forces generated, especially by the pan movement, are sufficient to bring the load bar or crosshead out of its rest position. Floodlights, which are now to be aligned to a position, then swing through the stage set with their light cones until the supporting structure has balanced out again.
Vibration situation
Situations in which one or more moving lights are attached to a load bar or truss with only one row of suspension means can often be found in theaters and their brochure holders, which are used as moving light supports without further ado.
But even in a television studio, you often find pantographs that are not structurally secured against rotation.
And of course the situation on the rock or musical stage, where the set and/or lighting designer wants to see individual moving lights "fly" and they should not hang rigidly on a truss construction.
Until now, the solution was to move the moving lights very slowly to the target position in order to avoid the swing effect. Thus the deflection forces remained sufficiently small, so that no recognizable swinging was caused.
If several moving lights were accelerated at the same time in one direction on one rod, this effect was increased accordingly due to the greater mass occurring simultaneously in the same direction.
With multiple moving lights, it was also possible to move every second lamp in the opposite direction to compensate for the resulting forces when they had nothing to illuminate and the remaining pan travel was approximately as large as the target movement of the illuminating first moving light.
Also, moving lights had been selected because of this characteristic, which also depends on the head weight and the acceleration and deceleration ramps of the stepper motors. The resulting impulse varies from fixture type to fixture brand.
View inside the Lightlock at the drive of the flywheel mass (Photo: Herbert Bernstadt)
Gyroscope holds against
In order to compensate the angular momentum of the moving light in a suspension with degrees of freedom, the company RSC has developed the Lightlock. The Lightlock was presented at the Plasa 2008 and received the Plasa Innovation Award.
The Lightlock compensates for the forces in a similar way to a counter-rotating moving light, but does not have to be programmed as well. The Lightlock has a gyro sensor that immediately registers the finest deflections and communicates them to the control electronics.
This control electronics drives a drive, which moves a flywheel mass and thus counteracts the angular momentum of the pan movement of the moving light. These sensors are known from the hobby area for remote-controlled helicopters, where the tail rotor counteracts accordingly, or from space travel, in order to move satellites with swirl wheels or. to keep gyroscopes stable in position.
The trick now is to optimize the control algorithm in such a way that the moving light remains as positionally stable as possible. The result, we could convince ourselves, is remarkable and worth seeing.
In the video you can see the comparison of the pan tilt movement: once with switched on Lightlock and once without switched on Lightlock – the difference becomes obvious
Flexibility
The Lightlock is a well thought-out, practicable tool. A wide variety of attachments such as eyebolts, bridle bars or couplers can be attached due to the support rail symmetrically incorporated on the top and bottom, allowing the Lightlock to be hung directly from ropes or slung over a pipe.
The slim Lightlock module can also be used to stabilize long tension rods. (Image: Herbert Bernstadt)
To strike moving lights universally, it is best to choose suspension via coupler and tube. The Lightlock is designed for a maximum of 100 kg. If larger distances are to be compensated with multiple moving lights, it is also possible to increase the counteracting accelerated momentum by simply stacking more Lightlocks on top of each other. Also for this there are accessories for the mounting rails.
The power supply is provided by a looped PowerCon connector, so that the moving light can be directly supplied with power, respectively. inverted, because the power consumption at a maximum of 150 W is usually hardly noticeable.
More topics about moving light accessories are covered on the following pages: