ABOVE: TOP VIEW
ABOVE: SIDE VIEW
ABOVE: SLIGHT CLOSE-UP SHOWING WIRE
In its full embodiment a similar wire or mobile track support would run parallel without fixed support for the marble during that portion of the motion. The marble would only apply full pressure on the bar side (not implemented here), leading up to full application on the long, unweighted end of the pendulum. The remainder (shown) would have a fixed track (shown) with the wire pushing upwards after activating the pendulum. The upwards motion during fixed support would compensate for the slight drop necessary to move the pendulum.
The motion is made possible by checking the range of the pendulum with some sort of stop, like the string shown.
These 'diagrams' are also available at a more official location, at: