The pendulum moves randomly thanks to the magnet at its lower end being of opsed polarity to the small magnets on the base (with stars on their face). The magnets used in this model are not Meccano parts — they were obtained from the “Staples” stationery store who stock a wide range for magnetic notice boards etc. Since the magnets can be moved anywhere on the base an infinite number of arrangments are possible.
A similar model could undoubtedly be constructed using Meccano Electrikit magnets but would not be as neat.
The sharp-eyed meccano enthusiast will notice that I have used some bespoke brass parts to allow the height of the horizontal rod to be easily adjusted. It would be possible to make similar adjustment screws usung electikit terminal nuts locked onto a suitable bolt.