A pendulum swinging in a single plane is highly predictable, and can easily be enhanced electronically. An omnidirectional pendulum, however, falls towards its center of gravity at different velocities and from many different angles, thus posing a greater  electronic challenge.

My Omnidirectional Pendulum described here is continually in motion, swinging rapidly through its center, or occasionally spiraling around it or bouncing away from it. It will form an interesting novelty display.

A neodymium (superstrength) permanent magnet is suspended from a point by an inelastic line, which prevents the magnet from jumping to the core of an electromagnet L1. The electromagnet is fixed below the pendulum at its center of gravity, see Fig.2b.

The pendulum’s length of swing is about 25cm and the point of suspension is 25cm to 50cm above the electromagnet (28cm is recommended). The magnet should pass with about 5mm clearance above the electromagnet’s core.

The electromagnet was salvaged from a 12V 200 ohm miniature mains relay, and is polarized to repel the pendulum when overhead. The magnet used was a small slug about 8mm long and 4mm in diameter (Consider a small voice coil magnet from an old speaker. ARW.)

A network of miniature glass reed switches, S1 to S15, surrounds the electromagnet and detects the incoming pendulum. The trigger network is built by soldering the reed switches to a thin wire perimeter (thick wire might cause the magnet to jump to the wire) at 2cm intervals to form the outer circle, see Fig.2c.

A thin wire ring is then soldered around its center to produce a circle of reed switches of about 11cm in diameter. The trigger network should be laid flush with the top of the electromagnet’s core, and wires taken from its inner and outer rings to the rest of the circuit.

Circuit Detail

Referring to the circuit diagram of Fig2a, as the pendulum falls towards the trigger network’s outer perimeter, monostable timer IC1 pulses and triggers 1C2a, which in turn disables the 555 monostable at pin 4 until the pendulum has crossed the entire trigger network.

At the same time, IC1 triggers 1C2b, via diode D3, which powers the electromagnet using transistor TR2. In order to kick start the
pendulum should it stall in a circular pattern of motion (particularly if a longer pendulum is used), components TR1 to C5 are included, causing the magnetic field to collapse at intervals indicated by LED D6. (It may be found that these components can be omitted.)

To set up, centralize all three presets VR1 to VR3 then power up (there will be a short delay before the pendulum kickstarts). Adjust preset VR1 so that green LED D1 pulses once only as the pendulum falls towards the center of gravity – not as it shoots away.

Some experimentation is needed using preset VR2 to synchronize the electromagnet’s repulsion with the pendulum’s swing, as indicated by LED D4 (note that too vigorous a swing may render the kick-start useless).

A 12V mains adapter is recommended as a power supply, since batteries would soon be exhausted.

Article reproduced by permission of Wimborne Publishing. www.epemag.com