DIY
CIRCUITS
Solar Pendulum
Sunshine is all you need to get this easy-to-build
pendulum swinging.
By Owen Tanner
IF YOU’RE STUCK FOR SOMETHING TO DO
MAKE Volume 06, page 76).
on a rainy weekend then this might be the
perfect thing to build, ready for when the
sun comes back out. The pendulum is self-starting, meaning that when light hits the solar
panels it’ll start swinging all by itself. There’s
something a bit magical about watching it
swing ever higher with no visible help, which is
the main reason I decided to build one.
BEAM bots generally use simple electronic
components, and they’re often solar powered.
Another hallmark of BEAM bots is that their
behavior is usually more complex than their
simple components would suggest, and this
pendulum is no different.
The inner workings of my pendulum are
built around a circuit that appeared in the
book Junkbots, Bugbots, and Bots on Wheels,
co-authored by the father of BEAM robotics,
Mark Tilden. BEAM stands for biology, electronics, aesthetics, and mechanics, and it’s a
style of robot-making that uses simple analog
circuits rather than microprocessors (see
The pendulum itself consists of a neodymium magnet suspended above a coil of
wire using fishing line. Capacitors in the base
store energy from the solar panels, which
is dumped into the coil below the magnetic
pendulum by transistors. The magnetic field
generated by the current flowing in the coil
attracts the hanging magnet, starting it swinging. With every swing the magnet gets another
pull from the coil, lifting it higher and higher.
Owen Tanner
146 Make: makezine.com/28
