At the 1933 Chicago Progress Exhibition, an interesting mechanism was on display. In the media of that time, he was called "a rubber-running perpetual motion machine." The "rubber pendulum" demonstrated a new way to make thermal energy work (a steam engine, which also converts heat into mechanical energy, used another working substance - steam).
The apparatus consisted of electrical heaters on each side of the vertical support. And an ordinary pendulum swung on the support. One end of a rubber band is attached to the top of the support and the other to the bottom of the pendulum.
The pendulum rod, topped with brass weights, could swing as far from the vertical as the tension of the rubber bands bounding its lower end would allow. The motor is started by turning on the current and starting the pendulum.
When the pendulum reached the end of its swing, the rubber band stretched about 300 percent and was directly in front of one of the heaters. The heat from the heater caused the rubber to exhibit the unusual property of shrinking when exposed to heat, rather than expanding like most other materials. And this made the pendulum swing again.
At that moment, a shadow from a sheet metal screen protected the rubber strip from the heat. It cooled down and allowed the pendulum to swing towards another heater. The impulse of the pendulum carried him to the other side, where the process was repeated. And so he continued to swing back and forth.
Illustration from * Modern Mechanix *, Dec, 1933.
Later, many tried to "think out-modify" the design of the mechanism in order to remove electric heaters from the circuit. Someone even suggested using the warmth of the sun's rays. But even so, the service life of the "rubber perpetual motion machine" would still be limited by the service life of two rubber strips.