|
this is a powered pendulum based on Roger Andrews' Novelty Electric Motor:
https://patents.google.com/patent/US3783550A/en
a magnet on a pendulum bob passes over a coil which induces a small current across the coil. this switches the transistors on, putting a short pulse of current through the coil to create a magnetic field opposing the polarity of the magnet, repelling it away from the coil. the transistors then switch off.
some implementations:
http://www.trainelectronics.com/Pendulum/article.htm
http://www.maxmcarter.com/pendulum/index.php
there is a flaw in this design. there is enough current to switch the transistors on when there is no magnet field from the coil, so it switches on as soon as it's powered up. once running, the gain of the pair of transistors is too large, so it goes into oscillation.
I've been trying to build this, but into the same problems using similar transistors, 2n3904/6 or pn100/200. Adding bias resistors works for a short while, but drifts over time. It's also very sensitive to changes in the supply voltage; if the supply is too low, the transistors won't switch on when the magnet passes over the coil.
|
