Final Pendulum Design & Construction Materials supplied by Dennis Ambrisco.
February 7, 2004. Mw 7.1
This sensor is my first attempt to make the compact pendulum described here. I have not been able to obtain a period longer than 2 seconds, possibly due to slight flexure of central threaded rod that carries the lead weight. When adjusted for a longer period, the pendulum will drift to one side or the other and is stable at either extreme.
The magnet/coil pickup is from a PC hard drive. It seems to have sufficient gain. One problem is that in this design the coil rotates as it moves back and forth so that the amount of free travel is quite limited.
Ted Rogers has built a horizontal based on the same principal.