St. John's Foucault Pendulum - Annapolis, Maryland
Posted by: 
flyingmoose
N 38° 58.908 W 076° 29.608
18S E 370641 N 4315817
Located in the stairwell of the Mellon Hall.
Waymark Code: WM12NGW
Location: Maryland, United States
Date Posted: 06/22/2020
Views: 3
The Foucault Pendulum is located at the top of the four-story tower in an area which also contains the St. John's College Observatory. The pendulum drive magnet is housed within a cast iron cone in the Observatory facility. The magnet is keyed to turn on and off as the pendulum swings by using resistive photocells that determing the center of the pendulum's swing.
The magnet is triggered a fraction of a second after the "pendulum center" signal is sent to the timing circuits. The timing circuits then maintain the power to the magnet for approximately 1.24 seconds. The magnet is designed to pull the pendulum drive disk (which is mounted on the support wire) radially outward. In this fashion, the magnet and timing circuit maintain the pendulum swing against friction.
An overdrive element to the control circuit senses when the swing is too large, and shuts down the drive electronics for a time thereafter.
A more complete discussion of this assembly is forthcoming. The impetus for the current project is a gift from the Annapolis Class of 2011, which provided funds to refurbish the pendulum control circuitry. Our thanks to the Annapolis Class of 2011 for its generosity!
For additional information, please feel free to contact:
J.H. Beall
St. John's College
Annapolis, MD 21404
or by email at the St. John's College Observatory.
http://thucydides.sjca.edu/~stars/index.html