Hi How much room do you have for the pendulum? Size is going to impact the choice of designs quite a bit.
Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Morris Odell Sent: Thursday, July 22, 2010 11:21 PM To: time-nuts@febo.com Subject: Re: [time-nuts] A different timenuts interest Hi all, I would like to thank everyone who responded to my post. This is a wonderful group of talented and erudite people and it was a pleasure to read the posts (and private emails) on the subject of the Foucault pendulum. Where else could the discussion range over timekeeping, mechanical suspension arrangements, Tesla coils, Napoleon, sustaining systems, blades on the pendulum bob, a host of references and all the other great stuff that turned up. This project is for a FP that will be part of an art installation. It's unlikely to be permanent though unless a major gallery or collector likes the work enough to buy it. Unfortunately this rules out commercial systems costing tens of thousands of dollars. >From my readings and suggestions from members of this group I have come to understand the following: The main issues in designing a FP are the sustaining system, avoidance or damping of elliptical motion and safety considerations in case the wire breaks. Of course keeping fingers and draughts away is also a consideration. Sustaining systems are mostly electromagnetic, either with a ring shaped electromagnet at the top near the suspension point controlled by optical sensors, or one or more coils below the centre point with a magnet on the bob. This acts as both a sensor and "motor". There is also a reluctance type driver described using mains frequency solenoids. The most elegant system is the parametric one where the suspension point is oscillated up and down sinusoidally at twice the pendulum frequency and there are no horizontal forces acting on the bob at all. I found a very complex mathematical analysis if that. It would be an interesting challenge using optical sensors and a stepper perhaps to move a cam or crank to realise that. Avoidance of elliptical motion and increasing the Q of the oscillator is one of the reasons why most FPs are so long with heavy bobs. Despite this I found some articles on short FPs, including one hanging from the wall and used as a clock with a pendulum less than a metre long. Elliptical movement is often controlled by a "Charron ring" which interacts with the wire to limit ellipsoidal movement. There are also magnetic eddy current damping systems described and one elegant method which uses a precisely timed pulsed sustaining system to cancel elliptical motion. As was pointed out, FPs are not primarily time keeping devices but there is a relationship between the period of their precession and the rotation of the planet, which is also dependent on Latitude. Perhaps unsurprisingly, someone has described a FP clock which required an electronic system to stop it for a few hours in the middle of the night to sync its movement to the 24 hour cycle. One can easily see GPS control creeping in there :-) I hope the discussion continues, It's been great so far. I'll keep the group posted on progress. Cheers, Morris _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.