PSN-L Email List Message

Subject: Re: Folded Pendulum
From: ChrisAtUpw@.......
Date: Wed, 27 Jun 2007 18:39:50 EDT


In a message dated 2007/06/27, tchannel1@............ writes:

> I have seen a few descriptions of the "Folded Pendulum" sensor concept.  
> Here is one http://jclahr.com/science/psn/youden/  from this one and others I 
> get the general idea.
>  
> I made a mock up using two pendulums 16" long and a cross member of about 
> 15"  By moving the mass L and R on the cross member beam, I could get up to 12 
> seconds period.

Hi Ted,

       A 16" pendulum has a period of 1.28 seconds. A factor of x10 increase 
in period should be quite easy. We can get >30 sec from a 1.4 sec Lehman, no 
problems. The limitation is likely to be in your suspension system.

       The Australians managed to get a period of 90 sec from a 1 sec folded 
pendulum without feedback, if my memory is correct. 

>  I guess the longer the pendulums the longer the period, so If I use 24" It 
> could be more than 12 secs.  This design by David H. Youden, uses 6.47" 
> pendulums, and I did not see what period it produced.  The overall dim of it, is 
> 10.27" tall....So perhaps it has a shorter period.

       Dave Youden's pendulums are 0.8 seconds. Since it is a feedback 
instrument, the period will depend on the electronics. It looks as if this 
corresponds to about 6 seconds. However, the SG pendulums can be extended to ~50 
seconds.

       What happens as you trim the mass closer to the balance point? Do you 
have a trim mass set by a screw thread?

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/06/27, tchannel1@............ writes:

I have seen a few descriptions=20= of the "Folded Pendulum" sensor concept.  Here is one http://jclahr.com/science/psn/youden/&n= bsp; from this one and others I get the general idea.

I made a mock up using two pendulums 16" long and a cross member of about 1= 5"  By moving the mass L and R on the cross member beam, I could get up= to 12 seconds period.


Hi Ted,

       A 16" pendulum has a period of 1.28 sec= onds. A factor of x10 increase in period should be quite easy. We can get &g= t;30 sec from a 1.4 sec Lehman, no problems. The limitation is likely to be=20= in your suspension system.

       The Australians managed to get a period= of 90 sec from a 1 sec folded pendulum without feedback, if my memory is co= rrect.


I guess the longer the pendul= ums the longer the period, so If I use 24" It could be more than 12 secs.&nb= sp; This design by David H. Youden, uses 6.47" pendulums, and I did not see=20= what period it produced.  The overall dim of it, is 10.27" tall....So p= erhaps it has a shorter period.


       Dave Youden's pendulums are 0.8 seconds= .. Since it is a feedback instrument, the period will depend on the electroni= cs. It looks as if this corresponds to about 6 seconds. However, the SG pend= ulums can be extended to ~50 seconds.

       What happens as you trim the mass close= r to the balance point? Do you have a trim mass set by a screw thread?

       Regards,

       Chris Chapman

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