In a message dated 2007/06/29, tchannel1@............ writes:

> Hi Folks, I am still experimenting with the basic structure of the folded 
> Pendulum linkage. One normal pendulum, one inverted pendulum and a horz 
> connecting arm.
>  
> 1 I am assuming the length of the two pendulums should be the same and as 
> long a practical.  I am thinking of 12 to 18" which would make the sensor about 
> 24" to 36" tall.  I may go shorter........

Hi Ted,

       It very much depends on what maximum period you want? This is often 25 
to 30 seconds for amateur equipment?

       I suggest that the shortest you consider should be 1 second at about 
9.8". Above that, what is the maximum framesize that you can easily make? Maybe 
2 ft square with 3" U channel? With your trial setup, you got a period 
extension of x10. You could probably get x20 fairly easily.

>  2 I gather the length of the horz connecting arm, should be a long a 
> practical.  In that, a longer arm would allow more room along the horz plane, on 
> which to tweak the balance.  A too short arm, would make the balance point too 
> small.
> I would be using a fine threaded rod with a threaded mass and a threaded 
> smaller mass, for extra fine adj.

       I suggest that you make the horizontal connecting arm out of brass to 
form the main mass. Then mount a small 'trim' mass just off centre. I don't 
think that the horizontal arm needs to be more than the pendulum length. You are 
critically dependant on the position of the mass to extend the period. Mount 
the main mass rgidly fixed. Don't mount it on threaded rod.

> 3 Would such a device still require the same type of enclosure as a Lehman 
> or Vertical?

       Yes. It may be convenient to use 1/8" or 3/16" Al alloy plate to form 
the two sides and connect them together with either square rod or U channel to 
support the arms and to give an enclosed box structure. Maybe cut a hole in 
the centre of one plate to mount and adjust the sensor and damping components 
and provide a cover plate?

> 4 Would the size of the mass be critical?  I would be using brass or SS 
> shim stock at all points for hinges.

       Don't use Brass shim. SS or bronze should be fine. You are very 
dependant on getting good bearings to be able to extend the period. The load bearing 
capacity of the shim stock should be considered when deciding on the mass. 
Don't go above 1/10 the max. rated load stress. Consider the handling stresses. 
Don't make the arms very long and narrow - max about 5:1, maybe less? Design 
in stops to prevent the arm moving more than about 1/2" either way.

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/06/29, tchannel1@............ writes:



Hi Folks, I am still experiment=
ing with the basic structure of the folded Pendulum linkage. One normal pend=
ulum, one inverted pendulum and a horz connecting arm.

 

1 I am assuming the length of the two pendulums should be the same and as l=
ong a practical.  I am thinking of 12 to 18" which would make the senso=
r about 24" to 36" tall.  I may go shorter........




Hi Ted,



       It very much depends on what maximum pe=
riod you want? This is often 25 to 30 seconds for amateur equipment?



       I suggest that the shortest you conside=
r should be 1 second at about 9.8". Above that, what is the maximum framesiz=
e that you can easily make? Maybe 2 ft square with 3" U channel? With your t=
rial setup, you got a period extension of x10. You could probably get x20 fa=
irly easily.



 2 I gather the length of the=20=
horz connecting arm, should be a long a practical.  In that, a longer a=
rm would allow more room along the horz plane, on which to tweak the balance=
..  A too short arm, would make the balance point too small.

I would be using a fine threaded rod with a threaded mass and a threaded sm=
aller mass, for extra fine adj.




       I suggest that you make the horizontal=
 connecting arm out of brass to form the main mass. Then mount a small 'trim=
' mass just off centre. I don't think that the horizontal arm needs to be mo=
re than the pendulum length. You are critically dependant on the position of=
 the mass to extend the period. Mount the main mass rgidly fixed. Don't moun=
t it on threaded rod.



3 Would such a device still re=
quire the same type of enclosure as a Lehman or Vertical?




       Yes. It may be convenient to use 1/8"=20=
or 3/16" Al alloy plate to form the two sides and connect them together with=
 either square rod or U channel to support the arms and to give an enclosed=20=
box structure. Maybe cut a hole in the centre of one plate to mount and adju=
st the sensor and damping components and provide a cover plate?



4 Would the size of the mass b=
e critical?  I would be using brass or SS shim stock at all points for=20=
hinges.




       Don't use Brass shim. SS or bronze shou=
ld be fine. You are very dependant on getting good bearings to be able to ex=
tend the period. The load bearing capacity of the shim stock should be consi=
dered when deciding on the mass. Don't go above 1/10 the max. rated load str=
ess. Consider the handling stresses. Don't make the arms very long and narro=
w - max about 5:1, maybe less? Design in stops to prevent the arm moving mor=
e than about 1/2" either way.



       Regards,



       Chris Chapman