Thanks for your thoughts guys

   hmmmm  am a bit worried that there is something fundamentally wrong with 
it.  There was a M6.2 off Japan
overnite only 8000km away and nothing recorded.  I would have
expected that even with underdampening that that event would
have showen up  There is a screen dump gif image on my wwww
site  http://www.sydneystormcity.com/untitled.gif

you will see that there is a pretty much steady low freq signal there, 
varying in intensity, in winquake it has a
~ 3.5 sec period.  The additional noise towards the end of
the display is the morning traffic becoming active with its
hi freq component.

Hey Pete R.  yes thats the coil you sent me  :)  it is putting
out plenty of signal.

Steve H.  the frame was propane gas aluminium welded.  The
frame is made of 10mm thick, 50mm wide aluminium bar.
The boom is 16mm diam aluminium bar.  The 2 lead weights are
2 pound diving belt weights, holes bored in them and then
slidden (<<-- horrible word haha) onto the end of the boom.
The pickup coil sits between 2 rare earth disc magnets
~ 1.5 cm diameter.
The dampening at the moment is just a cylindrical rare earth
magnet below the lower plate of the plates that support the
pickup magnets.

I am not totally happy with the lower pivot.  I was going to have ball 
bearings butted against each other. But they wont
sit together.  Even just the signle ball bearing in the end
of the boom wont sit happily against the vertical bar.
There is just so much upwards force at that end of the boom caused by the 
downwards force of the weight at the other end.

cheers
Dave




>Hi Dave,
>     It looks nice! What period have you set it to, please?
>I suggest that you aim for 25 seconds.
>I can't quite see how you have attached the mass plates to
>the arm. Are they crimped / punched in place?
>How does the variable damping work ? I can't see that either!
>See 
>http://www.jclahr.com/science/psn/chapman/lehman/index.html 
>
>
>I stick a label with a vertical line on it onto the mass and view the line 
>with a magnifying glass through a transparent plastic ruler. I deflect the 
>mass 10 mm and release it. The mass moves back toward the balance point 
>and usually past it.
>I observe how far it moves past the balance point. I increase / decrease 
>the damping until the mass goes 1/2 mm past the balance point and then 
>moves slowly back to zero without any oscillations. The arm is then set to 
>0.7 critical damping.
>The amount of damping needed decreases as the set period is
>increased.
>     I hope that this helps.
>      Regards,
>      Chris Chapman



Thanks for your thoughts guys


  hmmmm  am a bit worried that there is something fundamentally
wrong with it.  There was a M6.2 off Japan 

overnite only 8000km away and nothing recorded.  I would have

expected that even with underdampening that that event would 

have showen up  There is a screen dump gif image on my wwww

site 
http://www.sydneystormcity.com/untitled.gif


you will see that there is a pretty much steady low freq signal there,
varying in intensity, in winquake it has a

~ 3.5 sec period.  The additional noise towards the end of 

the display is the morning traffic becoming active with its 

hi freq component.


Hey Pete R.  yes thats the coil you sent me  :)  it is
putting 

out plenty of signal.


Steve H.  the frame was propane gas aluminium welded.  
The

frame is made of 10mm thick, 50mm wide aluminium bar.

The boom is 16mm diam aluminium bar.  The 2 lead weights are 

2 pound diving belt weights, holes bored in them and then 

slidden (<<-- horrible word haha) onto the end of the boom.

The pickup coil sits between 2 rare earth disc magnets 

~ 1.5 cm diameter.

The dampening at the moment is just a cylindrical rare earth 

magnet below the lower plate of the plates that support the 

pickup magnets.


I am not totally happy with the lower pivot.  I was going to have
ball bearings butted against each other. But they wont 

sit together.  Even just the signle ball bearing in the end 

of the boom wont sit happily against the vertical bar. 

There is just so much upwards force at that end of the boom caused by the
downwards force of the weight at the other end.


cheers

Dave







Hi
Dave,

    It looks nice! What period have you set it
to, please?

I suggest that you aim for 25
seconds.

I can't quite see how you have attached the mass plates to


the arm. Are they crimped / punched in place?


How does the variable damping work ? I can't see that either!


See
http://www.jclahr.com/science/psn/chapman/lehman/index.html




I stick a label with a vertical line on it onto the mass and view the line with a magnifying glass through a transparent plastic ruler. I deflect the mass 10 mm and release it. The mass moves back toward the balance point and usually past it. 

I observe how far it moves past the balance point. I increase / decrease the damping until the mass goes 1/2 mm past the balance point and then moves slowly back to zero without any oscillations. The arm is then set to 0.7 critical damping. 

The amount of damping needed decreases as the set period is 

increased.

    I hope that this helps.

     Regards,

     Chris Chapman