PSN-L Email List Message

Subject: RE: New Seismo
From: "Stephen Hammond" shammon1@.............
Date: Sun, 24 Jul 2011 10:14:16 -0700


Looks neat Dave. I'm about to also build new Lehmans so I have a few
questions. Is that J-B weld epoxy holding the frame together? Could you
also take a closer photo of the lower pivit? Additionally, can you give
a few specs: boom length, mass weight and a better look at the variable
damping frame.
Thanks-- Steve Hammond  PSN San Jose, Aptos CA

-----Original Message-----
From: psnlist-request@..............
[mailto:psnlist-request@............... On Behalf Of Christopher Chapman
Sent: Sunday, July 24, 2011 9:29 AM
To: psnlist@..............
Subject: Re: New Seismo



Dave Nelson dave.nelson@...............
Subject: New Seismo

ok got around to taking a pic of the new Lehman

http://www. 
sydneystormcity.com/IMGP2023a.jpg



still waiting for the first decent quake M6+ to see its response

Till then I am guessing at the amount of dampening I need for it.



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




Message



Looks=20 neat Dave. I'm about to also build new Lehmans so I have a few = questions. Is=20 that J-B weld epoxy holding the frame together? Could you also take a = closer=20 photo of the lower pivit? Additionally, can you give a few specs: boom = length,=20 mass weight and a better look at the variable damping = frame.
Thanks-- Steve Hammond  PSN San Jose, Aptos = CA
-----Original Message-----
From:=20 psnlist-request@.............. [mailto:psnlist-request@............... = On=20 Behalf Of Christopher Chapman
Sent: Sunday, July 24, = 2011 9:29=20 AM
To: psnlist@..............
Subject: Re: New=20 Seismo

Dave=20 Nelson dave.nelson@...............
Subject:=20 New Seismo
ok got around to taking a pic of the new =
Lehman
http://www.sydneystormcity.com/IMGP2023a.jpg

still waiting for the first decent quake M6+ to see its response
Till then I am guessing at the amount of dampening I need for it.

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

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