Hi Randall,

Thanks for the email and notes.  I agree that ball bearings aren't a very
good pivot point as I've seen
a comparison of ball bearings to a "crossed rod" pivot; i.e., the low level
mass pivot response of the ball
bearings was outright "locked" compared to the crossed rod pivot where mass
movement is less than
1/16"....right in the neighborhood range where most seismic response occurs.

I won't pretend to grasp totally all you've wrote of.  I do appreciate your
contributions!

Take care, Meredith Lamb


On 10/25/07, Randall Peters  wrote:
>
> It's a neat piece , Meredith; however, I see a serious problem with
> bearing friction when it comes to use in
> a seismometer.  Rolling friction is really complex, as evidenced by the
> paper I wrote at
> http://arxiv.org/abs/physics/0506143
> My expectation is that you will find challenges due to `stiction' since
> the decay of your system (independent
> of damping that you supply to the instrument by design) is more in the
> category of Coulomb friction than
> forms that result in exponential decay.  As is well known for Coulomb
> friction, the static coefficient is greater than the kinetic
> coefficient.  Consequently, you would probably need to provide some way to
> dither your instrument to have much in the way of sensitivity.
>
> Randall Peters
>
>
>
Hi Randall,
 
Thanks for the email and notes.  I agree that ball bearings aren't a very good pivot point as I've seen
a comparison of ball bearings to a "crossed rod" pivot; i.e., the low level mass pivot response of the ball
bearings was outright "locked" compared to the crossed rod pivot where mass movement is less than
1/16"....right in the neighborhood range where most seismic response occurs.
 
I won't pretend to grasp totally all you've wrote of.  I do appreciate your contributions!
 
Take care, Meredith Lamb     

 
On 10/25/07, Randall Peters <PETERS_RD@..........> wrote:
It's a neat piece , Meredith; however, I see a serious problem with bearing friction when it comes to use in

a seismometer.  Rolling friction is really complex, as evidenced by the paper I wrote at
http://arxiv.org/abs/physics/0506143
My expectation is that you will find challenges due to `stiction' since the decay of your system (independent

of damping that you supply to the instrument by design) is more in the category of Coulomb friction than
forms that result in exponential decay.  As is well known for Coulomb friction, the static coefficient is greater than the kinetic coefficient.  Consequently, you would probably need to provide some way to dither your instrument to have much in the way of sensitivity.


Randall Peters