hi Chris
Am really at the end of the rope here ... just total
frustration... spent all day
yesterday improving the period got down to 11 sec. set up a magnetic
dampening system
with a strip of aluminium 1.5cm wide going in between the 2 magnets.
The only thing that seems to achieve is dropping my period from 11 sec
down to
~ 7 sec. It doesnt appear to do any actual dampening as the unit will
just go on oscillating for ages and just slowly dying down on its own see...
http://www.sydneystormcity.com/screen%20dump.bmp
for the first 3/4 of the screen you can see it oscillating all nite
long. This morning I
gave it a nudge and as you can see the pendulum just slowly decreased in
amplitude
on its own.
I was so looking forward to making this work, and at the moment almost
ready to throw
it all out !!
BTW I did take your bottom pivot advice. I have a flat steel plate on
the end of the
boom against the ball in the vertical
maybe you can help further ? :)
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
hi Chris
Am really at the end of the rope
here ... just total frustration... spent all day
yesterday improving the period got down to 11 sec. set up a magnetic
dampening system
with a strip of aluminium 1.5cm wide going in between the 2
magnets.
The only thing that seems to achieve is dropping my period from 11
sec down to
~ 7 sec. It doesnt appear to do any actual dampening as the
unit will just go on oscillating for ages and just slowly dying down on
its own see...
http://www.sydneystormcity.com/screen%20dump.bmp
for the first 3/4 of the screen you can see it oscillating all nite
long. This morning I
gave it a nudge and as you can see the pendulum just slowly decreased in
amplitude
on its own.
I was so looking forward to making this work, and at the moment almost
ready to throw
it all out !!
BTW I did take your bottom pivot advice. I have a flat
steel plate on the end of the
boom against the ball in the vertical
maybe you can help further ? :)
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