Hi Dave,

I'll toss in a couple of words, too, if that's OK.

Clearly your damper isn't damping (much).
As I recall you were using a pretty hefty mass, and with a large mass 
you will have to use a correspondingly strong damper.  Chris' 
four-magnet design would be a good choice.

Any chance of seeing a photo or sketch of your damper setup?  I'd 
like to follow the magnetic flux paths.
Using copper in place of the Aluminum might make it damp a little 
better, but you're looking for an order of magnitude or two greater, 
not just a percentage improvement.  You should feel it really 
resisting you if you try to move the boom at all rapidly.

Regards,
Brett



At 10:18 PM 7/30/2011,  wrote:
>At 07:39 PM 7/30/2011, you wrote:
>>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


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