Re: ATM Truss tube vibrations - cloth jackets

[Archer Sully <archer@meer.net>]

Major Tom wrote:

> However, if I secure one end of the jacket and twist the other end of the
> jacket...I can adjust how tightly or loosely the jacket grips the truss
> tube.  With a little experimenting indoors it's easy to find a jacket
> tightness that does the best job of damping the fundamental/lowest frequency
> of a suspended truss tube.  

Perhaps rubber bands at strategic points could be pressed into service?

> (I think the fundamental of a truss tube fixed
> at both ends is lower than the fundamental frequency of a suspended/floating
> truss tube.)

Experimentation bears this out.  I think that securing both ends tends to
damp out some of the higher frequencies, but that's just a guess.

> I'll post more when I put the scope together and use the jackets in field
> conditions...but that may be some time...monsoon is very active in New
> Mexico this time of year and clear nights are hard to come by in August.

Its bad up here in Colorado, too ;-(.  Maybe Wyoming this weekend will
be better.

Anyway, I just did a "damping job" on my truss tubes using the 
rope in the middle method.  I cut some nylon rope to about 6" 
longer than the tube, and epoxied the ends of the rope to the
ubiquitous wooden plugs and the inside of the tube.
Seems to work well:  tubes that used to ring now just go 
"thud", and damp out in ~1 second.

Archer Sully
Boulder, CO