Re: [TowerTalk] collapsing steppIR elements

[Jim Lux <jimlux@earthlink.net>]

At 04:19 PM 5/7/2004 +0000, Jim Jarvis wrote:

> Interesting idea, to attach the tape to the tips of
> the nesting fiberglass tubes.  Couple of problems with that, though.
>
> First, it wouldn't be as well weather sealed.  Second,
> although the telescoping fiberglass WOULD go in and out,
> it's shaped and surfaced to grip when it's all the way out.
> That would need to be changed.
>
> Finally, 'homing' the steppIR motor would require a non-zero
> definition, and some way to index at the inboard stop.

What's the performance impact of using tape vs just running a wire?  Sure, 
the RF resistance of a flat conductor is lower, but compare that to several 
parallel wires?

Once one has separated the "actuator" from the "conductor" there's lots of 
approaches.  If one had telescoping tubes (with rudimentary seals, one 
could use air pressure to extend and retract them (assuming you can keep 
them clean enough), you could have a simple wire(s) fed from a springloaded 
spool.


There are a number of clever structures that deploy by twisting one part 
relative to another. Not all of them are as complex as, e.g., the 60 meter 
mast on the Shuttle Radar Topographic Mission.

There's also the accordion folding thing like used to hold a shaving mirror 
out from a wall: a series of links in X's. (imagine a stack of automotive 
scissor jacks)  You drive the center X with a lead screw and all the rest 
follow.  It's self balancing, but might be quite heavy.

There's also deployable structures like the Hoberman sphere and some of 
Snelson's tensegrity structures. 

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