On Tue, 11 Mar 2008 11:16:23 -0700, pdrahn wrote:

On Mar 11, 10:35 am, Tim Wescott wrote:
More design questions:

I need a stick-like thing, about 30 inches long, to go from a pivot
point to a little electric motor. It needs to be moderately rigid,
light and inexpensive in lots of 50 each or so. It would also be quite
nice if it's moderately attractive -- mill finish aluminum without too
many scuff marks is just fine for this. Prettier is better.

I'm thinking that thin-wall aluminum* tube of about 5/8" diameter will
work well, and I'm getting ready to be shocked once again by how much
things cost these days. While I'm waiting for quotes, I thought I'd
solicit the group for suggestions.

Fiberglass? Carbon fiber? Phenolic? Other plastics? Titanium**?
Extra thin-wall steel? Balsa wood comes to mind, but while it is low
tech I suspect it'll cost more than aluminum. Cooked spaghetti is too
limp, and uncooked is too brittle.

Anyone have suggestions? Do you have supplier names to go with your
suggestions?

* Alloy isn't terribly important. Even dead soft would work, although
harder would be better.

** OK, maybe it's more expensive than aluminum.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software? "Applied Control
Theory for Embedded Systems" gives you just what it says. See details
athttp://www.wescottdesign.com/actfes/actfes.html

Hi, Tim.
Should I say "here we go again!"? First, how will it be fastened to your
device? Will it be twisted, pushed or pulled? Will it matter if it is
solid or must it be a tube?

Asking dumb questions helps me think through all the details.

It'll (most likely) be glued into a hole (in a counterweight) on one end,
and either have a motor/propeller assembly held to the other with an
elastic on a peg, or a little ducted fan unit held to the other with a
tapped cross-peg or an expandable plug (if I can find one).

In normal use uncooked spaghetti would work, it mostly needs strength to
avoid damage during handling and while the student is learning about
stability and overshoot.

The first thing that comes to mind is using a piece of the white resin
electric fence post available in your local farm store. These are either
3 or 4 ft. long and about 1/2 inch or perhaps 3/8 inch in diameter. We
cut pieces off to use in a customer's product. I am not sure of what it
is used for, but sometimes I am sent to buy another stick or two. They
are quite stiff, but light.

I'll take a look the next time I'm at Wilco's.

balance snipped

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html