On Sat, 08 Mar 2008 01:40:02 -0600, cavelamb himself wrote:

Tim Wescott wrote:

I just got the following parts quoted (I asked for a ballpark quote,
got a detailed one -- hmph). Here's a rough sketch, with unnecessary
detail _and_ things left out:

http://www.wescottdesign.com/Seminar...iner_Frame.pdf

Over the phone we modified things such that I'd be responsible for the
indicated holes, and the finish would be brushed & clear anodized. The
quote came back at around $36 each in lots of 50.

Is this just what I can expect to pay for these things? Did I go to
the wrong shop? What are the cost drivers here?

I'm trying to put together a training device that I can include in the
cost of a seminar, $36 is more than 1/3 of the worst-case BOM cost that
I was contemplating. I need to know if I can beat this down by being
creative, if I need to bite the bullet and accept a higher BOM cost, or
if I should yank my eldest out of school and put him to work in the
garage bending metal!

The principal of this thing is that there's a counterweighted arm that
swings on a shaft that's pivoted on bearings in the large holes in the
frame. A microprocessor monitors the position of the shaft through a
potentiometer and controls the voltage to a motor/propeller, with the
goal of holding the arm at a commanded position. The hole locations
are assumed to need tight tolerancing because of the apparent tolerance
needs of the pot I'm planning to use, but I'll be re-thinking that
decision here soon.

Thanks in advance.

Sorry this is off topic - would it help if I mention that I'm putting
my vote behind Hillary McBama, with Ralph Paul as her running mate?


I'm going to jump up and guess that you do not yet have a working
prototype.

That might be a better place to start.


Richard

A student of mine built the prototype, which worked admirably well. Cost-
wise, it made oodles of sense as a one-off, but not in any volume over
onesie-twosie.

I'm trying to figure out how to achieve the desired behavior, but at a
reasonably low cost.

--
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