On Sat, 08 Mar 2008 02:01:42 -0600, cavelamb himself wrote:

Tim Wescott wrote:

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.


Shoot!

Welcome to engineering 101...

Well, yes. My frustration is compounded by the fact that I'm
accomplished at other aspects of engineering. Ask me how to make a low-
cost circuit, or how to write software to allow for a processor that
costs 1/2 as much, or to design a control system that maintains
performance with a cheaper sensor or actuator -- I can do any of those.

But a feel for how much it costs to put a bend in a sheet of metal, or a
hole, or what features of a mechanical design may drive the cost up or
down? Not there.

--
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