Re: Source Sealed Potentiometers?

On 7 Oct 2006 07:20:15 -0700, John Mianowski <spamfree@xxxxxxxxxx> wrote:

Frnak McKenney wrote:
...
You mentioned the possibility of the platform getting "dunked", ...
--snip--
Rotation speed will be very low, & the rotating assembly is supported
on a bearing, so loading on the gears is pretty low. Most plastic
gears are self-lubricating & maintenance is expected to be little more
than cleaning. Gears in need of maintenance typically start getting a
little noisy but still function for a good while. Optical sensors,
OTOH, tend to fail completely & suddenly - such as from dirt on a
sensor lens or a white reflective surface. Magnetic, I would expect
little trouble from.

Less trouble in terms of getting silt deposits, but it feels like
adding lots of tiny magnets (or the equivalent of gear teeth) could be
more work than simply printing an optical-encoder pattern.

I dimly recall that the platform is, what, three inches in diameter?

Yes.

Putting an optical pattern on its uderside would mean... 180 divisions,
so eight binary sensor "bits" to track -- an 180x8 grid, with fairly
closely-spaced "pickups".

Or around the edge, where I have about 0.5" to work with. This is
where I painted my black/white stripes on the 2nd prototype (1/2 black,
1/2 white to tell direction to "home"; narrow white on black to
indicate "home"; stepper to rotate, count/accumulate steps to determine
position) - which worked just fine, except that I'm not 100% satisfied
that it can handle the dirty environment or continue to keep track of
position when/if an external force rotates the turntable.

Well, optical or magnetic, you might check the parallel thread in this
newsgroup titled "Minimal encoder patterns" regarding doing absolute
position sensing with a one-track pattern -- sort of like a linear or
one-dimensional barcode vs. a complex X-Y pattern like a 2-D barcode.

--
The mere formulation of a problem is far more often essential
than its solution, which may be merely a matter of mathematical
or experimental skill. To raise new questions, new possibilities,
to regard old problems from a new angle requires creative
imagination and and marks real advances in science.
-- Albert Einstein
--

I hadn't seen that quote before, but I love it!!

Thank you. I try to only steal from the best. <grin!>


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
Never worry about theory as long as the machinery does what
it's supposed to do. -- R. A. Heinlein
--
.

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