Re: Source Sealed Potentiometers?

Frnak McKenney wrote:

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.

I recall that the OP wanted to be certain of the turntable position without
the need of any prior rotation. A serial encoding track would not fit this
bill.

--
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Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
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