Re: Source Sealed Potentiometers?

On 5 Oct 2006 07:56:41 -0700, John Mianowski <spamfree@xxxxxxxxxx> wrote:
Frnak McKenney wrote:
--snip--
I think I lost part of the picture here. If your "resolver wheel" makes
five turns for the one full turn of the platform, doesn't _every_
reported resolver output represent five possibple platform positions?

Exactly, & I need to narrow it down to just 1.

But... why do you need a separate resolver?

That was part of somebody's proposed solution, to figure out which of
the 5 possible positions is actual.

Ah. Sorry, thought that was you -- I got lost in the quoting. <grin>

So the idea was to divide up the job? A 1/5 absolute encoder on the
platform _combined_ with (say) a 1/36 absolute encoder on the secondary
"resolver"? Makes sense.

If you were using, for example,
optoreflector sensors, why not just paint a black and white "absolute
position" pattern on the bottom of the _platform_? It would cut down on
the number of moving parts.

I've done that & it works very well in prototype. I'm not confident,
though, that it will work reliably in the messy environment that the
final version will be going into. The need for frequent
maintenance/cleaning is something that I'd like to avoid if I can.

You mentioned the possibility of the platform getting "dunked", which
suggests outdoors: river water, pond water, rainwater. That kind of
exposure to the elements suggests that the platform and its drive
mechanism will need periodic maintenance, and any type of resolver or
encoder that is mechanically connected to that platform or its drive
will need at least as much maintenance (gears need greasing from time
to time <grin>). Given that, will adding mechanical, optical, or magnetic
sensors onto the platform require more?

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

--snip--
Let us know what you finally come up with. We'll be more than happy to
steal your solution and an use it in our own projects. <grin!>

Sure. You're all more than welcome to it. Whatever "the solution"
ends up being, probably won't be for awhile (it's hobby-related,
subject to the parameters of funding & time that all hobbies must exist
within - nothing planned to ever be sold).

It's too bad someone in Congress didn't sneak an "earmark" onto one of
those last-minute bills for an American Hobby Reaserch and Development
Grant Fund. Maybe next year... <grin?>


Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut minds pring dawt cahm (y'all)
--
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
--
.

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