Re: linear motion encoder

[John Barrer <forcejb@YAHOO.COM>]

I'd suggest that picket fences are good in this
application (reversal)PRECISELY because that data are
not automatically identified as to direction. The
student investigator must THINK.
--- John Denker <jsd@MONMOUTH.COM> wrote:
> At 07:15 AM 7/5/00 -0700, Sean McKeever wrote:
> > Just a note that PASCO scientific sells such a
> linear encoder. It is called
> > a rotary motion sensor ...
>
> By definition, a rotary encoder is not a linear
> encoder.
>
> > ... and can be used with air tracks as you
> suggested.
>
> How do you turn rotary motion into linear motion?
> Put a wheel on your air
> cart?  Or use strings as suggested below?
>
> > It also has many more uses and is one of the most
> important sensors you
> > can purchase.
>
> Agreed, shaft encoders are nifty things with many
> uses.  Nice versions can
> distinguish the two directions of motion, cruddy
> versions can't.
>
> At 08:11 AM 7/5/00 -0500, Mike Moloney wrote:
> > One version of what John refers to is a 'shaft
> encoder'.  We use these for
> > pendulum experiments, and many other applications.
> >
> > They can be mounted as pulleys at the end of the
> track. A light cord over the
> > pulley gives the displacement of the cart vs. time.
> The resolution of the
> > encoders is outstanding - much better than sonic
> rangers.
>
> I don't see a good way to get an accurate reading if
> the cart changes
> direction.  The best thing I can think of is a loop
> over two pulleys (one
> at each end of the track) with the cart clipped to
> the loop somewhere.  But
> I suspect that would perturb the cart a lot more
> than the _linear_ encoder
> I suggested.  One also needs to worry about lash and
> elasticity and lash in
> the cords.
>
> Bottom line:  I still think a linear motion encoder
> would be a cool
> thing.  It might make a good student project.  If
> anybody is interested let
> me know.....


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