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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.....