Subject:
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Re: Design wanted: Touch sensor for passing trains
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 30 Dec 1999 20:29:18 GMT
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Original-From:
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Ted Michon <tedmichon@home.SPAMLESScom>
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Viewed:
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440 times
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Carl-
We designed some that worked very well with the 4561 Railway Express sets that
we used for the Orange County Festival of Trees earlier this month.
The mechanism uses one of those 5 sided aircraft wing pieces held horizontally
flat near the side of the track. When a train approaches from either direction,
it contacts one of the 45 degree corners and pushes the piece outward. The
piece is attached by a 2 bump diameter thick cylinder to a #10 axle. The axel
pivots at its top with and has another (half as long) axle poking outward from
the joint at 90 degrees. The end of this axle meets the tip of the touch
sensor. The touch sensor is only depressed when the train is not there.
Parallel to and above the shorter axel is a #12 axel with a few cylinder bricks
at the end as dead weight. These push the 5 sided brick toward the track, but
another brick used as a stop keeps it aligned with the tip of the touch sensor.
One problem we originally encountered was that the dimple in the end of the
axle that contacted the touch sensor tended to make the axel stick. We solved
this by lightly filing the end of the axle to give it a flat and angled end.
From a few inches away, you can't even tell we touched it.
The mechanism worked very reliably, except for some copies made from brand new
bricks. New bricks are more "slippery" than old ones and constant banging made
them pop appart. Older bricks never gave a problem. Either way, you can
permanently solve the problem by gluing or clamping things together with
Technics or just adding more bricks.
My son Thomas offered to draw one up in LDRAW and I will post it when it's
ready.
-Ted
"Carl M. Kadie" wrote:
> I'm using Mindstorms to control Lego trains.
>
> Does anyone have a design for using a touch sensor to detect a train
> passing?
>
> My intuition is that the touch sensor could be more reliable than the light
> sensor (plus I have two touch sensors and only one light sensor).
>
> Thanks much for any help,
>
> Carl Kadie
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