Re: Pinewod Derby Tracks
Mark Wilson (mwilson@POLARIS.ORL.MMC.COM)
Tue, 24 Nov 1992 09:43:19 EST
Mike Box said:
> Each lane has a wooden dowel leaver suspended over the finish line. Attached
> to this lever is a tube filled with mercury that, when tilted, completes the
> circuit of an electric switch that turns on a light for that lane. This finish
> line circuit worked fine for two years until ... (suspense building) ...
> a parent with a camcorder showed that his son's car had actually won when the
> light showed another lane. How? The car's sleek design was able to slip the
> nose under the lever without tripping the switch until the car had traveled
> further across the finish line! Now is that a photo finish, or what?!
> An obvious EC (engineering change) is to extend the length of the levers.
> However, I am interested in other successful finish line designs.
Here are three ideas for you.
1. Place a metal tube in a hole in the center guide strip. The tube need only
be 1/4 inch ID mount a spring through the center of the tube and extended 1/2
inch above the top surface of the center guide. Attach one side of your detector
circuit to the spring and the other to the tube. As the car crosses the finish
line it contacts the spring which then bends over to make contact with the tube.
The spring should be a light one to prevent damage to the car. We used a
tickler method similar to this for years to protect a multi million dollar
2. Mount a photo transistor or photodiode in a tunnel through the centerguide.
This approach will require a tunable circuit to adjust sensitivity to the
ambient light. As the car crosses the finish, the light level will drop
providing an edge from the opto device. Radio Shack had a book with appropriate
circuits. You may also find a data book with applications.
3. Mount an IR emmitter in the center guide and an IR detector above the lane.
Again, the circuit can be found in a Radio Shack book or similar source. This
is better than (2) because the circuit does not need to be tuned.
CC Pack 565 and
Pinewood Derby Fanatic
Terry Howerton Sakima Group, Inc. SCOUTER Magazine Kansas City